1.6 The Periodic Table

Question 1

How are the elements arranged in the periodic table?

Answer 1

By increasing atomic number

Question 2

What are the vertical columns?

Answer 2

Groups

Question 3

How many groups are there?

Answer 3

8

Question 4

What do the elements in the same group share?

Answer 4

The same outer shell configuration, therefore, similar chemical properties.

Question 5

What are the horizontal rows in the periodic table?

Answer 5

periods

Question 6

Tell me the trends in ionisation energy in the periodic table.

Answer 6

General increase in ionisation energy across a period. (increase in nuclear charge in same energy level, so little extra shielding, therefore a greater attraction between the nucleus and outer electrons)

Decrease in ionisation between Grp 2 and Grp 3 (Grp 3 is in new subshell of higher energy level and is partly shielded by s electrons)

Decrease between Grp 5 and Grp 6 (Grp 6 is removed from an orbital containing a pair of electrons. repulsion makes it easy to remove. Electron removed from a singly occupied orbital in Grp 5)

Ionisation energy decreases down a group. (Outer electron has increased shielding from inner electrons and is further from the nucleus, outweighs the increases in nuclear charge)

Question 7

Tell me the trends in electronegativity in the Periodic Table.

Answer 7

Electronegativity increases across a period.

Electronegativity decreases down a group

Question 8

Why does electronegativity increase across a period?

Answer 8

There is an increase in nuclear charge, but the bonding electrons are always shielded by the same inner electrons, so there is a greater attraction between the nucleus and the bonding pair.

Question 9

Why does electronegativity decrease down the group?

Answer 9

Bonding electrons have increased shielding from the nucleus, so the attraction between the nucleus and the bonding electrons decreases.

Question 10

Tell me the trends in melting and boiling temperatures.

Answer 10

There is a general increase from the first to the fourth element, a large decrease to the fifth element then a small general decrease to the eight element.

Question 11

Why is there an increase in melting and boiling point from the first to the fourth element?

Answer 11

Sodium, magnesium and aluminium have metallic bonding. There is an increase because the metallic bonding gets stronger as the metal ions have a greater charge, so an increased number of delocalised electrons.

Silicon has a giant covalent structure. Each atom is bonded covalently to 4 other atoms. A large amt of energy is needed to break these bonds.

Question 12

Why is there a decrease in melting/boiling point from the fifth element to the eight?

Answer 12

Phosphorous, Sulfur and chlorine are simple molecular substances.

Intermolecular forces holding the molecules together are weak and don’t need much energy to break.

Question 13

Why does the eighth element have the lowest melting/boiling point?

Answer 13

Argon exists as separate atoms held together by very weak induced dipole-induced dipole forces, so it has the lowest melting/boiling point.

Question 14

In the equation:
Mg + CuO ——-> MgO + Cu

which element/compound is being oxidised/reduced?

Answer 14

Magnesium has gained oxygen so is oxidised.

Copper oxide has lost oxygen so is reduced.

Question 15

Write the half-equation for the oxidation of magnesium.

Answer 15

Mg ——-> Mg2+ + 2e

Question 16

Write the half-equation for the reduction of copper oxide.

Answer 16

Cu2+ + 2e ——–> Cu

Question 17

How can you tell if a reaction is a redox reaction?

Answer 17

Work out oxidation numbers of the atoms or ions.

If oxidation number increases, species is oxidised.

If oxidation number decreases, the species is reduced.

Question 18

Describe the trends in Group 1 metals’ reaction with water.

Answer 18

Group 1 metals react vigorously with cold water to form the hydroxide and hydrogen.

The reaction increases in vigour as you go down the group.

Question 19

How does lithium react with water?

Answer 19

Lithium floats on the water, gently fizzing

Question 20

How does sodium react with water?

Answer 20

Sodium melts into a ball that dashes around the surface

Question 21

How does potassium react with water?

Answer 21

Potassium melts into a ball and catches fire

Question 22

How does caesium react with water?

Answer 22

Caesium explodes and shatters the glass container.

Question 23

Describe the trends in Group 2 metal’s reaction with water.

Answer 23

Group 2 metals react less vigorously, in fact, magnesium only reacts very slowly.

The reactivity increases as you go down the group.

Question 24

How does calcium react with water?

Answer 24

Calcium produces a steady stream of bubbles and the liquid goes cloudy as a white precipitate of calcium hydroxide forms.

Question 25

How does barium react with water?

Answer 25

Barium produces greater effervescence and the solution is clearer since barium hydroxide is more soluble.

Question 26

How does magnesium react with water?

Answer 26

Magnesium reacts with steam to produce the oxide and hydrogen.

Question 27

State the trend in reactivity of group 1 and group 2 metals with acids.

Answer 27

All Group 2 metals react vigorously with hydrochloric acid to produce a colourless solution of the metal chloride and bubbles of hydrogen. The reactivity increases as you go down the group. Only magnesium reacts with sulfuric acid as other members have insoluble sulfates. Group 1 metals are too reactive to be added directly to acids.

Question 28

State the trend in reactivity of Group 1 and Group 2 metals with oxygen.

Answer 28

Apart from magnesium, all Group 2 metals tend to burn with a characteristic flame. All Group 2 metals burn to form solid white oxides. The Group 1 metals also form white solids and burn with a characteristic flame. Group 1 metals also form peroxides and superoxides.

Question 29

Metal oxides are ________

Answer 29

basic

Question 30

Non-metal oxides are _______

Answer 30

acidic.

Question 31

Group 1 oxides and barium oxides react with water to form _______

Answer 31

a soluble hydroxide. Since the hydroxides are soluble, they are alkali

Question 32

Group 2 hydroxides are ______

Answer 32

not very soluble, so saturated solutions of these hydroxides are only weakly basic because the concentration of hydroxide ion is very low.

Question 33

Li + ions

Answer 33

red flame

Question 34

Na+ ions

Answer 34

orange-yellow flame

Question 35

K+ ions

Answer 35

lilac flame

Question 36

Mg2+

Answer 36

no colour

Question 37

Ca2+

Answer 37

brick red

Question 38

Sr2+

Answer 38

crimson

Question 39

Ba2+

Answer 39

apple green

Question 40

List the solubility rules in water for Group 2 .

Answer 40

1. All nitrates are soluble 2. All carbonates are insoluble. 3. Hydroxides become more soluble as you go down group 2 (magnesium hydroxide is insoluble, while barium hydroxide is soluble) 4. The sulfates become less soluble as you go down group 2. (magnesium sulfate is soluble but barium sulfate is insoluble) 5. All the precipitates are white.

Question 41

Tell me the trends in thermal stability of Group 2 hydroxides.

Answer 41

All Group 2 hydroxides decomposes on heating to the oxide and steam. The thermal stability increases as you go down the group, i.e. hydroxides have to be heated more strongly before they will decompose

Question 42

Tell me the trends in thermal stability of Group 2 carbonates.

Answer 42

All Group 2 carbonates decompose on heating to the oxide and carbon dioxide Thermal stability increases as you go down the group

Question 43

How do you test for carbonates?

Answer 43

Heating the carbonates and seeing how long it takes the CO2 formed to turn limewater cloudy.

Question 44

Define volatility

Answer 44

Describes how readily a substance vaporises.

Question 45

Tell me the trends for volatility in halogens.

Answer 45

Volatility decreases down the group

Question 46

How do halogens react?

Answer 46

Halogens react by gaining electrons to form negative halide ions. Since they gain electrons during reactions, halogens are reduced and they oxidise the other substance. Halogens react directly with most metals to form the halide.

Question 47

How do halogens displace ions?

Answer 47

A halogen in a higher position in the group will oxidise a halide ion from lower in the group since oxidising powers decrease down the group. Chlorine displaces bromide and iodide Bromine displaces only iodide Iodine does not displace either chloride or bromide

Question 48

Describe the tests for halide ions.

Answer 48

A few drops of nitric acid are added first to make sure that any other anions are removed, as they would also form precipitates. Silver nitrate solution is added to give: Cl- ions: a white precipitate is observed. Br- ions: a cream precipitate is observed I- ions: a pale yellow precipitate is observed.

Question 49

How can we distinguish between different silver halide precipitates?

Answer 49

Aqueous ammonia is added to the precipitate AgCl: Precipitate dissolves in dilute ammonia AgBr: Precipitate does not dissolve much in dilute ammonia but does dissolve in conc. ammonia AgI: Precipitate insoluble in dilute and conc. ammonia

Question 50

Why are chlorate ions used in water treatment?

Answer 50

To kill bacteria and other microbes. Chlorination is used to prevent the outbreak of serious diseases like typhoid and cholera

Question 51

What are the risks of adding chlorine to water?

Answer 51

Chlorine is highly toxic and can reach with naturally occurring organic compounds found in the water supply to form chlorinated hydrocarbons which can cause liver and kidney cancer. Some people object to water chlorination as forced 'mass medication'

Question 52

Why is fluorine added to water?

Answer 52

To reduced tooth decay by preventing cavities. Water fluoridation reduces cavities in children but its effects in adults is less clear

Question 53

What are the adverse effects of fluorination?

Answer 53

Can cause dental fluorosis (tooth discolouration)

Question 54

Why do people object to fluorination?

Answer 54

As forced 'mass medication' Given the prevalence of fluoride in toothpaste, mouth rinses and other dental products, many people think that adding fluoride to water supplies can be detrimental to long-term dental health.

Question 55

How do you prepare copper (II) sulfate?

Answer 55

1. Some copper (II) oxide is added to dilute sulfuric acid. More is added until no more dissolves. Warming might be necessary. The solution turns blue. 2. All the acid has been used up. The excess solid is removed by filtering. The leaves a blue solution of copper (II) sulfate in water 3. The solution is heated to evaporate some of the water. 4. It is left to cool. Blue crystals of copper (II) sulfate start to form. The water should not be fully evaporated because if this happens, a powder will form rather than crystals. If copper carbonate is used, the method is exactly the same but effervescence is seen when the carbonate is added to the acid as carbon dioxide is given off. When no more effervescence is seen, all the acid has been used up.

Question 56

How is an insoluble salt formed?

Answer 56

1. Separately dissolve two soluble salts in water and mix together using a stirring rod in a beaker. 2. Filter to remove precipitate from mixture. 3. Wash precipitate with water to remove traces of other solutions. 4. Leave in an oven to dry

Question 57

How can you determine the % of chloride in a compound?

Answer 57

1. Accurately weigh a sample of the compound into a weighing bottle 2. Transfer all of the solid into a beaker. Add water and stir until all the solid dissolves. 3. Add aqueous silver nitrate to the solution and allow the precipitate to settle. Test for complete precipitation by adding more drops of aqueous silver nitrate to the clear solution 4. When no further precipitate forms, filter off the precipitate making sure that all of it has been transferred to the filter. 5. Wash the precipitate with distilled water. 6. Dry and weigh the precipitate