1. Fluorine has seven electrons in its outermost shell (s and p orbitals). The addition of a single extra electron to form the F− anion will bring the configuration to a 'full octet', and this is energetically favourable. Potassium has a lone 3s electron in its outermost shell. The loss of this electron to form the K+ cation is energetically favourable, as it leaves the atom with the stable 'noble gas' octet of argon.
  2. Fe: 1s2 2s2 2p6 3s2 3p6 4s2 3d6
  3. KClO3: K is always +1, O is always −2, the total charge is zero, hence Cl has an oxidation number, x, satisfying 1 + ( 3 × −2 ) + x = 0, i.e. 5. This is potassium chlorate(V).

  4. Name

    Formula

    Type of bond

    Number of σ

    Number of π

    Ethane

    H3C-CH3

    Single

    1

    0

    Propyne

    H3C-C≡CH

    Triple

    1

    2

    But-1-ene

    H3C-CH2-HC=CH2

    Double

    1

    1

    Propan-1-ol

    H3C-H2C-CH2OH

    Single

    1

    0

    Ethanenitrile

    H3C-C≡N

    Triple

    1

    2
  5. The bond order for Ne2 is zero. This is for the same reason as helium: the number of electrons in bonding and antibonding orbitals is the same: (σ1s)2(σ1s*)2(σ 2s)2(σ2s*)2(σ 2px) 2(π2py)4(π2py*) 4(σ 2px*)2.
  6. Although hydrogen bonds are relatively weak compared to covalent or ionic bonds, in large numbers, they can be very significant. Proteins and nucleic acids are full of oxygen and nitrogen, which may act as acceptors for hydrogen bonds, and indeed, this is the main determinant of the secondary, tertiary and quaternary structure of these macromolecules.