4.5	Elements in Group 17

• Also known as halogen.
• Very reactive elements.
• The elements in this group are; 
  • Fluorine, F
  • Chlorine, Cl
  • Bromine, Br
  • Iodine, I
  • Astatine, At
  • Tennessine, Ts

Physical properties

• Non-metals
• Does not conduct heat and electricity.

Element		As going down the group
F	\(\Downarrow\)	The atomic radius increases.   Reactivity decreases. Boiling and melting point increases. The van der Waals force increases as the size of the atom increases. The electronegativity decreases because the radius increases and the force between the valence electron and nucleus decreases.
Cl
Br
I

 

Chemical properties

• React with water to produce acids

Element	Reaction with water
Cl	\(Cl_2(g) + H_2O(l) \rightarrow HCl(aq) + HOCl(aq)\)
Br	\(Br_2(l) + H_2O(l) \rightarrow HBr(aq) + HOBr(aq)\)
I	\(I_2(s) + H_2O(l) \rightarrow HI(aq) + HOI(aq)\)

 

• React with metal to produce metal halides

Element	Reaction with iron
Cl	\(3Cl_2(g) +2Fe(s) \rightarrow 2FeCl_3(s)\)
Br	\(3Br_2(l) +2Fe(s) \rightarrow 2FeBr_3(s)\)
I	\(3I_2(s) +2Fe(s) \rightarrow 2FeI_3(s)\)

 

• React with sodium hydroxide to produce salts and water

Element	Reaction with sodium hydroxide
Cl	\(Cl_2(l) +2NaOH(aq) \rightarrow NaCl(aq) + NaOCl(aq) + H_2O(l)\)
Br	\(Br_2(l) +2NaOH(aq) \rightarrow NaBr(aq) + NaOBr(aq) + H_2O(l)\)
I	\(I_2(s) +2NaOH(aq) \rightarrow NaI(aq) + NaOI(aq) + H_2O(l)\)

 

Reactivity

• Group 17 is very reactive, but the reactivity decreases down the group.
• The elements will accept an electron to achieve a stable octet electron arrangement.
• The forces between the nucleus and the valence electron become weaker as going down the group.  

Element		As going down the group
F	\(\Downarrow\)	The atomic radius increases. \(\downarrow\) The attractive forces between the nucleus and the valence electrons become weaker \(\downarrow\) More difficult to receive or attract an electron to complete the valence shell \(\downarrow\) Reactivity decreases
Cl
Br
I