![]() Pale yellow to greenish-yellow to reddish-brown to gray There is also a gradation in the colour of the elements going down group 17 from top to bottom: We can infer that there is a gradation in the intermolecular forces acting between the molecules such that the strongest forces of attraction act between iodine molecules and the weakest forces of attraction act between fluorine molecules. The melting point of a substance reflects the amount of energy required to weaken the forces of attraction between molecules ( intermolecular forces), the higher the melting point the stronger the forces of attraction between the molecules. Going down Group 17 from top to bottom the elements change from gaseous state to liquid to solid. ![]() We can see a trend in the states of matter. Summary of trends in the properties of Group 17 elements is shown below: Metallic character of the group 17 elements increases down the group from top to bottom.Elements become darker in colour going down group 17 from top to bottom.Melting point and boiling point increase down Group 17 from top to bottom.First ionization energy decreases down group 17 from top to bottom.Chemical reactivity of group 17 elements decreases down group 17 from top to bottom.Electronegativity decreases down group 17 from top to bottom.Atomic radius increases down Group 17 from top to bottom.All Group 17 (group VIIA or halogen) elements have 7 valence electrons (7 electrons in the valence shell or highest energy level).(ii) covalent (eg, non-metal + halogen → non-metal halide) (i) ionic (eg, metal + halogen → metal halide) Group 17 elements can combine with nearly all the elements in the periodic table.Group 17 elements exist as diatomic molecules (X 2) when not combined with other elements.(a) halogens (2) (name still in common use)
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