topic 2 atoms, elements, molecules, ions, and compounds

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Topic 2

Atoms, Elements, Molecules, Ions, and Compounds

Early in the 19th century John Dalton developed atomic theory. His theory explained the best available experimental data at that time. His theory has been modified since then with the discovery of other data, but his work was the initial ground work that we will examine first.

Atomic Theory of Matter• Postulates of Dalton’s Atomic Theory

1.)All matter is composed of indivisible atoms. An atom is an extremely small particle of matter that retains its identity during chemical reactions. 2.)An element is a type of matter composed of only one kind of atom, each atom of a given element having the same properties. Mass is one such property. Thus the atoms of a given element have a characteristic mass.

2

Protons, neutrons, electrons

Atoms have different isotopes that have the same # protons but different # neutrons and hence different mass. Note: #protons gives identity of atom.

Later found indivisible to be untrue.

Later found all atoms of the same element does not have to have the same mass.

Atomic Theory of Matter

• Postulates of Dalton’s Atomic Theory

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3.) A compound is a type of matter composed of atoms of two or more elements chemically combined in fixed proportions.

– The relative numbers of any two kinds of atoms in a compound occur in simple ratios.

– Water, for example, consists of hydrogen and oxygen in a 2 to 1 ratio (2H: 1O) for all molecules of water.


• Postulates of Dalton’s Atomic Theory

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4.) A chemical reaction consists of the rearrangements of the atoms present in the reacting substances to give new chemical combinations present in the substances formed by the reaction (new chemical with different properties).

5.) Atoms are not created, destroyed, or broken into smaller particles by any chemical reaction.

Na (s) + Cl2 (g) 2 2 NaCl (s)

Protons, neutrons, electrons

i.e., solid sodium mixed with chlorine gas forms a new substance, salt, with totally different properties from the starting materials.

Once again, later found indivisible to be untrue.


• The Structure of the Atom

5

– Although Dalton postulated that atoms were indivisible, experiments at the beginning of the 1900’s showed that atoms themselves consist of particles.

– Experiments by Ernest Rutherford in 1910 showed that the atom was mostly “empty space.”


6

– These experiments showed that the atom consists of two kinds of particles: a nucleus, the atom’s central core, which is positively charged and contains most of the atom’s mass, and one or more electrons.

– Electrons are very light, negatively charged particles that exist in the region around the atom’s positively charged nucleus.

Nucleus

(+)

e-


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– In 1897, the British physicist J. J. Thompson conducted a series of experiments that showed that atoms were not indivisible particles but instead made of smaller particles.

– From his experiments, Thompson calculated the ratio of the electron’s mass, me, to its electric charge, e.


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– In 1909, U.S. physicist, Robert Millikan obtained the charge on the electron (1.602 x 10-19 C).

– These two discoveries (Millikan and Thompson) combined provided us with the electron’s mass of 9.109 x 10-31 kg, which is more than 1800 times smaller than the mass of the lightest atom (hydrogen) thereby proving that the atom is made up of smaller particles.

– These experiments showed that the electron was indeed a subatomic particle.

Atomic Theory of MatterThe nuclear model of the atom.

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– Ernest Rutherford, a British physicist, put forth the idea of the nuclear model of the atom in 1911, based on experiments done in his laboratory by Hans Geiger and Ernest Morrison.

– Rutherford’s famous gold leaf experiment gave credibility to the theory that the majority of the mass of the atom was concentrated in a very small nucleus.

– Positively charged alpha particles were directed at a metal foil. Only 1/8000 were deflected indicating that the nucleus was extremely small and positively charged. Only those alpha particles that directly hit the nucleus were deflected; the rest passed through.


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– Most of the mass of an atom is in the nucleus; however, the nucleus occupies only a very small portion of the space in the atom.

– The diameter of an atom is approximately 100 pm while the diameter of the nucleus is approximately 0.001 pm. For comparison, if an atom was 3 miles in diameter, the nucleus would be the size of a golf ball.

– The nucleus of an atom is composed of two different kinds of particles: protons (+) and neutrons (neutral).

– An important property of the nucleus is its positive electric charge.


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– A proton is the nuclear particle having a positive charge equal to that of the electron’s (a “unit” charge) and a mass more than 1800 times that of the electron. It is for this reason that we refer to H as a pure proton.

– The number of protons in the nucleus of an atom is referred to as its atomic number (Z) and gives the identity of an element. All species that have same #p have the same properties.

neutral species: #p = #e-

#p remains constant in species; #e- can vary and dictates the charge of species

H Z=1 1p, 1e-

Na Z=11 11p, 11e- Cl Z=17 17p, 17e-

Cl- Z=17 17p, 18e-Na+ Z=11 11p, 10e-

+ charge, more p than e-

- charge, more e- than p


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– An element is a substance whose atoms all have the same atomic number (Z). The #protons defines the identity of an atom and can be found on the periodic table (large number in top of element box).

– The neutron is a nuclear particle having a mass almost identical to that of a proton, but no electric charge. The charge of the nucleus comes from the #protons. The atoms may have different masses because of different #neutrons (isotopes).

– Summary of masses and charges of the three fundamental particles:

particle mass, kg charge, C relative charge

location

electron, e- 9.109 x 10-31 -1.602 x 10-19 -1 outside nucleus

proton, p 1.6726 x 10-27 1.602 x 10-19 +1 nucleus

neutron, n 1.6749 x 10-27 0 0 nucleus

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The mass number (A) is the total number of protons and neutrons in a nucleus.

Nasodium 2311 23

A nuclide is an atom characterized by a definite atomic number and mass number.The shorthand notation for a nuclide consists of its symbol with the atomic number, Z, as a subscript on the left and its mass number, A, as a superscript on the left.

A = #p + #n = Z + #n

How many neutrons does sodium 23 have?A = 23, Z = 11 (number on periodic table)A = Z + #n 23 = 11 + #n #n = 23 - 11 = 12

EAZ

11p, 12 n, 11e-

Na2311

+

11p, 12 n, 10e-

What is the nuclide symbol for a nucleus that consists of 17 protons, 18 neutrons, and 17 electrons?

How many protons, neutrons, and electrons are in the following nucleus Br80

35

14

HW 9HW 10

What’s the element? 17 p atomic number on periodic table for chorine

A = #p + #n = 17 + 18 = 35 Cl3517

35 p 45 nA = #p + #n 80 = 35 + #n #n = 80 – 35 = 45 n

36 e-

Note: #e- = #p; therefore, neutral species

Note: #e- > #p; therefore, negatively charged species

35e- + one additional e- based on -1 charge = 36 e-

code for both: proton


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– The fractional abundance is the fraction of a sample of atoms that is composed of a particular isotope.

– Isotopes are atoms whose nuclei have the same atomic number (Z) but different mass numbers (A); that is, the nuclei have the same number of protons but different numbers of neutrons thereby causing them to have different masses.

3517Cl

– Chlorine, for example, exists as two isotopes: chlorine-35 and chlorine-37.

17p, 18 n, 17e- 17p, 20 n, 17e-

Cl3717

(0.75771)(34.97 amu) + (0.24229) (36.97 amu) = 35.45 amu

Frac abund = 75.771%Mass = 34.97 amu

Frac abund = 24.229%Mass = 36.97 amu

Note: The mixture of isotope masses make up the actual mass of the element given on periodic table. Cl has a mass of 35.45 amu which is based on the two isotopes of Cl-35 and Cl-37.

Atomic WeightsCalculate the atomic weight of boron, B, from the following data: ISOTOPE ISOTOPIC MASS (amu) FRACTIONAL ABUNDANCE

B-10 10.013 0.1978 (19.78%)

B-11 11.009 0.8022 (80.22%)

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B-10: 10.013 amu x 0.1978 = 1.980B-11: 11.009 amu x 0.8022 = 8.831

10.811 = 10.811 amu ( = atomic wt.)

HW 11

Note: fractional abundances must add to 1 (100%)

Note: mass on periodic table matches 10.811 amu (weighted average of isotopes)

code: amu

Atomic Weights

Dalton’s Relative Atomic Masses

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– Since Dalton could not weigh individual atoms, he devised experiments to measure their masses relative to the hydrogen atom.

– Hydrogen was chosen as it was believed to be the lightest element. Daltons assigned hydrogen a mass of 1 (1 Dalton = mass of H).

– For example, he found that carbon weighed 12 times more than hydrogen. He therefore assigned carbon a mass of 12 ( mass of carbon = 12 Daltons).

Atomic Weights

Dalton’s Relative Atomic Masses

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– Dalton’s atomic weight scale was eventually replaced in 1961, by the present carbon–12 mass scale.

– One atomic mass unit (amu) is, therefore, a mass unit equal to exactly 1/12 the mass of a carbon–12 atom.

– On this modern scale, the atomic weight of an element is the average atomic mass for the naturally occurring element, expressed in atomic mass units. Periodic table is based on atom mass with units of amu.

Na - 23.1 amu mass of 1 atom of sodium

The Periodic TableIn 1869, Dmitri Mendeleev discovered that if the known elements were arranged in order of atomic mass (A), they could be placed in horizontal rows such that the elements in the vertical columns had similar properties.

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– periodic table - tabular arrangement of elements in rows and columns, highlighting the regular repetition of properties of the elements.

– periodic law – states that certain sets of physical and chemical properties recur at regular intervals (periodically) when the elements are arranged according to increasing atomic number (Z).

– Note: eventually changed from atomic mass to atomic number because of a couple of anomalies.

Figure: A modern form of the periodic table.

20anomalies

The Periodic Table

Periods and Groups

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– A period consists of the elements in any one horizontal row of the periodic table.

– A group consists of the elements in any one column of the periodic table (similar properties/structure).

– The groups are usually numbered (North American uses roman numbers and A/B; IUPAC 1-18).

– The eight “A” groups are called main group (or representative) elements.

The Periodic Table

• Periods and Groups

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– The “B” groups are called transition elements.

– The two rows of elements at the bottom of the table are called inner transition elements.

– Elements in any one group have similar properties because their outer shells have the same number of valence electron (discuss in later sections).

The Periodic Table• Periods and Groups

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– The elements in group IA (except H) - alkali metals

– The group VIIA elements - halogens

– The elements in group IIA - alkaline earth metals,

– The group VIIIA elements – noble gases (monoatomic)– Diatomic elements – H2, N2, O2, F2, Cl2, Br2, I2

– Most species are solids at room temperature; H2, N2, O2, F2, Cl2, and noble gases are gases; Br2 and Hg are liquids.

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HW 12

metalsnonmetalsMetallic character

Metallic character

Metals, Nonmetals, and Metalloids – generally, left of staircase are metals, touching staircase are metalloids, right of staircase are nonmetals. This is important for determining bond type, using proper terminology, and making decisions.

code:table

Chemical Formulas; Molecular and Ionic Substances

The chemical formula of a substance is a notation using atomic symbols with subscripts to convey the relative proportions of atoms of the different elements in a substance.

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– aluminum oxide, Al2O3 2Al:3O ratio

– sodium chloride, NaCl 1Na:1Cl ratio

– calcium nitrate, Ca(NO3)2 1Ca:2NO3- ratio

or 1Ca:2N:6O ratio

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– A molecule is a definite group of atoms that are chemically bonded together through sharing of electrons (covalent bonding, generally nonmetal-nonmetal including H).


• Molecular substances

– A molecular substance is a substance that is composed of molecules, all of which are alike.

– A molecular formula gives the exact number of atoms of elements in a molecule (i.e. C2H6O).

– Structural formulas show how the atoms are bonded to one another in a molecule.i.e. ethanol (C2H6O) has a structural formula of CH3CH2OH

involves covalent bond – share electrons between atoms – typically nonmetal/nonmetal

involves ionic bond – transfer electrons between atoms – attraction between charged particles – typically metal/nonmetal or polyatomic ions

C : C

Na+Cl-

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– Although many substances are molecular, others are composed of ions (charged particles) that have transferred electrons and have ionic bonding; occurs generally with metal-nonmetal interactions.

Ionic substances

– An ion is an electrically charged particle obtained from an atom or chemically bonded group of atoms by adding or removing electrons.

– Sodium chloride is a substance made up of ions.

Na Cl + 1e- -

Na+ Cl-

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– The formula of an ionic compound is written by giving the smallest possible whole-number ratio of different ions in the substance.


Ionic substances

– The formula unit of the substance is the group of atoms or ions explicitly symbolized by its formula.

Covalent bond (share e-) Ionic bond (transfer e-/ attraction charged particles

nm –nm m – nm and charged ionsMolecules Formula unitMolecular substance Ionic substanceMolecular formula formula

C : ONa+Cl-

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– When an atom gains extra electrons, it becomes a negatively charged ion, called an anion (more electrons than protons). i.e, Cl-

Ionic substances

– An atom that loses electrons becomes a positively charged ion, called a cation (more protons than electrons). i.e., Na+

– An ionic compound is a compound composed of cations and anions.

NaClCaBr2

Na2SO4

CO2

Answer the following questions for species below:ionic or molecular substance; formula unit or molecule; ionic or covalent bonds involved?

ionic substance; formula unit; ionic bond

ionic substance; formula unit; ionic bonds

ionic substance; formula unit; ionic and covalent bonds in SO42-

molecular substance; molecule; covalent bonds

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Ions in Aqueous Solution

Many (not all) ionic compounds (ionic bond/m-nm) dissociate into independent ions when dissolved in water

NaCl (s) Na+(aq) + Cl-(aq)

Soluble ionic compounds dissociate 100% - referred to as strong electrolytes – breaks into charged particles until reaches saturation point.

Soluble salt charges particles

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Ions in Aqueous SolutionMost molecular (covalent bond/nm-nm) compounds dissolve but do not dissociate into ions, exception acids.

C6H12O6 (s) C6H12O6 (aq)

These compounds are referred to as nonelectrolytes; no charged particles; soluble to saturation point but no ions formed.

How would sodium sulfate dissolve based on bonding?Na2SO4 (s) 2Na+(aq) + SO4

2-(aq)

no charges particles; remains whole

ionic bond dissociates while covalent bonds in sulfate remain intact

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– Most ionic compounds contain metal and nonmetal atoms (as well as polyatomic ions); for example, NaCl.

Chemical Substances; Formulas and Names

Ionic compounds

– You name an ionic compound by giving the name of the cation followed by the name of the anion with -ide.

Sodium chloride, NaCl Calcium Iodide, CaI2

Potassium Bromide, KBr

– We give the monatomic ion name for the cations and anions when naming compounds. A monatomic ion is an ion formed from a single atom.

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– Most of the main group metals form cations with the charge equal to their roman group number.

How do we get the charge for ions?Rules for predicting charges on monatomic ions

– The charge on a monatomic anion for a nonmetal equals the roman group number minus 8.

– Most transition elements form more than one ion, each with a different charge (exceptions Cd2+, Zn2+, Ag+).

– Other important elements with variable chargePb4+, Pb2+ Sn4+, Sn2+ As5+, As3+ Sb5+, Sb3+

1+2+ 3+ 4+

01-2-3-

4-

varies

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– Monatomic cations are named after the element. For example, Al3+ is called the aluminum ion.

Rules for naming monatomic ions

– If there is more than one cation of an element (charge), a Roman numeral in parentheses denoting the charge on the ion is used. This often occurs with transition elements.

Na+ sodium ion Ca2+ calcium ionFe2+ iron (II) ion Fe3+ iron (III) ionOlder name: higher ox state (charge) – ic, / lower, -ousFe3+ ferric ion Fe2+ ferrous ion Cu2+ cupric ion

Cu+ cuprous ion Hg2+ mercuric ion Hg22+ mercurous ion

also done with Pb4+, Pb2+ ; Sn4+, Sn2+ ; As5+, As3+ ; Sb5+, Sb3+.

For the names of the monatomic anions, use the stem name of the element followed by the suffix – ide. For example bromine, the anion is called bromide ion, Br-.

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The formula of an ionic compound is written by giving the smallest possible whole-number ratio of different ions in the substance.Sodium chloride Na+ Cl-

Iron (III) sulfate Fe3+ SO42-

Chromium (III) oxide Cr3+ O2-

Calcium nitrate Ca2+ NO3-

Sodium phosphate Na+ PO43-

Strontium oxide Sr2+ O2-

NaCl

SrO

Na3PO4

Ca(NO3)2

Cr2O3

Fe2(SO4)3

Based on the charge of the ions and balancing the overall charge on the compound by adjusting the number of ions, a formula is written. Note the sum of all the charges must equal zero, and you do not display the charges in the final formula.

ions and charges formula

2Fe3+ = 6+ charge3SO4

2- = 6- chargebalanced

1Na+ = 1+ charge1Cl- = 1- chargebalanced

Generally, you can crisscross the charge of one ion as the subscript on the second ion, reducing when possible.

Roman number tells charge of transition metal

2 3

HW 13 & 14 code for both: formula

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Naming Ionic Binary CompoundsNaF -

- lithium chloride

MgO -

MnBr2 -

- cobalt (III) oxide

- copper (II) chloride or cupric chloride

sodium fluoride

LiCl

magnesium oxide

manganese (II) bromide

Co2O3

CuCl2

To name a compound, you must know if it is a molecular or ionic compound so that you know which rules to follow. If you have a metal-nonmetal (or polyatomic ion), it is an ionic compound where you name the metal first then the nonmetal with changing the ending to –ide. If it is a transition metal, you must include the charge of the metal (Roman numbers).

If you have nonmetal-nonmetal, it is a molecular compound which we haven’t discussed yet.

The charge on Mn must be 2+ to balance out the 2Br- charges.

The Roman number 3 tells us the charge on Co is 3+ which helps us determine the formula knowing that O is 2-.

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– A polyatomic ion is an ion consisting of two or more atoms chemically bonded together and carrying a net electric charge. We name the compounds the same way we just discussed except each polyatomic ion has a particular name.

– Books typically have a table that lists common polyatomic ions. Most are oxo anions – consists of oxygen with another element (central element).

Chemical Substances; Formulas and NamesPolyatomic ions

NO3- nitrate SO4

2- sulfate

NO2- nitrite SO3

2- sulfiteMost groups have –ate, -ite endings and differ by #O.

Mn, Br, Cl, I have per- -ate, -ate, -ite, hypo- -ite.

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Ions You Should KnowPolyatomic ions• NH4

+ - Ammonium• OH- - Hydroxide• CN- - Cyanide• SO4

2- - Sulfate• SO3

2- - Sulfite• ClO4

- - perchlorate• ClO3

- - chlorate• ClO2

- - chlorite• ClO- - hypochlorite• Hg2

2+ - mercury (I) or mecurous

• S2O32- - thiosulfate

• SCN- - thiocyanate• CNO- - cyanate• MnO4

- - permanganate

• O22- - Peroxide

• PO43- - Phosphate

• PO33- - Phosphite

• CO32- - Carbonate

• HCO3- - Bicarbonate or

Hydrogen Carbonate• N3

- - azide• NO3

- - nitrate• NO2

- - nitrite• C2H3O2

- or CH3COO- - acetate• Cr2O7

2- - dichromate• CrO4

2- - chromate• C2O4

2- - oxalate• HSO4

- - bisulfate or hydrogen sulfate

• H2PO4- - dihydrogen

phosphate

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SnSO4 sodium sulfite

Ca(ClO)2

barium hydroxide potassium perchlorate

Cr2(SO4)3

magnesium nitride

Fe3(PO4)2

titanium (IV) nitrate

tin (II) sulfate or stannous sulfateNa2SO3

calcium hypochlorite

Ba(OH)2

KClO4

chromium (III) sulfate

Mg3N2

iron (II) phosphate or ferrous phosphate

Ti(NO3)4

Note: Not a polyatomic ion; monoatomic anion of N.

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Molecular compounds

– Binary compounds composed of two nonmetals are usually molecular and are named using a prefix system (name same as ionic except must indicate how many atoms are present using mono, di, tri, etc.). No charges (share electrons) involved with molecular compounds, but we typically put more metallic compound first.

Which way is the correct way to write the following formula based on putting the more metallic compound first?


NF3 F3N

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– The name of the compound has the elements in the order given in the formula.

Binary molecular compounds

– You name the first element using the exact element name.

– Name the second element by writing the stem name of the element with the suffix “–ide.”

– If there is more than one atom of any given element, you add a prefix (di, tri, tetra, penta, hexa, hepta, octa, etc.)


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• Binary molecular compounds– N2O3

– SF4

– chlorine dioxide

– sulfur hexafluoride

– Cl2O7

– HCl (g)Name this compound but think about bonding:MgCl2Older names: water - H2O, ammonia – NH3, hydrogen sulfide – H2S, nitric oxide – NO, hydrazine – N2H4

dinitrogen trioxide

sulfur tetrafluoride

ClO2

SF6

dichlorine heptoxide

hydrogen chloride

magnesium chloride; ionic comp, no prefix

To name a compound, you must know if it is a molecular or ionic compound so that you know which rules to follow. If you have a metal-nonmetal (or polyatomic ion), it is an ionic compound where you name the metal first then the nonmetal with changing the ending to –ide. If you have nonmetal-nonmetal, it is a molecular compound which you do similarly as the ionic compound except that you must use prefixes to indicate the number of atoms.

Drop the “a” on prefix if you encounter double vowel in name.

Since this is a gas, we name using molecular rules; however, if acid we have other rules.

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– Acids are traditionally defined as compounds with a potential H+ as the cation.

Acids

– Binary acids consist of a hydrogen ion and any single anion in aqueous solution. For example, HCl (aq) is hydrochloric acid. Binary acid: hydrostemic acid

– An oxoacid is an acid containing hydrogen, oxygen, and another element. An example is HNO3, nitric acid. The oxoacids are a derivation of the oxoanions we discussed earlier.


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oxoacidsAnion prefix/suffix acid prefix/sufficper- -ate ion per- -ic acid -ate ion -ic acid -ite ion -ous acidhypo- -ite ion hypo- -ous acid

NO3- nitrate ion HNO3 nitric acid

NO2- nitrite ion HNO2 nitrous acid

ClO4- perchlorate ion HClO4 perchloric

acidSO4

2- sulfate ion H2SO4 sulfuric acidPO4

3- phosphate ion H3PO4 phosphoric acid

If you learn the oxoanions, you can easily adapt to naming the oxoacids: -ate -ic and –ite -ous

For some species there is a change in spelling in the name.


Hydrates

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– A hydrate is a compound that contains water molecules weakly bound in its crystals.

– Hydrates are named from the anhydrous (dry) compound, followed by the word “hydrate” with a prefix to indicate the number of water molecules per formula unit of the compound.

CuSO4. 5H2O

Magnesium sulfate heptahydrate

HW 15 - 18

copper(II)sulfate pentahydrate

MgSO4 . 7H2O

code for all: names


Naming simple compounds

46

– Chemical compounds are classified as organic or inorganic.

– Organic compounds are compounds that contain carbon combined with other elements, such as hydrogen, oxygen, and nitrogen.

– Inorganic compounds are compounds composed of elements other than carbon.


Organic compounds

47

– An important class of molecular substances that contain carbon is the organic compounds.

– Organic compounds make up the majority of all known compounds.

– The simplest organic compounds are hydrocarbons - compounds containing only hydrogen and carbon.

– Common examples include methane, CH4, ethane, C2H6, and propane, C3H8.

Classifying CompoundsOrganic vs. Inorganic

• in the 18th century, compounds from living things were called organic; compounds from the nonliving environment were called inorganic

• organic compounds easily decomposed and could not be made in 18th century lab

• inorganic compounds very difficult to decompose, but able to be synthesized

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Modern Classifying CompoundsOrganic vs. Inorganic

• today we commonly make organic compounds in the lab and find them all around us

• organic compounds are mainly made of C and H, sometimes with O, N, P, S, and trace amounts of other elements

• the main element that is the focus of organic chemistry is carbon

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Carbon Bonding• carbon atoms bond almost exclusively covalently

– compounds with ionic bonding C are generally inorganic

• when C bonds, it forms 4 covalent bonds– 4 single, 1 double + 2 singles, 2 double, or 1 triple + 1 single

– carbon is unique in that it can form limitless chains of C atoms, both straight and branched, and rings of C atoms

50

Examples of Carbon Compounds

51

Classifying Organic Compounds

• there are two main categories of organic compounds, hydrocarbons and functionalized hydrocarbons

• hydrocarbons contain only C and H• most fuels are mixtures of

hydrocarbons

52

Classifying Hydrocarbons• hydrocarbons containing only single bonds

are called alkanes• hydrocarbons containing one or more C=C

double bonds are called alkenes• hydrocarbons containing one or more CC

triple bonds are called alkynes• hydrocarbons containing C6 “benzene” ring

are called aromatic

53

Naming Straight Chain Hydrocarbons• consists of a base name to indicate the number of

carbons in the chain, with a suffix to indicate the class and position of multiple bonds– suffix –ane for alkane, –ene for alkene, –yne for alkyne

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Base Name No. of C Base Name No. of C

meth- 1 hex- 6

eth- 2 hept- 7

prop- 3 oct- 8

but- 4 non- 9

pent- 5 dec- 10

Functionalized Hydrocarbons

• functional groups are non-carbon groups that are on the molecule

• substitute one or more functional groups replacing H’s on the hydrocarbon chain

• generally, the chemical reactions of the compound are determined by the kinds of functional groups on the molecule

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Functional Groups

57

Chemical Reactions: EquationsWriting chemical equations

58

– The reactants (consumed; left side of reaction) are starting substances in a chemical reaction. The arrow means “yields.” The formulas on the right side of the arrow represent the products (produced).

– A chemical equation is the symbolic representation of a chemical reaction in terms of chemical formulas.

NaCl2ClNa2 2

– For example, the burning of sodium and chlorine to produce sodium chloride is written

Reactants (consumed) Products (produced)

Chemical Reactions: Equations

Writing chemical equations

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– In many cases, it is useful to indicate the states of the substances in the equation (s, g, l, aq).

– When you use these labels, the previous equation becomes

)s(NaCl2)g(Cl)s(Na2 2

We write above the arrow any conditions for the reaction such as pressure, catalyst, heat, etc. A reaction gives a recipe for the amount of reactants needed to produce the amount of products. Species with no coefficient have an understood coefficient of 1.

Chemical Reactions: EquationsWriting chemical equations

60

– The law of conservation of mass dictates that the total number of atoms of each element on both sides of a chemical equation must match. The equation is then said to be balanced.

OH CO O CH 2224 22We must have the same number of atoms on both sides for a reaction to be considered balanced and obeying the law of conservation of mass. To balance a reaction:1. First, balance the atoms for elements that occur in only one substance on each side of the

reaction. In this problem, O is involved with two substances on the product side; therefore, I will wait on balancing O until later. C & H are only in one species on both sides so I will balance them first. C needs no changes because there are one on each side, but H needs a 2 in front of H2O to balance the 4H on the reactants side.

2. Now that we have changed the coefficient of one of the O on the product side, it is easier to balance the O. We determine that we need a 2 coefficient on the O2 to balance the O on both sides at 4. Now the equation is balanced with 1C, 4O, and 4H on both sides.


61

Fe2(SO4)3: has 2-Fe, 3x1 = 3-S, 3x4 = 12-O

Caution: For formulas that have subscripts, you must account for all atoms especially when dealing with parentheses for polyatomic species.

For example,

Caution: Remember that you can’t change the subscripts in formulas to balance equations; you may only change coefficients. If you change the subscripts, you are changing the substance.


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332 POCl PCl O

26424 N OP ON P

232232 SO O As O SAs

2323 BaClNaNO NaCl )Ba(NO

HW 19

22

6 6

3

232232 SO 6 OAs 2 O 9 SAs 2

2 [ ]

22

Technique to handle odd numbers: determine number needed and divide by subscript of species. Next, you multiple the entire equation by the subscript to obtain whole numbers.

code: balance

topic 2 atoms, elements, molecules, ions, and compounds

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