Group 7:

Halogens

The halogens are elements that are non-metals from the second last of the periodic table, they all have 7 valence electrons. Also, they are existed naturally in diatomic molecule form, such as fluorine(F2) and chlorine(Cl2).

characteristics and properties

The halogens become darker as you move down the group, fluorine is pale-yellow and , have low boiling points and melting points compared to other non-metal elements. Their state of the different elements are different with the other groups, where not all the elements have the same state at room temperature, unlike the other groups, the first two element of the halogens are gas, the third element is liquid, and the rest are solid.

trends: (As you go down the group)

- Melting point and boiling point increases

- Colour becomes darker

- Reactivity decreases

Bonding

The reactivity of the halogens decreases as you go down the group .Since all of the atoms of the halogens have 7 valence electron, when bonding, they usually take one electron so they can gain a full shell of valence electrons and  become a positive charged ion with a -1 charge. 

 

For example, look at the diagram in the right side, it is a bonding diagram of sodium  and chloride. You can see that chlorine gain one extra electron from sodium so they both can have full shell of valence electrons, and so chlorine become a -1 charged ion.

sources:

-The halogens - trends in physical properties. (n.d.). Retrieved December 17, 2016, from  http://www.bbc.co.uk/schools/gcsebitesize/science/edexcel_pre_2011/patterns/groupsrev4.shtml 

-Electron arrangement and chemical properties of Group 7 - Higher. Retrieved December 17, 2016, from  http://www.bbc.co.uk/schools/gcsebitesize/science/add_ocr_pre_2011/periodic_table/electronsrev4.shtml

-The group 7 elements. Retrieved December 19, 2016, from http://www.bbc.co.uk/schools/gcsebitesize/science/add_ocr_gateway/periodic_table/group7rev1.shtml

Properties of the Halogens - Boundless Open Textbook. (n.d.). Retrieved December 19, 2016, from https://www.boundless.com/chemistry/textbooks/boundless-chemistry-textbook/nonmetallic-elements-21/halogens-155/properties-of-the-halogens-597-6573/