Electrons Bonding & Structure

Last Minute Revsion For Module 2

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Electrons, Bonding & Structure
Electron Structure
S sub-shell = 2 electrons P sub-shell = 6 electrons D sub-shell = 10 electrons F sub-shell = 14 electrons
Orbital = space an electron moves in. S orbitals are spherical. P orbitals are dumbbell shaped.
Rule 1: 4s before 3d (write normal in notations). Rule 2: Fill single before sharing.
Ionisation Energy (I.E)
First ionisation energy: The energy required to remove 1 electron from each atom in 1 mole of gaseous atoms to form 1
mole of gaseous 1+ ions.
Successive ionisation energy: The energy required to remove each subsequent electron from each ion in 1 mole of
positively charged gaseous ions.
Factors affecting ionisation energy
o Nuclear charge ­ The more protons, more positively charged, stronger attraction on the electrons.
o Distance from the nucleus ­ Attraction falls rapidly with distance, less pull from the nucleus than inner shells.
o Shielding ­ Electrons feel less pull due to the inner shells attraction to the +ve nucleus.
First I.E ­ O(g) O+(g) + e- Second I.E ­ O+(g) O²+(g) + e- Third I.E ­ O²+(g) O³+(g) + e-
Ionic Bonding
Definition: An electrostatic attraction between oppositely charged ions.
Nitrate: NO- Carbonate: CO²- Sulfate: SO²- Ammonium: NH+
Behaviour of ionic compounds
o Electrical conductivity ­ Only when molten or dissolved. Ions in liquid are free to move (and can carry a charge).
Cannot when solid because ions are fixed in position by strong ionic bonds.
o Melting & boiling points ­ High because giant lattices are held together by strong electrostatic forces. Requires
loads of energy to overcome.
o Solubility ­ Tend to dissolve in water. Water molecules are polar so pull ions away from the lattice.
Covalent Bonding
Definition: A shared pair of electrons.
Special case ­ (Boron trifluoride with 6 outer electrons (BF)) (Sulphur hexafluoride with 12 outer electrons (SF))
Dative covalent bonding: One atoms provides both shared electrons (also called coordinate bonding)
Behaviour of simple covalent compounds
o Electrical conductivity ­ Doesn't conduct electricity as there are no free ions or electrons to carry the charge.
o Melting & boiling points ­ Low due to weak forces of attraction between molecules, easily over come.
o Solubility ­ Some, depending how polarised the molecules are.
Graphite ­ Flat hexagonal sheets, 4th election is delocalised, sheets held by weak van der Waals forces.
o Can slide over each other due to weak bonds between layers, great dry lubricant (e.g. pencils).
o Can carry an electrical current because of the delocalised electrons.
o Low density & strong used for lightweight sports equipment. This is due to layers being far apart.
o Very high melting point.
o Insoluble in any solvent, covalent bonds are too hard to break.
Diamond ­ Tetrahedral (crystal lattice), 4 covalent bonds.
o Very high melting point.
o Extremely hard ­ used in diamond-tripped drills and saws.
o Vibrations travel easily through the stiff lattice, good thermal conductor.
o Doesn't conduct electricity.
o Won't dissolve in any solvent.
Shapes of Molecules

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Calculating the number of electron pairs:
o Find the central atom and work out the number of outer electrons.
o Find the number of atoms bonded to the central atom.
o Add up the electrons and divide by 2.
o Work out the number of lone pairs.
Electronegativity is the ability of an atom to attract the bonding electron in a covalent
Diatomic gases are non-polar because the atoms have equal electronegativities. Some
elements e.g.…read more


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