Physical properties across Period 3
Physical properties across Period 3
- Periodicity means properties repeat in a regular pattern across each period.
- Period 3 (Na to Ar) is the standard example.
- The trends follow from the structure and bonding.
Practice
Periodicity means that properties:
Periodicity is the repeating pattern of properties across the periods of the table.
Atomic radius
- Across Period 3 the atomic radius gets smaller.
- The nuclear charge rises but the electrons go into the same outer shell, so the stronger pull draws it in.
Practice
Across Period 3, the atomic radius:
More protons pull the outer shell in more strongly, while shielding stays about the same.
Melting point and conductivity
- Na, Mg, Al are giant metallic — melting points rise, and they conduct well.
- Si is giant covalent — the highest melting point; it barely conducts.
- P, S, Cl, Ar are simple molecular — low melting points (weak forces); they don't conduct.
Practice
Which element has the highest melting point in Period 3?
Silicon's giant covalent network needs strong covalent bonds broken, giving the highest melting point.
Practice
Which Period 3 elements conduct electricity well?
The metals Na, Mg, Al conduct well; from silicon onwards conductivity is almost zero.
You've got it
Key idea
- periodicity = properties repeat across each period
- atomic radius decreases across (more nuclear charge, same shell)
- melting point peaks at silicon (giant covalent); high for metals, low for molecular
- Na/Mg/Al conduct (metallic); from Si onwards they barely conduct