Periodicity

Question 1

What happens to the oxidation states of the period 3 elements in their oxides as we go across the period left to right
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Answer 1

It increases

Question 2

What type of bonding is present in metal oxides

Answer 2

ionic bonding

Question 3

Explain why metal oxides have a high melting point

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Answer 3

The strong electrostatic forces between the oppositely charged ions need a large amount of energy to break.

Question 4

Which period 3 metal forms an oxide with some covalent character
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Answer 4

Aluminium oxide

Question 5

Explain why aluminium oxide has some covalent character

Answer 5

Aluminium forms a very small ion with a large positive charge. This high electron density distorts the electron cloud of the oxygen ion and leads to some covalent character in the bond.

Question 6

What property can be used to predict whether an ionic compound exhibits any covalent character?

Answer 6

Electronegativity - the bigger difference between this, the greater the ionic character of the bond.

Question 7

Describe the bonding in silicon oxide

Answer 7

Giant covalent / macromolecular

Question 8

Explain why silicon oxide has a high melting point

Answer 8

It is a macromolecular structure. The strong covalent bonds extend throughout the whole structure and require a lot of energy to break.

Question 9

Describe the bonding in phosphorous oxide and sulphur oxide

Answer 9

Simple covalent molecule with strong covalent bonds within the molecule and weak intermolecular forces

Question 10

Explain why phosphorous oxide and sulphur oxide have low boiling and melting points

Answer 10

Simple covalent molecule with strong covalent bonds within the molecule and weak intermolecular forces. These weak intermolecular forces do not require much energy to overcome.

Question 11

Which two oxides of period 3 elements are insoluble?

Answer 11

Aluminium and silicon

Question 12

Explain why magnesium and sodium oxides dissolve in water to give alkaline solutions

Answer 12

The oxide ions are strong bases as they readily attract protons so they react with water to give hydroxide ions. This forms an alkaline solution.

Question 13

Explain why magnesium oxide forms a weaker alkaline solution than sodium oxide

Answer 13

Magnesium oxide is less soluble so there are less oxide ions available to react with the water to produce hydroxide ions.

Question 14

Explain why aluminium oxide is insoluble

Answer 14

The bonding in aluminium oxide is very strong and is strengthened by the covalent character so the ions will not separate in water.

Question 15

Explain why silicon dioxide is insoluble in water

Answer 15

Silicon dioxide is a giant macromolecule. These types of structure do not dissolve in water.

Question 16

What ions are formed when phosphorous oxide dissolves in water?

Answer 16

H+ and H2PO4(-)

Question 17

What ions are formed when sulphur dioxide dissolves in water?

Answer 17

H+ and HSO3(-)

Question 18

What ions are formed when sulphur trioxide dissolves in water?

Answer 18

H+ and HSO4(-)

Question 19

equation illustrates acidic nature SiO2

Answer 19

2NaOH + SiO2 –> Na2SiO3 + H20

Question 20

Exceptions to increase in ionisation E across period

Answer 20

There is a small drop between Mg + Al. Mg has its outer electrons in the 3s sub shell, whereas Al is starting to fill the 3p subshell. Al’s electron is slightly easier to remove because the 3p electrons are higher in energy.
There is a small drop between phosphorous and sulphur. Sulphur’s outer electron is being paired up with an another electron in the same 3p orbital.
When the second electron is added to an orbital there is a slight repulsion between the two negatively charged electrons which makes the second electron easier to remove.

Question 21

Colour flames in period 3 oxides

Answer 21

Sodium burns with a yellow flame to produce a white solid
Mg, Al, Si and P burn with a white flame to give white solid smoke
S burns with a blue flame to form an acidic choking gas.

Question 22

What reacts with water to give an acid

Answer 22

non metal simple molecular compounds

Question 23

Why is aluminium hydroxide insoluble

Answer 23

Very positive Hsol

LE much larger than hydration enthalpy