Ions and Bonding

• Define ion, ionic bond, ionic compound.

• Use Bohr models to show how ionization and ionic bonding occur

Key Wordsionic compound formula unitnegative ions ionic bondpositive ions

The Octet Rule

An atom with eight electrons in its outer orbit is very stable.

Chemical reactions occur as atoms try to obtain a full outer orbit like the Noble gases.

Atoms will acquire a full outer shell in 3 ways:

• Give away an e- to another atom.• Take an e- from another atom.• Share an e- with another atom.

When a neutral atom gives an e- away it ends up with a positive charge.

The atom is now called a positive ION OR cation.

Sodium atom:11 p+

11 e-

Na

Sodium ion:11 p+

10 e-

Na + (cation)

+

Atoms that take an e- end up with a negative charge – called a negative ion (anion)

Chlorine atom:17 p+

17 e-

Cl

Chlorine ion:17 p+

18 e-

Cl - (anion)

-

Metals will lose (give) e- to become cations.

Non-metals will gain (take) e- to be anions.

The number of e- an atom must lose or gain is called the combining capacity ( = charge of ion).

Group # of Valence e- Lose or gain Combining capacity

Alkali metals 1 Lose 1 +1

Earth metals 2 Lose 2 +2

Chalogens 6 Gain 2 -2

Halogens 7 Gain 1 -1

Noble Gases 8 ---- ---

Calcium atom:20 p+

20 e-

Ca

Calcium ion:20 p+

18 e-

Ca +2 (cation)

+2

Oxygen atom:8 p+

8 e-

O

Oxygen ion:8 p+

10 e-

O -2 (anion)

-2

Nitrogen atom:7 p+

7 e-

N

Nitrogen ion:7 p+

10 e-

N -3 (anion)

-3

*The LESS electrons to move, the GREATER the reactivity of the element.

A Chemical Reaction: Movement of electrons between combining atoms that results in the formation of a NEW substance.

Attractive forces hold opposite charges together – IONIC BOND.

Ionic compounds - a positive ion (METAL) joins with a negative ion (NON-METAL).

Sodium atom (Na) Chlorine atom (Cl)

Sodium ion (Na+) Chlorine ion (Cl-)

+ -

Sodium ChlorideNaCl

(ionic bond)

Atoms combine together to form compounds in fixed ratios or definite proportions.

1 Na forms an ionic bond with 1 Cl10 Na 10 Cl65 Na 65 Cl

The smallest unit of an ionic compound is called a formula unit.

Aluminum

1 : 1

Nitrogen

Al+3 N-3

As atoms combine in definite proportions:

AlNAluminum Nitride

As atoms combine in definite proportions:

1 : 3

Aluminum Fluorine

Al+3 3 F-

AlF3

Aluminum Fluoride

Use Bohr diagrams to illustrate the compounds formed from the following reaction:

Ca and F

Na and P

Mg and N

formula unit

Ionic Compounds