polarities and intermolecular forces Flashcards
Octet rule exceptions
Beryllium is stable with 4 electrons, boron is stable with 6 electrons, phosphorous has 10 electrons in its shell in PCl 5, sulfur has 12 electrons in its shell in SF6
Valence shell electron pair repulsion theory
way of predicting the shape of a molecule based on the number of bonding and lone pairs of electrons in polyatomic species
What is valence shell electron pair repulsion theory based on
Based on the fact that the electron pairs interact and repel each other due to electrostatic repulsion meaning they adopt a spatial arrangement where the electron pairs are as fair apart as possible meaning electrostatic attraction is minimised
What is polarity
Results form uneven partial charge distrubution
What does polarity result from
Results from uneven partial charge distribution between various atoms in a molecule
What atoms have partial negative charges
Atoms with more electronegativity
What atoms have a partial positive charges
Atoms that are more neutral
Electrons in a polar covalent bond
unequally shared between the 2 bonded atoms resulting in positive and negative charges
Dipole
Separation of partial charges
Polar bonds
covalent bonds which have a separation of charge, larger the difference in electronegativity between the 2 atoms the more polar the bond
Non-polar covalent bonds
forms between 2 identical atoms when the electronegativities of the 2 atoms are equal and the electrons are shared equally (electronegativity difference is 0)
Polar covalent bond
difference in electronegativities of the 2 atoms is greater than 0 but less than 2.0
When is a bond ionic
If the difference in electronegativities is 2.0+
What must occur for a molecule to be a polar
Contain one or more polar bonds, not be symmetrical
3 types of intermolecular forces
Dispersion, dipole-dipole, hydrogen bonding
Dispersion forces (4)
Exists between all molecules, Weakest intermolecular force, Only force of attraction between non-polar molecules, More significant as the molecules become larger
What makes dispersion forces
Due to the creation of temporary dipoles when the molecules come close together, Dipoles form from uneven spread or dispersion of the constantly moving electrons, induced on one molecule by the other by forcing the electrons to the other side of the molecule, Dispersion forces result from the opposite charges attracting each other
Dipoles
in polar molecules where the electron arrangement which causes one end of the molecules to be positively charged whilst the other end is negatively charged
Dipole-Dipole interactions (forces)
Attraction between oppositely charged regions of different polar molecules, Stronger than dispersion forces, Significant intermolecular forces for small molecules
Hydrogen bond
Extreme form of dipole-dipole attraction occurring in polar molecules, Strongest intermolecular force as the hydrogen is attracted to the most electronegative atoms (N,O,F)
Strength of intermolecular forces
Hydrogen bonding > dipole-dipole > dispersion forces
Comparing substances with the same intermolecular forces
Substance with the largest molecular mass/longest chain has higher melting/boiling point as it has a greater No of electrons
Solubility
Measure of the ability for a solute to dissolve in a solvent at a given temperature, determined by knowing the type of binding that exists in both the solvent and solute, Depends on the strength of the attraction between the particles
Solubility when substances have a similar type of bonding
solute will dissolve, polar solvents dissolve in a polar solute (like dissolves like)