14 — Periodic table

Question 1

Groups

Answer 1

Vertical column of elements
18 groups
Elements in same group hv same number of valence electrons and thus hv similar chemical properties

Question 2

Periods

Answer 2

Horizontal row of elements
7 periods
Number of electron shells an element has is the same as its period number

Question 3

Metalloids

Answer 3

Contain properties of both metals and non-metals

Question 4

Trends across the period

Answer 4

Across the period, there is a decrease in metallic property and an increase in non-metallic properties -> increasing tendency to gain e-

Question 5

Explain why the metallic property of elements across the period decreases

Answer 5

The number of protons in the nucleus increases while number of electron shells remain the same. The increase in nuclear charge results in a stronger forces of attraction between the nucleus and valence electrons. More energy is needed to lose electrons, resulting in lower tendency for the atom to lose electrons. Thus, the metallic property decreases.

Question 6

Why there is an increase in metallic properties and decrease in non-metallic properties down the group

Answer 6

Down the group, the size of the atom increases due to an increase in the number of electron shells. The valence electrons r further away from the nucleus. Hence, there is weaker forces of attraction between the nucleus and the valence electrons. There is a higher tendency for the atom to lose its valence electrons to form a positive ion.

Question 7

Group 1 properties

Answer 7

Elements in group 1 — alkali metals. They react w water to form soluble metal hydroxides.
Physical properties of alkali metals:
1. Soft and can be cut easily
2. Good conductors of heat and electricity due to presence of delocalised mobile electrons
3. Low melting and boiling points
4. Low densities

Question 8

Group 1 physical properties trend

Answer 8

Down the group, the melting and boiling points of alkali metals decreases. Size of atom down the group increases due to increase in number of electron shells, the valence electrons r further away from the positive nucleus, hence the forces of attraction between the nucleus and valence electrons r weaker. Metallic bonding is weaker and less energy is needed to overcome the forces of attraction.

Furthermore, the density of alkali metals generally increases.

Question 9

Chemical properties of group 1 elements

Answer 9

1. They have 1 valence electron and react by losing 1 valence electron to achieve noble gas electronic configuration
2. Reducing power of alkali metals increases down the group (powerful reducing agents)
3. Reactivity increases down the group
   Size of atom increases due to increase in number of valence electron shells. The valence electrons are further away from the nucleus hence there are weaker forces of attraction betw the nucleus and the valence electrons. There is an increase in the ease of losing valence electrons.
4. They react with water to form alkali and hydrogen gas

Order of reactivity: Li<Na<K<Rb<Cs<Fr

Question 10

Group 1 elements and their reaction w water

Answer 10

1. Lithium -> reacts quickly. Lithium floats on water
   2Li(s) + 2H2O (l) -> 2LiOH (aq) + H2 (g)
2. Sodium -> reacts violently. Sodium darts around the water surface. Reaction may be explosive.
   2Na(s) + 2H2O (l) -> 2NaOH (aq) + H2 (g)
3. Potassium -> reacts very violently. Reaction is explosive.
   2K(s) + 2H2O (l) -> 2KOH (at) + H2 (g)

Question 11

Physical properties of halogen

Answer 11

1. Group 17 elements
2. Exist as diatomic molecules
3. Are non-metals
4. Have low melting and boiling points
5. Are coloured

Question 12

Appearance of halogen at rtp

Answer 12

Fluorine -> pale yellow gas
Chlorine -> yellow-green gas
Bromine -> red-brown liquid
Iodine -> purple-black solid
Astatine -> black solid

Question 13

Trend in physical properties down group 17 and explanation

Answer 13

1. Down the group, melting and boiling point increases.
   Size of molecule increases, resulting in stronger intermolecular forces of attraction. Thus more energy is needed to overcome the stronger forces of attraction.
   2.colour intensity increases

(Covalent bonds in diatomic molecule stronger as size increases)

Question 14

Chemical properties of halogens

Answer 14

1. Reactive non-metals -> have 7 valence electrons -> have a tendency to gain 1 e- to achieve noble gas electronic configuration
2. Oxidising power of halogens decrease down the group (Oxidising agents)
3. React w most metals to form salts called halides (eg fluoride bromide)
4. Reactivity of halogens decreases down the group as size of atom increases due to increase in number of electron shells. Forces of attraction betw the +ve nucleus and the valence e- r weaker, making it harder for the nucleus to attract 1 more electron.

Order of reactivity: F2>Cl2>Br2>I2>At2>Ts2

Question 15

Displacement of halogens

Answer 15

The more reactive the halogen, the higher tendency it has to gain electrons to form negative ions compared to a less reactive halogen. Thus a more reactive halogen will displace a less reactive halogen from its halide solution.

Question 16

Displacement of halogens: aq Cl2 + aq NaBr

Answer 16

Cl2 (aq) + 2NaBr (Aq) -> 2NaCl (aq) + Br2(aq)
Light yellow—colourless—colourless—red-brown

Observation: solution changes from colourless to red-brown
Explanation:
Chlorine is more reactive than bromine hence chlorine displaces bromine rom aqueous sodium bromine

Products in halogen displacement r alw aq.
Halides (eg KBr, KI) (halogens in ions state) r colourless

Question 17

What is the similarity between displacement of metals and displacement of halogens

Answer 17

Both are always redox reactions
Both always involve colour change

Question 18

Physical properties of group 18

Answer 18

Noble gases:
1. Monoatomic non-metals
2. Colourless gases at rtp
3. Low melting and boiling points
4. Insoluble in water
5. Unreactive
Noble gases are unreactive as they have a fully filled valence electron shell. They do not lose, gain or share electrons and hence rarely react to form compounds.

Question 19

Noble gases and their uses

Answer 19

Helium: used in balloons
Argon/neon: used to fill tungsten bulbs to provide an inert atmosphere that prevents oxidation of the filament
Argon: used in manufacturing of steel
-> iron is the main component of steep but can oxidise thus argon provides an inert atmosphere to prevent iron from Oxidising (rusting)

Question 20

Transition elements

Answer 20

Metals found in groups 3 to 11
Group 12 does not belong in transition elements as they have no variable oxidation states.

Question 21

Physical properties of transition elements

Answer 21

1. High melting and boiling points
2. High densities
3. Has variable oxidation states (unique)
4. Forms coloured compounds (unique)
5. Transition metals and their compounds are good catalysts for many reactions, both in laboratory and in industry. (Unique)

Element and reaction w water
Iron: haber process for manufacture of ammonia
Nickel: manufacture of margarine from vegetable oil
Manganese (IV) oxide: decomposition of hydrogen peroxide

Question 22

Give three characteristic properties of transition metals

Answer 22

Has variable oxidation states
Forms coloured compounds
Transition metals and their compounds are good catalysts for many reactions

Question 23

Why elements in group 18 do not have oxidation states.

Answer 23

Elements in group 0 are inert gases as they have fully filled valence electron shell and noble gas electronic structure. Thus, they do not lose, gain or share electrons to form compounds so their oxidation state is 0, which is not present in the table.

Question 24

Describe the trend in melting point and reactivity down group 1 and group 7.

Answer 24

MP:
Down group 1, MP decreases.
Down group 7, MP increases.

R:
Down group 1, reactivity increases
Down group 7, reactivity decreases.

Question 25

Give 2 similarities betw H2 and elements in group 1

Answer 25

Both has 1 valence electrons
Both tend to lose an electron to form cations of charge +1

Question 26

Give 2 differences betw H2 and elements in group 1

Answer 26

H2 exists as gas but group 1 metals exist as solid metals w low melting points at rtp

H2 exists as diatomic molecules but group 1 metals exist as cations held tgt by metallic bonds

H2 does not react w water but group 1 metals react w water.

Question 27

When sodium is heated in hydrogen, the metal glows as an exothermic reaction takes place. How would the observation differ from when potassium is heated in hydrogen?

Answer 27

Potassium would glow more brightly and reaction would be more exothermic as potassium is more reactive than sodium.

Question 28

Which 2 elements react tgt most vigorously?

Answer 28

1. Answ must be 1 cation and 1 anion!
2. Most reactive group 1 element + most reactive group 7 element
   Eg potassium + chlorine
   Instead of sodium + chlorine

Question 29

A: aq bromine + aq iodide ions
B: aq iodine + aq bromide ions
A and B r both brown. Why.

Answer 29

A: when aq bromine mix w aq iodide ions, aq iodine is formed, thus mixture A is brown

B: when aq iodine mixed w bromide ions, no reaction takes place, brown aq iodine remains unchanged, causing B to be brown.

Question 30

Explain in terms of electrons why fluorine is an Oxidising agent.

Answer 30

Fluorine has a high tendency to gain electrons to form anion F-, resulting in a loss of electrons in the substance it reacts w, thus Oxidising the substance.

Question 31

In practice, when x is reacted w y, the yield of xy is never 100%. Explain why.

Answer 31

X + y is a reversible reaction thus xy formed can decompose back to x and y, thus yield is never 100%.

Question 32

Desc the trend in atomic radii for group 1 and explain.

Answer 32

Atomic radii increases down group 1. Down the group, no. Of electron shells increases, thus size of atoms increases, resulting in an increase in atomic radii.

Question 33

Moving across period 2 from lithium to neon, behaviour of the elements when they form compounds change from metal to non-metal. Explain why.

Answer 33

Across period 2, lithium, beryllium and boron behave like metals as they lose valence electrons, resulting in the formation of positive ions to achieve stable electronic configuration.
Carbon, Nitrogen, oxygen and fluorine behave like non-metas as they tend to gain electrons to achieve noble gas electronic structure and thus forms negative anions.
Neon does not form compounds as it has a stable electronic configuration with fully filled valence electron shell. Thus, it is inert.

Question 34

A jet of chlorine gas and a jet of iodine gas aimed at filter papers soaked in potassium bromide solution. State and explain observations.

Answer 34

Cl2:
Solution on filter paper turns brown. Chlorine is more reactive than bromine and thus displaces bromine from potassium bromide solution. Aq bromine solution is brown.

I2:
Colourless solution on filter paper remains colourless. Iodine is less reactive than bromine thus cannot displace bromine from potassium bromide solution. Some iodine gas dissolves in water to form aq iodine which appears to be brown in colour.

Question 35

Give 2 reasons why catalysts reduce costs in the long run

Answer 35

Catalysts provide an alternative pathway by lowering activation energy.

1. It reduces time required for a reaction to take place, which saves time and therefore reduce costs
2. It lowers activation energy, therefore lowering operating tempt such that lesser energy is required, hence lowering cost of industrial processes in the long run
3. Chemically unchanged/regenerated and reused, therefore reducing cost of materials required.