Molecules and compounds have properties which arise from the atoms making them up. For example, water is polar, meaning it has a positive charge on one side (the hydrogen side) and a negative charge on the other side (the oxygen side). This allows it to interact with other molecules in very specific ways, such as dissolving solids. Atoms are the smallest units that can take part in chemical reactions.
Different Types of Chemical Bonds
- A polar covalent bond forms from an unequal sharing of electrons between atoms. Because of this unequal distribution, partial charges are generated for each atom. Water (H2O) is an example of a compound with a polar covalent bond. The nucleus of the oxygen atom is strongly attracted to the electrons of the hydrogen atoms because oxygen has a high electronegativity. Electronegativity is the tendency of an atom to attract electrons. Because of this unequal sharing, the oxygen atom carries a partial negative charge and the hydrogen atoms both carry a partial positive charge. Bonds formed in this manner are weaker than ionic and standard covalent bonds.
- A nonpolar covalent bond forms when two atoms share electrons equally. They can form between two atoms of the same element or between atoms of different elements. An example includes the hydrogen gas (H2) molecule—two hydrogen atoms equally share electrons to form this molecule. The molecule methane (CH4) is another molecule formed from nonpolar covalent bonds. Nonpolar covalent bonds are considered standard covalent bonds and are thus strong bonds.
Hydrogen Bonding and Dispersion Forces
This transient dipole in one molecule encourages nearby molecules to also create transient dipoles. Then, the van der Waal's forces can occur between oppositely charged dipoles. When the motion of electrons creates temporary dipoles between molecules, a London dispersion force is formed. Because of this interaction between molecules, the dispersion force is also called an induced dipole-dipole attraction. Typically, the attractive forces between nonpolar substances rely on London dispersion forces. For example, benzene is a nonpolar substance that is liquid at room temperature. It is a 6-carbon compound that is used as a solvent in paints and varnishes.