what are oxidation numbers of first 18 elements?

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The maximum oxidation number of an element can be obtained from knowledge of its position in the periodic table. The maximum positive oxidation number is the group number, or the number of electrons in the valence shell of an element, or 8 – group number. Thus for Mg (Gr. II), it is +2, for P (Gr. V), it is +5 and so on. Apart from the maximum positive oxidation state, all lower oxidation states are possible, though not every state is stabilized, owing to various reasons. For certain heavier elements, however, the inert pair effect becomes obvious, resulting in a dominance of lower oxidation states. The maximum negative oxidation state can be obtained by (group number – 8). Thus for Oxygen (Gr. VI), it is -2, for P (Gr. V), it is -3, for Cl (Gr. VII), it is -1, and so on. Working in this way, the possible oxidation of first twenty elements are: H (+1, -1), He (0), Li (+1), Be (+2), B(+3, -3), C (+4, -4), N (+5, +4, +3, +2, +1, -3), O (+2, +1, -2, -1), F (-1), Ne (0), Na (+1), Mg (+2), Al (+3, -3), Si (+4, +3, -4), P (+5, +3, +1, -1, -3), S (+6, +4, +2, -2), Cl (+7, +6, +5, +4, +3, +2, +1, -1), Ar (0), K (+1), Ca (+2).

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