4.6	Elements in Period 3

• The elements in Period 3 will show a gradual change in physical and chemical properties, as going across the period. 
• The elements in Period 3 are; 
  • Sodium, Na
  • Magnesium, Mg
  • Aluminium, Al
  • Silicon, Si
  • Phosphorus, P
  • Sulphur, S
  • Chlorine, Cl
  • Argon, Ar

 

Going across Period 3

Group	1	2	13	14	15	16	17	18
Element	Na	Mg	Al	Si	P	S	Cl	Ar
	\(\xrightarrow[]{\text{Across period}}\)

 

• Atomic radius decreases:
  • There are only three shells, but the number of electron increases.
  • The increase in the number of electrons means there is an increase in the number of protons, which result in the higher electrostatic force.
  • The increase of electrostatic force pulls the valence electron closer to the nucleus.

 

• The number of valence electrons increases:
  • The number of electrons of the element increases.  

 

• The electronegativity increases:
  • The atomic radius decreases as the number of protons increases.
  • As the number of protons increases, the electrostatic force also increases and creates a tendency to attract electrons.
  • The left side of the period is less electronegative than the right side of the period.

 

• The melting point and boiling point:
  • Increases from the left to the middle of the period, and then decrease again.

 

• Nature of metals:
  • The elements change from metal to metalloid, and then non-metal as the electronegativity increases.

 

• Nature of oxides:
  • The oxides of the elements change from basic to amphoteric and then to acidic across the period.