A chemical linking is that one that occur for the electric attraction of íons positive (cátions) and íons negative (ânions). In general way, these íons are formed when together metal atoms and ametais meet. Metals: very eletropositivos elements. Normally the 3 electrons in the valence layer possess of 1. Trend to lose electrons and to form cátions. Ametais: elements many eletronegativos. Normally the 7 electrons in the valence layer possess of 5. Trend to gain electrons and to form ânions. The crystalline arrangement and the ion-formula In an ionic composition we have a indeterminate number great e of cátions and ânions very grouped alternatingly, as one forms geometric defines that we call crystalline arrangement. For example: In a crystalline arrangement formed by In + and CL, it is observed that each ion of In + is surrounded by 6 íons of CL. Hydrogen The hydrogen (z=1) also makes chemical linkings with metals. To complete its layer of valence, that is the first one, the necessary hydrogen to gain 1 electron, forming ânion h. As the metals lose electrons to acquire stability, they will form ionic composites with hydrogen. Example: Ionic made up of magnesium and hydrogen. Mg= loses 2 electrons H = loses 1 electron Therefore the Mg makes linkings with two íons hydrogen forming MgH2. Covalentes linkings: It is the sharing of pairs of desemparelhados electrons. When two atoms need to gain electrons to acquire to the electronic configuration of a noble gas (to acquire stability), they share its more external electrons, in way that an atom can use electrons of the other. The common linking covalente is based on a sharing of 1 or more pairs of electrons, made between two atoms, so that both acquire stability, being that the pair of electrons shared is formed by 1 desemparelhado electron of each involved atom. Other types of covalentes linkings exist, the sigma, pi.