Chemical Bonding 4

Covalent bonds

• electrostatic force of attraction between a shared pair of electrons and the positively charged nuclei

• formed between elements of small electronegativity difference

sigma bonds

• formed when valence orbital overlap head-on with one another

• can be between same or different type of orbital

pi bond

• formed when parallel valence p orbitals overlap sideways with one another

• formed only after the sigma bond is formed to ensure that the 2 atoms are close enough for sideways overlap

dative bond

• a covalent bond in which the shared pair of electrons is provided by only one of the bonded atoms

• donor atom must have at least a lone pair of electrons in its valence shell

• acceptor atom must have a vacant and energetically accessible orbital to accept the lone paid of electrons

factors affecting strength of covalent bonds

1. bond length

• distance between the 2 nuclei in a covalent bond

• shorter bond length, stronger bond

2. bond energy

• average energy required to break 1 mol of covalent bond in the gas phase into constituent gaseous atoms under standard condition

• greater bond energy, stronger bond

3. bond order

• greater the bond order, stronger bond

• triple bond>double bond>single bond

bond polarity

how equally the electrons are shared between the 2 bonded atoms

polar covalent bond

2 atoms have different electronegativity, bonding electrons are not equally shared

non-polar covalent bonds

2 atoms have the same electronegativity — bonding electrons are equally shared

dipole

atom with greater electronegativity pulls the electrons of the covalent bonds towards itself - partial negative charge

atom depleted of electrons - partial positive charge

dipole formed by the permanent partial separation of charges