Chem Easy: GROUP 17

GROUP 17

Fluorine, Chlorine, Bromine, Iodine, Astatine

1. Group 17 elements are known as halogens.

2. They are exist as DIATOMIC MOLECULES with molecular formula of F₂, Cl₂, Br₂, I₂

3. Electronegativity is a measurement of the strength of an atom in a molecule to pull electrons towards its nucleus.

When going down to the Group 17, the electronegativity of halogens decreases.

Explanation:

- The number of shells occupied with electrons increases.

- This cause the outermost occupied shells further away from the nucleus.

- Thus, the strength of nucleus to attract electrons becomes weaker.

5. General physical of halogens:

- Very low melting points and boiling point. (Weak forces of attraction between MOLECULES )

- Low density

- Cannot conduct electricity

When going down the Group 17, The changes in physical properties.
Atomic radius/ atomic size	Melting point and boiling point	Densities ( )
Increase	Increase	Increase
- Reason : Number of shells increases	- Molecular size increases down the group. - Thus, forces of attraction between molecules become stronger. - Therefore, more energy is needed to overcome the strong force of attraction.	- Increase in atomic mass is more than the increase in atomic radius (volume of atom)

6. All the atoms of the halogens exhibit similar chemical properties because they have same valence electrons.

7. The reactivity of halogens decreases down the Group 17.

Explanation :

- All halogens have seven valence electrons.

- Each atom of the halogens will gain one more electron to achieve stable octet electron arrangement and form ion with a charge of negative.

Examples:

F + ē → F^-

- When going down to the group 17, atomic size of halogens increases down the group

- Thus, outermost occupied shell becomes further away from nucleus.

- The strength to attract one electron into outermost shell by nucleus becomes weaker.

- It causes the reactivity to decrease down the group

Chem Easy