1. Chemical Bond
Forms when 2 or more atoms rearrange valence electrons to increase stability
Electrical attraction between the valence electrons of one atom and the nucleus of another
Episode 501

2. Ionic Bond
Forms when valence electrons are transferred from one atom to another
Cation
Atom loses electrons to become (+) charged
Anion
Atom gains electrons to become (-) charged
In ionic compounds the ions are arranged in a crystal lattice; strong forces hold the ions together.
Episode 501

3. Properties of Ionic compounds
High melting and boiling points
Hard – not easily crushed
Conduct electricity when melted or dissolved because the ions are free to move
Episode 501

4. Covalent Bond Electrons are shared , forming molecules
Covalent compounds have weaker forces holding the molecules together
Properties of covalent compounds
Lower melting and boiling points
Many covalent compounds are volatile liquids or gases
Softer – easier to crush
Are not conductors of electricity
Episode 501

5. Electronegativity
Property that tells how strong an atom’s attraction is for electrons
Oxygen en. = 3.5
Hydrogen en. = 2.1
Since oxygen has a greater electronegativity than hydrogen, oxygen holds onto the electrons stronger, giving oxygen a partial negative charge and the hydrogen a partial positive charge.
Episode 501

6. Nonpolar Covalent Bond
Electrons are shared unequally creating partially charged ends or poles
Nonpolar covalent bonds
Electrons are shared equally because the atoms have the same or nearly the same electronegativities
Electronegativity difference
Type of Bond
Greater than or equal to 1.7
Between 1.7 and 0.3
Less than or equal to 0.3
Ionic Bond
Polar Covalent Bond
Nonpolar Covalent Bond
Episode 501

7. Examples: Problem Set #1 Li and Cl? C and O? Na and Cl? Cl and Br?
Mg and F?
Mg en.= 1.2
F en.= 4.0
4.0 – 1.2 = 2.8
Ionic
S and Cl?
S en.= 2.5
Cl en.= 3.0
3.0 – 2.5 = 0.5
Polar covalent
Problem Set #1
Li and Cl?
C and O?
Na and Cl?
Cl and Br?
S and H?
Episode 501