The group of elements best known to bond by a covalent bond is the group of non-metals. Non-metals are elements that are poor conductors of heat and electricity, and they typically have low melting and boiling points. Non-metals also tend to be more electronegative than metals, meaning that they have a greater attraction for electrons. This electronegativity difference between non-metals causes them to share electrons in order to form covalent bonds. Some common examples of covalent bonds include the bonds between hydrogen and oxygen in water (H2O), the bonds between carbon and hydrogen in methane (CH4), and the bonds between nitrogen and oxygen in nitrogen dioxide (NO2).