Chemistry Chemical Bonding: Polarity & Intermolecular Forces (IMF)

Polar covalent

• share electrons unequally

• typically, liquids at room temperature

• low melting points

• low boiling points

• soluble in water

nonpolar covalent

• share electrons equally

• gases at room temperature, some liquids and soft solids

• volatile (evaporates easily) gases

• very low melting points

• very low boiling points

• insoluble in water

• diatomic molecules

polar

If the covalent bond between the atoms has a large difference (uneven sharing) in electronegativity the bond is _________. A dipole is created.

dipole

A separation of opposite charges that are on either end of a bond or molecule. 

nonpolar

If the covalent bond has little or no electronegativity difference (even in sharing) the bond is _________. No dipole.

polar covalent molecule (electrons are not shared equally)

• one end of the molecule is slightly negative and the other slightly positive

• two different elements surrounding central atom OR unshared (lone) pair of e- around center

non-polar covalent molecule (electrons shared equally)

• diatomic molecules are always non-polar

• only one type of element surrounds central atom AND no unshared pair of e- around center

ionic bonds, covalent bonds, metallic bonds

Name the 3 types of intramolecular forces from strongest to weakest.

hydrogen bonding, dipole-dipole forces, London dispersion forces

Name the 3 types of intermolecular forces from strongest to weakest.

intramolecular forces

• bonds between atoms inside a molecule

• ex: ionic bonding, covalent bonding, metallic bonding

• in forming these bonds, atoms will attain noble gas configurations (full valence shell), a lower energy state and greater stability

stronger

Are intramolecular forces stronger or weaker than intermolecular forces?

intermolecular forces

• bonds formed between molecules

• these forces hold solid and liquid states together

hydrogen bonding (strongest), dipole-dipole forces, London dispersion forces (weakest)

What are the types of intermolecular forces in polar molecules?

London dispersion forces (weakest) (ex: diatomic molecules, carbon dioxide)

What is the only type of intermolecular forces in non-polar molecules?

hydrogen bonding

• strongest type of intermolecular force

• compounds have higher boiling points compared to other IMF

• occurs between polar covalent molecules

• occurs between hydrogen and (nitrogen, oxygen, and fluorine)

• bonding is due to large electronegativity difference

boiling points

are a good indicator of intermolecular strength in hydrogen bonding

gas phase

During boiling, the particles pull away from one another and enter a ________.

higher

The _________ the boiling point, the stronger the forces of attraction.

viscous

Hydrogen bonding substances are more ________ substances. The liquids typically are thicker to pour.

surface tension

Hydrogen bonding substances have high ________ _________. An inward pull that minimizes the surface area of a liquid.

dipole-dipole forces

• only polar (unequal sharing) covalent molecules have the ability to form this type of IMF attraction between molecules

• polar covalent molecules act as little magnets, they have positive ends and negative ends which attract each other

• the greater the difference in electronegativity the greater the dipole (bond that has a separation of charges)

London dispersion forces

• the only types of forces that non-polar covalent molecules can form

• these forces result from the movement of electrons, which generate a temporary positive and negative regions in the molecules

• these forces exist in all substances

• these are the only forces between noble gases and diatomic molecules

London dispersion forces

What are the weakest forces?