Group 3 A2

Question 1

All the elements in Period 3 except ______ and _______ combine directly with oxygen to form oxides.

Answer 1

except chlorine and argon

Question 2

Give the equation for sodium combining with oxygen

Answer 2

4Na(s) + O2(g)  2Na2O(s)

Question 3

Give the equation for magnesium combining with oxygen

Answer 3

2Mg(s) + O2(g)  2MgO(s)

Question 4

Give the equation for aluminium combining with oxygen

Answer 4

4Al(s) + 3O2(g)  2Al2O3(s)

Question 5

Give the equation for silicon combining with oxygen

Answer 5

Si(s) + O2(g)  SiO2(s)

Question 6

Give the equation for phosphorous combining with oxygen

Answer 6

P4(s) + 5O2(g)  P4O10(s)

Question 7

Give the equation for sulfur combining with oxygen

Answer 7

S(s) + O2(g)  SO2(g)

Question 8

What is unique about the structure/bonding of Al2O3?

Answer 8

Mostly ionic, but with significant covalent character.

Question 9

Na2O, Al2O3 and MgO are ____ oxides and hence have a ______ melting point.

Answer 9

Na2O, Al2O3 and MgO are ionic oxides and hence have a high melting point.

Question 10

Why do MgO and Al2O3 have a higher melting point than Na2O?

Answer 10

The charges are higher, resulting in a stonger attraction between the ions. Also Al2O3’s bonding contains a lot of covalent character.

Question 11

Are ionic oxides acidic/basic? State the equation.

Answer 11

Basic: O2-(aq) + H2O(l)  2OH-(aq)

Question 12

Are covalent oxides acidic/basic? State the equation.

Answer 12

Acidic: MO(s) + H2O(l)  MO(OH)-(aq)+ H+(aq)

Question 13

Why are covalent oxides acidic?

Answer 13

They do not contain ions, but have a strongly positive dipole on the atom which is not oxygen. This attracts the lone pair on water molecules, releasing H+ ions.