CHAPTER 2 ATOMS and MOLECULES. Periodic Table Atomic Mass – number below the element – not whole numbers because the masses are averages of the masses.

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.

Example

Isotopes % Abundance12C 98.89 %13C 1.11 %14C 11C

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

Determination of Aver. Mass

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

Take Note:• 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:–284Uus (283.4 a.m.u.) 34.6 %–285Uus (284.7 a.m.u.) 21.2 %–288Uus (287.8 a.m.u.) 44.20 %

Solution

• Ave. Mass of Uus =• [284Uus] (283.4 a.m.u.)(0.346)• [285Uus] +(284.7 a.m.u.)(0.212)• [288Uus] +(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 P - phosphide• N - nitride 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- • Na3N -

Answers:

• CaO - calcium oxide• NaCl - sodium chloride•MgO - magnesium oxide• CaS- calcium sulfide• Na3N - 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 #) + 1st 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 Cu2S• Iron (II) oxide FeO• Tin (II) iodide SnI2

• Iron (III) nitride FeN

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. SO4 2-, SO3 2-, PO4 3-,PO3 3-

Rule 3 – Covalent Compounds• III. For Non-metals (grps IV, V, VI VII), use

prefixes.Mono – 1 Hepta - 7Di - 2 Octa - 8Tri – 3 Nona - 9Tetra – 4 Deca - 10Penta – 5Hexa - 6

Rule 3 – Covalent Compounds (only have Non- Metals)

• Name 1st element as is. Use prefix, if necessary.

• Prefix + 1st element + prefix + 1st syllable of anion + ide

Name the following compounds

• CO2 - carbon dioxide

• N2O – dinitrogen oxide

• SO3 – sulfur trioxide

• N2O5 – dinitrogen pentoxide

• P2S5 – diphosphorus pentasulfide• CO – carbon monoxide

Naming Acids

• I. Acids without Oxygen–Use hydro + 1st syllable + “- ic acid”

• Example: HCl = hydrochloric acidHCN = hydrocyanic acid HBr = hydrobromic acid

II. Acids with oxygen• Polyatomic “ate” converts to “ic” + acid• Polyatomic “ite” converts to “ous” + acid

- H2SO3 sulfurous acid

–H2SO4 sulfuric acid

–HNO3 nitric acid

–HNO2 nitrous acid

–H3PO4 phosphoric acid

Trick!

• If anion ends in “ – ate”, acid ends in “ – ic”

• Example:• HClO4 perchlorate perchloric acid

• HClO3 chlorate chloric acid

Trick!

• If anion ends in “ – ite”, acid ends in “ – ous”

• Example:• HClO2 chlorite chlorous acid

• HClO hypochlorite hypochlorous acid

Name the following:

• HBrO4 (perbromate)

• HBrO3 (bromate)

• HBrO2 (bromite)• HBrO (hypobromite)

Pure Acids (not diluted)

• Simply use Rule 3. Use prefixes, if necessary.