Unit 1: Section 3 - Bonding

Question 1

What are the compound ions to remember?

Answer 1

Sulfate - SO4^2-
Hydroxide - OH-
Nitrate - NO3-
Carbonate - CO3^2-
Ammonium - NH4+

Question 2

What is ionic bonding?

Answer 2

Strong electrostatic forces of attraction between oppositely charged ions held in a lattice

Question 3

What is an ionic crystal?

Answer 3

They are giant lattices of ions.
A lattice is just a regular structure
It’s called giant because it’s made up of the same basic unit repeated over and over again
Different ionic compounds have different shaped structures

Question 4

Do ionic compounds conduct electricity?

Answer 4

They do when they’re molten or dissolved but not when they’re solid
The ions in a liquid are free to move and carry a charge
In a solid the ions are fixed in position by strong ionic bonds

Question 5

What are the melting points of ionic compounds like?

Answer 5

High melting points
Giant ionic lattices are held together by strong electrostatic forces
It takes lots of energy to overcome these forces

Question 6

Do ionic compounds dissolve in water?

Answer 6

They tend to, yes
Water molecules are polar, these charged parts pull ions away from the lattice causing it to dissolve

Question 7

What are molecules?

Answer 7

Form when 2 or more atoms bonded together
Held together by strong covalent bonds

Question 8

What are giant covalent structures?

Answer 8

Macromolecular structures which have a huge network of covalently bonded atoms

Question 9

What is the structure and what are the properties of graphite?

Answer 9

1. Macromolecular covalent, with each C atom bonded to 3 others
2. The weak bonds between the layers in graphite are easily broken, so the sheets can slide over each other - used as a dry lubricant and in pencils
3. The delocalised electrons are free to move along the sheets carrying a charge, so it’s an electrical conductor
4. The layers are quite far apart compared to the length of the covalent bonds, therefore has a low density - used to make strong, lightweight sport equipment
5. Due to the strong covalent bonds in the hexagon sheets graphite has a very high melting point (sublimes over 3900K)
6. Insoluble in any solvent, as the covalent bonds in the sheets are too strong to break

Question 10

What are the properties of diamond?

Answer 10

1. Very high melting point (also sublimes over 3900K)
2. Extremely hard - used in diamond-tipped drills and saws
   3.. Vibrations travel easily through the stiff lattice so it’s a good thermal conductor
3. Can’t conduct electricity because all the outer electrons are held in localised bonds
4. Won’t dissolve in any solvent
5. It can be cut to form gemstones, its structure makes it refract light a lot which is why it sparkles

Question 11

What is the structure of diamond?

Answer 11

3D tetrahedral structure of C atoms, with each C atom bonded to 4 others

Question 12

What is dative covalent bonding?

Answer 12

Forms when an atom provides both of the shared electrons

Question 13

What are charge clouds?

Answer 13

An area where you have a high chance of finding an electron pair, the electrons don’t stay still, thy whizz around inside the charge cloud

Question 14

What is Valence-shell electron-pair repulsion theory?

Answer 14

This is how much electron charge clouds repel each other
Lone pair - lone pair repulsion > Lone pair - bonded pair > Bonded pair - bonded pair

Question 15

How to predict the shape of a molecule

Answer 15

1. Work out what the central atom is
2. Use the periodic table to work out the number of electrons in the outer shell of the central atom
3. Work out how many of those electrons are in a covalent bond, that’s the number of bonding pairs
4. The remaining electrons around the central atom divide by t 2 and they’re the lone pairs

Question 16

What is the shape when a molecule has 2 electron pairs?

Answer 16

0LP Shape - Linear Bond Angle - 180°

Question 17

What is the shape when a molecule has 3 electron pairs?

Answer 17

0LP Shape - Trigonal planar Bond Angle - 120°

Question 18

What are the shapes when a molecule has 4 electron pairs?

Answer 18

0LP Shape - Tetrahedral Bond Angle - 109.5°
1LP Shape -Trigonal pyramidal Bond Angle - 107°
2LP Shape - Bent Bond Angle - 104.5°

Question 19

What are the shapes when a molecule has 5 electron pairs?

Answer 19

0LP Shape - Bipyramidal Bond Angle - 120° and 90°
1LP Shape - Seesaw Bond Angle - 102° and 87°
2LP Shape - T-shaped Bond Angle - 88°

Question 20

What are the shapes when a molecule has 6 electron pairs?

Answer 20

0LP Shape - Octahedral Bond Angle - 90°
1LP Shape - Square pyramidal Bond Angle - 90°
2LP Shape - Square planar Bond Angle - 90°

Question 21

What is electronegativity?

Answer 21

An atom’s ability to attract the electron pair in a covalent bond
Fluorine is the most electronegative

Question 22

Why are some bonds polar?

Answer 22

1. A covalent bond between 2 atoms of the same element is non-polar because the atom shave equal electronegativities, so the electrons are equally attracted to both nuclei
2. Some elements have similar electronegativities, so the bonds between them are essentially non-polar
3. In a polar bond, the difference in electronegativity between the 2 atoms causes a permanent dipole
4. The greater the difference in electronegativity, the more polar the bond

Question 23

What is a dipole?

Answer 23

A difference in charge between 2 atoms caused by a shift in electron density in the bond

Question 24

How can a molecule be polar?

Answer 24

When a molecule contains polar bonds with an uneven distribution of charge across the whole molecule, the molecule is polar
If the polar bonds are arranged symmetrically in a molecule, then the charges cancel out and there is no permanent dipole

Question 25

What are permanent dipole-dipole forces?

Answer 25

In a substance made up of molecules that have permanent dipoles, there will be weak electrostatic forces of attraction between the delta+ and delta-charges on neighbouring molecules

Question 26

What are the 3 types of intermolecular forces in order of strength?

Answer 26

1. Induced dipole-dipole or Van der Waals forces
2. Permanent dipole-dipole forces
3. Hydrogen bonding

Question 27

How do Van der Waals forces arise?

Answer 27

1. Electrons in charge clouds are always moving really quickly, at any moment, the electrons in an atom are likely to be more to one side than the other, at this moment the atom would have a temporary dipole
2. This dipole can induce another temporary dipole of the opposite charge on a neighbouring atom, the 2 dipoles are then attracted to each other
3. Because the electrons are constantly moving, the dipoles are being created and destroyed all the time, even though the dipoles keep changing, the overall effect is for the atoms to be attracted to each other

Question 28

What is hydrogen bonding?

Answer 28

Strongest type of intermolecular forces
1. Only happens when hydrogen is covalently bonded to fluorine, nitrogen or oxygen
2. F, N and O are very electronegative, so they draw bonding electrons away from the hydrogen atom
3. The bond is polarised, and hydrogen has such a high charge density (because it’s so small), that the hydrogen atoms form weak bonds with lone pairs of electrons on the F, N or O atom sof other molecules

Question 29

What is the effect of hydrogen bonding on the properties of substances?

Answer 29

1. Substances with hydrogen bonds have higher boiling and melting points than other similar molecules because of the extra energy needed to break the hydrogen bonds
2. As liquid cools to form ice, the molecules make more hydrogen bonds and arrange themselves into a regular lattice structure, in this regular structure the H2O molecules are further apart on average than the molecules in liquid water - so ice is less dense than liquid water

Question 30

How do metals exist, and what is metallic bonding?

Answer 30

Metals exist as giant metallic lattice structures
1. The outermost shell of electrons of a metal atom are delocalised and are free to move about the metal
2. The positive metal ions are attracted to the delocalised negative electrons, they form a lattice of closely packed positive ions in a sea of delocalised electrons

Question 31

How does metallic bonding explain the properties of metals/

Answer 31

1. Metals have a high melting point because of the strong electrostatic forces of attraction between the positive metal ions and the sea of delocalised electrons
2. The number of delocalised electrons per atom affects the melting point, the more there are, the stronger the bonding will be and the higher the melting point
3. The delocalised electrons can pass kinetic energy to each other, making metals good thermal conductors
4. Metals are good electrical conductors because the delocalised electrons can move and carry a current
5. Metals are insoluble (except in liquid metals) because of the strength of the metallic bonds

Question 32

How does the strength of metallic bonds change across the periodic table? Why?

Answer 32

Increases - higher melting and boiling points, stronger
1. Higher charge on metal ions
2. More delocalised electrons per ion
3. Stronger force of attraction between them

Question 33

What are the properties of solids?

Answer 33

Particles are very close together - high density and incompressible, the particles vibrate around a fixed point and can’t move about freely

Question 34

What are the properties of liquids?

Answer 34

Has a similar density to a solid and is virtually incompressible, the particles move about freely and randomly within the liquid, allowing it to flow

Question 35

What are the properties of gases?

Answer 35

The particles have lots more energy and are further apart, so the density is very low and it’s compressible, the particles move about freely with not a lot of attraction between them, so they’ll quickly diffuse to fill a container

Question 36

Why do simple covalent structures have low melting and boiling points?

Answer 36

You only have to overcome the weak intermolecular forces and not the strong covalent bonds

Question 37

Why do giant covalent structures have high melting and boiling points?

Answer 37

You have to break the covalent bonds between atoms, it tends to sublime rather than melt

Question 38

What are the properties of ionic bonding?

Answer 38

Melting and boiling points - High
Typical state at room temperature and pressure - Solid
Does solid conduct electricity - No
Does liquid conduct electricity - Yes
Is it soluble in water - Yes

Question 39

What are the properties of simple covalent structures (molecular)?

Answer 39

Melting and boiling points - Low
Typical state at room temperature and pressure - May be solid like I2 but usually liquid or gas
Does solid conduct electricity - No
Does liquid conduct electricity - No
Is it soluble in water - Depends on how polarised the molecule is

Question 40

What are the properties of giant covalent structures (macromolecular)?

Answer 40

Melting and boiling points - High
Typical state at room temperature and pressure - Solid
Does solid conduct electricity - No (except graphite)
Does liquid conduct electricity - N/a sublimes rather than melting
Is it soluble in water - No

Question 41

What are the properties of metallic structures?

Answer 41

Melting and boiling points - High
Typical state at room temperature and pressure - Solid
Does solid conduct electricity - Yes
Does liquid conduct electricity - Yes
Is it soluble in water - No

Question 42

Why is ice less dense than water?

Answer 42

• In liquid water, hydrogen bonds constantly break and reform as molecules move about
• In ice, the hydrogen bonds hold the molecules in fixed poisitions; this makes them slightly further apart than in liquid water