Covalent and Ionic Compounds
Covalent Compounds
Formed between non-metal and non-metal atoms.
Involve the sharing of electrons between atoms to achieve a full set of valence electrons (8 electrons, except for Hydrogen and Helium).
Electrons Sharing
Atoms share electrons to achieve a full set of valence electrons, similar to ionic compounds seeking a full valence shell.
Properties of Covalent Compounds
Lower melting and boiling points: Covalent bonds are generally weaker than ionic bonds; therefore, covalent compounds tend to have lower melting and boiling points.
Often exist as liquids or gases at room temperature.
Non-conductive: Covalent compounds do not conduct electricity because they do not have ions.
Also known as molecular compounds.
Nonmetals can combine in multiple ways.
Covalent Bond
A covalent bond results from the sharing of valence electrons.
A molecule is formed when two or more atoms bond covalently.
Shared electrons are considered part of the outer energy levels of both atoms involved.
Diatomic Molecules
Examples: H2, N2, O2, F2, Cl2, Br2, and I_2.
Form when two atoms of each element share electrons.
They exist this way because the two-atom molecule is more stable than the individual atoms.
Naming Covalent Compounds
Use prefixes to distinguish between different compounds.
First nonmetal: prefix (except "mono") + name of element.
Second nonmetal: prefix + name of element + "-ide" ending.
Prefixes
1 - Mono
2 - Di
3 - Tri
4 - Tetra
5 - Penta
6 - Hexa
7 - Hepta
8 - Octa
9 - Nona
10 - Deca
Examples of Covalent Compounds
CO
BF_3
C2Cl4
NO
NO_2
N2O4
P4S5
Common Names
Some compounds are known by their common names instead of their formal names.
H_2O – water
NH_3 – ammonia
CH_4 – methane
Acids
Water solutions of some molecules are acidic and are named as acids.
If a compound produces hydrogen ions (H^+) in solution, it is an acid.
Categories of Acids
Acids WITHOUT oxygen (binary acids).
Acids WITH oxygen (oxyacids).
Naming Acids WITHOUT Oxygen (Binary Acids)
Prefix: Hydro-
Suffix: -ic
Examples:
HCl: Hydrochloric acid
HF: Hydrofluoric acid
HBr: Hydrobromic acid
HI: Hydroiodic acid
H_2S: Hydrosulfuric acid
Naming Acids WITH Oxygen (Oxyacids)
No prefix.
Suffix: -ic
Examples:
HNO_3: Nitric acid
H2CO3: Carbonic acid
H2SO4: Sulfuric acid
H3PO4: Phosphoric acid
HC2H3O_2: Acetic acid
Practice Examples
NaBr
N2O5
SiO_2
HI
CaCO_3
MgO
H_2S
SO_2
HNO_3
More Practice Examples
Ammonium nitrate
Hydrosulfuric acid
Potassium iodide
Phosphorus trioxide
Carbonic acid
Carbon tetrachloride
Lewis Dot Structure
Single Covalent Bond: A bond in which atoms share one pair of electrons.
Examples: F2, H2
Double Covalent Bond: A bond in which atoms share two pairs of electrons.
A double bond is shorter and stronger than a single bond.
Example: O_2
Triple Covalent Bond: A bond in which atoms share three pairs of electrons.
A triple bond is shorter and stronger than a single and a double bond.
Examples: N_2, HCN
Lewis Structure Practice
Carbon monoxide
Carbon dioxide
Water
H2O2
Sulfur dioxide
Sulfur trioxide
Ammonia
Dinitrogen monoxide
Carbon tetrachloride
Exceptions to the Octet Rule
Odd number of electrons.
Stable with less than 8 electrons.
Stable with 8, 10, or 12 electrons.
Odd Number of Electrons
Nitrogen monoxide
Nitrogen dioxide
Less than 8 Electrons
Hydrogen (2 electrons)
SiH_4
Boron (6 electrons)
BF_3
More than 8 Electrons
Sulfur (8, 10, or 12 electrons): SF_6
Phosphorus (8, 10, or 12 electrons): PCl_5
Xenon (8, 10, or 12 electrons): XeF_4
Lewis Dot Activity
Methane
Ammonia
C2H2
C2H4
Nitrogen tribromide
Carbon tetrachloride
Lewis Dot Activity continued
Bromine
Oxygen
NH_4^+
Sulfate
CH_2O
NH_2Cl
Lewis Dot Activity Continued
Phosphorus pentachloride
Hydrosulfuric acid
Boron trichloride
HCN
Nitrogen tribromide
Nitrite
Nitrate
Bond Polarity
Covalent bonds involve the sharing of electrons between atoms.
However, this sharing is more like a tug-of-war between the atoms.
Nonpolar Covalent Bonds
Electrons are shared equally.
Bonds between diatomic molecules are nonpolar because the atoms have the SAME electronegativity.
Bonds between carbon atoms and hydrogen atoms are also nonpolar because they have very similar electronegativities.
Polar Covalent Bonds
Electrons are shared unequally.
Unequal sharing takes place because the more electronegative atom has a stronger electron attraction and will have a stronger pull on the electrons.
Dipole Moment
A molecule with a dipole moment is a polar molecule.
This means one end of the molecule is slightly negative while the other is slightly positive.
Polar vs Non-Polar Molecules
A molecule may have polar bonds and NOT have a dipole moment.
This happens when the polar bonds cancel each other out.
Polarity Practice
NH_2Cl
Hydrosulfuric acid
Boron trihydride