Chemistry - 3.2.1: Periodicity

Periodic Table

A list of all the elements in order of increasing atomic number

4 areas of the periodic table

1. s-block
2. d-block
3. p-block
4. f-block

How are elements arranged into each block?

All the elements have their highest energy electrons in the orbitals with the same letter (e.g. Na has highest energy electrons in s-orbitals, so it is in s-block)

What 2 elements aren't transition metals and why?

Scandium and zinc - do not form any compounds where they have partly filled d-orbitals

Group

A vertical column of elements where all elements have the same number of electrons in the outer main level (so they have similar chemical properties).

What is the trend in reactivity for s-block?

Elements get more reactive as you go down the group.

What is the trend in reactivity for non-metals?

Elements get more reactive as you go up the group.

What is the trend in reactivity for transition metals?

They are rather unreactive.

What is the trend in reactivity for lanthanides and actinides?

Lanthanides all have similar reactivity and all form 3+ ions.
Actinides are radioactive.

Periods

Horizontal rows of elements

What is on period 1?

Hydrogen and helium

Types of elements in period 3?

Groups 1-3: metals
Group 4: semi-metal (has some metallic properties)
Group 5-7: Non-metals
Group 0/8: Noble gas

What is the trend in atomic radii in period 3 and why?

Atomic radius decreases as you go across the period.
More protons in nucleus so greater nuclear charge but similar shielding, so attraction between nucleus and electrons increases.

What is the trend in first ionisation energy in period 3 and why?

Generally increases across a period, due to increase in nuclear charge but similar shielding, greater attraction so more energy needed.
Dip between group 2 and group 3 due to outer p-electron in Al being on higher energy level, further away so less energy needed to remove.
Dip between group 5 and group 6 as S has pair of electrons in one orbital, which repel.

What is the trend in melting and boiling points in period 3 and why?

Increases group 1-3: all metals and have metallic bonds - go across period, increasing positive charge, increasing number of delocalised electrons and smaller atomic radius SO metallic bonds increase in strength, require more energy to break
Increases to group 4: forms macromolecular substance / giant covalent structure, has strong covalent bonds between atoms that require a lot of energy to be overcome
Decreases to group 5, slight increase group 6, then decreases group 7: g5-7 form simple molecular substances - melting points depend on strength of induced dipole-dipole forces, which are weak and need little energy to be overcome. More atoms, more electrons, so stronger induced dipole-dipole forces - S8 is biggest, so has higher than P or Cl; P4 is next biggest, so has higher than Cl; Cl2 is smallest, so has lowest melting point
Decreases group 8: Ar is monatomic (exists as individual atoms), so has very weak induced dipole-dipole forces that require little energy to break

Group 4-7 non-metals in order of decreasing boiling point

S8 > P4 > Cl2

Why are noble gases not included when comparing atomic radii?

They do not bond covalently with one another, so do not have covalent radii (atomic radii normally used to compare)

What is the trend in atomic radii as you go down a group and why?

Atomic radii increases as you go down the group.
Going down, atom of each element has an extra complete energy level of electrons, so outer energy level is further away from nucleus.

What is the trend in first ionisation energy as you go down a group?

Decreases as there are more energy levels so more shielding + greater atomic radius so less attraction and less energy is needed to remove an outer shell electron.

Why is there a drop in first ionisation energy from one period to another (e.g. from neon to sodium)?

On next period, next energy level starts - further away from nucleus (greater atomic radius) so less attraction and less energy is needed to remove.

What element in period 3 has the highest melting point?

Silicon

Periodicity

The repeating pattern/trends of the physical or chemical properties of elements when they are arranged in atomic number order as in the periodic table.

How do you test for ammonium ions and what gas forms?

Warm the solution with NaOH, then hold damp red litmus paper at mouth of test tube (testing fumes) - turns blue as ammonia gas forms (alkaline)

How do you test for hydroxide ions?

Use red litmus paper to test pH - should turn blue

Why is the third ionisation energy of magnesium larger than the second ionisation energy?

The outer electron is in on the 2p energy level, which is closer to the nucleus and is less shielded

Why is a particular element considered to be in its block of the periodic table?

Its highest energy electron is in the orbital of the same letter