1. Properties of Ionic and Covalent Compounds

2. Properties of Ionic Compounds
Solids at room temperature
Very high melting points (>> 300◦C)
Do not conduct electricity in solid state
Many are highly soluble in water
Solutions of ionic compounds are electrolytes – they conduct electricity

3. Ionic compounds do NOT form molecules!
NaCl – formula unit water – H2O – molecular formula
Chemical structure of ionic compounds are known as formula units – the simplest whole number ratio of the ions.

4. The Octet Rule in Action
sodium, (2-8-1) or 1s2 2s2 2p6 3s1
when it loses its electron, it has an octet in its highest (2nd) energy level.
3s  loss of valence electron
2p         
2s   
1s    +

5. Electron Configurations of Anions
When non-metal atoms gain valence electrons, they become negative ions - anions.
For fluorine (and all group 17 elements) form halide ions:
1s2 2s2 2p5 + e-  1s2 2s2 2p6 an octet in n=2!
e-  2-8
2p      
2s  + e-  
1s   -

6. Properties of Covalent Compounds
Covalent bonds are weaker than ionic or metallic bonds
Small covalent compounds tend to be gases, with relatively weak intermolecular forces
Larger molecules have greater attractive forces; can be liquids or solids
Polar molecules have considerably higher melting and boiling points than non-polar molecules

7. A Tale of Three Compounds
Methane CH4
BP -160°C
Methanethiol CH3SH Boiling Point 6°C
Methanol
CH3OH
Boiling Point 70°C

8. Phosphine PH3 Boiling Point - 87°C
Two More to Ponder
Phosphine PH3 Boiling Point - 87°C
Ammonia NH3
Boiling Point -33°C

9. Ionic vs. Covalent Compounds
Ionic compounds have much higher melting and boiling points than covalent compounds (both polar and non-polar)
Binary ionic compounds have higher melting and boiling points than ternary ionic compounds – the polyatomic ions have covalent bonds – they decompose at high temperatures.
Melting point of NaCl: ⁰C
Melting point of NaNO3: 308⁰C
Melting point NO2: ⁰C
Melting point N2: ⁰C

10. Ionic vs. Covalent Compounds
Ionic compounds generally are soluble in water
Polar covalent compounds are soluble in water
Non-polar covalent compounds are insoluble in water

11. Electrolytes
Ionic compounds are electrolytes when dissolved in water – their solutions conduct electricity.
Most covalent compounds are non-electrolytes – their solutions do not conduct electricity.
Acids and bases (polar covalent compounds) are exceptions – they do conduct electricity, because they dissociate into ions when added to water

12. Characteristics of Ionic and Covalent Compounds
Characteristic
Representative Unit
Bond Formation
Types of elements
Physical state
Ionic
Compounds
Covalent

13. Characteristics of Ionic and Covalent Compounds
Melting Point
Solubility in water
Conductivity in aqueous solution
Dot Diagram

14. Electronegativity Difference
Chemical Formula
Metal
Non-metal
Both
Electronegativity Difference
Nonpolar Covalent
Polar Covalent
Ionic Bond
Molecule Polarity H2
HCl
CH4
CF4
MgF2
H2O O2
CCl4
KCl
NH3
Cl2
CO2
H2S
CaBr2
HBr