Basic Chemistry Facts

Atoms are made up of a nucleus (protons and neutrons - positive charge) surrounded by a number of electrons (negative charge)
Molecules are made up of at least two atoms that can either be the same (e.g. Oxygen molecule, O2 or Hydrogen molecule, H2) or different (e.g. Water molecule, H20).
In certain molecules where the atoms are held together through co-valent bonds, electrons can be pulled more toward one side than the other. The end of the molecule toward which the electrons are pulled becomes more negative when compared with the other. Such molecule is said to be POLAR.
In the case of ionic bonds, the atoms that make up the compound dissociate into charged ions when dissolved in water Typically these ions are hydrated i.e. each ion is surrounded by a number of water molecules producing what are called as hydrogen spheres.
As hydrogen has a weak positive charge, it has a weak attraction for a second electronegative atom (in the case of water, oxygen). This weak attraction is called a hydrogen bond. This weak attraction is largely responsible for the folding and bending of long organic chains (e.g. DNA and proteins).