Key Questions

  • Answer:

    covalent bond is a chemical bond that involves sharing of electron pairs between atoms.


    In covalent bonding electrons are shared between two atoms. So those electrons belong to both of those atoms. If you look at an actual image of say the covalent bond between two Hydrogen atoms, you can see that the electron cloud surrounding these two atoms sort of merge between them. This means that both the atoms are exerting an attractive force on the electrons being shared. Thus this is a covalent bond.

    Don't get too confused with the Lewis dot structures that show a straight line joining two H atoms. It's just simpler to write it that way as one cannot actually show the bonding on a piece of paper.

    In ionic bonding, electrons are donated by one atom and another atom receives them. Ex: Na gives 1 electron to Cl to form the ionic compound NaCl.

    Both ionic and covalent bonding arise out of the need for electrons or the need to remove electrons in order to have a complete octet, which is stable.
    So while solving problems just look at the electronic configurations of the participating atoms and try to figure out which atom receives and which atom gives electrons.

    Note that you will automatically realise the significance of covalent bonding when you do that as when neither can give nor receive, they will share!

  • Answer:

    Chemical bonds do not store energy.


    Chemical bonds certainly "contain" potential energy, and the atoms want to move to a lower potential energy (become more stable).

    When methane, #"CH"_4#, forms, the valence electrons end up in more stable (lower energy) C-H bonds.

    These bonds are fairly strong, so methane is relatively inert.

    However, if you add energy to the methane in the form of a flame or a spark in the presence of oxygen, some of the molecules will have enough energy to overcome an activation energy barrier.

    Some of the #"C-H"# bonds will break.

    The electrons can then enter an even lower energy state by forming #"C=O"# and #"O-H"# bonds rather than staying as #"C-H"# and #"O=O"# bonds.

    So they “rearrange” themselves to form #"CO"_2# and #"H"_2"O"#.

    The excess energy of 794 kJ/mol is released as heat, which we can then use to cook our food, among other things.

    Thus, chemical bonds do not “store” energy. The energy for breaking bonds comes only when stronger bonds are formed instead.

    This is the true driving energy for biochemistry, where cellular respiration provides energy by breaking the weaker bonds in carbohydrates and sugars and forming the strong oxygen bonds in carbon dioxide and water.

    More energy is "available" because the weaker bonds are broken in favor of the stronger bonds being formed.

    Many people say that ATP stores energy and releases it when the phosphoester linkage is broken and forms ADP. But it takes energy to break a phosphate group from ATP.

    Rather, ATP provides energy when it breaks the weakly bonded phosphoester linkages and forms more strongly bonded glucose or fructose phosphate molecules.


    Energy release comes from the net chemical reaction that produces new, more stable bonds to replace the less stable ones in the starting materials.