Bonding Flashcards
Define the metallic bond
The attraction between positive metal ions and delocalised electrons
Define ionic bonding
The electrostatic attraction between oppositely charged ions.
Boron
Does not form ions
A covalent bond is
A shared pair of electrons
Non-Octet molecules do not have
A full outer shell
A coordinate bond is
A covalent bond in which both electrons of the shared pair come from the same atom. They can be shown using an arrow.
-The atom that donates the e- had a lone pair.
-The atom that accepts the e- does not have a full outer shell so it is electron deficient.
How to work out # of e- pairs in a molecule
(Group # of central atom + #of bonded atoms - charge) / 2
Then the # of lp can be calculated using the formula:
#e- pairs - #Bonded atoms
Shapes of molecules with no lone pairs
2 bp & 0 lp = Linear - 180 degrees
3 bp & 0 lp = Trigonal planar/Trigonal bonds - 120 degrees
4 bp & 0 lp = Tetrahedral - 109.5 degrees
5 bp & 0 lp = Trigonal bypyramid - 120 and 90 degrees
6 bp & 0 lp = Octahedral - 90 degrees
Shapes of molecules with lone pairs
2 bp & 1 lp = V-shaped - 117.5 degrees
3 bp & 1 lp = Pyramidal - 107 degrees
2 bp & 2 lp = V-shaped - 104.5
3 bp & 2 lp = Trigonal planar - 120 degrees
4 bp & 2 lp = square planar - 90 degrees
Electronegativity is
The power of an atom to attract the pair of electrons in a covalent bond.
-it increases across a period and decreases down a group.
Distinguish between polar and non-polar bonds
Non-polar covalent bond - no or very small difference in electronegativity.
Polar covalent bond - a significant difference in electronegativity.
-A bond is polar when N, O, F, Cl, Br and Iodine atoms bond to a different atom.
Polar molecules
A molecule is non-polar if its symmetrical as the bond dipoles cancel.
A molecule is polar if it’s asymmetrical as the bond dipoles do not cancel - molecules with lone pairs are often but not always asymmetric.
Intermolecular forces: VDW
Van der Waals’ forces arise from the movement of electrons, creating a temporary dipole in 1 molecule. This temporary dipole induces a dipole in a neighbouring molecule and these dipoles attract. VDW forces strength depends on the number of electrons in a molecule.
Intermolecular forces: Permanent dipole-dipole forces
These occur between polar molecules and occur in addition to VDW forces.
The S+ end of 1 molecule attracted to the S- end of a neighbouring molecule (one has to be below the other).
Intermolecular forces: hydrogen bonds
Occurs between molecules which contain a hydrogen atom bonded to either F, O or N.
Hydrogen bonds are formed between a S+ Hydrogen atom in one molecule and a lone pair of electrons on a O, N or F in a neighbouring molecule.
When drawing hydrogen bonds you must show
-2 molecules
-All lone lairs
-Partial charges
-The correct alignment of atoms
