Chapter 8
When two atoms both want to gain electrons they cannot form an ionic bond They can form a covalent bond Atoms are held together by sharing e -
A neutral group of atoms joined together by covalent bonds A molecule, consisting of two atoms, is a diatomic molecule H 2, N 2, O 2, Cl 2, etc.
A compound consisting of two or more molecules Molecular compounds tend to have lower boiling points (bp) than ionic compounds
Molecular compounds are generally a liquid at room temperature Ionic compounds are generally a solid
The chemical formula of a molecular compound Shows how many atoms of each element a molecule contains C 7 H 2 (NO 2 ) 3
Also describe molecules with one type of element O 2 N 2
H2OH2OC2H6C2H6
CO 2 NH 3
p. 216 #1-6
In covalent bonding, e - sharing usually occurs so that the e - configurations of noble gases Covalent bonding usually occurs between metalloids and nonmetals Groups 4, 5, 6, and 7
Two atoms held together by sharing a pair of electrons
An e - dot structure such as H:H represents the shared pair of e - of the covalent bond by two dots
Represents the covalent bonds by dashes and shows the arrangement of covalently bonded atoms H - H
A pair of valence electrons that is not shared between atoms
2H + O O−H + O−H | | H H
NH 3 CH 4
Practice Problems p. 220 # 7-8
Sometimes atoms bond by sharing more than one pair of e - Atoms can form double or triple bonds
A bond involving two shared pairs of e -
A bond formed by sharing three e -
O2N2O2N2
p 222 Table 8.1
Sometimes atoms do not combine ideally CO – e - configuration
A covalent bond in which one atom donates both bonding electrons Represented with an arrow
Once formed a coordinate covalent bond is just like any other covalent bond
Tightly bound group of atoms that has a positive or negative charge and behaves as a unit
Sometimes in chemistry we use MAGIC!
H + + NH 3 NH 4 + Hydrogen Ammonia Ammonium Ion Molecule Ion
SO 3 How do you find the charge?
p. 225 #9-12 Attempt to do by yourself first We will go over this!!!!!!
The energy to break a covalent bond Usually given for 1 mole of molecule 6.02 x 10 23
A large dissociation energy shows a strong covalent bond and vice versa C-C 347 kJ/mol C=C 657 kJ/mol CΞC 908 kJ/mol
Molecules containing bonds with high dissociation energies typically do not react The bonds are very stable
A structure that can be correctly drawn in two or more valid e - dot structures
Given the structures, what are all the resonance structures C 3 H 5 - C 6 H 6
For some molecules or ions it is impossible to draw correct e - dot structures NO 2
Octet rule cannot be applied to molecules with an odd number of total valence e -
Some molecules will have more or less than 8 valence e -
BF 3 PCl 5 SF 6
p. 229 #13-22 Try #22 we didn’t go over this!
Molecular Orbital VSEPR Hybrid Orbital
Two kinds of bonds Sigma bonds (single) Pi bonds (double and triple)
Valence-Shell Electron-Pair Repulsion Theory The repulsion between e - pairs causes them to stay as far apart as possible
This repulsion causes molecules to form specific shapes p. 213
VSEPR Theory does a great job explaining shape However, doesn’t explain types of bonds
Gives information about both shape and bonds
p 236 #23-25, 27
In polar bonds e - are not shared equally Atoms with higher electronegativity attract e - more
One end of the molecule is slightly negative
Van der Waals London Dispersion Dipole-Dipole Hydrogen Bonding
p 244 #32-34, 36, 37
p. 247 #40-47, 49, 51, 54, 58-60