intermolecular forces

Define intermolecular force.

forces that occur occur between molecules

Define intramolecular force.

forces that occur within molecules

What do intermolecular forces determine?

physical properties

What do intramolecular forces determine?

chemical properties - how the compound reacts

Why do some substances have low melting and boiling points?

• substances have low melting and boiling point due to the fact that their intermolecular forces are weak and require very little heat energy to break them.

Why do covalent molecules require high temperatures to decompose?

covalent bond force within the molecule is strong its require high temperature to break/ decompose them.

What are induced dipole-dipole interactions?

• weakest type of intermolecular bond

• between molecules, eg H2

Can non-polar molecules form dipoles?

• can form temporary dipoles

how do temporary dipoles form in non- polar molecules?

• Electrons are in constant motion around nuclei,

• sometimes they become unevenly distributed on one side of the molecule, creating a temporary dipole

What happens when a temporary dipole forms in one molecule?

It induces a dipole in a neighbouring molecule shifting toward the partial positive side.

What is dipole-dipole forces?

• still weak

• creates permanent dipole-dipole forces

How do dipole-dipole interactions work?

• polar molecule has dipole

• one end positive, one end negative .

• These molecules arrange themselves so that negative region is close to the positive region, creating attraction

What is hydrogen bonding?

• strongest of the intermolecular forces

• happens between molecules that contain hydrogen and atoms bounded to fluorine, oxygen and nitrogen ( atoms with high electronegativity and lone pairs)

What happens to boiling point as intermolecular forces increase?

boiling point increases

What boiling point trend can be seen down group 4 hydrides?

increases in boiling point down the group

Why is group 4 trend broken in group 5,6 and 7?

• because they form hydrogen bonds raising their boiling points usually high

• this increases boiling point as hydrogen bonds strengthens intermolecular forces