Inorganic Chemistry A1

Question 1

The structure of the periodic table.

Answer 1

1. Elements in the periodic table are arranged in order of increasing atomic number.
2. Across a period the atomic number increases but element have the same number of shells.
3. Down a group the number of outer electrons remain the same which allows us to predict chemical and physical reactions.
4. We can also arrange our periodic table in other ways:
   a) blocks - there are s, p and d blocks.
   b) step ladder - elements on the left of the step ladder are metals, elements on the right of the step ladder are non-metals and elements that touch the ladder are metalloids.

Question 2

Period 3 properties and trends.

Answer 2

1. Period 3 elements are in the 3rd period of the periodic table.
2. The elements include;
   a) metals - sodium, magnesium and aluminium.
   b) metalloids - silicon.
   c) non-metals - phosphorous, sulfur and chlorine.
   d) noble gases - argon.
3. We observe trends in:
   a) melting points - depending on the structure.
   b) atomic radius - decreases across the period.
   c) ionisation energy - increases across the period.

Question 3

Electron configuration.

Answer 3

1. The periodic table is structured in blocks that reflect the position of the elements’ outermost electrons. There is an s, p and d block.
2. We can shorten the electronic configuration of an element by using the nearest pervious noble gas and following it by the appropriate remaining electronic configuration.

Question 4

Ionisation energy.

Answer 4

1. Ionisation energy is the energy required to remove one electron from each atom in one mole of the gaseous element to form one mole of gaseous 1+ ions.
2. Factors that affect I.E. include:
   a) atomic radius.
   b) nuclear charge.
   c) electron shielding.
3. Atomic radius - a larger atomic radius results in a smaller attraction for outer electrons which results in a smaller I.E.
4. Nuclear charge - a larger nuclear charge results in a larger I.E.
5. Electron shielding - the inner shells repel outer shells of electrons so the outer electrons are held less tightly.
6. We can see trends in ionisation energies too. Across the period the first ionisation energy increases and down a group the first ionisation energy decreases.
7. Successive ionisation energies increase. Increasing amounts of energy are required to remove successive electrons and a large jump can be observed when electrons are removed from the next inner-most shell.

Question 5

Periodicity and melting points.

Answer 5

1. Across periods 2 and 3 the changes we see are metals to non-metals.
2. We see trends in boiling and melting points. In groups 1-14 boiling and melting points increase as elements have giant structures. In groups 14-15 there is a sharp decrease as elements now have a simple molecular structure. In groups 15-17 melting and boiling points remain low as elements are still simple molecules.

Question 6

Group 2 elements.

Answer 6

1. Group 2 is in the s-block of elements so their outer electrons are held in an s-orbital.
2. Group 2 elements have 2 electrons in their outer shells.
3. Known as the ‘alkaline earth metals’.
4. We see a trend in the reactivity of group 2; Be is the least reactive and Ba is the most reactive.
5. Group 2 elements share properties; they all have reasonably high melting and boiling points, they are light with low densities, they form white or colourless compounds and their outer shells contain 2 electrons.

Question 7

Reactivity of group 2 elements.

Answer 7

1. Down group 2 we see a trend in reactivity; it increases down the group because of the increased atomic radius and affect of shielding. This means that the outer electrons are lost more easily down the group.
2. Group 2 elements react with oxygen to form oxide with the general formula MO.
3. Group 2 elements react with water (except beryllium) to form hydroxides and hydrogen gas. This general formula is M(OH)2.
4. Group 2 elements react with dilute acid (except beryllium) to form salt and hydrogen gas.

Question 8

Reactions and uses of group 2 elements.

Answer 8

1. Group 2 hydroxides can be soluble in water, they form alkaline solutions as they release OH- ions.
2. We see trends down the group. Solubility of hydroxides increases down the group as does alkalinity. Solubility of sulphates decreases down the group.
3. The Solubility of the hydroxides and sulphates can be remembered using the ham salad acronym.
4. Group 2 compounds have many uses:
   a) magnesium - ingestion remedy and titanium extraction.
   b) calcium - building materials, neutralising acidic soils and flue gases.
   c) barium - barium meal and testing for sulphate ions.

Question 9

The halogens.

Answer 9

1. The halogens are in group 17 and have 7 electrons in their outer shell.
2. They lie in the p-block so their 5 outer electrons are held in a p-orbital.
3. We see trends in the halogens:
   a) atomic radius - this increases down the group as each successive element in the group gains a shell of electrons.
   b) electronegativity - this decreases down the group as the outer electrons are held further from the nucleus which increases the levels of shielding.
   c) boiling and melting points - these increase down the group as each successive element gains a shell of electrons, increasing the surface area of the molecules. A greater degree of London forces then occur meaning more energy is required to overcome these forces.
4. In general the halogens exist as diatomic molecules, they have different, distinct appearances and they have relatively low melting and boiling points.

Question 10

The reactivity of halogens.

Answer 10

1. The halogens are incredibly reactive, they are strong oxidising agents and they tend to form 1- ions.
2. A more reactive halogen will displace a less reactive halogen from solution.
3. We observe a colour change when a displacement reaction occurs.
4. These displacement reactions are redox reactions.
5. We can apply our understanding of the trends in reactivity of the halogens to predict the reactions of fluorine and astatine.

Question 11

Disproportionation of the halogens.

Answer 11

1. Chlorine undergoes disproportionation reactions which means the same element is both oxidised and reduced.
2. Chlorine reacts with water to form hydrochloric acid and chloric acid. This is used to sanitise water.
3. When exposed to the sun, a slightly different reaction occurs. It forms hydrochloric acid and oxygen.
4. Sodium chlorate can be used as an alternative method to chlorinate swimming pools as it prevents the transmission of bacteria.
5. Chlorine reacts with cold alkali to form sodium chloride and sodium (I) Chloride. This is used in household bleach.
6. Chlorine reacts with hot alkali to form sodium chloride and sodium chlorate (V). This is used as household bleach and as weed killer.

Question 12

Reactions of halide ions.

Answer 12

1. Halide ions are reducing agents. Their reducing power increases down the group.
2. Halide ions react with sulfuric acid but all react slightly differently;
   a) chloride - not strong enough to reduce sulfuric acid, sulfuric acid acts as an acid and produces hydrogen chloride.
   b) bromide - reduces sulfuric acid, sulfuric acid acts as an acid and redox reaction occur. Produces hydrogen bromide, bromine and sulfur dioxide.
   c) iodide - sulfuric acid acts as an acid and redox reactions occur. This produces hydrogen iodide, iodine, sulfur dioxide, sulfur and hydrogen sulfide.
3. Halide ions react with ammonia to form ammonia salts.
4. Halide ions react with water to form acidic solutions.

Question 13

Chemical tests.

Answer 13

1. There are a number of chemical test for ions:
   a) carbonate ions - acid is added to test solution, gas evolved is bubbled through lime water, positive result = lime water turning cloudy.
   b) sulfate ions - barium chloride is added to the test solution, positive result = white precipitate of barium sulfate forms.
   c) ammonium ions - sodium hydroxide is added to the test solution, the mixture is warmed, test gas evolved with damp red litmus paper, positive result = the damp red litmus paper turns blue.
   d) halide ions - acidify the solution with nitric acid, add silver nitrate, a precipitate will form (silver chloride = white, silver bromide = cream, silver iodide = yellow), adding ammonia will further distinguish between halide ions.
   The results are as follows:
   Silver chloride dissolves in dilute aqueous ammonia.
   Silver bromide dissolves in concentrated aqueous ammonia.
   Silver iodide does not dissolve in either.