![]() When they do react they produce hydroxides and hydrogen. The reactions of the elements with water become more vigorous down the group. Four major factors affect reactivity of metals: nuclear charge, atomic radius, shielding effect and sublevel arrangement (of electrons). For similar reasons the electronegativity decreases. This is because as the ions get larger the distance between the bonding electrons and the positive nucleus gets larger and reduces the overall attraction between the two. The first impression that is sometimes given that the fall in reactivity is because the incoming electron is held less strongly as you go down the group and so the negative ion is less likely to form. Generally the melting point of the alkali metals decreases down the group. This trend of lower electron affinities for metals is described by the Group 1 metals: Lithium (Li): 60 KJ mol-1 Sodium (Na): 53 KJ mol-1. Another property of atoms that exhibits periodic trends is ionization energy. There is more shielding between the nucleus and the outer electrons and the distance between the nucleus and the outer electron increases and therefore the force of attraction between the nucleus and outer most electrons is reduced. Going down the group, the first ionisation energy decreases. Progressing down group 1, the atomic radius increases due to the extra shell of electrons for each element. the energy given off when a neutral atom in the gas phase grabs an extra electron and forms a anion (gain electron/s, give off energy.) chemical reactivity. They are called s-block elements because their highest energy electrons appear in the s subshell. Group 1 elements are known as Alkali Metals. ![]() It can be used as a differentiated activity for the more able students within a group. This could be used to follow up some work on the periodic table where the trends in reactivity in groups 1 and 7 have been identified. When two different atoms are bonded together their sizes can be altered. For example, the internuclear distance in Cl 2 is 198 pm, so the atomic radius is taken to be 99 pm or 0.99 Å. Note: Even though Hydrogen will appear above Lithium on the periodic table it is not considered a part of Group 1. Chemistry for the gifted and talented: trends in reactivity in the periodic table. The bonding atomic radius of an element is taken as one half the distance between the nuclei when two identical atoms are bonded together. ![]()
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