Topic outline

  • Intramolecular bonds - the bonds within the molecules


    The types of bonding incorporated in Intramolecular bonding:
    1. Ionic
    2. Covalent
    3. Metallic

    A review of the forces present within molecules.

    Recall that intermolecular forces control the physical properties of a substance, while intramolecular forces control its chemical properties. Such properties include bond energy (heat required to break molecule into individual atoms) and flammability.

    Ionic Bonding

    Ionic bonds are electrostatic forces (attraction or repulsion of particles or objects because of their electric charge) that arise from the transfer of electrons from one atom to another. This type of bond forms between a metal and a non-metal, where the metal donates electrons to the non-metal, and results in oppositely-charged ions.

    Ionic compounds, such as NaCl, form structures called crystal lattices. These structures consist of a network of ionic bonds, where the ions keep the same orientation to one another and repeat at regular intervals. The chemical formula of an ionic compound is the simplest whole number ratio of cations to anions within the crystal lattice and represents one formula unit.

    Covalent Bonding

    Covalent bonds arise from the sharing of valence electrons between two atoms. This type of bond normally forms between two non-metals. It results in the formation of either molecular compounds or network solids (complex structures composed of a continuous network of covalent bonds).

    Coordinate covalent bonds are a special type of covalent bond where one atom donates both electrons in a bond as opposed to both atoms donating one electron. There is no difference in nature between a coordinate covalent bond and an ordinary covalent bond.

     

    Electronegativity

    Electronegativity is a measure of an atom’s electron attracting ability for a bonding pair of electrons. On a periodic table, it increases from left to right (closer to filling an orbital) and decreases down a group (more electron shielding). The noble gases, which all have an electronegativity of 0, are exceptions to this trend because they already have full orbitals. Elements with a high electronegativity have a strong attraction for electrons, while those with low electronegativity have a weak attraction for electrons. Fluorine is the most electronegative element.

    The difference in electronegativity between two bonded atoms gives rise to polarity if the electrons are not shared equally between them and there is a large difference in electronegativity. The electron density would be closer to the more electronegative atom, causing partial charges to occur: the more electronegative atom would have a partial negative charge and the less electronegative atom the partial positive charge. Partial charges are expressed with δ+/-.



    Difference in electronegativity

    Bond character

    >1.7

    Ionic

    0.4-1.7

    Polar covalent

    ≤ 0.4

    Non-polar covalent

    Metallic Bonding

    If a molecular has polar bonds, it does not necessarily mean the molecule overall is polar as the forces may cancel each other out, depending on the molecule’s geometry. (eg. CCl4)

    Metals have low ionization energies and low electronegativities; thus, they easily lose their electrons. Because of this, in a metal, the metal atoms are positive ions packed closely together while their electrons are delocalized. This means that the electrons are free to travel from ion to ion, and spend little time with one particular ion. As such, metals are capable of conducting heat and electricity (electrons move freely), are malleable and ductile (electrons act as a cushion), and are lustrous (electrons on surface reflect photons).

    Go to this animation from virtual laboratory,  to review intramolecular bonding with animations: Intramolecular Animation