8th September 2003

Trends of the Group 7 halogens

Trends:

„h All Group VII metals have 7 valence electrons (7 electrons in the highest energy level)

„h Atomic radius increases down the Group as successive

‘electron shells’ (energy levels) are filled

„h Electronegativity (the relative tendency shown by a bonded atom to attract electrons to it) decreases down the group, as the elements become more metallic in nature. (Typically, metals have low electronegativity, little ability to attract electrons, while non-metals have high electronegativity, greater ability to attract electrons). The reactivity of Group VII elements is related to the element’s ability to attract electrons, so the greater the electronegativity, the more reactive the Halogen. So, chemical reactivity of Group VII elements decreases down the Group, from the most reactive (Fluorine) to the least reactive (Iodine).

„h Down the Group, first ionisation energy (the energy required to remove 1 electron from the gaseous atom) decreases. As the atomic radius increases and the electron is further from the nucleus it is less attracted to the nucleus (electron is said to be ‘shielded’)

„h melting point and boiling point increase down the Group as the elements become more metallic in nature

„h There is a gradation in colour going down the group, the elements become darker in colour as they become more metallic in nature. Similarly there is a gradation in physical appearance at STP, from gas to liquid to solid, as the elements become more metallic in nature.

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