Covalent structures

Question 1

VESPR stands for? What is the meaning?

Answer 1

Valence shell electron pair repulsion theory: the theory that because electron pairs in the same valence shell carry the same charge, they repel each other and spread themselves as far apart as possible

Question 2

Which is the correct arrangement of the bonds around the silicon atoms in silicon dioxide (SiO2)?

Answer 2

tetrahedral, as each silicon atom is bonded to 4 oxygen atoms, so there are 4 bonding domains, resulting in a tetrahedral arrangement with the bonding angle of 109.5º

Question 3

properties of SiO2

Answer 3

very hard, poor conductor of electricity, high melting and boiling point

Question 4

Why is diamond a poor electrical conductor

Answer 4

no delocalised electrons, no electrons are free to conduct electricity

Question 5

allotropes

Answer 5

Different forms of the same element in the same physical state, they have different physical properties such electrical conductivity and hardness (eg: allotropes of carbon are diamond, graphite, and graphene)

Question 6

bond angle carbon atoms in diamond

Answer 6

109.5º

Question 7

Repulsion between electron pairs (weakest to strongest)

Answer 7

bonding pair-bonding pair, lone pair-bonding pair, lone pair-lone pair

Question 8

Difference between electron domain geometry and molecular geometry

Answer 8

EDG: determined by the positions of all electron domains
MG: depends only on the positions of bonded atoms

Question 9

Species with 2 electron domains EDG and MG

Answer 9

MG and EDG: linear

Question 10

Species with 3 electron domains

Answer 10

EDG: trigonal planar
MG: trigonal planar (0LP) or bent (1LP)

Question 11

Species with 4 electron domains

Answer 11

EDG: Tetrahedral
MG: Tetrahedral (0 LP), Pyramidal (1LP), bent (2LP)

Question 12

Why would a molecule with polar bonds be non-polar?

Answer 12

If the bonds are of equal polarity (same elements) and the shape of the molecule is arranged symmetrically they will be non polar.

Question 13

Delocalised meaning & stability & example

Answer 13

Instead of being confined to one location they show a tendency to be shared between more than one bonding position, adds stability to the molecule/ion (eg: ozone)

Question 14

strength of oxygen-oxygen bonds in O3 relative to single and double bond

Answer 14

Intermediate strength between single and double bonds

Question 15

Draw the resonance structures for the carbonate ion CO3 2-

Question 16

Resonance structure

Answer 16

A way of describing delocalized electrons within certain molecules or polyatomic ions where the bonding cannot be expressed by a single Lewis structure.