2. chem bonding

What is a covalent bond

Electrostatic forces of attraction between shared electrons and the positively charged nuclei

How are covalent bond formed

Non metal atoms share valence electrons through overlap of orbitals → increased electron density between the two nuclei where the shared electrons are most likely to be found.

Where is highest electron density found in covalent bond

Covalent bond

What is a sigma bond

A pair of electrons is shared between two atoms. Formed due to head on overlap of an orbital with each atom.

What is a pi bond

Bond formed due to the sideway iverlap of a p orbital on each atom

Pi bind can only form __ a sigma bond is formed

After

Why is pi bond less weaker than sigma bond?

Pi bind (sideway overlap) is less effective that sigma

What is a dative bond

The donor atom provides two electrons (lone pair of electrons) to an acceptor atom (empty valence orbital)

What is electronegativity

Ability of an atom to attract the shared pair of electrons in a covalent bond

when is a polar covalent bond formed

Two atoms involved in different electronegativities → bonding electrons unequally shared between 2 atoms → permanent separation of partial charges (dipoles) between 2 atoms

how is strength of dipole measured

Dipole moment

what is the relationship between dipole moment and electronegativities?

The bigger the difference in electronegativities of the atoms, the larger the dipole moment, the more polar the covalent bond.

What is bond energy

The amount of energy required to break one mole of covalent bonds in the gaseous state

What are the 3 factors jn strength of covalent bonds

1. Bond Order

2. Effectiveness of orbital overlap

3. Bond polarity

As bond order increases…

1) number of bonding electrons within inter-nuclei region increases

2) ESFOA for these electrons increases

Larger orbitals are more diffuse which results in…

1) less effective orbital overlap

2) lower bond strength

Explain how bond polarity affects covalent bond strength

1) in polar bond, there are additional attractive forces between 8+ and 8- that strengthens the covalent bond, leading to higher bond strength.

What is bond length

The average distance between the nuelci of two atoms

Why is it that although F is smaller than Cl, (more effective overlap of orbitals hence stronger bond), Cl-Cl has a stronger bond? (O2 too)

F is very small, so its bond length is very short. This results in the non bonding electrons on F being in close proximity with those of the other F atom. Thus, repulsion occurs which weakens the covalent bond.

Why can period 3 elements expand beyond octet structure?

Only elements from period 3 onwards have vacant and energetically accessible d orbitals to expand beyond octet structure

Why is there ionic character in covalent bonds?

Atoms have considerable electronegativity difference. Increase electronegativity difference = greater extent of ionic character.

Why is there covalent character in ionic bond?

It arises due to polarisation, which is the distortion of anion electron cloud by a neighbouring cation in an ionic compound. → forms electron sharing on oppositely charged ions

How to measure polarisation?

Cation: charge density (q/r)

Anion: large radius