Bonding, Structure, Properties and Energy

Question 1

Is energy is released or taken in when atoms combine

Answer 1

Released. This means that bond-making is an exothermic process. Because energy is released, the atoms now have less energy and this is considered stable.

Question 2

Are single or pairs of e- more stable

Answer 2

Pairs

Question 3

Ionic Bond

Answer 3

an electrostatic attraction between a positively charged metal ion (cation) and a negatively charged non-metal ion (anion). It is formed via transfer of e- from metal to non-metal

Question 4

Covalent Bond

Answer 4

valence e- are shared between non-metal atoms to achieve a full outer shell.

Question 5

Why does covalent bonding occur

Answer 5

Because e- are more stable when attracted to two nuclei than one

Question 6

How are the e- in covalent bond regarded as?

Answer 6

Electron clouds. They are not in a fixed position. They are in constant motion.

Question 7

Metallic Bond

Answer 7

Attraction between a metal atom with a positive nucleus and a sea of electrons. The atoms’ valence e- are lost and attracted to all nuclei in the metal lattice. The e- are said to be delocalised because they are not attached to any one metal nucleus.

This is non-directional bonding as this attraction is not in any particular direction.

Draw diagram

Question 8

What is EN

Answer 8

EN is the relative ability of an atom to attract shared e- in a covalent bond.

Question 9

What does the EN value of an element depend on?

Answer 9

-size of nuclear charge (total protons in the nucleus so as the atom gets bigger, the nuclear charge increases)
As nuclear charge increases, the EN value will increase because the atom is able to attract shared e- better.

So across the period, EN increases (as there are same number of shells).

-size of atom. As the atom gets bigger, there are more shells/energy levels so the valence e- are further from the nucleus, so the nucleus charge is less effective. This decreases the EN value (as it’s the valence shell that reacts) because the extra energy values supersede the increase nuclear charge.

So down a group, EN decreases.

Question 10

Rules for EN

Answer 10

Atoms of same element have same EN so e- are shared equally = non-polar bond.

If 2 non-metal atoms of different EN = share e- unevenly = polar bond.

If EN diff very large e.g. between metal and non-metal, then the e- sharing is so uneven there is a transfer of e- and an ionic bond forms.

Question 11

Arrangement of ionic substances

Answer 11

As ions are formed, they come together in a giant 3D lattice of ions electrostatically attracted to each other (ionic bond). They form a repeating arrangement of cation/anion.

Draw diagram 3D

Question 12

Melting points of ionic substances

Answer 12

The attraction between ions is very strong. Therefore, a lot of heat E is required to break the forces holding the ions together (overcome the attractive forces)

= mpt and bpt high

Question 13

Why is the bpt higher than mpt

Answer 13

Because all bonds/forces are broken so need more energy

Question 14

Which ionic compounds have higher mpt

Answer 14

ions with higher charge and/or smaller size are more attracted to each other so more energy is needed to change state.

Question 15

Electrical conductivity of ionic substances

Answer 15

Electrical conductivity depends on the mobility of ions or electrons (charged particles) in a substance.

Ionic substances have ions which are the charged particles responsible for conducting electricity.

When solid, the ions are fixed in place so cannot conduct electricity.

When molten or aqueous, the ions are free to move as the lattice structure is destructed so the ionic substance can conduct electricity.

Question 16

Mechanical properties of ionic substances

Answer 16

Not malleable as ions are fixed in place and cannot move around each other = hard and brittle.

Draw diagram.

Brittle means that if a strong force is applied, the layers of ions move and if the ions of the same charge come in contact, they will repel and cause the crystal to shatter.

Ionic substances are hard because the ions are held together so strongly.

Question 17

Solubility of ionic substances in water

Answer 17

Many are soluble in water and form hydrates in aqueous solution.

Soluble because the negative end of water molecules attracts to the positive ion and the positive end of the water molecule attracts to the negative ion.

The water molecules surround the ions causing the solid to dissolve. Draw diagram.

The attraction between polar water molecule and the ion is able to overcome the attraction between the ions.

if the solvent is non-polar, there are no attractions to the ions as it has no permanent dipole. So, the ionic solid does not dissolve.

Question 18

Why go across the group if all form Chlorides the mpt decreases

Answer 18

Because it’s going from an ionic to covalent bonds. Ionic attracts are very strong and require lots of E to overcome and melt. However, covalent molecules are held together by intermolecular forces which are very weak so do not need lots of energy to overcome, so the mpt is low.

Question 19

Metallic structure

Answer 19

3D lattice of metal atoms with positive nuclei and a sea of delocalised e-.

Draw diagram.

The metallic bond is an electrostatic force of attraction between the positive nuclei of atoms and the negative electrons in the lattice. It is a strong bond.

Question 20

Electrical conductivity of metals

Answer 20

Electrical conductivity depends on the ….

Metals have delocalised electrons which are able to carry the charge through the lattice (towards the positive terminal) as they can freely move throughout the structure.

Question 21

Mpt and bpt of metals

Answer 21

Although not as strong as an ionic bond, metals still have relatively high mpt/bpt

This means that a lot of heat energy is required to overcome the forces in a metal. This is because the electrostatic forces between the positive nuclei and the negative e- are very strong.

Question 22

Malleability and ductility of metals

Answer 22

Metals have non-directional bonding. This means that if the metal atoms are moved around, the delocalised e- will move with the structure as well and the metal atoms can still hold together without breaking.

= metals can be bent and shaped (malleable) or drawn into wires (ductile)

Question 23

Hardness of metals

Answer 23

Hardness of metal is related to its ability to resist deformation and is due to the strength of the bond.

Question 24

Solubility of metals

Answer 24

Forces between the metal atoms (between the positive nuclei and the delocalised e-) are too strong to be overcome by forces of attraction with water molecules, so metals are not soluble in water.

Question 25

Bonding in graphite

Answer 25

It is a 2D network and has a layer structure.

Draw diagram.

Each C atom uses three of its e- to form covalent bonds with 3 other C atoms. The fourth electron from each C atom becomes delocalised over the whole sheet of atoms in one layer. So each C contributes one e- to the delocalised e- between the layers.

The atoms within a sheet are held by strong covalent bonds. Weak intermolecular forces hold the sheets (hexagonal layers) together.

Question 26

mpt of graphite

Answer 26

High. Similar to diamond.

This is because in order to melt graphite, the covalent bonds between the C atoms must be broken throughout the structure, not just the intermolecular forces between the sheets. So, a lot of energy is required to do so so it has a high mpt.

Question 27

Slippery feel of graphite

Answer 27

This is due to the weak intermolecular forces between the layers, allowing the hexagonal layers to slide past each other.

This is why it is used for pencils and dry lubricant e.g. locks.

Question 28

Density compared to diamond

Answer 28

Lower because of the relatively large amount of space between the layers.

Question 29

Solubility of graphite

Answer 29

Insoluble in water and organic solvents. The attractions between the solvent molecules and C atoms will never be strong enough to overcome the strong covalent bonds in graphite.

Question 30

Electrical conductivity of graphite

Answer 30

Conducts electricity. The delocalised e- are free to move between the hexagonal layers. If a piece of graphite is connected to a circuit, e- can fall off one end of the sheet and be replaced with new ones at the other end.