Group VII elements are called halogens. They exist as diatomic molecules (F2, Cl2, Br2, I2) and have seven electrons in their outer shell. Fluorine has the smallest atomic radius while iodine has the largest due to more electron shells. Melting and boiling points decrease from fluorine to iodine due to weaker van der Waals forces between larger molecules. Electronegativity decreases from fluorine to iodine as the nucleus attracts electrons less. Halogens can gain electrons to form ions or share electrons to form covalent bonds. More reactive halogens can displace less reactive ones from solutions.

1. GROUP VII ELEMENTS
BY THUGIANG

2. WHAT ARE GROUP VII ELEMENTS?
• They are called halogens.

3. PHYSICAL PROPERTIES
• These elements are non-metals.
• At room temperature (25°C), they exist as diatomic
molecules: F2, Cl2, Br2, and I2.
• Their atoms have seven electrons in the outer
principal quantum shell.

4. ELECTRON ARRANGEMENTS

5. ATOMIC RADIUS
Atomic Radius
0.14
0.12
0.1
0.08
Atomic Radius
0.06
0.04
0.02
0
Fluorine
Chlorine
Bromine
Iodine

6. WHY?
• Causeeee…
• The number of layers of electrons around the
nucleus.
• The more layers, the bigger the atomic radius.

7. MELTING AND BOILING POINTS
250
200
150
100
50
Melting point
0
-50
-100
-150
-200
-250
Fluorine
Chlorine
Bromine
Iodine
Boiling point

8. MELTING AND BOILING POINTS
• The boiling points show us the volatility (how easy
can they evaporate) of the halogens.
• They are relatively low cause they have simple
molecular structure and weak van der Waals’
forces between their diatomic molecules.
• These forces increase as the no. of electrons
increase with increasing atomic number (the
greater number no. of electrons, the greater the
opportunities for dipoles arising within molecules).
• => the larger the molecules, the stronger the van
der Waals’ forces.

9. COLOUR
Fluorine
Pale yellow
Chlorine
Green/ Yellow

10. COLOUR
Bromine
Iodine
Orange/ Brown
Grey/ Black

11. REACTIONS
• The halogen atoms require just one more electron
to achieve a complete outer shell => they can
react with metallic elements by gaining an electron
to become ions with a 1- charge.
• For example:
• Cl2(g) + Ca(s)  CaCl2(s)
• Each halogen atom tends to gain one electron
• => halogens are oxidising agents, their oxidation no. is
reduced from 0 to -1 in the compound formed.

12. REACTIONS
• They also react with non-metals, forming covalent
bonds.
• For example:
• H2(g) + Cl2(g)  2HCl(g)
• The halogens get less reactive going down Group
VII. This correspond to the trend in electronegativity
going down the group.
• Electronegativity is a measure of the tendency of an atom to
attract a bonding pair of electrons.
•

13. ELECTRONEGATIVITY
Electronegativity
4.5
4
3.5
3
2.5
2
Electronegativity
1.5
1
0.5
0
Fluorine
Chlorine
Bromine
Iodine

14. WHY?
• Causeeeee…
• The electrons are not as near to the nucleus as the
number of electrons increase. Therefore, the
nucleus and the electrons are not as attracted to
each other as much. An increase in shielding is
observed so the ability to attract electrons
decrease. Which means electronegativity decrease
down the group.

15. DISPLACEMENT REACTIONS
• A more reactive halogen can displace a less
reactive halogen from a halide solution of the less
reactive halogen.
• For example:
• Cl2(aq) + 2NaBr(aq)  2NaCl(aq) + Br2(aq)
• Ionic equation:
• Cl2(aq) + 2Brˉ(aq)  2Clˉ(aq) + Br2(aq)
• Halogens dissolve well in cyclohexane.

16. HALOGENS AND CYCLOHEXANE

17. REACTION WITH HYDROGEN
• Halogens form hydrogen halides with hydrogen
gas.
Equation for reaction
Description of reaction
H2(g) + F2(g)  2HF(g)
Reacts explosively even
in cool, dark conditions
H2(g) + Cl2(g)  2HCl(g)
Reacts explosively in
sunlight
H2(g) + Br2(g)  2HBr(g)
Reacts slowly on heating
H2(g) + I2(g)  2HI(g)
Forms an equilibrium
mixture on heating

18. WHYYYY? T_T
• Because e e e e e. . . . . .. . .
Hydrogen-halogen bond
Bond energy / kJ/mol
H-F
562
H-Cl
431
H-Br
366
H-I
299
• => HF is most thermally stable; HI is the least
thermally stable.

19. THE END
YAYYYY!!!