Group 7 (17) : The Halogens | A-level Chemistry | OCR, AQA, Edexcel

Описание: Group 7 (17) : The Halogens in a Snap!

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The key points covered in this video include:
1. What are the Halogens?
2. Trends of the Halogens
3. Properties of the Halogens

What are the Halogens?

The Halogens are in Group 17 of the Periodic table. They have 7 electrons in their outer shell. They lie in the p-block. 5 outer electrons are held in a p-orbital. Example: Fluorine, 9 electrons. Example: Bromine, 35 electrons.

Properties of the Halogens

In general the Halogens: Are diatomic molecules. X2 Example: Fluorine. They have different appearances. Low melting and boiling points. Only weak intermolecular forces of attraction exist between the molecules.

Trends of the Halogens

Atomic Size: Down the group, atoms get larger, Each successive element has another shell of electrons. Electronegativity: Down the group, electronegativity decreases, This is because: The outer electrons are held further from the nucleus, Increased levels of shielding. Boiling and Melting Points. As we move down the group the boiling point increases. This is because: Each successive element has an extra shell of electrons. This allows for a greater surface area of the molecule. There will be a greater degree of London forces of attraction occurring. The lower the boiling point, the more volatile the element. Down the group, we see a change in physical state.

Summary
The Halogens are in Group 17
a. 7 electrons in their outer shell
Lie in the p-block
a. 5 outer electrons are held in a p-orbital
We see trends in the Halogens
a. Atomic Radius
i. Increases down the group
ii. Each successive element in the group gains a shell of electrons
b. Electronegativity
i. Decreases down the group
ii. Outer electrons are held further from the nucleus
iii. Increased levels of shielding
c.Boiling and Melting Points
i. Increases down the group
ii. Each successive element in the group gains a shell of electrons, increasing the surface area of the molecules
iii. A greater degree of London forces occur
iv. More energy is required to overcome these forces of attraction
In general:
a. The halogens exist as diatomic molecules
i. X2
b. Have different, distinct appearances
c. Have relatively low melting and boiling points