Two electrons shared between two atoms creates a force or bond that holds the atoms together. More than two electrons are sometimes shared between atoms. Covalent bonds can only form between atoms that can ionize. Ionization of a hydrogen atom produces a proton. Methane is an isotope of carbon.
Water molecules are smaller than molecules of oxygen gas.
Hydrogen and oxygen share the electrons equally in the covalent bonds of a water molecule. A polar molecule is one that is most stable at the poles of reaction. Water is a liquid at room temperature because the water molecules are strongly sympathetic to one another. Hydrophilic substances dissolve readily and easily in water.