Periodicity

How are elements arranged in the periodic table?

In order of increasing atomic number

Period

A horizontal row of elements in the periodic table

Group

A vertical column of elements with the same number of outer electron shells (therefore similar chemical properties) in the periodic table

Periodicity

A repeating pattern of properties shown across different periods

What happens to first ionisation energy across the periodic table?

• Increases

• Dip between group 2 and 3

• Dip between group 5 and 6

First ionisation energy

The energy needed to remove one mole of electrons from one mole of atoms in the gaseous state

Explain why first ionisation energy increases as you go across the periodic table

As you go across the period the electron being removed is:

• in the same shell with similar shielding

• in an element where there are more protons in the nucleus

So the nuclear attraction to the outer electrons increases and more energy is needed to remove it

What happens to atomic radius across the periodic table?

Decreases

Explain why atomic radius decreases as you go across the periodic table

Across a period:

• There are the same number of shells (similar shielding)

• More protons in the nucleus

So nuclear attraction is greater and electrons are held more tightly

What happens to ionic radius in positive ions and why?

• Positive ions are smaller than their atoms

• Same number of protons attracting fewer electrons

• Therefore they are held together more tightly

What happens to ionic radius in negative ions and why?

• Negative ions are larger than their atoms

• Same number of protons attracting more electrons

• Therefore they are held together less tightly

Electronegativity

The power of an atom to attract the pair of electrons in a covalent bond

What happens to electronegativity across the period?

Increases

Why does electronegativity increase across a period?

As you go across the period

• There are more protons in the nucleus

• Same number of shells with similar shielding

Therefore the pair of electrons in the covalent bond are more strongly attracted

Why is there variation in melting and boiling points across period 3?

Changes in structure and bonding across the period

What is the pattern in melting and boiling points between Na → Al in period 3?

Increase in melting and boiling point

Why do melting and boiling points between Na → Al increase across period 3 ?

• The charge on the ion increases

• The number of delocalised electrons increases

• Therefore the metallic bonds get stronger and need more energy to break them

What is the structure and bonding of elements between Na → Al

Structure: Giant metallic lattice

Bonding: Metallic bonding

What is the structure and bonding of Si?

Structure: Giant covalent lattice

Bonding: Covalent bonds

What is the melting and boiling point of Si and why?

• Very high

• Very strong covalent bonds between silicon atoms

What is the structure of P₄, S₈ and Cl₂?

Simple molecular

What are the forces between P₄, S₈ and Cl₂?

Weak van der Waals forces between molecules

What is the order of melting and boiling point for P₄, S₈ and Cl₂? Why?

• From highest to lowest: P₄ > S₈ > Cl₂

• The bigger the molecule, the more electrons in the molecule, the stronger the Van der Waals forces between the molecules

What is the structure of Ar?

Simple atomic

What forces are between Ar?

Weak can der Waals between atoms