4.4	Unsur dalam Kumpulan 1

• The elements are;
  • Hydrogen, H (non-metal)
  • Lithium, Li
  • Sodium, Na
  • Potassium, K
  • Rubidium, Rb
  • Caesium, Cs
  • Francium, Fr
• Also known as alkali metals, except for hydrogen.  

 

Physical properties

• These metals are soft.
• Good conductors of heat and electricity.

 

Element	As going down the group
Li	The atomic radius increases.   Density increases. The melting point decreases. Electeopositivity also increase The attractive force between the nucleus and the single electron decreases as the radius increases.
Na
K

 

Chemical properties

• React with water to produce hydrogen gas and alkaline solution

Element	Reaction with water
Li	\(2Li(s) + 2H_2O(l) \rightarrow 2LiOH(aq) + H_2(g)\)
Na	\(2Na(s) + 2H_2O(l) \rightarrow 2NaOH(aq) + H_2(g)\)
K	\(2K(s) + 2H_2O(l) \rightarrow 2KOH(aq) + H_2(g)\)

 

• React with oxygen to produce metal oxide.

Element	Reaction with oksigen
Li	\(4Li(s) + O_2(g) \rightarrow 2Li_2O(s)\)
Na	\(4Na(s) + O_2(g) \rightarrow 2Na_2O(s)\)
K	\(4K(s) + O_2(g) \rightarrow 2K_2O(s)\)

 

• React with halogen to produce metal halide.

Element	Reaction with chlorine
Li	\(2Li(s) + Cl_2(g) \rightarrow 2LiCl(s)\)
Na	\(2Na(s) + Cl_2(g) \rightarrow 2NaCl(s)\)
K	\(2K(s) + Cl_2(g) \rightarrow 2KCl(s)\)

 

Reactivity

• The elements are very reactive as going down the group.
• The elements will tend to donate an electron and become positive ions.
• The donation of an electron is to make sure it can attain a stable duplet or octet electron arrangement.
• The attractive force between the nucleus and the valence electron is weak, thus making it easier to be donated or released.
• As going down the group, the atomic radius of the elements increases, causing the force between the nucleus and the electron to be weaker. 

 

Element		As going down the group
Li	\(\Downarrow\)	The atomic radius of the elements increases \(\downarrow\) The attractive force between the nucleus and the valence electron becomes weaker.  \(\downarrow\) Easier to release the valence electron \(\downarrow\) The reactivity of the reaction increases
Na
K