The Periodic Table

Question 1

John Newlands

Answer 1

1864:
Arranged atoms according to atomic weights and realised that every 8th element had similar properties.
This was called Newland’s octaves - only worked up till calcium and some metals were grouped with non-metals, so was rejected.

Question 2

Mendeleev’s

Answer 2

1869:
- Elements are arranged in order of increasing atomic mass.
- Groups and periods.
- Elements grouped with similar properties.
- Gaps left for undiscovered elements.
- Switched elements that didn’t match.

Scientists accepted Mendeleev’s table as he predicted many of the undiscovered elements’ properties correctly.
Modern table is largely based on his version.

Question 3

Modern Periodic Table

Answer 3

• Elements are arranged in order of atomic number.
• No gaps
• Grouped by the number of electrons in outer shell.
• Metals = left, Non-metals = right.

Question 4

Group 0

Answer 4

NOBLE GASES
Full outer shell - no need to gain or lose electrons so inert (unreactive).
Exist as single atoms - monatomic.
Boiling points increase down the group.

Question 5

Group 1

Answer 5

ALKALI METALS
1 electron in the outer shell so all need to lose an electron to react.

Reactivity increases as we move down the group as atoms increase in size - the valence electron is further away from the positive nucleus so there is more shielding and weaker electrostatic forces between them - easier to lose electron.

Melting and boiling point decrease down Group 1.

Question 6

Properties of alkali metals

Answer 6

• All reactive to water
• Silver colour
• Soft - easily cut to reveal a shiny surface that quickly dulls
  due to fast oxidation.

Question 7

Group 1 metal + water equation and products

Answer 7

2Li + 2H20 -> 2LiOH + H2

Forms hydrogen gas and a metal hydroxide.
Produce an alkali (universal indicator turns purple), which is why they are known as alkali metals.

Question 8

Lithium/Sodium/Potassium vs. water

Answer 8

Lithium and Sodium = effervescence + float and move on the surface.
Potassium = (II) + LILAC flame

Question 9

Group 1 metals + non-metals

Answer 9

e.g. Iodine/Bromine/Chlorine/Fluorine
The reactions get more vigorous as we go down the group - lose a single electron to become a 1+ ion.

sodium + chlorine -> sodium chloride
2Na + Cl2 -> 2NaCl

Question 10

Group 7

Answer 10

HALOGENS
Non-metals that exist as diatomic molecules - covalent bonds between each pair.
Low melting and boiling points which increase down the group.
Need 1 electron to gain full outer shell

Question 11

Halogens w/ metals

Answer 11

Ionic bonds between halogens and metals - they form ions with 1- charge.

Question 12

Halogens w/ non-metals

Answer 12

Need to gain 1 electron to achieve a full outer shell - they react with non-metals by forming covalent bonds and sharing electrons.

Question 13

Displacement Reactions of Halogens

Answer 13

A more reactive halogen will displace a less reactive halogen from solutions of its salts - see notes on example reactions.