Atoms bond chemically to form molecules.
Types of bonding
The periodic table is organized in columns, called groups or families, and rows, called periods. There are several groups or periods that have specific names.
| Bond type |
Happens between |
Electrons are |
Ionic |
Metal & non-metal |
Transferred |
Covalent |
Non-metals |
Shared |
Polar Covalent |
Non-metals |
Shared unevenly |
Metallic |
Metals |
pooled |
There are general characteristics of each type of bonding:
- Ionic: High melting points, most dissolve in water, conduct electricity when dissolved in water, brittle
- Covalent: Low melting points, most do not dissolve in water, do not conduct electricity when dissolved in water
- Polar covalent: Medium melting points, some dissolve in water, do not conduct electricity when dissolved in water
- Metallic: Soft, conduct heat and electricity, do not dissolve in water
Bond Polarity
When nonmetals bond covalently with a large difference in electronegativity, a polar bond is formed. A polar bond has a partial separation of charges. Polar bonds are symbolized with an arrow pointing towards the more electronegative element and a crossed tail by the less electronegative element
Isomers and Resonance
Isomers are compounds with the same chemical formula but different chemical structure. Resonance occurs when a double bond can be placed in more than one place in a structure without creating isomers.
Bonding theory
The Valence Shell Bonding Theory assumes that bonds are formed when atomic orbitals overlap. Direct overlap leads to sigma bonds and parallel overlap leads to pi bond. The Hybridization Theory says that the sigma bonds are all identical around an atom, therefore the orbitals forming them must be identical. Therefore, any atomic orbitals involved in sigma bonds hybridize into identical orbitals to bond. The Molecular Orbital Theory says that rather than overlapping atomic orbitals, or hybridized atomic orbitals, new orbitals are formed in the molecule that are separate. Some of the new orbitals formed pull the two nuclei together and are bonding orbitals. However, some of them pull the two orbitals apart and are anti-bonding orbitals. The bond order is the number of bonding orbital electrons – the number of antibonding orbital electrons divided by 2. The bond order can be used to determine the type of bond (single, double, triple).
