group 2 and 7

Question 1

What is the electron configuration of group 2 elements?

Answer 1

2e- in outer shell

Question 2

What is the trend in atomic radius of group 2?

Answer 2

Increases down the group, as there are more energy levels being filled with electrons and the outermost electrons are further from the nucleus

Question 3

What is the trend in first ionisation energy in group 2?

Answer 3

Decreases down the group as the electron being removed is from successively higher energy levels and is increasingly shielded from the nucleus- and so less attracted

Question 4

What is the trend in melting point in group 2?

Answer 4

Decreases going down the group. Attraction of the positive ions to the delocalised electrons decreases as the size of the positive ions increases and hence the charge density decreases.

Magnesium doesn’t fit, as this metal has a different crystal structure

Question 5

Why do group 2 metals sink?

Answer 5

All are more dense than water

Question 6

How does magnesium react with cold water?

Answer 6

Mg(s) + 2H2O(l) –> Mg(OH)2(aq) + H2(g)

reacts slowly, slow bubbling

Question 7

How does magnesium react with steam?

Answer 7

Mg (s) + H2O (g) –> MgO (s) + H2 (g)

Burns with bright white light , gas produced very quickly

Question 8

What is the trend in the reactivity of group 2 metals with water?

Answer 8

React with increasing vigour as group is descended, as easier to lose electrons further away from the nucleus

Question 9

What is the trend in the solubility of the group 2 metal hydroxides?

Answer 9

Solubility increases down the group
Mg(OH)2 is sparingly soluble, whilst Ba(OH)2 is very soluble

Question 10

What is the trend in the strength of the group 2 metal hydroxides as bases?

Answer 10

Strength increases down the group, as [OH-] increases

Question 11

What is magnesium hydroxide used for?

Answer 11

Milk of magensia is a tablet used as an antacid- weak base and therefore won’t harm stomach as it neutralises excess acid
Also used as a laxative

Question 12

What is calcium hydroxide used for?

Answer 12

Reduces the acidity of soils so that a wider range of crops can be grown as they are able to extract nutrients from the soil
Also provides calcium ions which are essential for plant growth

Question 13

What is lime?

Answer 13

a mixture of calcium hydroxide and calcium carbonate

Question 14

What is the trend in solubility of the group 2 sulfates?

Answer 14

Decreases going down the group
MgSO4 is soluble, whilst BaSO4 is very insoluble

Question 15

What is barium sulfate used for?

Answer 15

Used as a test for sulfate ions in solution- solution acidified first with HCl or HNO3 to remove BaCO3, then solution of barium chloride added, and the formation of a white ppt confirms presence of sulfate

Barium sulfate can also be used in x-rays as its opaque to x-rays and not toxic

Question 16

How can magnesium be used in the extraction of titanium?

Answer 16

Titanium oxide first converted to titanium chloride at around 900ºC
TiO2 + C + 2Cl2 –> TiCl4 + CO2
Titanium chloride then reduced by a more reactive metal
TiCl4 + 2Mg –> Ti + 2MgCl2

Question 17

Why is the reaction of TiCl4 with Mg carried out in an atmosphere of argon?

Answer 17

Argon is inert, and orevents any reaction or contamination with oxygen or nitrogen

Question 18

What is calcium carbonate and calcium oxide used for?

Answer 18

To remove sulfur dioxide from flue gas, which could cause acid rain

CaO + 2H2O + SO2 –> CaSO3 + 2H2O
CaCO3 + 2H2O + SO2 –> CaSO3 + 2H2O + CO2

Question 19

What does acid rain do?

Answer 19

Causes acidification of lakes, damages plant and can lead to the death of aquatic plants and fish

Question 20

What are the halogens at room temp?

Answer 20

all covalently bonded diatomic molecules

Question 21

What are the colours of each of the halogens vapours?

Answer 21

F2 pale yellow
Cl2 green/yellow
Br2 amber (red/brown)
I2 purple

Question 22

What is the trend in boiling point in group 7?

Answer 22

As the group is descended, the boiling group increases. This is because the size of the molecules increases so increases the number of Van de Waals forces and thus the energy required to overcome these

Question 23

What is the trend in electronegativity in group 7?

Answer 23

As the group is descended, the electronegativity decreases

Question 24

What are the three factors that affect electronegativity?

Answer 24

Nuclear charge- as the group is descended, this increases and leads to an increases in the attraction of the nucleus for the bonding electrons
Atomic radius- this increases down the group and causes the outermost electrons to be further away, reducing the attraction for the bonding electrons
Shielding- increase in the number of filled energy levels down the group so decreases attraction for bonding electrons

Question 25

How do the halogens displace each other?

Answer 25

Chlorine displaces bromine and iodine, bromine displaces iodine byt not chlorine, iodine will not displace chlorine or bromine, fluorine displaces all other halogens

Question 26

What is the trend in the strength of oxidising agents of group 7?

Answer 26

F2>Cl2>Br2>I2

Not due to the relative electron affinities but mostly due to the relative hydration energies and to a lesser extent the low atomisation of fluorine

Question 27

What is the trend in the halogens as reducing agent reducing agents?

Answer 27

I- > Br- > Cl- > F-

outer electron is further from nucleus, has more shielding and is held less strongly as less attraction to the nucleus

Question 28

How do sodium halides react with sulfuric acid?

Answer 28

Conc. sulfuric acid is an oxidising agent as well as a strong acid. The products formed depend on the reducing power of the halide ion

Question 29

What is the reaction between NaF and sulfuric acid?

Answer 29

Acid-base reaction
steamy fumes produced
NaF + H2SO4 –> NaHSO4 + HF

Question 30

What is the reaction between NaCl and sulfuric acid?

Answer 30

Acid-base
steamy fumes
NaCl + H2SO4 –> NaHSO4 + HCl

Question 31

What are the reactions between NaBr and H2SO4?

Answer 31

acid-base
steamy fumes
NaBr +H2SO4 —> NaHSO4 + HBr

redox of product
colourless gas and brown fumes
2HBr + H2SO4 –> Br2 + SO2 + 2H2O

Question 32

What are the reactions between NaI and H2SO4?

Answer 32

acid-base
Steamy fumes
NaI + H2SO4 –> HI + NaHSO4

redox
colourless gas
yellow solid
smell of bad eggs
purple fumes

2HI + H2SO4 –> I2 + SO2 + 2H2O
8HI + H2SO4 –> H2S + 4I2 + 4H2O
6HI + H2SO4 –> S + 3I2 + 4H2O

Question 33

What colour precipitates do the halide ions form with silver?

Answer 33

Cl- = white
Br- = cream
I- = yellow

Question 34

What is the trend in the solubility of the silver halides in ammonia?

Answer 34

AgF > AgCl > AgBr > AgI

Question 35

What is the reaction between chlorine and water and what type of reaction is this?

Answer 35

forms a green solution
Cl2 + H2O –> HCl + HClO

this is a disproportionation reaction, as chlorine is both oxidised and reduced in the same reaction

Question 36

What is the reaction if chlorine is bubbled through water in bright sunlight?

Answer 36

2Cl2 + 2H2O –> 4 HCl + O2

Question 37

Why is chlorine used in water treatment?

Answer 37

Kills disease causing bacteria

Question 38

What is the reaction of chlorine with cold dilute NaOH?

Answer 38

Cl2 + 2NaOH –> NaCl + NaClO + H2O

this is the basis of bleach