Covalent bonding is usually made between nonmetals and nonmetals, hydrogen and nonmetals, and hydrogen with hydrogen. This bond is characterized by electron sharing.
Hydrogen has an electron in its valence shell. To be identical to the noble helium gas with 2 electrons in the last shell, it needs one more electron. So 2 hydrogen atoms share their electrons, becoming stable:
Ex. H (Z = 1) K = 1
H - H → H2
The trace represents the pair of shared electrons.
In this situation, everything happens as if each atom had 2 electrons in its electrosphere. The electrons belong to both atoms at the same time, that is, the two atoms share the 2 electrons. The smallest portion of a resulting covalent bonding substance is called a molecule.
So the H2 is a molecule or molecular compound. A compound is considered a molecular compound or molecule when it has only covalent bonds. Note the covalent bond between two chlorine atoms:
Lewis Formula or Electronic Formula
Cl - Cl
Depending on the number of electrons atoms share, they can be mono, bi, tri or tetravalent.
Covalent bonding can also occur between atoms of different elements, for example water.
Water, in the example, makes three covalent bonds, forming the molecule H2O. Oxygen is 6 ° in the last layer and needs 2 ° to be stable. Hydrogen is 1 is and needs 1 more to stabilize. There are still two pairs of electrons left over the oxygen atom.
Covalent bonding can be represented in various ways. The formulas in which they appear indicated by the signs . orx they are called the Lewis formula or electronic formula.
When electron pairs are represented by dashes (-) we call the flat structural formula, showing the number of bonds and which atoms are bonded. The molecular formula is the simplest, showing only which and how many atoms are in the molecule. See the model:
H . . H (Lewis formula or electronics)
H - H (flat structural formula)
H2 (molecular formula)
Note the table of some elements with their valence (covalence) and their representation.
- O - and O =
- S- and S =