1. Refresh
Nitrogen and silicon belong to different groups in the periodic table.
Distinguish in terms of electronic structure, between the terms group and period.
State the maximum number of orbitals in the n = 2 energy level.

2. Lesson 2
Physical Properties

3. Lesson 2: Physical Properties
Objectives:
Identify and explain the trends in the physical properties of the first 20 elements including:
Atomic radius
Ionic radius
First ionisation energy
Electronegativity
Melting point
Effective nuclear charge
Electron affinity

4. Atomic Radius This is the ‘size’ of an atom
There is no simple measure as atoms do not have a well defined ‘edge’
We use the: covalent radius
This is half the distance between the nuclei of two atoms in a covalent bond
This means we don’t have values for the noble gases as they do not form bonds
Values range from are measured in picometres ( 1 pm = 1x10-12 metres…a thousand-billionth of a metre) and range over:
270 picometres Francium
30 picometres for Hydrogen (helium would be smaller but does not form covalent bonds to be measured)
The main factors influencing atomic radius are:
Number of shells (the principal quantum number)
The charge in the nucleus

5. Ionic Radius
This is the ‘size’ of an ion and is measured in a similar way to atomic radius
It is measured in a picometres with values ranging over:
272 pm for the Ge4- ion
16 pm for the B3+ ion
The main factors influencing ionic radius are:
Number of shells (the principal quantum number)…don’t forget this can be affected by the type of ion formed
The charge in the nucleus

6. First ionisation energy
This is the energy required to remove one mole of electrons from one mole of gaseous atoms to form positive ions i.e.:
A(g)  A+(g) + e-
Values range over:
393 kJ mol-1 for Caesium
1681 kJ mol-1 for Helium
Values are positive because this is an endothermic process
Values are influenced by:
Number of inner electron shells (and their shielding)
Charge on the nucleus
HL: At the finest level – repulsion between electrons in their orbitals

7. Electronegativity
This is a measure of the degree to which an element attracts the shared pair of electrons in a covalent bond
Again, this means there are no values for the noble gases
Values range over:
4.0 for Fluorine
0.7 for Francium
Values are influenced by:
Number of inner electron shells (and their shielding)
Charge on the nucleus
Values are unit-less as this is a relative measure

8. Melting Point
This is the temperature (in Kelvin…i.e. Celsius + 273) at which an element melts
Values range over:
3935 K for Carbon
1 K for Helium
Values are influenced by:
Nature of bonding: giant covalent, giant ionic, metallic
Strength of bonding
Strength of intermolecular forces

9. Web quest
On wikispaces
2 periodicity an introduction

10. Key Points
Each of the following physical parameters follow trends and patterns in the PT
These patterns are generally explained by:
Charge in the nucleus
Number of electron shells
Electron shielding