GEN CHEM 1 | Polarity and Intermolecular Forces of Attraction

Electronegativity

ability or tendency of an atom to attract electrons and thus form bonds.

Electronegativity Trends

an element’s electronegativity increases from left to right and bottom to top of the periodic table

Nonpolar Covalent Bond

there is equal sharing of electrons between atoms; electronegativity difference is less than 0.5

Polar Covalent Bond

there is unequal sharing of electrons between atoms; electronegativity difference is from 0.5 and 1.9

Ionic Bond

has an electronegativity difference of 2.0 or greater

Partial Charge

occurs in polar covalent bonds; the more electronegative atom has a negative partial charge while the less electronegative atom has a positive partial charge

Polar Substances

happens when there is a net dipole moment, where one end is more negatively charged than the other

Molecular Dipole

the vector sum of all the bond dipoles present in the molecule

Dipole Moment

It occurs when there is a separation of charges and acts in the direction of the vector quantity, which is towards more electromagnetic atom. It increases as the electronegativity difference increases.

Nonpolar Substances

when there is no net dipole moment or it is equal to zero, occurs when all bonds are nonpolar or all of the polar bonds cancel each other out

How to determine the polarity of molecules

1. Draw the shape of the molecule based on the VSEPR Theory.

2. Determine if each of the bonds with the main atom are polar or nonpolar.

3. For polar bonds, draw the direction of the dipole moment with arrows. Write + for the less electronegative atom and - for the more electronegative atom.

4. Point arrow heads at the more electronegative atom

5. Combine the dipole moment of the entire molecule, dipole moments with opposite direction on the same axis will cancel out.

6. If the total dipole moment is zero, its nonpolar. Otherwise, it is polar.

Intermolecular Forces

forces of attraction or repulsion which act between neighboring particles; affecting a substance’s various properties

Intramolecular Forces

forces of attraction that occur within the molecule

London Dispersion

the weakest intermolecular force as it happens when amidst the constant movement of electrons, there is a momentary unequal electron distribution; happens in all molecules

Dipole-dipole

only occurring in polar molecules, they are attractive forces between the positive region of one polar molecule and the negative region of another

Hydrogen bonding

Only occuring in H-N, H-O, and H-F molecules, the bonds’ high electronegativity difference form strong dipole-dipole attractions; happens between the partially positive H atom of one molecule and the partially negative F, O, or N atom of another

Ion-dipole Forces

occurs between an ion and polar molecule