Bonding

A chemical bond is a force that holds atoms together.

Two Types of Bonds

1. Ionic Bond – the attraction between two oppositely charged ions. An ionic bond is formed when atoms gain or lose electrons. Ionic bonds form compounds.

Ion – an atom or group of atoms that has become electrically charged. It is a

charged particle.

When an atom loses an electron, it loses a negative charge and becomes

a positive ion.When an atom gains an electron, it

gains a negative charge and becomes a negative ion.

Ionic bond

Atoms that gain electrons have a negative valence. (charge)

Atoms that lose electrons have a positive valence. (charge)

2. Covalent Bonding – A type of bonding in which electrons

are shared.

When covalent bonding occurs, molecules are formed.

Covalent Bond

Compound – two or more elements chemically combinedby gaining, losing, or sharing

electrons.

Molecule – a particle made of 2 or more atoms covalently

bonded together.

Chemical formulas – a shorthand way to represent a

compound. ( H2O)

In a chemical formula, the element with the positive

charge is always written first.

Valence number – The number of electrons an atom needs to gain, lose, or share to become

stable. (Gain electrons – negative

valence)(Lose electrons – positive

valence.)

Subscript – the number that shows how many atoms of an element are in the compound.

How to Write Formulas

• 1. Write the symbol correctly for both elements.

• 2. Write the valence number above each symbol. Make sure you have a positive first, and then a negative.

• 3. Criss-cross valences to make a subscript.

• 4. NEVER write 1 as a subscript. (It is understood to be 1 if there is no number.)

• 5. Reduce to lowest terms.

Examples

• Sodium Chloride Aluminum Oxide

• Copper (I) Sulfide Iron (III) Iodide

1. Calcium Sulfide 2. Copper (I)Iodide

3. Potassium Chloride 4. Iron(III) Bromide

5. Sodium Nitride 6. Antimony (V) Oxide

Practice Problems• Aluminum Bromide

• Calcium Iodide• Copper (I) Chloride

• Hydrogen Oxide

• Magnesium Nitride

• Potassium Sulfide

• Barium Fluoride

• Lead Bromide

Binary Compound – a compound composed of 2

elements.

Polyatomic Ion- a group of positively or negatively charged

covalently bonded atoms.

Calcium Phosphate

Tin (IV) Chromate

Ammonium Oxide

Magnesium Sulfate

Naming compounds – change the ending of the second

element to – “ide”.(Do not change the names of

polyatomic ions.)Check to see if Roman numeral

is needed.Ex: NaCl - Sodium Chloride

Fe2O3 – Iron (III) Oxide

Examples

• Zn3N2 ______________________

• K2SO3 ______________________

• CuO ______________________

• Ba(C2H3O2)2 _____________________