Chapter 6: Chemical Names & Formulas

Molecule– an aggregate (or unit) of at least two atoms in a definite arrangement joined together by chemical bonds.

• a neutral chemically bonded group of atoms that act as a unit

• smallest unit that a compound exists as

• a bunch of molecules of the same type make up a compound

Diatomic Molecules– 7 elements known to exist as diatomic molecules in nature

BOFINCH

Br2, O2, F2, I2, N2, Cl2, H2

Polyatomic Molecules– molecules that contain more than two atoms. Most molecules are polyatomic

Ex: H2O (water), NH3 (ammonia)

Molecular Compounds– compounds composed of molecules

Ex: one atom of Carbon can combine with one atom of Oxygen to produce one molecule of the compound Carbon Monoxide (CO)

Ex: two Hydrogen atoms combine with one oxygen atom to produce one molecule of the compound water (H2O)

Molecular Formula– shows the exact number of atoms of each element present in one molecule of a substance.

• chemical formula for a molecular compound

• shows the composition of the molecule not the structure

Ex: H2O2 is the molecular formula for hydrogen peroxide

C2H6 ethane, CO2 carbon dioxide, H2O water

Ions– atoms or groups of atoms that have gained or lost 1 or more e-

--either positively charged or negatively charged

Cation– positively charged ion that is produced by the loss of 1 or more e- (atoms of metallic elements)

Examples of cation formations:Na atom (sodium) e- + Na+ (sodium ion) (11p, 11e-) (11p, 10e-)Group 1A representative elements tend to

lose 1e- to form cations with a +1 charge

Ca atom (calcium)2e- + Ca2+ (calcium ion)(20p, 20e-) (20p, 18e-)Group 2A representative elements tend to lose

2e- to form cations with a +2 charge

Al atom(aluminum)3e- +Al3+ (aluminum (13p,13e-) (13p, 10e-) ion)Group 3A representative elements usually lose

3e- to form cations with a +3 charge

Group 4A representative elements do not tend to gain or lose e-; they tend to share e- instead (learn more later)

A cation is named by taking the name of the atom and adding the word “ion” after it.

Anion– a negatively charged ion that is produced when an atom gains 1 or more e- (atoms of nonmetallic elements)

Examples of anion formations:

N atom (nitrogen)+ 3e-N3- (nitride ion)(7p, 7e-) (7p, 10e-)Group 5A representative elements usually gain

3e- to form anions with a -3 charge

O atom (oxygen)+ 2e-O2- (oxide ion)(8p, 8e-) (8p, 10e-)Group 6A representative elements usually gain

2e- to form anions with a -2 charge

Cl atom (chlorine)+1e-Cl- (chloride ion)(17p, 17e-) (17p, 18e-)Group 7A representative elements tend to

gain 1e- to form anions with a -1 charge

Anion is named by dropping the last few letters of the name of the atom and adding the ending –ide followed by the word “ion”

Group 8A (or noble gases) we will learn about later(gain, lose, give, take, share e-)

p.143 Ionic charges of representative elements

All transition elements tend to form cations by losing 1 or more e-. Some transition elements can form 2 different types of cations. (p. 144 common metal ions with more than 1 ionic charge)

Ex:Fe atom (iron)2e- + Fe2+(iron (II) ion)(26p, 26e-) (26p, 24e-) (Ferrous ion)Fe atom (iron)3e- + Fe3+(iron (III) ion)(26p, 26e-) (26p, 23e-) (Ferric ion)

Cu atom(copper)1e- + Cu+( copper (I) ion)(27p, 27e-) (27p, 26e-) (Cuprous ion)Cu atom(copper)2e- + Cu2+(copper(II) ion)(27p, 27e-) (27p, 25e-) (Cupric ion)When an atom can form more than one type of

cation, the cation is named by placing the roman numeral designating the charge of the atom before the word “ion”

Transition metals with one ionic charge do not need a roman numeral

Ex: Silver ion Ag+, Cadmium ion Cd2+, Zinc ion Zn2+

Summary:

Group 1A, 2A, 3A lose e- to form cations, the charge is positive and numerically equal to the group number. Name the ion by using the name of the atom plus the word “ion”

Group 5Again 3e-

Group 6Again 2e- { -ide ion}

Group 7Again 1e-

*all of the ions we’ve done so far are monoatomic ions– derived from a single atom

Polyatomic ions– ions that contain more than one atom joined together

--behave as a unit

Ex: Nitrate ion (NO3-)

Nitrite ion (NO2-) {end in –ite or –ate}

Carbonate ion (CO32-)

Chlorite ion (ClO2-)

Chlorate ion (ClO3-)

See pg. 147 in text and Chem. Ref.Exceptions to the –ite –ate ending:

Hydroxide ion (OH-), Ammonium ion (NH4+),

Cyanide ion (CN-), Hydronium ion (H3O+), Peroxide ion (O2

2-), Dimercury (I) ion (Hg22+)

When the formula for a polyatomic ion begins with hydrogen, H represents H+ ion combined with another polyatomic ion

Ex:

HCO3- H+ + CO3

2-

the charge on the new ion is the sum of the ionic charges

H+ + CO32- HCO3

- Hydrogen carbonate

H+ + PO43- HPO4

2- Hydrogen phosphate

H+ + HPO42- H2PO4

- Dihydrogen phosphate

H+ + SO42- HSO4

- Hydrogen sulfate

Ionic compounds– compounds composed of cations and anions (metal cations and nonmetal anions)

• oppositely charged ions get together to form ionic compounds or “salts”

• neutral charge--+charge of cation equals the – charge of anion

• the sum of the charges on the cation and the anion added together in the formula of an ionic compound must equal zero

Ex: sodium chloride (table salt)Sodium cations and chloride anionsNa+ + Cl- NaCl+1 -1 0

Characteristic Molecular Compound

Ionic compound

Representative unit

Molecule Formula unit (balance of oppositely charged ions)

Type of elements

Nonmetallic Metallic combined with nonmetallic

Physical state Solid, liquid, or gas

solid

Melting point Low, usually below 300 C

High, usually above 300 C

Chemical formula– shows the kinds and numbers of atoms in the smallest representative unit of the substance

Ex: chemical formula of monoatomic elements (He, Ne –atomic symbol)

Diatomic (O2, H2, F2, Cl2, N2, Br2, I2) the subscript tells how many atoms there are (2).

Molecular formula– kinds and numbers of atoms present in a molecule of a compound. *chemical formula of a molecular compound

Formula units– lowest whole-number ratio of ions in the compound. *chemical formula for ionic compounds (NaCl, MgCl2)

**No such thing as a molecule of NaCl, etc. These compounds exist as collections of + and – charged ions arranged in a repeating 3-D pattern

Law of Definite Proportions– In samples of any chemical compound, the

masses of the elements are always in the same proportions.

Ex: one sample of the compound MgS (Magnesium Sulfide) has the same mass ratio (Mg:S) as another sample of that same compound. The ratio of Mg:S is 0.7584:1, for every sample the ratio is the same.

Law of Multiple Proportions–

Whenever two elements form more than one compound, the different masses of one element that combine with the same mass of the other element are in the ratio of small whole numbers.

Ex: H2O2 and H2O

16gO:1gH 8gO:1gH

16gO = 2 = 2:1

8gO 1