Chemistry A Levels

Question 1

Describe and explain the trend in atomic radius across period 3

Answer 1

As you go across the period atomic radius decreases,

1. Number of protons in the nucleus or nuclear charge increases number of electrons in the outer shell increases
2. Shielding remains the same
3. Nuclear attraction between the electrons in the nucleus increases so electron shells are drawn closer to the nucleus decreasing the atomic radius.

Question 2

Describe and explain the trend in ionic radius across period 3

Answer 2

1. from sodium to magnesium to aluminum,
   Ionic radius decreases because the number of electrons decreases so there is greater attraction between outer shell electrons and the nucleus meaning the electrons are drawn inwards
2. From P³- to S to Cl ionic radius increases because the number of electrons increases which weakens the nuclear attraction meaning the electrons are not drawn inwards is strongly

Question 3

Use a diagram to describe the trends in melting points across period 3.

Answer 3

Diagram to be put.

Question 4

Describe the trend in melting points across period 3

Answer 4

1. Melting points increases from sodium to silicon
2. There is a sharp decrease in melting point between silicon and phosphorus
3. This is slight increase in melting point between phosphorus and sulfur
4. Melting points then decreases from sulfur to argon

Question 5

Why does melting point increase from sodium to silicon

Answer 5

1. Sodium, magnesium and aluminum are all giant metallic structures
2. As you go down the group from Na to Mg to Al, number of protons and electrons increases that’s atomic radius decreases.
3. This leads to greater electric attraction between nuclei and electrons which requires more energy to overcoming melt the metal
4. Silicon is a giant covalent lattice structure which has strong covenant bonds between atoms which require a lot of energy to overcome.

Question 6

Why is there a shop decrease in melting point between silicon and phosphorus

Answer 6

1. Silicon has a giant covalent lattice structure while phosphorus has a simple covalent structure.
2. The strong covalent bonds between silicon atoms require a lot of energy to overcome
3. The weak London forces between P4 molecules require little energy to overcome

Question 7

Why is there a slight increase in melting points between phosphorus and Sulfur

Answer 7

1. Sulfur has more atoms per molecule than phosphorus so sulfur molecules contain more protons and electrons
2. As a result the London forces between molecules are stronger so more energy is required to overcome this forces during melting.
3. The increase is only small because sulfur is still a simple molecular compounds

Question 8

Why does the melting point decrease from sulfur to argon

Answer 8

1. S8, Cl2 and Ar are simple covalent substances.
2. From S8 to Cl2 to Ar the molecules are getting smaller
3. This means that they are weaker intermolecular London forces between molecules
4. As a result less energy is required to overcome this forces and melt the substance

Question 9

Describe and explain how electrical conductivity varies across period 3

Answer 9

1. Conductivity increases from sodium to magnesium to aluminium because metallic bonding means that the contain delocalized electrons that are free to move
2. Silicone is a semiconductor
3. Elements from phosphorus to argon are non-conductors because they are simple molecular substances they have no delocalized electrons or mobile charges

Question 10

How does ionisation energy vary across period 3

Answer 10

In general ionization energy increases across a period because

1. Nuclear charge in the atomic radius increase shielding remains the same
2. Nuclear attraction increases
3. As a result more energy is required to remove an electron so ionisation energy increases

Question 11

What are the properties of ceramics

Answer 11

1. Strong
2. High melting points
3. Electrically insulating

Question 12

Give some examples of ceramics

Answer 12

1. Magnesium oxide ionic
2. Aluminum oxides ionic
3. Silicon dioxide covalent

Question 13

How are the properties of ceramics based on their structure

Answer 13

1. Strength: the ionic or covalent bonds in ceramics are very strong they are giant structures
2. High melting points. lots of energy is required to overcome this strong ionic covalent bonds to melt the substance
3. Electrically insulating. Non-conductors. Covalent compounds have no mobile electrons and when ionic compounds are solid the ions are fixed in a giant ionic lattice

Question 14

Describe how sodium reacts with 
1. Oxygen
2. Chlorine
3. Water
4. Its oxide with water
5. Its chloride with water
 Include equations

Answer 14

2Na + ½O2=Na2O

Sodium burns in oxygen with an orange flame to produce sodium oxide a white solid

Question 15

Describe how magnesium reacts with

1. Oxygen
2. Chlorine
3. Water
4. Its oxide with water
5. Its chloride with water

Answer 15

1. Eq....
Magnesium burns in oxygen with an intense white flame  to form magnesium oxide a white solid
2.
3.
4.
5.

Question 16

Describe how aluminum reacts with

1. Oxygen
2. Water
3. Chlorine
4. Its oxide with water
6. It’s chloride with hot boiling water

Answer 16

1. 4Al + 3O2 = 2Al2O3
Aluminium burn in oxygen if powdered. Sprinkling this powder into a Bunsen gives white sparkles and forms aluminum oxide a white solid
2.
3.
4.
5.
6.

Question 17

Describe how phosphorus reacts with

1. Oxygen
2. Chlorine
3. Cold water
4. Its oxide and water
5. Its chloride and cold water
6. Its chloride and hot water

Answer 17

1. White phosphorus catches fire spontaneously in air it burns with a white flame. In excess oxygen phosphorus v oxide forms
2. P4 + 10Cl2 = 4PCl5
   white phosphorus been spontaneously in excess chlorine to form PCl5 and off white or almost yellow solid
3. I don’t think there is a rxn.. will confirm.
4. P4O10 + 6H2O = 4H3PO4
   Forms an acidic solution. The rxn is violent
5. PCl5 + H2O = POCl3 + HCl
6. If the water is boiling the POCl3 will continue to react to form phosphoric acid
   PCl5 + 4H2O = H3PO4 + 5HCl

Question 18

How a primary alcohols oxidised to aldehydes

Answer 18

if a primary alcohol is heated with a acidified potassium dichromate (VI), the alcohol will be oxidized to form an aldehyde.
The acidified potassium dichromate VI change color from Orange to Green
CH3CH2OH + [O] = CH3CHO + H2O