Unit 2 Section 2 Group 2 and Group 7 Elements

Question 1

What is electronegativity?

Answer 1

The tendency of an atom to attract a bonding pair of electrons to a covalent bond

Question 2

What is the trend in electronegativity in Group 7?

Answer 2

As the the atomic number od the halogen increases, electronegativity decreases

Question 3

What is the trend in boiling points as you go down the Halogens? Why?

Answer 3

It increases as you go down,
because the vdw force increases with the size of the molecoule.

Question 4

What is the trend in oxidising power for Halogens?

Answer 4

As you go down it decreases

Question 5

How do you test for Halogen oxidising power?

Answer 5

Reactions of Halogens with Potassium Halides (colourless). A positive test can be seen by a colour change due to the displacement of the halide.

Question 6

Give an example of a displacement reaction that tests for the oxidising power of Halogens.

Answer 6

Cl2 + 2KBr –> 2KCl + Br2 (full ionic)
Cl2 + 2Br- –> 2Cl- + Br2 (half)

Question 7

What is the disproportionation reaction that creates Bleach?

Answer 7

A REDOX reaction
Sodium Hydroxide + Chlorine –> Bleach + Sodium Chloride + Water
2NaOH(aq) + Cl2(g) –> NaClO(aq) + NaCl(aq) + H2O(l)

Question 8

Why is it called a dispropotionatiom reaction?

Answer 8

Because Chlorine has been simultaneously reduced and oxidised.
Began with an oxidation state of 0.
It’s products have an oxidation state of +1 (Bleach) and -1 (Sodium Chloride)

Question 9

What are the uses of Sodium Chlorate (NaClO3) ? NOT BLEACH!!

Answer 9

treating water
bleaching paper/fabrics
as a cleaning agent

Question 10

How do you sterilise water + reaction? (NOT WATER TREATMENT)

Answer 10

Add Chlorine to water to produce ClO- ions.
H2O(l) + Cl2(g) –> 2H+(aq) + Cl-(aq) + ClO-(aq)

Question 11

What are the advantages of treating drinking water?

Answer 11

kills micro organisms that cause disease
long lasting
reduces bacteria growth further down supply
reduced algal growth - bad smell and taste

Question 12

What are the disadvantages to treating drinking water?

Answer 12

Chlorine gas is toxic - inhalation can cause respiratory problems
liquid Chlorine can cause chemical burns
Chlorine can react with organic compounds forming chlorialkanes- carcinogenic

Question 13

Why does the reducing power of halide ions increase as you go down?

Answer 13

Because the ionic radius increased, more shielding, so the attractive force is weaker, outer electrons are lost more easily so they themselves get oxidised.

Question 14

How to test for the reducing power of Halide ions?

Answer 14

A reaction with Sulfuric Acid (H2SO4), iodide ions will reduce the acid the most, goubg from an oxidation state of +6 to -2 in H2S

Question 15

What is the test for halide ions + gwneral reaction?

Answer 15

A test with silver nitrate (AgNO3) and an ammonia (NH3) confirmation
Chloride ions will show a white ppt
Bromide ions will show a cream ppt
Iodide ions will show a yellow ppt
Ag+(aq) + Br-(aq) –> AgBr(s)

Question 16

How does ammonia confirm the Halide ions test?

Answer 16

Adding dilute ammonia to silver chloride will make it redissolve
To silver Bromide, it will redissolve with a concentrated solution
To Silver Iodide, it will not redissolve because it is insoluble

Question 17

What are the melting point trends in group 2 elements?

Answer 17

Generally decreases because the radius increased, so charge density decreases so the force density
weaker forces between the ions and the delocalised electrons

Question 18

What is the trend in first ionisation energies down Group 2?

Answer 18

Decrease
distance between outermost Electron and nucleus there is more shielding so the electrons are less strongly attracted so less energy is needed to remove the electron

Question 19

What is the general equation of Group 2 metals with water?

Answer 19

(Beryllium won’t react)
M(s) + 2H2O –> M(OH)2(aq) + H2(g)
forming a metal hydroxide and hydrogen