+ unit 2 – 2014-2015 periodicity. + lesson 1: review of periodic table structure thursday, october...
TRANSCRIPT
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Unit 2 – 2014-2015
Periodicity
2
+Lesson 1: Review of Periodic Table StructureThursday, October 2nd
3+Periodicity
IB Understandings
The periodic table is arranged into four blocks associated with the four sublevels – s, p, d and f
The periodic table consists of groups (vertical columns) and periods (horizontal columns)
The period number (n) is the outer energy level that is occupied by electrons
The number of the principal energy level and the number of the valence electrons in an atom can be deduced from its position on the periodic table
The periodic table shows the positions of metals, non-metals and metalloids
4+3.1 Applications and Skills
Applications and skills:
Deduction of the electron configuration of an atom from the element’s position on the periodic table, and vice versa.
Guidance:
The terms alkali metals, halogens, noble gases, transition metals, lanthanoids and actinoids should be known.
The group numbering scheme from group 1 to group 18, as recommended by IUPAC, should be used.
+ 5
Periodic Table• The development of the periodic table brought a
system of order to what was otherwise an collection of thousands of pieces of information.
• The periodic table is a milestone in the development of modern chemistry. It not only brought order to the elements but it also enabled scientists to predict the existence of elements that had not yet been discovered .
6+Early Attempts to Classify Elements Dobreiner’s Triads (1827)
• Classified elements in sets of three having similar properties.
• Found that the properties of the middle element were approximately an average of the other two elements in the triad.
6
7
Dobreiner’s Triads
Element Atomic Mass(amu)
Average Density(g cm-3)
Average
ClBrI
35.579.9126.9
81.21.563.124.95
3.25
CaSrBa
40.187.6137.3
88.71.552.63.5
2.53
Note: In each case, the numerical values for the atomic mass and density of the middle element are close to the averages of the other two elements
8+Newland’s Octaves -1863John Newland attempted to
classify the then 62 known elements of his day.
He observed that when classified according to atomic mass, similar properties appeared to repeat for about every eighth element
His attempt to correlate the properties of elements with musical scales subjected him to ridicule.
In the end his work was acknowledged and he was vindicated with the award of the Davy Medal in 1887 for his work.
.8
9+Dmitri Mendeleev
Dmitri Mendeleev is credited with creating the modern periodic table of the elements.
He gets the credit because he not only arranged the atoms, but he also made predictions based on his arrangements His predictions were later shown to be quite accurate.
.9
10+Mendeleev’s Periodic Table
• Mendeleev organized all of the elements into one comprehensive table.
• Elements were arranged in order of increasing mass.
• Elements with similar properties were placed in the same row.
.10
11+ Mendeleev’s Periodic Table
12+Mendeleev’s Periodic Table
Mendeleev left some blank spaces in his periodic table. At the time the elements gallium and germanium were not known. He predicted their discovery and estimated their properties.
13+Periodic PropertiesElements show gradual changes in certain
physical properties as one moves across a period or down a group in the periodic table. These properties repeat after certain intervals. In other words they are PERIODIC
Periodic properties include:
-- Ionization Energy-- Electronegativity-- Electron Affinity-- Atomic Radius-- Ionic Radius .
13
14+REVIEW: Periodic Table
Elements are arranged by increasing atomic number, Z
Groups, or vertical columns, group elements with the same number of valence electrons and therefore similar chemical properties
Periods, or rows, are horizontal groups; the period number is equal to the principal quantum number, n, of the highest occupied energy level of the elements in that period
15+Important Group To Remember
Group Number
Recommended name
Characteristics
1 Alkali metals Very reactive metals
2 Alkaline metals
Less reactive metals
15 Pnictogens
16 Chalcogens
17 Halogens Very reactive non-metals
18 Noble Gases Non-reactive non-metals; stable octet
16+Arrangement
Metals make up most of the periodic table and are found on the left side
Metalloids include B, Si, Ge, As, Sb and Te and separate metals and non-metals (Po and At are sometimes considered metalloids); have characteristics of both metals and nonmetals
Non-Metals are on the right side of the periodic table after the metalloids
17+Metals and Nonmetals
NONMETAL
S METALS
METALS
Transition metals
Metalloids
18+Additional Groupings in the Periodic Table
Nonmetals, Metals, Metalloids, Noble gases
19+IB Goodness!
You have a large number of periodic tables in your data booklet
All groups are numbered 1-18
The position of an element is related to its electron configuration
Know the s-block, p-block, d-block and f-block; those blocks represent which valence electrons are getting filled
20+Blocks
S
dp
f
+ 21
Let’s Practice!
+ 22
Let’s Practice
23
+Lesson #2 – Review of Periodic Table FamiliesFriday, October 3rd
24+3.2 Periodic Trends
IB Understandings
Vertical and horizontal trends in the Periodic Table exist for atomic radius, ionic radius, ionization energy, electron affinity, and electronegativity.
Guidance
Only examples of general trends across periods and down groups are required. For ionization energy the discontinuities in the increase across a period should be covered. Trends in metallic and non-metallic behaviour are due to the trends
above. Oxides change from basic through amphoteric to acidic across a
period.
25+Topic 3.2 Applications and Skills
Applications and skills:
Prediction and explanation of the metallic and non-metallic behaviour of an element based on its position in the Periodic Table.
Discussion of the similarities and differences in the properties of elements in the same group, with reference to alkali metals (Group 1) and halogens (Group 17).
Guidance
Group trends should include the treatment of the reactions of alkali metals with water, alkali metals with halogens and halogens with halide ions.
Construction of equations to explain the pH changes for reactions of Na2O, MgO, P4O10, and the oxides of nitrogen and sulfur with water.
26+Periodicity
Properties of elements repeat themselves periodically
The Periodic Table is arranged to show these trends
27+Effective Nuclear Charge
Nuclear charge is the number of protons in the nucleus of an atom and increases steadily from left to right on the Periodic Table
HOWEVER, the outer electrons are shielded from the nuclear charge by the inner electrons and feel less of this positive pull
The effective nuclear charge experience by the outer electrons is less than the full nuclear charge
28+Effective Nuclear Charge - Trends
Effective nuclear charge INCREASES from left to right across the Periodic Table (no change in number of inner electrons)
Effective nuclear charge REMAINS THE SAME as we go down a group
29+Atomic Radius
Atomic radius is measured as ½ the distance between neighboring nuclei
Atomic radii DECREASE from left to right across the period and INCREASE down a group
30+Atomic Radius (cont.)
Atomic radii increase down a group because we are adding Principle Energy Levels
Atomic radii decrease from left to right as we increase effective nuclear charge
31+Ionic Radius
Positive ions (cations) have a smaller radius than the parent atom; lose outer valence shell
Negative ions (anions) have a larger radius than the parent atom; adding electrons to outer shell which increases electron repulsion
Atomic radii decrease from Groups 1 to Group 14 for the positive ions as we increase effective nuclear charge
Atomic radii decrease from Groups 14 to Group 17 for the negative ions as we increase effective nuclear charge
Ionic radii increase down the group as number of energy shells increases
32+Let’s Practice
Describe and explain the trend in radii of the following atoms and ions: O2–, F–, Ne, Na+, and Mg2+.
The ions and the Ne atom have 10 electrons and the electron configuration 1s22s22p6. The nuclear charges increase with atomic number:
O: Z = +8, F: Z = +9, Ne: Z = +10, Na: Z = +11, Mg: Z = +12
The increase in nuclear charge results in increased attraction between the nucleus and the outer electrons. The ionic radii decrease as the atomic number increases.
33+Ionization Energies
34+Ionization Energy Trends
Ionization energy increases across a period as we increase effective nuclear charge
Ionization energy decreases down a group as we increase the shielding effect
Exceptions to these trends can be explained in terms of electron configuration stability (i.e. it takes more energy to remove an electron from a full sub-level or shell)
35+Electron Affinity
The first electron affinity of an element is the energy change when one mole of electrons is added to one mole of gaseous atoms to form one mole of gaseous ions:
X(g) + e– → X–(g)
Values are tabulated in Table 8 of the IB data booklet.
1st electron affinity is general exothermic as the electron is attracted to the positive nucleus; 2nd and 3rd electron affinities become endothermic as the atom already has a negative charge!
36+Electron Affinity Trends Group 17 have the highest electron affinity
Group 1 has the lowest electron affinity
Group 2 and Group 15 have the highest electron affinities; here you are adding the first electron to a half-filled sub-level; electrostatic repulsion
37+Electronegativity
The electronegativity of an element is a measure of the ability of its atoms to attract electrons in a covalent bond
Electronegativity increases from left to right across a period owing to the increase in nuclear charge, resulting in an increased attraction between the nucleus and the bond electrons.
Electronegativity decreases down a group. The bonding electrons are furthest from the nucleus and so there is reduced attraction.
38+Metals vs. Non-Metals
The ability of metals to easily conduct electricity is due to their low ionization energy and ability to move their electrons away from the nucleus
As you move from left to right on the Periodic Table, there is a slow transition from metal to semi-metal to non-metal
39
+Lesson #3 – Review of Periodic Table FamiliesTuesday, October 7, 2014
40+Nota Bene
Remember when studying that the group of an element on the Periodic Table also tells you the number of valence electrons for that element!
+The Electron Shielding Effect
Electrons between the nucleus and the valence electrons repel each other making the atom larger.
.41
+How is atomic radius measured?
Half the distance between neighboring nuclei. OR
Distance from the nucleus to the outermost electron.
+Atomic Radius Across a Period
Why does atomic radius decrease across a period?
Think about the effective nuclear charge!
How many occupied energy levels does each atom have?
Fluorine’s radius is almost half of Lithium’s.
+Atomic Radius
45+Atomic Radius
Extra Info:
We typically measure atomic radius at bonding atomic radius where we look at atoms in chemical bonds with other atoms of the same element and take ½ the diameter between the two nuclei
There is also nonbonding atomic radius or van der Waals’ radius for things like Noble Gases that do not bond; take a look at these atoms in the solid phase and measure the distance between two nuclei
46+Ionic Radius – Some More Info
The factors that effect ionic radius include nuclear charge, number of filled energy shells, electrostatic repulsion and overall charge
At the HL level, the IB likes to ask questions about ionic radius that are not clear-cut and require you to think
Which ion would have a larger ionic radius, Na+ or Mg2+?
Let’s think about this…we cannot directly compare these thinking about trends from left to right because they have different charges! But, we can recognize that both now have the electron configuration of Neon. However, Mg has one more proton in the nucleus meaning electrons are pulled in tighter!
+Atomic Radius
.47
+ Trends in Ion SizesRadius in pm
.48
49+Effective Nuclear Charge
Extra Info (way beyond IB!)
The formula for effective nuclear charge is:
Zef = Z – S
Where s= screening or shielding constant
50+Melting Points
Comparing melting points is complex because it depends on bonding as well as nuclear charge
Trends down Groups 1 through 17 can be explained as elements in each group bond in the same way!
Melting points DECREASE down Group 1 as these metallic bonds have delocalized electrons and as you move down the group the attraction decreases
Melting points INCREASE down Group 17 because these diatomic elements are held together by London Dispersion forces which get stronger as the electron cloud gets bigger
Melting points generally rise from left to right until Group 14 and then fall from Group 14 to Group 18
51+Melting Points
52+Let’s Practice
1 (a) Explain what is meant by the atomic radius of an element.(b) The atomic radii of the elements are found in Table 9 of the IB data booklet. (i) Explain why no values for ionic radii are given for the noble gases. (ii) Describe and explain the trend in atomic radii across the Period 3
elements.
2 Si4+ has an ionic radius of 4.2 × 10–11 m and Si4– has an ionic radius of 2.71 × 10–10 m. Explain the large difference in size between the Si4+ and Si4– ions.
53+Answers
1 (a)Half the distance between the nuclei of neighbouring atoms of the same element.
(b) (i) The noble gases do not form stable ions and engage in ionic bonding so the distance between neighbouring ions cannot be defined.
(ii) The atomic radii decrease from Na to Cl. This is because the number of inner, shielding, electron is is constant (10) but the nuclear charge increases from +11 to +17. As we go from Na to Cl, the increasing effective nuclear charge pulls the outer electrons closer.
2. Si4+ has an electronic configuration of 1s22s22p6 where Si4– has an electronic configuration of 1s22s22p63s23p6. Si4+ has two occupied energy levels and Si4− has three and so Si4− is larger.
54+Let’s Practice
More practice!
55+Even more practice
Yay!
56+Answers
(a) The electron in the outer electron energy level (level 4) is removed to form K+. The net attractive force increases as the electrons in the third energy level experience a greater effective nuclear charge.
(b) P3− has electronic configuration of 1s22s22p63s23p6 whereas Si4+ has an electronic configuration of 1s22s22p2. P3– has one more principal energy level than Si4+ so its valence electrons will be further from the nucleus and it will have a larger ionic radius.
(c) The ions have the same electron configuration, 1s22s22p63s23p6: both have two complete shells; the extra proton in Na+ attracts the electrons more strongly
57+More Practice
Cl- < Cl < Cl+
Phosphorus exists as molecules with four atoms: P4. Sulfur exists as molecules with eight atoms: S8. There are stronger London dispersion forces between the larger S8 molecules as there are more electrons.
58+More
59+More Practice
60
+Lesson #4 – Vertical and Horizontal Periodic TrendsWednesday, October 8, 2014
61+Warm-Up
Why does I2 have a higher melting point than F2?
Why does aluminum have a higher melting point than sodium?
62+Metals
Metallic properties are related to ionization energy; the lower the ionization energy, the more metallic an element is
A metallic structure consists of a regular lattice of positive ions in a sea of delocalized electrons
Metallic character decreases from left to right and increases from top to bottom
63+Metals
1. Are good conductors of heat and electricity
2. Are malleable (capable of being hammered into thin sheets)
3. Are ductile (capable of being draw into wires)
4. Have lustre (they are shiny)
5. Typically lose electrons; i.e. they like to be oxidized
** Note: Mercury is the only metal that is liquid at room temperature! It can actually dissolve other metals and solutions formed this way are called amalgams
64+Non-Metals + Metalloids
Non-Metals
Are poor conductors of heat and electricity
Typically gain electrons; i.e. they like to be reduced
Metalloids
Are semiconductors meaning they are able to conduct electricity only at high temperature which has widespread applications in electronics (e.g. Silicon Valley)
65+Group 1 Alkali Metals
These metals are highly reactive, soft and have low melting points
Tend to form +1 ions
Held together by metallic bonds; as you go down Group 1 melting point decreases because electrons are held less tightly meaning you can disrupt the lattice more easily
66+Group 1 Reactions
Reaction With Oxygen
All alkali metals react vigorously with oxygen to form an oxide
4Na(s) + O2(g) 2Na2) (s)
As you go down the group, the reactions become more vigorous because of their lower ionization energy.
Reaction With Water
All alkali metals react rapidly with water; more reactive down the group
2Na(s) + 2H2O(l) 2NaOH(aq) + H2(g)
The products are highly basic!
67+Group 1 Reactions With Water
Lithium floats and reacts slowly. It releases hydrogen but keeps its shape.
Sodium reacts with a vigorous release of hydrogen. The heat produced is sufficient to melt the unreacted metal, which forms a small ball that moves around on the water surface.
Potassium reacts even more vigorously to produce sufficient heat to ignite the hydrogen produced. It produces a lilac coloured flame and moves excitedly on the water surface.
Cesium just EXPLODES!
68+Group 17 Elements Group 17 are known as the halogens
They all exist as diatomic elements; Cl2, I2, etc.
Reactivity decreases down the group (opposite of Group 1)
Reactions with Group 1:
All halogens react with Group I to form a salt (halides)
2Na(s) + Cl2(g) 2NaCl(s)
69+Salts
Just as a reminder, salts are ionic compounds, positive and negative ions held together by the electrostatic attraction
Salts have high melting points and only conduct electricity in the liquid phase, gas phase or dissolved in water
More on this in the future!
70+Displacement Reactions With Halogens More reactive halogen with displace a less reactive halogen
(REMEMBER from last year – single displacement reactions!)
Reactivity: F2 > Cl2 > Br2 > I2
Example:
Cl2(g) +2KBr(aq) 2KCl(aq) + Br2(g)
All of these reactions are redox reactions, meaning one atom gains elements and another atom loses electrons
You need to know that solutions of chlorine are green, bromine are orange and iodine are violet (red-brown); solutions of the halides are colorless
71+Silver + Halides
Halogens form an insoluble (i.e. not able to be dissolved in water) solution when combined with silver
Adding these together produces a precipitate
72+Group 18 Noble Gases
Group 18 consists of the Noble Gases which are all extremely stable because they have a stable octet They are colorless They are monatomic; they exist as single atoms They are very unreactive
Other elements all want to be the Noble Gases! Elements in Groups 1, 2, and 13 lose electrons to adopt the
arrangement of the nearest noble gas with a lower atomic number. Elements in Groups 15 to 17 gain electrons to adopt the electron
configuration of the nearest noble gas on their right in the Periodic Table.
The metalloids in the middle of the table show intermediate properties.
+Chemical Properties
1. Why are alkali metals called alkali?
2. How are halides formed?
3. Why does Cl- displace Br- in a displacement reaction?
+Chemical Properties in Groups 1,2,and 7
4. How do the reactivities of the alkali metals and the halogens vary down a group?
5. Which property of the halogens increases from fluorine to iodine?
A. ionic charge
B. electronegativity
C. melting point of the element
D. chemical reactivity with metals
+ 75
Let’s Practice
+ 76
Let’s Practice
77
+Lesson 5 – Construction of Oxide Equations and Explaining pH ChangesThursday, October 9th
+Warm up: Explain why each trend occurs below in terms of effective nuclear charge:
+Oxides
What is an oxide?
Oxides are formed from the combination of an element with oxygen
80+pH of Oxides
Metal oxides are basic; they react with water to form metal hydroxides
CaO(s) + H2O(l) Ca(OH)2(aq)
Non-metallic oxides are acidic: they react with water to form acidic solutions
CO2(g) + H2O(l) H2CO3(aq) Carbonic Acid
If an oxide can act both as an acid and a base, it is classified as amphoteric!
Al2O3(s) + 2NaOH(aq) + 3H2O(l) 2NaAl(OH)4 (acts as an acid)
Al2O3(s) + 6HCl(aq) 2AlCl3(aq) + 3H2O(l) (acts as a base)
81+Group 3 Oxides – Know the Trends!
Formula of Oxide
Na2O MgO Al2O3 SiO2 P4O10 SO3 and SO2
Metal/Non-Metal
Metal Metal Metal Nonmetal
Nonmetal
Nonmetal
Nature of Oxide
Basic Basic Amphoteric
Acidic Acidic Acidic
+Metal Oxides
The transition from metallic to non-metallic character is illustrated by the bonding of the Period 3 oxides. Ionic compounds are usually formed between metals and non-metal elements, so the oxides of elements Na to Al have what we call super ionic structures.
+Metalloid Oxides
Covalent Bonds
Giant Molecular Structure
Ex: SiO2
Silicon dioxide does not dissolve in water but it is still classified as acidic because it can react with NaOH to form Na2SiO3(aq)
+Non-metal Oxides
Molecular covalent bonds
Ex: P4O10, SO3, Cl2O7
+Oxides of Period 3
Oxide Formula
Na2O (s)
MgO (s) Al2O3 (s)
SiO2 (s) P4O10(s)/P4O6 (s)
SO3(l)/SO2(g)
Cl2O7(l)/Cl2O (g)
Oxidation number
+1 +2 +3 +4 +5/+3 +6/+4 +7/+1
Electrical conductivity in molten state
high high high very low
none none none
Structure giant ionic giant covalent
molecular covalent
+Oxide Trends
As you go across period 3, the ionic character decreases.
As you go down a group of oxides, the ionic character increases.
How can you explain these trends in terms of electronegativity differences within the oxide?
Li2O
Na2
O
K2O
Rb2
O
Cs2O
MgO Al2O3 SiO2 P4O10 SO3 Cl2O7
87
+Acid-Base Character
Formula of oxide
Na2(s) MgO(s) Al2O3(s) SiO2(s) P4O10 (s) /P4O6 (s)
SO3(l)/SO2(g)
Cl2O7(l)/Cl2O (g)
Acid-Base character
basic amphoteric acidic
+Basic Character
Sodium and magnesium oxides will dissolve in water to form alkaline solutions:
Na2O (s) + H2O (l) 2NaOH (aq)
MgO (s) + H2O (l) Mg(OH)2 (aq)
+Basic Oxides
Basic oxides react with an acid to form a salt and water:
MgO (s) + HCl (aq) MgCl2 (aq) + H2O (l)
Li2O (s) + HCl (aq) LiCl (aq) + H2O(l)
+Acidic Oxides
Non-metallic oxides react with water to produce acidic solutions:
P4O10(s) + 6H2O 4H3PO4(aq)
P4O6(s) + 6H2O 4H3PO3 (aq)
+Acidic OxidesSulfur trioxide reacts with water to produce
sulfuric acid:
SO3 (l) + H2O (l) H2SO4 (aq)
Sulfur dioxide reacts with water to produce sulfic acid
Dichlorine heptoxide reacts with water to produce chloric acid
Dichlorine monoxide reacts with water to produce chlorous acid
Silicon dioxide does not react with water, but will react with
alkalis to form silicates.
+
+
95
96
97
+Lesson 7 – Intro to Transition MetalsTuesday, October 14
98+Mole Day Is Coming!Let’s plan a party!
99+IB Understandings
Transition elements have variable oxidation numbers, form complex ions with ligands, have coloured compounds, and display catalytic and magnetic properties.
Guidance
Common oxidation numbers of the transition metal ions are listed in the IB Data booklet in sections 9 and 14.
Zn is not considered to be a transition element as it does not form ions with incomplete d orbitals.
Transition elements show an oxidation number of +2 when the s electrons are removed.
100+Applications and Skills
Explanation of the ability of transition metals to form variable oxidation states from successive ionization energies.
Explanation of the nature of the coordinate bond within a complex ion.
Deduction of the total charge given the formula of the ion and ligands present.
Explanation of the magnetic properties in transition metals in terms of unpaired electrons.
101+Periodic Trends The d-block elements show a lull in the periodic patterns we
have seen in the s and p block
The 10 d-block elements all show similar characteristics to each other (as an example look at the small range of atomic radii)
102+Electron Configuration Any of the d-block elements in the same group as chromium (Cr)
and Copper (Cu) have electron configurations that are exceptions to Aufbau’s principal because s electrons get promoted to either half-fill or fully fill the d-sublevel
103+Effective Nuclear Charge
The small decrease in atomic radii across the d-block is due to the fact that there is only a small increase in the effective nuclear charge as you move left to right
Why is this?
Remember that the d-sublevel is not the valence shell! It is actually an inner shell so each time you add a proton, you are also adding an electron to an inner shell which provides some shielding effect!
Why is this amazing?
Since most of the d-block metals have similar radii, they can easily form alloys or metal mixtures because mixing two different elements does not disrupt the metallic bond structure!
+ 104
Let’s Practice
+ 105
Answer!
106+Physical Properties
High electrical and thermal conductivity
High melting point
Malleable – they are easily beaten into shape
High tensile strength – they can hold large loads without breaking • ductile – they can be easily drawn into wires
Iron, cobalt, and nickel are ferromagnetic.
Properties can be explained by the fact that the s and d sublevel electrons all delocalize to form a sea of electrons! Sea of electrons hold metal lattice together.
107+Chemical Properties Form compounds with more than one oxidation number • form a
variety of complex ions
Form coloured compounds
Act as catalysts when either elements or compounds.
+Zinc
Why is zinc not considered to be a transition element? Discuss.
109+Zinc
Zinc only forms a +2 ion AND in both its natural state and as an ion it has a completely filled d-sublevel
Scandium3+ (Sc3+) also forms a colorless solution because it has NO d sublevel electrons but it is still a transition metal because it has an incomplete d sublevel. It can also sometimes for the +2 ion!
110+Oxidation States One of the key features of transition metals is their ability to
form multiple ions with various oxidation states!
This is different than alkali metals which only form +1 ions and alkaline metals which only form +2 ions
Look at the different in ionization energies between Calcium, which only forms a +2 ion, and Titanium, a transition metal. Ti is lacking the big jump Ca has from the 2nd to 3rd Ionization Energy
111+Multiple Oxidation States
This is because in Calcium, once you remove 2 electrons, you get to a noble gas configuration; removing one more electron makes that ion very unstable!
In Titanium, the 3d and 4s electrons are very close in energy so it can lose from both sublevels until they are all gone; the jump doesn’t happen until the next electron lost would have to be from the 3p sublevel!
+Oxidation States
What is the most common oxidation state of the transition elements? Look at the red!
Sc Ti V Cr Mn Fe Co Ni Cu Zn
+1
+2 +2 +2 +2 +2 +2 +2 +2 +2 +2
+3 +3 +3 +3 +3 +3 +3 +3 +3
+4 +4 +4 +4 +4 +4 +4
+5 +5 +5 +5 +5
+6 +6 +6
+7
113+Important Points For IB!!
All the transition metals show both the +2 and +3 oxidation states. The M3+ ion is the stable state for the elements from scandium to chromium, but the M2+ state is more common for the later elements. The increased nuclear charge of the later elements makes it more difficult to remove a third electron.
The maximum oxidation state of the elements increases in steps of +1 and reaches a maximum at manganese. These states correspond to the use of both the 4s and 3d electrons in bonding. Thereafter, the maximum oxidation state decreases in steps of –1.
114+Important Points For IB!! Oxidation states above +3
generally show covalent character. Ions of higher charge have such a large charge density that they polarize negative ions and increase the covalent character of the compound (see Figure 3.13).
Compounds with higher oxidation states tend to be oxidizing agents. The use of potassium dichromate(VI) (K2Cr2O7), for example, in the oxidation of alcohols.
+ 115
Let’s Practice!
+ 116
Answers!
117+Next Week
Quiz on Tuesday!!! Short + review
Complex Ions – Wednesday
D-Sublevel Split – Thursday
Colored Ions – Friday
Exam the following week!!! Thursday, October 23rd tentatively unless we need one more day of review!
118
+Lesson 8 – Complex Ions and Coordinate ComplexesTuesday, October 14th, 2004
119+Complex Ions
Transition metal ions in solution have a high charge density
These ions attract polar water molecules which form coordinate bonds
REMBEMBER: A coordinate bond is a bond where one atom provides both of the electrons to the covalent bond
120+Ligands
When a complex is formed where a central ion is surrounded by molecules or ions which possess a lone pair of electrons that can enter into a coordinate bond, the surrounding species are called ligands
Ligands have to have a lone pair of electrons to donate!
The number of coordinate bonds from the ligands to the central atom is called the coordination number
6 ligands attached to the central ion! Coordination number = 6
121+Shapes of Complex Ions These complex ions form a variety of 3-dimensional shapes
Think back to VSEPR (electron cloud repulsion) and the shapes of covalent molecules; electron clouds want to be as far apart as possible
122+Shapes of Complex IonsCoordination Number
Oxidation Number of Central Ion
Shape
6 +3 Octahedral4 +7 Tetrahedral4 +2 Square Planar4 +2 Tetrahedral2 +1 Linear
Yikes! Why?! There is no easy way to predict whether it will be square planar or tetrahedral. Sad!Most are tetrahedral…that’s all I can tell ya!
123+Oxidation Number of Metal and Charge of Ion Don’t cheat! Let’s try to figure out the oxidation state of the
metal in each of these ions…Let’s look at Fe(H2O)6
3+ first… The overall charge is +3. H2O does not have a charge itself so the charge of the iron must be +3.
+3 + 0 = +3
Now, let’s look at [CuCl4]2-. The chlorine here is chlorine ion which always has a charge of -1. We have four of them so they contribute an overall charge of -4. The total charge on the ion is -2 so…
X + (-4) = -2, X= +2, the oxidation state of the copper
Let’s try the rest!
HINT: CN-1 is a polyatomic ion with a charge of -1.
124+Oxidation Number of Central Ion
1. Ligands can either be neutral (H2O, NH3, etc.) or negatively charged (Cl-, CN-, etc.). Decide the ligands’ charges
2. Add up all the charges on the ligands
3. Set up the following equation:
X (oxidation # of trans. Metal) + Y (sum of charges of ligands) = Z (overall charge)
HINT: The complex ion will always be kept in brackets [ ]! [Fe(H2O)6]2+ Fe has a +2 oxidation #
[Ni(CN)4]2- Ni has a +2 oxidation #
Hint 2: These can enter into ionic compounds! Reverse criss-cross Li2[Ni(CN)4] I know Lithium forms a +1 ion so the complex ion has to
have a -2 charge (+2 + -2 = 0)
125+Examples
126+Determining Charge of Complex Ion When a complex ion bonds with another ion, we can use the
reverse criss-cross method to determine the charge on that ion!
EXAMPLE: What is the charge for the complex ion in compound? [Cr(H2O)6]Cl3?
So, we know that chlorine always has a charge of -1. Since the overall charge for this compound is zero (I don’t see a charge on the outside), I know that the charge of the ion has to be +3 to balance out the 3 -1 charges from the chlorine. Let’s try two more!
What is the charge for the complex ion in the following compounds? [CrCl(H2O)5]Cl2.H2O and [CrCl2(H2O)4]Cl.2H2O
+2 and +1
127+Let’s Practice
Platinum (II) can form a complex ion with 1 ammonia and 3 chloride ligands. What is the overall charge and formula for this complex ion?
Platinum forms a +2 ion. Ammonia is neutral and chloride ions each have a -1 charge. So, +2 + (3*-1) = -1 overall charge
[Pt(NH3)Cl3]-1
128+Monodentate vs. Polydentate
Monodentate ligands contain a single donor atom and have one lone pair contributing to the coordinate bond in a complex E.g. Cl- and H2O
Polydentate (chelate) ligands contain two or more donor atoms that form coordinate bonds with a transition metal center. E.g. 1,2-ethanediamine (en) Ethanedioate (ox)
129+Chelating Agents If something has more than one lone pair of electrons and can
coordinate bond with a central metal ion in more than one place, it is called a polydentate ligand
EDTA4– (old name ethylenediaminetetraacetic acid) is an example of a polydentate ligand as it has six atoms (two nitrogen atoms and four oxygen atoms) with lone pairs available to form coordinate bonds.
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130+Chelating Agents
Since compounds like EDTA4+ can grip the central atom in more than one place, it is called a chelate
The resulting complex ions formed with chelates are very energetically stable, more stable than if individual ligands are bound to the central ion
131+EDTA Usage
1. Removal of heavy metals Example: lead poisoning
2. Chelating Therapy Reduces calcium ions in the blood and can remove gunk from
hardened arteries
3. Water Softening Getting rid of metal ions in water
4. Food preservation Gets rid of metal ions that would otherwise spoil food
5. Restoring metal scultures
6. Cosmetics - presevative
132+Use In Medicine and Food
Chelating agents are use widely in food because they remove transition metals by forming very energetically stable complex ions; these transition metals would otherwise catalyze oxidation reactions and spoil the food
Chelating agents are also used in medicine to remove toxic metals in the body
+ 133
Let’s Practice
+ 134
Answers
135
+Lesson 9 – d-Block Elements as Catalysts and MagnetsWednesday, October 15, 2014
136+Catalysts A catalyst alters the rate of reaction by providing an alternate
pathway with a lower activation energy
Catalysts are extremely important as they allow reactions to proceed faster
In a homogeneous catalyst, the catalyst is in the same state as the reactants
In a heterogeneous catalyst, the catalyst is in a different state as the reactants
Transition metals are super effective heterogeneous catalysts since they can use their s and d electrons to weakly interact with reactant molecules and arrange them in the correct orientation (remember that in order for a reaction to occur, the reactants must combine with enough energy in the correct orientation!)
137+Examples of Transition Metals as Heterogeneous Catalysts Iron – Used in the Haber process to make ammonia
N2(g) + 3H2(g) 2NH3(g)
Nickel – Converts alkenes to alkanes
Palladium and Platinum (and Nickel) – Used in cars’ catalytic converters
2CO(g) + 2NO(g) 2CO2(g) + N2(g)
MnO2 – Decomposition of H2O2 (we did this last year in lab!)
2H2O2(l) 2H2O(l) + O2(g)
V2O5 – Used in Contact process - 2SO2(g) + O2(g) 2SO3(g)
Fe
Pd or Pt or Ni
MnO2
V2O5
138+Hydrogenation of Oil
Nickel can be used to add hydrogen to unsaturated oils
RCH=CHR + H2 RCH2CH2R
This allows these oils to be solid at room temperature and is useful for cooking
However, this process forms unhealthy trans fats which are not metabolized correctly in the body and leads to cardiovascular problems!
139+Examples of Transition Metals as Homogeneous Catalysts The ability of transition metals to show various oxidation states
makes them effective homogeneous catalysts in redox reactions
Many of these reactions are important in Biochemistry!
Fe2+ in heme Oxygen gets transported throughout the body by forming a weak bond the the iron ion held in the center of the hemoglobin protein! Why would you want a weak bond here?
Co3+ in Vitamin B12 Part of the vitamin B12 molecule consists of an octahedral Co3+ complex. Vitamin B12 is needed for the production of healthy red blood cells and for a healthy nervous system
In a biological setting, catalysts are called enzymes!
140+Catalytic Converters in Cars
In a running car engine, nitrogen gas in the air and oxygen can react in the high heat to form nitrogen monoxide
When NO is released into the air, it combines with more oxygen to form NO2
This NO2 pollutes the air forming smog and can also react with water to form acid rain! (Think about our oxide trends!!!)
Also, carbon monoxide can be formed – CO
Therefore these gases pass through a catalytic converter – often Pd, Pt or Rd, which helps convert these dangerous high energy molecules into more stable ones!
141+Magnetism
Every spinning electron can behave like a tiny magnet
However, when electrons are paired and have opposite spins, their spins cancel out this magnetic effect
Some transition metals are unusual because of the number of unpaired electrons they have and when aligned create highly magnetic substances!
142+Types of Magnetism
Diamagnetism is a property of all materials and produces a very weak opposition to an applied magnetic field.
Paramagnetism, which only occurs with substances which have unpaired electrons, is stronger than diamagnetism. It produces magnetization proportional to the applied field and in the same direction.
Ferromagnetism is the largest effect, producing magnetizations sometimes orders of magnitude greater than the applied field.
* Note: all substances with paired electrons exhibit diamagnetism but the effect is much smaller than paramagnetism and certainly much smaller than ferromagnetism!**
143+Transition Metals
Iron, nickel, and cobalt are ferromagnetic; the unpaired d electrons in large numbers of atoms line up with parallel spins in regions called domains.
Paramagnetism increases with the number of unpaired electrons so generally increases from left to right across the Periodic Table, reaches a maximum at chromium, and decreases. Zinc has no unpaired electrons and so is diamagnetic.
144+Let’s Practice Fe2+
145+Let’s Practice
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+
QuizThursday, October 16, 2014
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+Lesson 10 – d-Sublevel SplitsFriday, October 17, 2014
148+IB Understandings
Understandings:
The d sub-level splits into two sets of orbitals of different energy in a complex ion.
Complexes of d-block elements are coloured, as light is absorbed when an electron is excited between the d orbitals.
The colour absorbed is complementary to the colour observed.
Guidance
The relation between the colour observed and absorbed is illustrated by the colour wheel in the IB Data booklet in section 17.
149+Applications and Skills
Explanation of the effect of the identity of the metal ion, the oxidation number of the metal, and the identity of the ligand on the colour of transition metal ion complexes.
Guidance
Students are not expected to recall the colour of specific complex ions.
Explanation of the effect of different ligands on the splitting of the d orbitals in transition metal complexes and colour observed using the spectrochemical series.
The spectrochemical series is given in the IB data booklet in section 15. A list of polydentate ligands is given in the data booklet in section 16. Students are not expected to know the different splitting patterns and their relation to the coordination number. Only the splitting of the 3-d orbitals in an octahedral crystal field is required.
150+Crystal Field Theory (CFT)
The d-sublevel consists five orbitals – dxy, dyz, dxz, dx2-y2, dz2
151+Colored Ions The color of the ions is related to the presence of partially filled
d-sublevel orbitals
Any ions that do not have any electrons in the d sublevel will not be colored!
152+Visible Spectrum
The visible spectrum ranges from about 400nm to 700nm. The color we see depends on the wavelength
The color depends on which colors are absorbed and which colors are transmitted or reflected!!
153+LightWhite light contains all
wavelengths in the visible spectrum
Transition metals absorb some light and transmits others
The light emitted is the composite of the wavelengths
154+D-Level Splits
But, why do these transition metals absorb light?!
In an isolated transition metal, the d-orbitals are said to be degenerate or have the same energy
However, when ligands bond with the central atom, an electric field is produced which causes the d sublevel to split into two – a higher and a lower energy level
When light passes through these d sublevels, the d electrons jump from the lower energy d orbitals to the higher energy d orbitals
155
156+Energy Level SplitsThe energy separation between the orbitals is ∆E and hence the color of the complex depends on the following factors:
1. the nuclear charge and the identity of the central metal ion
2. the charge density of the ligand
3. the geometry of the complex ion (the electric field created by the ligand’s lone pair of electrons depends on the geometry of the complex ion)
4. the number of d electrons present and hence the oxidation number of the central ion.
157+Nuclear Charge
The strength of the bond between the ligand and the ion depends on the electrostatic attraction
Ligands interact more efficiently the higher the nuclear charge
Example: [Mn(H2O)6]2+and [Fe(H2O)6]3+ both have the same electron configuration but the iron nucleus has a higher nuclear charge and so has a stronger interaction with the water ligands
Mn absorbs in the green region and therefore look pink in solution
Fe absorbs in the higher energy blue region and therefore look yellow/brown
158+Charge Density of Ligand
The greater the charge density of the ligand, the greater the energy level split between the d orbitals and the higher energy that is absorbed
The spectrochemical series arranges the ligands according to the energy separation, ∆E, between the two sets of d orbitals
The wavelength at which maximum absorbance occurs, λmax, decreases with the charge density of the ligand, as shown in the table below and in Section 15 in your IB Booklet!!
159+Geometry of the Complex
The coordination number and geometry of the complex ion also affects the color
160+Number of d electrons and oxidation state of central ion The strength of the interaction between the ligand and the
central metal ion and the amount of electron repulsion between the ligand and the d electrons depends on the number of d electrons and hence the oxidation state of the metal.
EXAMPLE: [Fe(H2O)6]2+ absorbs violet light and so appears green/yellow, whereas [Fe(H2O)6]3+ absorbs blue light and appears orange/brown.
161+Let’s Practice!
State the formula and the shape of the complex ion formed in the following reactions.(a) Some iron metal is dissolved in sulfuric acid and then left exposed to air until a yellow solution is formed.
(b) Concentrated hydrochloric acid is added to aqueous copper sulfate solution to form a yellow solution.
(c) A small volume of sodium chloride is added to aqueous silver nitrate solution. The white precipitate dissolves to form a colourless solution when ammonia solution is added.
162+Answer
(a) [Fe(H2O)6]3+
The oxidation number is +3 as the complex is left exposed to air. The shape is octahedral as the coordination number = 6 (see left).
(b) The complex [CuCl4]2– is yellow.The shape is tetrahedral as the coordination number = 4 (see left).
(c) NaCl(aq) + AgNO3(aq) → AgCl(s) + NaNO3(aq)The complex [Ag(NH3)2]+ is linear as the coordination number is 2. [H3N—Ag—NH3]+
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Lesson 11 – Colored IonsWednesday, October 22nd
+The D Block Colored Compounds In an isolated atom all of the d sublevel electrons
have the same energy.
When an atom is surrounded by charged ions or polar molecules, the electric field from these ions or molecules has a unequal effect on the energies of the various d orbitals and d electrons.
The colors of the ions and complex ions of d block elements depends on a variety of factors including:
The particular element The oxidation state The kind of ligands bound to the element
Various oxidation states of Nickel (II)
+Colors in the D Block
The presence of a partially filled d sublevels in a transition element results in colored compounds.
Elements with completely full or completely empty subshells are colorless, For example Zinc which has a full d subshell. Its compounds
are white
A transition metal ion exhibits color, if it absorbs light in the visible range (400-700 nanometers)
If the compound absorbs a
particular wavelengths of light its
color is the composite of those
wavelengths that it does not absorb.
It shows the complimentary color. .168
+Colors and d Electron Transitions The d orbitals may split into two groups so that two orbitals
are at a lower energy than the other three
The difference in energy of these orbitals varies slightly with the nature of the ligand or ion surrounding the metal ion
When white light passes through a compound of a transition metal, light of a particular frequency is absorbed as an electron is promoted from a lower energy d orbital to a higher one.
When the energy of the transition: ∆E =hn may occur in the visible region, the compound is colored
+Magnetic Properties Paramagnetism --- Molecules with one
or more unpaired electrons are attracted to a magnetic field. The more unpaired electrons in the molecule the stronger the attraction. This type of behavior is called
Diamagnetism --- Substances with no unpaired electrons are weakly repelled by a magnetic field.
Transition metal complexes with unpaired electrons exhibit simple paramagnetism.
The degree of paramagnetism depends on the number of unpaired electrons
.170
+Catalytic Behavior Many D block elements are catalysts
for various reactions
Catalysts speed up the rate of a chemical reaction with out being consumed.
The transition metals form complex ions with species that can donate lone pairs of electrons.
This results in close contact between the metal ion and the ligand.
Transition metals also have a wide variety of oxidation states so they gain and lose electrons in redox reactions
.
+Some Common D Block CatalystsExamples of D block elements that
are used as catalysts:
1. Platinum or rhodium is used in a catalytic converter2. MnO2 catalyzes the
decomposition of hydrogen peroxide 3. V2O5 is a catalyst for
the contact process 4. Fe in Haber process 5. Ni in conversion of alkenes to alkanes
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+
Lesson 12 – ReviewTuesday, October
174+Hints
Know the EXACT definition of electronegativity
Remember that silicon forms network solids; these have VERY high melting points!
Any elements in Group 12 (where Zinc lives) are not considered transition metals