Chemistry 2.2 Covalent Bonding

covalent bonding

occurs between 2 non-metals, an electrostatic attraction between a shared pair of electrons and the positively charged nuclei

octet rule

stable arrangement of 8 electrons in the outer shell

octet rule exceptions

Hydrogen - gain 1 electron

Lithium - lose 1 electron

Beryllium and Magnesium - 2 bonding pairs

Boron and Aluminum - 3 bonding pairs

bond length & strength

more electron bonds = shorter bond length = stronger bonds

covalent character

differences more than 0.4 and less than 1.8 in electronegativity are considered polar covalent

coordination bonds

both electrons in a covalent bond come from the same atom

VESPR definition

representation of molecular geometry

3 rules of VESPR

1. electron pairs repel each other & arrange themselves as far apart as possible

2. non-bonding electron pairs occupy more space than single bonds

3. double & triple bonds occupy more space than single bonds

electron domain

region of high electron density due to electron pairs

linear geometry

2 bonding domains, angles at 180

trigonal planar geometry

3 bonding domains, angles at 120

trigonal bent geometry

2 bonding and 1 non-bonding domain, angles less than 120

tetrahedral geometry

4 bonding domains, angles at 109.5

tetrahedral trigonal pyramidal geometry

3 bonding and 1 non bonding domain, angles at less than 109.5

tetrahedral bent geometry

2 bonding 2 non bonding domains, angles at less than 109.5

VESPR multiple bonds concept

multiple bonds count as one domain but exert more repulsion

molecular polarity

electron distribution throughout the whole molecule resulting in a partial positive and negative poles (dipole moment)

allotropes of carbon

London Dispersion Forces

experienced by all molecules due to temporary instantaneous dipoles, electrostatic attraction between the opposite charged regions of 2 molecules

Dipole-induced Dipole Forces

occurs between a polar and nearby nonpolar molecule, presence of a permanent dipole induces a temporary dipole in the neighboring molecule

dipole-dipole imf

involve permanent dipoles resulting in dipole-dipole attraction between polar molecules

hydrogen bonding

a dipole with hydrogen resulting in a positively charged hydrogen than forms attraction with electrons

van der waals forces

LDF, dipole-induced, dipole-dipole

volatility of covalent network structure

high melting and boiling point due to strong IMFs

volatility of molecular substances

lower melting and boiling point due to weaker IMFs

electrical conductivity of covalent substances

usually not electrical conductors due to lack of free electrons

solubility of covalent substances

generally insoluble but dependent on IMF between solute and solvent

exceptions to electrical conductivity of covalent substances

graphite and silicon

allotropes of carbon

diamond, graphite, graphene, C60 fullerene

characteristics of diamond

composed of carbon, tetrahedral, poor electrical conductor

characteristics of graphite

composed of carbon, trigonal planar, good electrical conductor

characteristics of graphene

composed of carbon, linear, excellent electrical conductor

characteristics of C60 fullerene

composed of carbon, hexagonal/pentagonal, good electrical conductor