Chemical Bonding(2)

Question 1

What is ionic bonds with covalent character

Answer 1

• when there is polarisation of electron cloud of the anion by the positively charged cation
• electron density is drawn into the region between 2 nuclei resulting in partial sharing of electrons
• greater the polarisation of electron cloud, the higher the degree of covalency

Question 2

Polarising power of cation in extent of polarisation

Answer 2

• dependent on charge density
• higher the charge density, the greater the polarising power in distorting the electron cloud of anion

Question 3

Polarisability of anion

Answer 3

• size of anion

Question 4

What is instantaneous dipole- induced dipole

Answer 4

• constant movement of electron density in a molecule
• cause temporary polarisation or distortion of electron cloud in the molecule
• results in an instantaneous dipole formed in molecule
• induce new dipoles in molecules that surround it and forms weak attractions between molecules

Question 5

Factors affecting id-id attractions

Answer 5

• increase in no. of electrons in molecules result in greater ease of distortion of electron cloud and thus stronger id-id attractions
• attraction between elongated molecules is stronger than attraction between spherical molecules as it has greater surface area of contact which allows for stronger id-id attraction between molecules

Question 6

What is permanent dipole-permanent dipole attraction

Answer 6

• occurs between polar molecules
• due to difference in electronegativity between 2 atoms in polar bond,
• the bonding electron will be drawn towards the more electronegative atom resulting in permanent uneven distribution of electronic charges within the bond
• partial positive end of one polar molecule will attract the partial negative of nearby polar molecule
  -this weak electrostatic attraction is known as pd-pd attractions

Question 7

Factor affecting strength of pd-pd attraction

Answer 7

• magnitude of dipole moment

Question 8

What is hydrogen bonding

Answer 8

• dipole-dipole attraction between a hydrogen covalently bonded to a small highly electronegative atom and a lone pair on F,O,N of a neighbouring molecule

Question 9

Factors affecting strength of hydrogen bonding

Answer 9

• average number of hydrogen bonds
  — the larger the number of hydrogen bonds that can be formed per molecule the greater the amount of energy needed to break the hydrogen bonds between molecules
• electronegativity difference between the H atom and the atom bonded to the H atom in the molecule
  — electronegativity difference increases in the order N-H<O-H<F-H

Question 10

What is intramolecular hydrogen bonding

Answer 10

• occurs when H atom in a molecule is in close proximity to the electronegativity atom of the same molecule