Group 7, The halogens

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The group 7 elements are also known as the 'halogens'. The group consists of the elements Fluorine (F), Chlorine (Cl), Bromine (Br), Iodine (I) and Astatine (At), decending in that order. 

They are non-metals, which all exist as separate diatomic molecules e.g: Cl2 they are considered P block elements as their valence (outermost,bonding) electrons are located in P orbitals (subshells). 

(http://www.drcruzan.com/Images/Chemistry/Chemistry_PeriodicHalogens.png)

GROUP TRENDS:

APPEARANCE:

General trend down the group: Increase in darkness of molecules

BOILING POINTS:

General trend down the group: Increase

Explaination: As you move down the group, each atom of each element has more electrons. This increases the size of the molecules which leads to greater van der waals forces to be formed between molecules with require more energy to overcome. 

ELECTRONIC CONFIGURATION:

General trends down the group: Both atomic and ionic radius increase

Explaination for the atomic radius: The greater the atomic number, the more electrons there are which enter subshells further away from the nucleus increasing the size of the atoms.

Explaination for the ionic radius: The addition of electrons are repelled by others which force them further away from the nucleus and therefore increase the ionic radius. 

ELECTRONEGATIVITY:

General trend down the group: Decrease

Explaination: There is an increase in electrons as you move further down the group, this creates more sheilding which causes the nucleus to be further away from the bonding valence electrons and reduces the attraction of bonded electrons from the nucleus. 

REACTIVITY:

General trend down the group: Decrease

Explaination: This is due to the group 7 elements only requiring the addition of one electron to obtain a full octet. Those elements higher up in the group have less electrons and sheilding, reducing the distance between the nucleus and valence electrons and therefore increasing the electrostatic attraction from the nucleus to attract an electron. However, as you move down the group this shielding increases, and causes a decrease in the amount of attraction coming off the nucleus to pull another electron. 

This pattern in reactivity is obvious from the way the halogens react in displacement reactions:

- In a displacement reaction, a more reactive halogen will displace a less reactive one. 

For example: 

Chlorine + Sodium Bromide --> Bromine + Sodium Chloride

Chlorine + Sodium Iodide --> Iodine + Sodium Chloride 

Bromine + Sodium Iodide --> Iodine + Sodium Bromide

OXIDISING POWER OF HALOGENS:

In displacement reactions between halogens and halides, the halogen acts as an oxidisng agent. Because group 7 elements only require one extra electron to obtain a full octet they make good oxidising agents allowing each halogen atom to accept one electron from each halide ion. 

General trend down the group…

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