• Electronegativity depends on
  (1) Nuclear charge
  (2) The distance between the nucleus and the outer shell electrons
  (3) The shielding of the nuclear charge by electrons in the inner shells
• The smaller the atom, the closer outer electrons are to the nucleus.
• The most electronegative atoms are found at the top right of the periodic table.
• The most electronegative atoms are: fluorine, oxygen and nitrogen followed by chlorine.

• Electron density is often used to describe the way in which the negative charge is distributed in a molecule.

• The Pauling scale is used to measure electronegativity > running from 0 to 4.

• Noble gases have no number because they form covalent bonds.

• Polarity is the unequal sharing of the electrons between atoms that are bonded covalently.

• If a covalent bond with two atoms of different electronegativity, the electrons will not be shared equally.
• E.g. Hydrogen has an electronegativity of 2.1 and fluorine of 4.0.

Do you still remember the intermolecular forces acting between molecules in AS/A-level Chemistry?

Intermolecular forces

1. Dipole - dipole forces: Acting only between certain types of molecules
2. Van der Waals forces (strongest): Acting between all atoms and molecules
3. Hydrogen bonding (weakest): Acting only between certain types of molecules

• Carbon dioxide is linear and the dipoles cancel out.
• The way in which some dipole moments cancel out is through the shape of the molecule.

• Weak electrostatic attractions between all atoms and molecules.
• Electrons are constantly moving therefore the distribution of the charge is changing at every instant.
• The dipole may be in a different direction.
• Distribution effects nearby atoms.
• They are in addition to other intermolecular forces.
• Size of the van der Waals forces increases with the number of electrons present.
• The boiling points of noble gases increase with atomic mass/ numbers.
• The boiling points of hydrocarbons increase with increased chain length.

• Intermolecular force with characteristics of a dipole – dipole attraction (d-d attractions) and some of a covalent bond.
• A hydrogen atom is in between two electronegative atoms.
• A very electronegative atom with a lone pair of electrons covalently bonded to a hydrogen atom.
• Hydrogen atoms are highly electron deficient – oxygen is very electronegative and attracts shared electrons towards itself.
• Exposed protons have a very strong electric field due to their small size.
• Stronger than d-d attractions but weaker than covalent bonds.
• The only atoms that can form hydrogen bonds are oxygen, nitrogen and fluorine.
• Noble gases show a gradual increase in boiling point because the only forces acting between the atoms are the van der Waals forces and these increase with the number of electrons present.
• Boiling point of H20, HF and ammonia are higher than the hydrides because of the other elements in their group.

References:

1. https://www.chemistrylearner.com/

That's the end of the topic!

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