chem bonding

Question 1

(i) outline the importance of hydrogen bonding to the physical properties of substances, including ice and
water

Answer 1

Ice:
1. h2o molecules are bonded tgt by H-bonding

2. each water molecule is H-bonded to 4 other water molecules, tetrahedral
3. Ice is less dense than water, because of its open structure(for orientation of water molecules to maximise the intermolecular H-bonds). However, when ice melts, some of these H-bonds are broken and the lattice breaks up. The water molecules can pack more closely together. Hence the liquid has a higher density at 0C

Question 2

(j) explain bond length for covalent bonds

Answer 2

distance between the nuclei of atoms

Question 3

ionic substance - hard and brittle

Answer 3

hard:
oppositely charged ions are held tgt by strong efoa in lattic structure

brittle:
- stress applied on ionic lattic causes sliding of layers of ions
- ions of similar charges come together & the resultant repulsion shatters the ionic structure

Question 4

metallic substance - malleable and ductile

Answer 4

• when a force is applied, the layers of ions can easily slide over each other without breaking the metallic bond
• metallic bodns are easily reformed and the crystal lattic is restored

Question 5

giant molecular layered covalent substance - soft and slippery

Answer 5

-adjacent layers are held together by weak id-id interactions.
-hence, layers can easily slide over each other

Question 6

giant molecular covalent substance - extremely hard

Answer 6

atoms are held tgt by EXTENSIVE strong covalent bonds in the giant 3d structure

Question 7

what is a dative bond

Answer 7

electrostatic forces of attraction that exist between the donor and acceptor nuclei and the shared pair of electrons

covalent bond in nature

Question 8

electron-rich donor

Answer 8

must have pair on non-bonding electrons available for donation

Question 9

electron-deficient acceptor

Answer 9

must have an empty/vacant low-lying orbital to accept the pair of electrons

Question 10

–> used in dative bonds:

Answer 10

pointing from donor to acceptor

Question 11

Decrease with the effectiveness of orbital overlap means

Answer 11

larger atoms have larger orbitals that are more diffused and so the overlap of orbitals is less effective. weaker bonds

Question 12

conditions for h bond

Answer 12

1. H atom from H-F/O/N bond
2. lone pair from F/O/N of another molecule

Question 13

Use the Valence Shell Electron Pair Repulsion theory to predict the shape of the BF4 − ion.

Answer 13

Since there are 4 bp and no lp around central B atom, shape of the BF4 – ion is tetrahedral with a bond angle of 109.5°.

Question 14

Define covalent bond

Answer 14

Efoa between shared pair of e and positively charged nuclei

Question 15

Define metallic bond

Answer 15

Efoa between a lattice if positive ions and sea of delocalised electrons