Chapter 6Sections 1,2 and 3

Key Terms Only a few atoms exist as isolated atoms – Noble Gases Molecule

Smallest electrically neutral unit of a substance that still has the properties of the substance.

Made up of two or more atoms that behave as a unit. Some are diatomic (appear as pairs)

Br2I2N2Cl2H2O2F2

Molecular Compounds Atoms of different elements combine chemically Compounds composed of molecules are called

molecular compounds. Some general characteristics:

Low melting and boiling points Most are liquids or gases

Composed of two or more non-metals

Ionic Compounds Ions – atoms or groups of atoms that have positive or

negative charges (that means the # of p+ does not equal the # of e-)

Metallic elements tend to form cations (positive charges) The protons outnumber the electrons

The charge is usually written after the symbol and to the upper right (Na+)

Cations are named the same as the element. Ions behave very differently than the atoms they came from.

Anions Non-metals usually form anions. Negative (electrons outnumber the protons). Happens when elements gain electrons The name of a typical monatomic anion (1 atom that

is negative) ends in –ide

Example: Cl- = chloride

Compounds composed of cations and anions are called ionic compounds. Usually made of metals with non-metals Ionic compounds are electrically neutral Usually solids at room temperature and melt at

extremely high temperatures.

Chemical Formulas

Shows the kinds and number of atoms in the smallest representative unit of the substance.

Use elemental symbols Subscripts show haw many of each atom are

present. Example: oxygen = O2

Molecular Formula

Chemical formula for a molecular compound. Tells nothing about structure or arrangement of

atoms. Example = carbon dioxide = CO2

One carbon atom and two oxygen atoms tightly bound to each other.

Formula Unit Used for ionic compounds Ionic compounds are not molecules It is the lowest whole number ration of ions in a

compound. Example: NaCl (sodium chloride or table salt) is made of one

sodium ion and one chloride ion. Thus, the ratio is 1:1 (sodium = +1 charge and chloride = -1 charge)

Example #2: MgCl2 (magnesium chloride) is made of one magnesium cation (+2 charge) and two chloride anions (-1 each) thus the ratio is 1:2

Laws Law of multiple proportions

If two or more compounds made of the same elements exist they are a whole ratio of each others composition.

Law of definite proportions Samples of the same compound have the elements

present in the same ratio.

Monatomic Ions Ions consisting of only one atom Table 6.2 (p143) Can be predicted from group on the periodic table.

1A 2A 3A 4A 5A 6A 7A 8A

Li+ Be+2 N-3 O-2 F-

Na+ Mg+2 Al+3 P-3 S-2 Cl-

K+ Ca+2 As-3 Se-2 Br-

Rb+ Sr+2 I-

Cs+ Ba+2

Transition Metals Most can have multiple charges

Exceptions = Silver (Ag+), Zinc (Zn+2) and Cadmium (Cd+2)

Roman Numeral is used to show the charge on the cation Example: Copper (I) = Cu+1

Roman Numeral is the charge!

Table 6.3 Page 144

Formula Stock Name Classical Name

Cu+ Copper (I) Cuprous ion

Cu+2 Copper (II) Cupric ion

Fe+2 Iron (II) Ferrous ion

Fe+3 Iron (III) Ferric ion

Pb+2 Lead (II) Plumbous ion

Pb+4 Lead (IV) Plumbic ion

Sn+2 Tin (II) Stannous ion

Sn+4 Tin (IV) Stannic ion

Polyatomic Ions Tightly bound groups of atoms that

behave as a unit and carry a charge. Change the prefix and suffix to show a

change in the number of oxygen present. Exceptions = Cyanide, Hydroxide and

ammonium Practice with the common ion sheet