Covalent bonding is performed according to the electronegativity difference. It usually occurs between nonmetal and nonmetal, hydrogen and nonmetal and hydrogen with hydrogen.
This bond is characterized by the sharing of electrons between atoms. Hydrogen has an electron in its valence shell. To be identical to the noble helium gas with 2 electrons in the last shell. He needs one more electron. So 2 hydrogen atoms share their electrons being 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 =
Some rules for mounting the covalent bond:
- placing the central element in the middle;
- place the most electronegative element around the central atom;
- put the hydrogen attached to oxygen.
Covalent Bonding Properties:
- form molecules;
- are generally soluble in nonpolar solvents;
- have low FP and PE;
- In general, do not conduct electricity except acids.
THE normal covalent bond It is the union between atoms established by pairs of electrons, so that each pair is formed by one electron of each of the atoms. Example:
This type of binding appears very often in compound substances.
THE dative covalent bond is the bond where the electron pair is given by only one of the atoms of the bond.
In the bonding of sulfur dioxide (SO2) looks like this:
In this connection, sulfur yields its electron pair to the oxygen atom. There is no sharing.
The dative covalent bond is represented by an arrow that goes from the donor atom to the atom that received the electron pair. As with normal covalent bonding, the dative also continues with the octet around each atom, thus maintaining stability.
Another example is sulfur trioxide (SO3):
Another example is carbon monoxide (CO), which has two normal covalent bonds and one dative covalent between carbon and oxygen.
It is important to remember that substances formed only by normal or dative covalent bonds are called molecules or molecular compounds.
A substance can have ionic as well as covalent bonds. If it has at least one ionic bond then it will be considered an ionic compound.
If the substance is formed only by ionic bonds, then we call it an ionic aggregate. In an ionic compound, there are no molecules.