CHAPTER 2
ATOMS and MOLECULES

Periodic Table
• Atomic Mass
– number below the element
– not whole numbers because the masses are averages of the masses of the different isotopes of the elements

Ions
• Are charged species
• Result when elements gain electrons or lose electrons

2 Types of Ions
• Anions – (-) charged
• Example: F -
• Cations – (+) charged
• Example: Na +

Highly Important!
• Gain of electrons makes element (-) = anion
• Loss of electrons makes element (+) = cation

Charges
•
When elements combine, they have to be in the form of IONS.
•
Cations and anions combine to form compounds.
•
For a neutral compound, the sum of the charges must be ZERO.
•
For a polyatomic ion, the sum of the charges must equal the charge of the
ION.

Isotopes
• Are atoms of a given element that differ in the number of neutrons and consequently in atomic mass.

Isotopes
12 C
13 C
14 C
11 C
Example
% Abundance
98.89 %
1.11 %

– For example, the mass of C =
12.01 a.m.u is the average of the masses of 12 C, 13 C and 14 C.

Determination of Aver. Mass
• Ave. Mass =
[(% Abund./100) (atomic mass)] + [(% Abund./100)
(atomic mass)]

• If there are more than 2 isotopes, then formula has to be re-adjusted

Sample Problem 1
• Assume that element Uus is synthesized and that it has the following stable isotopes:
– 284 Uus (283.4 a.m.u.) 34.6 %
– 285 Uus (284.7 a.m.u.) 21.2 %
– 288 Uus (287.8 a.m.u.) 44.20 %

Solution
• Ave. Mass of Uus =
• [ 284 Uus] (283.4 a.m.u.)(0.346)
• [ 285 Uus] +(284.7 a.m.u.)(0.212)
• [ 288 Uus] +(287.8 a.m.u.)(0.4420)
• = 97.92 + 60.36 + 127.21
• = 285.49 a.m.u (FINAL ANS.)

Oxidation Numbers
• Is the charge of the ions (elements in their ion form)
• Is a form of electron accounting
• Compounds have total charge of zero
(positive charge equals negative charge)

Oxidation States
• Are the partial charges of the ions. Some ions have more than one oxidation states.

Oxidation States
• - generally depend upon the how the element follows the octet rule
• Octet Rule – rule allowing elements to follow the noble gas configuration

Nomenclature
• - naming of compounds

Periodic Table
• Rows (Left to Right) - periods
• Columns (top to bottom) groups

Rule 1 – IONIC COMPOUNDS
• Metals w/ Fixed Oxidation States
– Name metal or first element as is
- Anion always ends in “–ide”

Terminal element or anion
• O oxide
• N nitride
P - phosphide
Se - selenide
• S - sulfide Cl - chloride
• F fluoride I - iodide
• Br bromideC - carbide

Note
• Only elements that come directly from the periodic table WILL end in
–IDE.
• POLYATOMIC IONS will be named AS
IS.

Name the following:
• CaO -
• NaCl -
• MgO -
• CaS -
• Na
3
N -

Answers:
• CaO calcium oxide
• NaCl sodium chloride
• MgO magnesium oxide
• CaS calcium sulfide
• Na
3
N sodium nitride

Where do the subscripts come from?
• Answer: From the oxidation states of the ions.
• Remember: Ions are the species that combine.
• Target: Compounds! (No charges!)

Second Rule
• II. Ionic Compounds - Metals with no fixed oxidation states (Transition Metals) except for Ag, Zn and Al
• Metal(Roman #) + 1 st syllable + ide
– Use Roman numerals after the metal to indicate oxidation state

Name the following:
• Copper (I) sulfide
• Iron (II) oxide
• Tin (II) iodide
• Iron (III) nitride

Answers:
• Copper (I) sulfide
• Iron (II) oxide
Cu
2
FeO
• Tin (II) iodide
• Iron (III) nitride FeN
SnI
2
S

What about…….?
• Cesium hydroxide
• Iron (III) acetate
• Lithium phosphate
• Aluminum Sulfite
• Lead (II) sulfate
• Silver nitrate

POLYATOMIC IONS
• Consist of more than 1 element.
• Have charges.
• Ex. SO
4
2, SO
3
2, PO
4
3,PO
3
3-

Rule 3 – Covalent Compounds
• III. For Non-metals (grps IV, V, VI VII), use prefixes.
Mono – 1
Di - 2
Tri – 3
Hepta - 7
Octa - 8
Nona - 9
Tetra – 4
Penta – 5
Hexa - 6
Deca - 10

Rule 3 – Covalent Compounds (only have Non- Metals)
• Name 1 st element as is. Use prefix, if necessary.
• Prefix + 1 st element + prefix + 1 st syllable of anion + ide

Name the following compounds
• CO
2
- carbon dioxide
• N
2
O – dinitrogen oxide
• SO
3
– sulfur trioxide
• N
2
O
5
– dinitrogen pentoxide
• P
2
S
5
– diphosphorus pentasulfide
• CO – carbon monoxide

Naming Acids
• I. Acids without Oxygen
– Use hydro + 1 st syllable + “- ic acid”
• Example: HCl = hydrochloric acid
HCN = hydrocyanic acid
HBr = hydrobromic acid

II. Acids with oxygen
• Polyatomic “ate” converts to “ic” + acid
• Polyatomic “ite” converts to “ous” + acid
- H
2
SO
3
– H
2
SO
4
– HNO
3
– HNO
2
– H
3
PO
4 sulfurous acid sulfuric acid nitric acid nitrous acid phosphoric acid

Trick!
• If anion ends in “ – ate”, acid ends in “ – ic”
• Example:
• HClO
4 perchlorate perchloric acid
• HClO
3 chlorate chloric acid

Trick!
• If anion ends in “ – ite”, acid ends in “ – ous”
• Example:
• HClO
2 chlorite chlorous acid
• HClO hypochlorite hypochlorous acid

Name the following:
• HBrO
4
(perbromate)
• HBrO
3
(bromate)
• HBrO
2
(bromite)
• HBrO (hypobromite)

Pure Acids (not diluted)
• Simply use Rule 3. Use prefixes, if necessary.