L8 Covalent bonding I

Question 1

What is a covalent bond?

Answer 1

A bond formed

Question 2

What is a covalent bond?

Answer 2

= A directional bond formed by a pair of atoms shared by both participating atoms and the electrostatic attraction between oppositely charge nuclei & shared e-, both atoms aim to attain a stable configuration on a Nobel gas by sharing 1, 2 or 3 e- pairs.

• Formed between non-metallic elements -> most electronegative elements don’t want to give e-s away so they share.
• Atomic orbitals overlap to form molecular orbitals

Question 3

How does forming a covalent bond effect the no. of orbitals?

Answer 3

When atoms become molecules the overall no. of orbitals must remain the same
- e- fill the molecular orbitals the same way they do atomic orbitals = into the lowest energy first

Question 4

What is a bonding orbital?

Answer 4

= electron density between the two nuclei

Question 5

What is an anti bonding orbital?

Answer 5

= electron density outside two nuclei

Question 6

What is a double covalent bond?

Answer 6

= the sharing of two pairs of e-

Question 7

What is a triple covalent bond?

- give common examples

Answer 7

= the sharing of three pairs of e-

e.g. CC, CN, NN

Question 8

What factors favour covalent bonding?

Answer 8

• High ionisation energies
• High electron affinities
• Equal/similar electronegativity
• High nuclear charge
• Small atomic size
• No. of valence e-: gaining/losing 4 e- is really hard so carbon forms covalent bonds
• Elements on the RHS = high electronegativity, don’t ionise

Question 9

What is a non-polar bond?

Answer 9

= a covalent bond between two atoms of equal (or very similar = no dipole

Question 10

What is a polar bond?

Answer 10

= a covalent bond between two atoms of significantly different electronegativity (>0.5) = has a dipole

• Distortion of the electron cloud, because the electron density is greater towards the more electron negative atom -> a more negative partial charge on the more electronegative atom = delta negative
• A large enough difference in electronegativity leads to a ionic bond

Question 11

What are the differences in properties between covalent and ionic compounds?

Answer 11

1. State:
   - Covalent = gases, liquids or solids
   - Ionic = crystalline solids
2. Melting & boiling point:
   - Covalent = depends on size & intermolecular bonding
   - Ionic = high
3. Conductivity:
   - Covalent = mostly poor
   - Ionic = good when molten
4. Solubility:
   - Covalent = depends on intermolecular bonding
   - Ionic = many soluble in water but non in non-polar liquids
5. Following trends:
   - Covalent = many counter examples
   - Ionic = most compounds obey these ‘rules’

Question 12

What is a giant covalent structure?

- what properties do they have?

Answer 12

= Giant lattice formed because Group 4 elements can form up to four strong bonds between atoms
e.g. Diamond, Graphite, Silicon dioxide
Properties:
- very strong
- hard
- insoluble in all solvents
- non-conductive EXCEPT graphite (can conduct in one direction) & silicon (semi-conductor)

Question 13

What is an allotrope?

Answer 13

= each of the two or more physical forms in which an element can exist
e.g. graphite, charcoal & diamond are all allotropes of carbon