Covalent bonding

Question 1

What is a covalent bond?

Answer 1

Shared pair of electrons between two non-metals.

Question 2

Pair of electrons in an atom not used up for covalent bonds are called what?

Answer 2

Lone pairs

Question 3

What is an expansion of the Octet?

Answer 3

When an atom uses all the electrons in the 3d subshell form covalent bonds regardless of whether the atom ends up with a noble gas electronic configuration or not.

Question 4

What is a dative/co-ordinate bond?

Answer 4

When a lone pair of electrons are used to form a covalent bond. The two electrons come from the same atom instead if different.

Question 5

Dative/co-ordinate bond has the same what as covalent bonds?

Answer 5

1. Length

2. Strength (average bond enthalapy)

Question 6

The acceptor ion in a dative/co-ordinate bond must be what?

Answer 6

Electron deficient (have spaces for those electrons).

Question 7

How do u show a dative/co-ordinate bond?

Answer 7

• ->

eg. NH3 –> H

Question 8

Shapes of molecules are based on what fact?

Answer 8

Electron pairs repel each other and move as part apart from each other as possible in order to minimise replusion.

Question 9

Give shape name and angle for 2 total pairs

Answer 9

Linear 180*

Question 10

Give shape name and angle for 3 total pairs

Answer 10

Trigonal planar 120*

Question 11

Give shape name and angle for 4 total pairs

Answer 11

Tetrahedron 109.5*

Question 12

Give shape name and angle for 5 total pairs

Answer 12

Trigonal bipyramidal 90/120*

Question 13

Give shape name and angle for 6 total pairs

Answer 13

Octahedral 90*

Question 14

What effect does lone pair have on bond angles and why?

Answer 14

Lone pairs repel more strongly than bonding pairs so each pair reduces the bonding angle by 2.5

Question 15

Overall how to do the shape of molecules: (3steps)

Answer 15

1. Find the base shape according to the total no. of pairs.
2. Reduce the angles according to lone pairs.
3. Ignore the lone pairs and find a new name of shape with the modified angles.

Question 16

What is electronegativity?

Answer 16

The ability of an atom to attract the pair of electrons to itself in a covalent bond.

Question 17

Describe and explain the trends of electronegativity across and down a group.

Answer 17

1. Increases across a period (as atomic radius decreases and nuclear charge increases).
2. Decreases down a group (as shielding increases)

Question 18

How is electronegativity measured?

Answer 18

Using a Pauling scale (1-4)

Question 19

Different between pure covalent bond and polar covalent bond.

Answer 19

In pure covalent bonds, the shared pair of electrons lie midway between the two equally electronegative nuclei. Whereas, in polar covalent bonds, the pair of electrons are attracted more towards a more electronegative nuclei causing a separation of charge (dipole) and creating an overall polarity (dipole moment).

Question 20

How is a polar bond shown.

Answer 20

S+ S-
S= small charge
–!–> points towards more electronegative element

Question 21

Give/explain 4 properties of simple molecular substances

Answer 21

1. Low MP (weak intermolecular forces)
2. Soft and breaks easily
3. Does not conduct electricity( no charged ions to carry charge).
4. Non-polar soluble in non-polar solvent and polar in polar solvent.

Question 22

Give 3 properties of diamond (macromolecular)

Answer 22

1. Hard
2. High MP/BP
3. Does not conduct electricity (each C atom bonded to 4 other so no free charge).

Question 23

Give 3 properties of graphite (macromolecular)

Answer 23

1. Soft (layers can slide)
2. High MP/BP
3. Does conduct electricity (Each carbon bonded to 3 other- free electron to carry charge).