Intermolecular forces of attraction are what hold molecules together.
There are three different types of intermolecular forces, London Dispersion forces, Dipole-Dipole forces, and Hydrogen Bonding forces.
London Dispersion forces happen because electrons are constantly in motion one end of a molecule is either temperarily positive or temperarily negative creating temperary dipoles, this makes molecules able to attract each other. This form of attraction happens during every single molecular bond.
Dipole-Dipole forces happen because of an electrostatic attraction between the positive end of one molecule and the negative end of another molecule. This form of attraction only happens to Polar molecules.
Hydrogen Bonding is a temperary form of a covalent bond. This form only happens in Polar molecules and it only occurse between Hydrogen atoms and Nitrogen atoms, Hydrogen and Oxygen atoms, and Hydrogen and Floride atoms.
The above picture of Acetaldehyde shows that all three types of intermolecular forces of attraction are going on. Since this is a molecular bond London Dispersion forces are happening. Dipole-Dipole forces are happening because the Oxygen atom is more negative than the Hydrogen atom, this is shown by a solid line. Hydrogen Bonds are happening between the Hydrogen and Oxygen atoms, this is shown by a dotted line.
