8. The Periodic Table

Question 1

Transition elements

Answer 1

Metals from the middle section of the periodic table

Question 2

Transition elements properties

Answer 2

• Generally they have high densities, high meltingpoints, not bery reactive and are strong (these are metal properties)
• Bc of low reactivity some metals are used in jewellery (eg. gold)
• Many transition elemnets + their compound are used as catalysts (eg. iron)
• Form brightly coloured compounds

Question 3

Transition elements - oxidation states

Answer 3

• Form brightly coloured compounds
• Thsi is because they usually have variable oxidation numbers

(They can form different ions by losing a different number of electrons

Oxidation number of a transition element –> written using roman numberals in brackets, eg. Iron (III) Chloride

Question 4

Halogens

Answer 4

• Group VII elements, 7 electrons in outer shell –> form diatomic molecules by sharing one electron covalently, (non-metals)

Question 5

Halogens - Trends

Answer 5

Going down the group…

Density increases
Reactivity decreases (bc ability to attract extra electron weakens)
Melting point increases

Question 6

Halogens - Displacement reactions

Answer 6

• When halogens react with metals, they produce salts
• Halogens also undergo displacement reactions with halide ions (compounds formed between a metal ion and a halogen)

eg. Chlorine + Sodium Bromide –> Sodium Chloride + Bromine

(Chlorine is further up group so more reactive than bromine –> therefore displaces bromine.

Question 7

Halogen colours (at room temperature)

Answer 7

Chlorine - Yellow-green gas
Bromine - Dark red liquid
Iodine - Dark purple/ grey-black solid

(Colour of halogens increases in darkness going down the group)

Question 8

Alkali metals

Answer 8

Metal elements from group I of the Periodic Table. Readily form alkaline hydroxides on reaction with water.

Question 9

Alkali metals properties

Answer 9

• Relatively soft - can be cut with knifes
• When cut, the surface seems shiny but will tarnish due to reaction with oxygen (becomes dark/dull)
• Low densities (some float on water)
• Relatively low melting point
• React vigorously with water

Question 10

Alkali metals - Trends

Answer 10

• Time taken for freshly cut elements to tarnish decreases (reactivity increases going down group)
• Density increases going down the group
• Melting point decreases going down the group
• Reactivity increases going down the group (Elements further down the group react more vigorously with water)

The reason why reacitvity increases is because the electron shells are further from the nucleus –> This means there is less electrostatic attraction between the electrons and the nucleus –> easier to lose an electron.

Question 11

Reacting lithium with cold water

Answer 11

• Reaction can be seen on surface of water bc Li floats
• Effervescence can be seen as hydrogen gas is released
• Li moves around on water surface bc of hydrogen gas being produced
• Water becomes slightly alkaline during reaction

Question 12

Covalent radius

Answer 12

How large the radius of the atom is, affected by amount of neutrons + electron configuration

• As you move down a group the covalent radius increases (more protons etc.)
• Typically the larger the covalent radius –> the more reactive the element (bc less attraction between positive nucleus and negative electrons)
• (Covalent radius dereases going across a period because more protons and electrons are added. This increases force of attraction between nucleus and electron shells)

Question 13

Metals vs Non-metals

Answer 13

Metals - Large atomic radius, conduct heat + electricity, range of melting point values, malleable + ductile, shiny

Non-metals - Smaller atomic radius, don’t conduce heat/electricity, generally low melting points, brittle, dull.