chapter 2: atoms, molecules and ions. 2 the language of chemistry atoms –composed of electrons,...

Chapter 2:Atoms, Molecules and Ions

Chapter 2:Atoms, Molecules and Ions

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The Language of ChemistryThe Language of Chemistry

• Atoms– Composed of electrons, protons and neutrons

• Molecules– Combinations of atoms

• Ions– Charged particles

3

Laws of Chemical CompositionLaws of Chemical CompositionLaws of Chemical CompositionLaws of Chemical Composition

1790 Antoine Lavoisier, The Father of Modern Chemistry

• Law of Conservation of Matter

• Total mass remains constant during a chemical reaction; or

• Total mass of reactants = total mass of products.

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Law of Conservation of Mass: A Law of Conservation of Mass: A Conceptual ExampleConceptual Example

Law of Conservation of Mass: A Law of Conservation of Mass: A Conceptual ExampleConceptual Example

Jan Baptista van Helmont (1579–1644) first measured the mass of a young willow tree and, separately, the mass of a bucket of soil and then planted the tree in the bucket. After five years, he found that the tree had gained 75 kg in mass even though the soil had lost only 0.057 kg. He had added only water to the bucket, and so he concluded that all the mass gained by the tree had come from the water. Explain and criticize his conclusion.

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Laws of Chemical CompositionLaws of Chemical CompositionLaws of Chemical CompositionLaws of Chemical CompositionJoseph Proust, Law of Constant

Composition (Law of Definite Composition, or Definite Proportions)

• All samples of a compound have the same composition, or all samples have the same proportion by mass of the elements present.

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Law of Constant Composition: ExampleLaw of Constant Composition: ExampleLaw of Constant Composition: ExampleLaw of Constant Composition: Example

Example: CuHCO3 is ALWAYS

57.48% Cu, 5.43% C, 0.91% H and

36.18% O by mass

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John Dalton and the Atomic Theory John Dalton and the Atomic Theory of Matterof Matter

John Dalton and the Atomic Theory John Dalton and the Atomic Theory of Matterof Matter

Importance

• Explained Laws of Conservation of Mass and Constant Composition andextended them to cover another law.

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Main ideas of Dalton’s modelMain ideas of Dalton’s model

1. All matter consists of of small, indivisible particles called atoms.

2. All atoms of a given element are alike but atoms of any one element are different from the atoms of every other element.

3. Compounds are formed when atoms of different elements unite in small, whole-number ratios.

4. Chemical reactions involve rearrangement of atoms; no atoms are created, destroyed or broken apart in a chemical reaction.

According to Dalton, atoms are indivisible and indestructible.

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Dalton’s Atomic Theory: Conservation of Mass and

Definite Proportions

Dalton’s Atomic Theory: Conservation of Mass and

Definite Proportions… six fluorine atoms and four

hydrogen atoms after reaction. Mass is conserved.

Six fluorine atoms and four hydrogen atoms before reaction …

HF always has one H atom and one F atom; always

has the same proportions (1:19) by mass.

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Another Important LawAnother Important Law

Law of Multiple Proportions

• A given set of elements may combine to produce two or more different compounds, each with a unique composition.

• Example: H2O (water) and

H2O2 (hydrogen peroxide)

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Law of Multiple Proportions (cont’d)

Law of Multiple Proportions (cont’d)

• Four different oxides of nitrogen can be formed by combining 28 g of nitrogen with:

• 16 g oxygen, forming Compound I• 48 g oxygen, forming Compound II• 64 g oxygen, forming Compound III• 80 g oxygen, forming Compound IV

• Compounds I–IV are N2O, N2O3, N2O4, N2O5

What is the ratio 16:48:64:80 expressed as small whole numbers?

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Dalton’s Model of the AtomDalton’s Model of the Atom

NO subatomic particles!

In modern atomic theory, the atom is divided into protons, neutrons and electrons

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1897 JJ Thomson1897 JJ Thomson

Cause Cause stream of stream of negative negative particles that particles that are always are always the same, no the same, no matter what matter what gas is usedgas is used

Thomson experimented with CATHODE RAY TUBES

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1897 JJ Thomson1897 JJ Thomson

Known as Known as discoverer of discoverer of the the ELECTRON—ELECTRON—led to the led to the “plum pudding “plum pudding model” of the model” of the atomatom

Mass to charge ratio for an electron:

m/c = 5.69 x 10-9g/coulomb

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MillikanMillikan

• Obtained the charge of an electron, which coupled with Thomson’s work, allowed the calculation of the mass of an electron.

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Millikan’s ConclusionsMillikan’s Conclusions

• Measured the charge of an electron:

1.602 x 10-19 coulomb (C)

• Calculated the mass of an electron:

9.109 x 10-31 kg

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The modern view of the atom was The modern view of the atom was

developed by developed by Ernest Ernest RutherfordRutherford of New Zealand of New Zealand (1871-1937).(1871-1937).

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Ernest RutherfordErnest RutherfordErnest RutherfordErnest Rutherford

Canterbury Canterbury University in University in Christchurch, NZ Christchurch, NZ

Rutherford laboratoryRutherford laboratory

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Gold Foil ExperimentGold Foil Experiment

Screen 2.9Screen 2.9

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Rutherford’s Main Rutherford’s Main ConclusionsConclusions

1. The atom is mostly empty space. 1. The atom is mostly empty space.

2.2. All of the positive charge, and most of the mass, is All of the positive charge, and most of the mass, is concentrated in a very small volume: concentrated in a very small volume:

THE NUCLEUSTHE NUCLEUS

3. Electrons are outside the nucleus.3. Electrons are outside the nucleus.

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ProtonsProtons

Mass of proton about same as an H Mass of proton about same as an H atom (1 atomic mass unit)atom (1 atomic mass unit)

Positive charge = negative charge Positive charge = negative charge from electrons in a neutral atom.from electrons in a neutral atom.

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Neutrons (Chadwick, 1932)Neutrons (Chadwick, 1932)

• the nucleus also contains neutrons: particles with masses almost identical to protons but with no charge

• neutrons also help disperse the strong repulsion of positive charges

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SummarySummary

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Atomic SymbolsAtomic Symbols

An atomic symbol An atomic symbol represents the represents the element.element.

1313

AlAl

26.98126.981

Atomic numberAtomic number

Atom symbolAtom symbol

Atomic mass or weightAtomic mass or weight

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Mass Number, AMass Number, A• The Mass NumberThe Mass Number (A) (A)

= # protons + # neutrons= # protons + # neutrons

• A boron atom can have A boron atom can have A = 5 p + 5 n = 10 amuA = 5 p + 5 n = 10 amu

A

Z

10

5B

A

Z

10

5B

Named as boron-10

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Atomic Number, ZAtomic Number, Z

Atomic number, Z, is Atomic number, Z, is thethe number of number of protons in the nucleus.protons in the nucleus. (same for (same for every atom of that element)every atom of that element)

1313

AlAl

26.98126.981

Atomic numberAtomic number

Atom symbolAtom symbol

Atomic mass or weightAtomic mass or weight

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IsotopesIsotopes

• Atoms of the same element (Atoms of the same element (same Zsame Z) ) but different mass number (but different mass number (AA).).

• Boron-10 has 5 p and 5 n: Boron-10 has 5 p and 5 n: 101055BB

• Boron-11 has 5 p and 6 n: Boron-11 has 5 p and 6 n: 111155B B

10B

11B

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Hydrogen IsotopesHydrogen IsotopesHydrogen IsotopesHydrogen Isotopes

Hydrogen has 3 isotopesHydrogen has 3 isotopes

1111HH

2211HH

3311HH

1 proton and 2 neutrons, tritium

radioactive

1 proton and 1 neutron, deuterium

1 proton and 0 neutrons, protium

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Isotopes & Isotopes & Their UsesTheir UsesIsotopes & Isotopes & Their UsesTheir Uses

Heart scans with Heart scans with radioactive radioactive technetium-99. technetium-99.

99994343TcTc

Emits gamma raysEmits gamma rays

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Sample ProblemSample Problem

• Example 2.1 Write the atomic symbols for the following species:

• a. the isotope of carbon with a mass of 13

• b. the nuclear symbol when Z = 92 and the number of neutrons = 146.

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Solution to ProblemSolution to Problem

13 C 6

238 U 92

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IonsIonsDefinition:

• Atoms GAIN electrons to become negative ions, or anions.

• Atoms LOSE electrons to become positive ions, or cations.

• How are ions represented?

Charges are always shown to upper right of symbol. 119

9 F

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Sample ProblemSample Problem

• Example 2.2 Write the atomic symbols for the following:

• a. a species having 16 protons, 16 neutrons and 18 electrons

• b. the phosphide ion (P) with an overall charge of -3

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SolutionSolution

32 S 2-

16

31 P 3-

15

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Atomic MassAtomic Mass• F. An atomic mass unit (amu or u) is

defined as exactly one-twelfth the mass of a carbon-12 atom

• 1 u = 1.66054 × 10–24 g

• The atomic mass of an element is the relative mass of an atom compared to a standard (carbon-12). It is NOT equal to the mass number!

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Atomic Mass Is Not Atomic Mass Is Not Equal to Mass Equal to Mass

Number!!Number!!The atomic mass is a weighted The atomic mass is a weighted average average of of

the masses of the naturally occurring the masses of the naturally occurring isotopes.isotopes.

(also called atomic weight)(also called atomic weight)

1313

AlAl

26.98126.981

Atomic numberAtomic number

Atom symbolAtom symbol

Atomic mass or weightAtomic mass or weight

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Atomic MassAtomic Mass

• Weighted average is the addition of the contributions from each isotope

• Isotopic Abundance is the percent or fraction of each isotope found in nature.

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Most Abundant Most Abundant IsotopeIsotope

1313

AlAl

26.98126.981

Atomic numberAtomic number

Atom symbolAtom symbol

Atomic mass or weightAtomic mass or weight

Usually can round atomic mass Usually can round atomic mass on p.t. to nearest whole numberon p.t. to nearest whole number

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Atomic MassAtomic Mass

Example 2.3 Determine the average atomic mass of magnesium which has three isotopes with the following masses: 23.98 (78.6%), 24.98 (10.1%), 25.98 (11.3%).

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RadioactivityRadioactivity

• Radioactive isotopes are unstable– These isotopes decay over time– Emit other particles and are transformed into

other elements– Radioactive decay is not a chemical process!

• Particles emitted– High speed electrons: β (beta) particles– Alpha (α) particles: helium nuclei– Gamma (γ) rays: high energy light

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Nuclear StabilityNuclear Stability

• depends on the neutron/proton ratio– For light elements, n/p is approximately 1– For heavier elements, n/p is approximately

1.4/1

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Figure 2.5 – The Nuclear Belt of Stability

Figure 2.5 – The Nuclear Belt of Stability

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The Periodic Table: Elements OrganizedThe Periodic Table: Elements Organized

• Know location and description of: – groups or families

– periods or series

– metals, metalloids, nonmetals and their properties

– main group elements

– transition metals

– lanthanides and actinides

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Groups or FamiliesGroups or Families

• Vertical columns are groups– Numbered as 1-18 (new)– Old system uses Roman numerals and A,B

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Periods or SeriesPeriods or Series• Horizontal rows are periods• 7 periods total

– First period is H and He– Second period is Li to Ne– Etc.

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Group Names to MemorizeGroup Names to Memorize

- Group 1 (IA): alkali metals.

- Group 2 (IIA) : alkaline earth metals.

- Group 17(VIIA): halogens.

- Group 18 (VIIIA): noble gases

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Group 1A: Alkali MetalsGroup 1A: Alkali MetalsLi, Na, K, Rb, CsLi, Na, K, Rb, Cs

Group 1A: Alkali MetalsGroup 1A: Alkali MetalsLi, Na, K, Rb, CsLi, Na, K, Rb, Cs

Cutting sodium metalCutting sodium metal

Reaction of potassium + H2O

https://www.youtube.com/watch?v=oqMN3y8k9So https://www.youtube.com/watch?v=Jy1DC6Euqj4

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MagnesiumMagnesium

Magnesium Magnesium oxideoxide

Group 2A: Alkaline Earth MetalsGroup 2A: Alkaline Earth MetalsBe, Mg, Ca, Sr, Ba, RaBe, Mg, Ca, Sr, Ba, Ra

https://www.youtube.com/watch?v=qSr39UwpELo

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Group 7A: Group 7A: HalogensHalogens

F, Cl, Br, I, AtF, Cl, Br, I, At

Group 7A: Group 7A: HalogensHalogens

F, Cl, Br, I, AtF, Cl, Br, I, At

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Group 8A: Noble Gases Group 8A: Noble Gases He, Ne, Ar, Kr, Xe, RnHe, Ne, Ar, Kr, Xe, Rn

Group 8A: Noble Gases Group 8A: Noble Gases He, Ne, Ar, Kr, Xe, RnHe, Ne, Ar, Kr, Xe, Rn

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Regions of the Periodic TableRegions of the Periodic TableRegions of the Periodic TableRegions of the Periodic Table

Metals are on the left of stair step line

NON-METALS are on the right of stair step line

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Exception:Exception:Group 1A: Hydrogen is a Group 1A: Hydrogen is a

Non-metal!Non-metal!

Exception:Exception:Group 1A: Hydrogen is a Group 1A: Hydrogen is a

Non-metal!Non-metal!

Shuttle main engines Shuttle main engines use Huse H22 and O and O22

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Properties of Metals/Non-metals/Metalloids

Properties of Metals/Non-metals/Metalloids

• Metals-shiny,smooth, solid at room temperature, good conductors of heat and electricity, malleable and ductile.

• Metalloids (along stair step line) physical and chemical properties of both metals and nonmetals- B, Si, Ge, As, Sb, Te

• Nonmetals-low melting and boiling points, brittle, dull-looking solids, poor conductors of heat and electricity.

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The Periodic Table: Elements OrganizedThe Periodic Table: Elements Organized

• Main group elements -tall columns (Groups 1,2,13,14,15,16,17,18)

• Transition metals- short columns (10)

• Lanthanides and actinides- long rows below main part of table.

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Transition ElementsTransition ElementsTransition ElementsTransition Elements

Lanthanides and actinidesLanthanides and actinides

Iron in air gives Iron in air gives iron(III) oxideiron(III) oxide

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Periodic TablePeriodic Table• Dmitri Mendeleev Dmitri Mendeleev

developed the modern developed the modern periodic table. Argued that periodic table. Argued that element properties areelement properties are periodic functions of their periodic functions of their atomic weightsatomic weights..

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Periodic TablePeriodic TablePeriodic Law:Periodic Law:

• We now know that element We now know that element properties are periodic properties are periodic functions of their functions of their ATOMIC ATOMIC NUMBERS.NUMBERS.

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Germanium:Prediction vs. Observation

Germanium:Prediction vs. Observation

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Henry MoseleyHenry Moseley

• A student of Rutherford’s

• Arranged the periodic table in order of increasing atomic number

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Molecules Molecules • A molecule is a group of two or more

atoms held together in a definite shape by covalent bonds.

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Empirical and Molecular FormulasEmpirical and Molecular Formulas

Empirical formula: the simplest whole number ratio of elements in a compound

Molecular formula: gives the ACTUAL number of each kind of atom in a molecule.

Example: Molecular formula of glucose – C6H12O6Can divide all subscripts by 6, so the empirical

formula is CH2O

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Structural FormulasStructural Formulas

• Structural formulas show how atoms are attached to one another.

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Ions: Atoms with a ChargeIons: Atoms with a ChargeDefinition:• Cations: positive ions• Anions: negative ions• Polyatomic ion: A group of atoms with a

charge

–You must memorize all the polyatomic ions (structure, name and charge) found on your purple flashcard sheet!

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Ionic CompoundsIonic Compounds• Ionic Compounds are

cations and anions held together by electrostatic attraction.

• Their formulas are the simplest ratio of numbers of atoms (called an empirical formula) and represent one formula unit.

There is NO net charge in an ionic compound!

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Solutions of Ionic CompoundsSolutions of Ionic Compounds• Solutions of Ionic

Compounds are strong electrolytes: their solutions conduct electricity.

• Non-electrolytes do not conduct electricity in water solution. (sugar, molecular compounds) There is NO net charge

in an ionic compound!

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Charge Balance of Ionic Compounds

Charge Balance of Ionic Compounds

• See Handout and practice worksheets.

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Monatomic IonsMonatomic Ions

• • Group IA metals form ions of 1+ charge.• Group IIA metals form ions of 2+ charge.• Aluminum, a group IIIA metal, forms ions with a

3+ charge.• Nonmetal ions of groups V, VI, and VII usually

have charges of:• VA: -3• VIA: -2• VIIA: -1

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•Atoms that are close to a noble gas (group 18) form ions that contain the same number of electrons as the neighboring noble gas atom•Applies to Groups 1, 2, 16 and 17, plus Grp 13 metals (e.g., Al 3+) and Grp 15 non-metals/metalloids (e.g., N 3-)

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•

• Some metal ions have > one possible charge. A Roman numeral are used for the charge.

• If a metal only has ONE charge, a Roman numeral is NOT used.

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Symbols and Periodic Table Locations of Some Monatomic Ions

Symbols and Periodic Table Locations of Some Monatomic Ions

Titanium forms both titanium(II) and

titanium(IV) ions.

Copper forms either copper(I) or copper(II) ions.

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Polyatomic IonsPolyatomic Ions

• See handouts: MUST MEMORIZE!!!

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Polyatomic IonsPolyatomic Ions• Oxyanions: the anions are composed of

oxygen and one other element

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Nitrate and SulfateNitrate and Sulfate

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Polyatomic IonsPolyatomic Ions• Oxyanions: the anions are composed of oxygen and one other

element

Ex:SO42- (sulfate), NO2

- (nitrite) , MnO4- (permanganate)

• two oxyanions of the same element(a)The anion with the smaller number of oxygens uses the roots of the

element plus “ite”(b)The higher number use the root plus “ate”

Ex: SO32- sulfite, NO2

- nitrite, PO3-3 phosphite

SO42- sulfate, NO3

- nitrate, PO4-3 phosphate

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Four oxyanionsFour oxyanionsThere are four oxyanions containing Cl

The middle two are named as two oxyanions

The one with one less oxygen than the chlorite has a prefix of hypo

The one with one more oxygen than the chlorate has a prefix of per

Ex: ClO- :hypochlorite

ClO2- :chlorite

ClO3- :chlorate

ClO4- :perchlorate

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Naming binary compoundsNaming binary compounds

• Use name of metal with no changes• Change the name of the anion by taking

the “stem” and add the suffix –ide ex: CI2: chlorine Cl-: chlorine ( ine ) + ide = chloride• Examples:

– NaCl - sodium chloride– MgCl2 - magnesium chloride

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Naming Binary Ionic CompoundsNaming Binary Ionic Compounds

• Name the following binary ionic compounds

• Metal nonmetal compound name

• KI potassium iodine potassium iodide

• Li2S lithium sulfur lithium sulfide

• Mg3N2 magnesium nitrogen magnesium nitride

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Metals with multiple oxidation states

Metals with multiple oxidation states

• Two methods: Stock and “classical” system

Stock system (used at CHS)metal name and the oxidation state in Roman numbers in

parenthesis

Ex: Fe2+ = iron (II)

• Form compound by balancing charge of metal with correct number of nonmetalsEx: CoCl3 = cobalt(III) chloride

Charge of metal = |charge of anion x subscript|

subscript of cation

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Example 2.4 Write names or formulas for:Example 2.4 Write names or formulas for:

• rubidium bromide AlCl3• barium nitride Ca3P2

• cobalt (II) bromide NaI

• Strontium oxide PbS2

Sample ProblemSample Problem

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SolutionSolution

• RbBr Aluminum Chloride

• Ba3N2 Calcium Phosphide

• CoBr2 Sodium Iodide

• SrO Lead (IV) sulfide

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Example 2.5 Write names or formulas for:Example 2.5 Write names or formulas for:

• (NH4)2S strontium hydroxide• K2Cr2O7 cobalt (II) sulfate• Al(NO2)3 calcium phosphate• Fe(CN)2 tin (IV) carbonate

Sample ProblemSample Problem

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SolutionSolution

• ammonium sulfide Sr(OH)2

• potassium dichromate CoSO4

• aluminum nitrite Ca3(PO4)2

• Iron (II) cyanide Sn(CO3)2

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Binary Molecular CompoundsBinary Molecular Compounds

• (Two nonmetals bonded together; may also include a metalloid in formula)

e.g., CO, NO, HF, SiO2

• a. First symbol is usually element to furthest left in p.t.

• b. Numbers of atoms indicated by subscripts are written as prefixes.

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Binary Molecular CompoundsBinary Molecular Compounds

• The name consists of two words.

• Directions:

• 1. Write name of first element preceded by prefix EXCEPT do not write mono- if only have ONE of first element.

• 2. Name of second element ends with -ide; is also preceded by prefix.

86

Names of Binary CompoundsNames of Binary Compounds

87

ExampleExample

• Consider the compounds CO and CO2

Name the element that appears first in the formula: CARBON

The second element has an altered name: retain the stem of the element name and replace the ending by -ide

OXYGEN OXIDE

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Sample ProblemSample Problem

Example 2.4 Write names or formulas for the following:B2O3 tetraphosphorus pentachloride

AsO5 dihydrogen monoxide As2O7

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SolutionSolution

• Diboron trioxide P4Cl5• Arsenic pentoxide H2O

• Diarsenic heptoxide

90

AcknowledgementsAcknowledgements

• Thomson/Brooks Cole (Textbook Publishers)

• Mark P. Heitz, State University of New York at Brockport (Prentice Hall, Book Publishers)