Trends in Group VIIA (Halogen) Elements

Properties of Group VII Elements

Period	Name (Symbol)	Atomic Number (Z)	Simple Electronic Configuration	Atomic Radius (picometres)	Electro- negativity	1^stIonization Energy(I_A(kJ/mol)	Melting point (^oC)	Boiling point (^oC)	Physical Appearance at STP (0^oC, 1atm)
2	Fluorine (F)	9	2,7	68	4.0	1690	-223	-187	pale yellow gas

3	Chlorine (Cl)	17	2,8,7	99	3.0	1260	-102	-35	greenish-yellow gas

4	Bromine (Br)	35	2,8,18,7	114	2.8	1150	-7.3	59	reddish-brown liquid

5	Iodine (I)	53	2,8,18,18,7	133	2.5	1020	114	183	purple solid

6	Astatine (At)	85	2,8,18,32,18,7	Astatine doesn't occur naturally (longest lived isotope's half-life=8hours). It resembles iodine in chemical properties but is more metallic

all Group VII metals have 7 valence electrons (7 electrons in the highest energy level)
atomic radius increases down the Group as successive 'electron shells' (energy levels) are filled
electronegativity (the relative tendency shown by a bonded atom to attract electrons to itself) 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).
down the Group, first ionization 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')
melting point and boiling point increase down the Group as the elements become more metallic in nature
there is a gradation in color 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.