UNIT 1: SECTION 3 - BONDING

Question 1

What are ionic bonds?

Answer 1

electrostatic attraction between atoms - v.strong

Question 2

what are covalent bonds?

Answer 2

large difference in electronegativity between non-metals. electron pair found in the middle of cov. bond.

Question 3

Two types of covalent structures.

Answer 3

simple covalent molecules & giant macromolecular structures.

Question 4

Two macromolecular structures.

Answer 4

Graphite: Forms bond with 3 other Carbon atoms.
Carries delocalised electrons; carries charge
Sheets of hexagons; sheets held by weak IMF’s; layers can break off and slide.
Strong cov. bonds; insoluble and high MP & BP.
Layers far apart - low density; strong light equipment.

Diamond: Forms bond with 4 other Carbons (tetra).
No delocalised electrons; doesn’t carry charge.
High MP & BP (strong cov. bonds); vibrations travel so it is good thermal conductor.
v.tough - diamond drills.

Question 5

What is a dative cov. bond?

Answer 5

When one atom donates its lone pair to an acceptor.

shown by an arrow coming from donor.

Question 6

What is a simple cov. molecule?

What are properties of it?

Answer 6

Few atoms held by covalent bonds, e.g. H2O.
Weak IMF’s hold simple cov. molecules together;
low mp & bp.
Insoluble in water (cov. bonds v.strong).

Question 7

What is a giant ionic lattice?

What are the properties of it?

Answer 7

Same units repeated e.g. NaCl
Water-soluble (water polar)
High MP.
When molten, they conduct electricity.

Question 8

What is the valence shell electron pair repulsion theory?

Answer 8

Charge clouds repel each other as much as they can;
Lone Pair - Lone Pair
Lone Pair - Bonding Pair
Bonding Pair - Bonding Pair

Question 9

What is the method to predict the shape?

Answer 9

1) Group of central atom + Number of bonded atoms.
2) Divide by two = number of electron pairs.
3) Number of bonding pairs = number of bonded atoms.
4) Any remnant pairs, Lone Pairs.
5) Work out shape from here.

Question 10

Bond angles for 2 electron regions?

Answer 10

180 degrees

Question 11

Bond angles for 3 electron regions?

Answer 11

120 degrees

Question 12

Bond angles for 4 electron regions?

Answer 12

109.5 degrees

Question 13

Bond angles for 5 electron regions?

Answer 13

90 & 120 degrees

Question 14

Bond angles for 6 electron regions?

Answer 14

90 degrees

Question 15

What are the most electronegative elements?

Answer 15

NOF

Question 16

What does electronegativity mean?

Answer 16

The ability to attract electrons in a covalent bond.

Question 17

What does a high electronegativity lead to?

Answer 17

Polar bond with a permanent dipole.

Question 18

What is a dipole?

Answer 18

difference in charge caused by shift in electron charge density.

Question 19

How can molecules be polar?

Answer 19

If molecules are unsymmetrical, the charge distribution is uneven and it is polar.

Question 20

True or false:

Polar molecules have permanent dipole-dipole IMF’s.

Answer 20

True because there is a permanent difference due to shift of electron charge density (due to high EN atom pulling electron pair).

Question 21

What is the order of IMF strength?

Answer 21

Strongest:
Hydrogen bonds,
Permanent dipole-dipoles,
London forces.

Question 22

What are London Forces?

Answer 22

Forces which occur due to a temporary shift of electrons towards one side of charge cloud.
LF’s can cause chain effect; neighbouring molecules repelled by slightly negative/positive end, and turn into temporary dipole and so on…
Constantly created/destroyed making them have weak attraction.

Question 23

One lattice which is held by LF’s?

Answer 23

Iodine lattice.

Question 24

What effect does London Forces have on the physical properties of molecules?

Answer 24

Increases the Boiling point -

• a larger molecule has a larger electron cloud; further distance for LF’s to cover.
• longer, straighter molecules can also lie closer together; forces stronger.
• IMF’s need to be overcome to boil.

Question 25

What is hydrogen bonding?

Answer 25

A polar bond formed due to hydrogen’s high electron charge density and NOF’s high electronegativity.
H forms weak bond with LP of other atoms.

Question 26

What effect does hydrogen bonding have on the physical properties of molecules?

Answer 26

When ice forms, Hydrogen bonds spread further apart in physical state, density decreases;
ice density < water density; floats.

Question 27

Describe metallic bonding.

Answer 27

• Giant metallic structures of positive ions with
  delocalised sea of electrons; strong forces of
  electrostatic attraction causes high MP & BP.
• Delocalised electrons carry charges and heat:
  good thermal & electrical conductors.
• Insoluble due to strong bond enthalpy.

Question 28

Properties of solids?

Answer 28

Vibrate around fixed point..

Closely packed together; high density; incompressible.

Question 29

Properties of liquids?

Answer 29

Closely packed together; similar density to solids; virtually incompressible.
Particles move more freely.

Question 30

Properties of gases?

Answer 30

Freely move about, far apart; loads of energy; compressible.