1. Covalent Bonding
Chemistry Chapter 9

2. The Covalent Bond
Covalent bond – chemical bond that results from the sharing of valence electrons
Generally occurs when elements are relatively close to each other on the periodic table
Majority form between nonmetallic elements
Molecule – formed when 2 or more atoms bond covalently

3. Single covalent bonds (sigma bonds)
Group 7A form a single covalent bond
Ex: F2
Group 6A share 2 electrons to form 2 covalent bonds
Ex: H2O
Group 5A form 3 covalent bonds with atoms of nonmetals
Ex: ammonia NH3
Group 4A form 4 covalent bonds
Ex: methane CH4

4. Multiple covalent bonds
Atoms of C, N, O, and S most often form multiple bonds
O molecule shares 2 electron pairs, forming a double bond: O2
N molecule shares 3 electron pairs, forming a triple bond: N2
Pi bond – parallel orbitals overlap to share electrons
Double covalent bond has 1 sigma and 1 pi bond

5. Strength of covalent bonds
Bond length – distance between 2 bonding nuclei at the position of maximum attraction
As the number of shared electron pairs increases, bond length decreases
Shorter bond length makes stronger bond
Bond dissociation energy – amount of energy required to break a specific covalent bond
As 2 atoms are bonded closer together, more bond energy is needed to separate them

6. Naming Molecules
Naming binary molecular compounds – prefixes indicate number of atoms
Exception – first element never uses mono-
Common names
1-mono
6-hexa
2-di
7-hepta
3-tri
8-octa
4-tetra
9-nona
5-penta
10-deca

7. Naming acids – if compound produces H+ ions in solution, it is an acid
Binary acids – contains H and one other element
Use prefix hydro-, root word of other element, suffix –ic, followed by acid
Ex: HBr is hydrobromic acid
Oxyacids – contains H and a oxyanion
If anion suffix is –ate, it is replaced w/ -ic
If anion suffix is –ite, it is replaced w/ -ous
Ex: HNO3 is nitric acid
HNO2 is nitrous acid
Considered acids only when in solution (i.e., dissolved in water)
Ex: HCl at STP is hydrogen chloride gas but in solution is hydrochloric acid

8. Molecular structures
Structural formulas – letter symbols and bonds show relative positions of atoms
H is always on the end
Central atom is usually closer to the left on the periodic table
If central atom is not surrounded by 4 e- pairs, it does not have an octet
Must have double or triple bond
Ex. problems 9-3 – 9-5

9. Exceptions to Octet Rule
Resonance structures – more than one valid Lewis structure can be written; differ only in position of e- pairs and never atom positions
Exceptions to Octet Rule
Uneven number of valence electrons - some molecules have an odd number of valence electrons and can’t form an octet
Ex: NO2
Suboctet - some compounds form w/ fewer than 8 electrons present
Reactive and can share an entire pair of electrons donated by another atom
Coordinate covalent bond – when one atom donates a pair of electrons to be shared w/ an atom or ion that needs 2 electrons to become stable
Ex: BH3
Expanded octet - some compounds have central atoms that contain more than 8 valence electrons
Ex: PCl5

10. Molecular shape
Valence Shell Electron Pair Repulsion (VSEPR) model – used to determine molecular shape
Based on arrangement that minimizes repulsion of shared and unshared pairs of electrons around the central atom
Bond angle – angle formed by any 2 terminal atoms and the central atom
Lone pairs of electrons are not shared between 2 nuclei, therefore they occupy a slightly larger orbital than shared electrons
Shared bonding orbitals are pushed together slightly by lone pairs, therefore they occupy a slightly smaller orbital than lone pairs
Table 9-3

11. Hybridization – atomic orbitals are mixed to form new, identical hybrid orbitals
Hybrid orbitals – contain one electron that it can share w/ another atom
Ex: methane CH4

12. Electronegativity and polarity
Polar covalent bond – unequal sharing of electrons due to differences in electronegativity
Ex: water H2O
Microwave ovens
Water molecules are constantly moving as they align themselves w/ the changing polarity of the microwave energy field
How it Works, p. 270