Covalent bond
A covalent chemical bond results from the sharing of electrons between two atoms with similar electronegativities A single covalent bond represent the sharing of two valence electrons (usually from two different atoms). The Lewis structure below represents the covalent bond between two hydrogen atoms in a H2 molecule.
The polarity of a covalent bond is defined by any difference in electronegativity the two atoms participating. Bond polarity describes the distribution of electron density around two bonded atoms. For two bonded atoms with similar electronegativities, the electron density of the bond is equally distributed between the two atom is This is a nonpolar covalent bond. The electron density of a covalent bond is shifted towards the atom with the largest electronegativity. This results in a net negative charge within the bond favoring the more electronegative atom and a net positive charge for the least electronegative atom. HCl forms a polar covalent bond.
Double Covalent Bond
Triple Covalent Bond
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Coordinate Covalent
A coordinate covalent bond (also called a dative bond) is formed when one atom donates both of the electrons to form a single covalent bond. These electrons originate from the donor atom as an unshared pair.
Both the ammonium ion and hydronium ion contain one coordinate covalent bond each. A lone pair on the oxygen atom in water contributes two electrons to form a coordinate covalent bond with a hydrogen ion to form the hydronium ion. Similarly, a lone pair on nitrogen contributes 2 electrons to form the ammonium ion. All of the bonds in these ions are indistinguishable once formed, however.
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Ammonium (NH4+)
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Hydronium (H3O+)
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Network Covalent
Some elements form very large molecules by forming covalent bonds. When these molecules repeat the same structure over and over in the entire piece of material, the bonding of the substance is called network covalent. Diamond is an example of carbon bonded to itself. Each carbon forms 4 covalent bonds to 4 other carbon atoms forming one large molecule the size of each crystal of diamond.
Silicates, [SiO2]x also form these network covalent bonds. Silicates are found in sand, quartz, and many minerals.
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