Week 3 - Intermolecular Fores

Intramolecular Forces

exists between two atoms that make up the molecule or the

formula unit of a compound.

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It is a **strong** force of attraction formed by either an ionic or covalent bond

Intermolecular Forces

Attraction is between the substance *-* molecules or formula units *(weak force of attraction)*.

Dipole-Dipole

It is a type of IMF that act between **POLAR MOLECULES**. - *Irregular amount of Valence Electrons in the Lewis Structure*

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If the structure of a molecule is such that the individual bond dipoles do not cancel one another, then it is a dipole interaction. *(Positive and Negative Attracts, it’s the Negative that will Attract the Positives)*

Hydrogen Bonding

occurs only between molecules that contain hydrogen bonded to small, highly electronegative atoms like **fluorine, nitrogen, oxygen**

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It is a special type of dipole-dipole interaction wherein hydrogen stabilizes the lewis structure or formation of elements.

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**EXAMPLES:**

HF *(has 3 valence electrons remaining)*

H2O *(has 2 VE remaining)*

NH3 *(has 1 VE remaining)*

Dispersion Forces

attractive forces between **NONPOLAR GASES** like diatomic

molecules: O2 and N2 and noble gases which can be liquefied under correct conditions of pressure and temperature

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they act not only between **nonpolar** **molecules** but also between **all** molecules. these are the **ONLY** intermolecular forces exhibited by **nonpolar molecules.**

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**It usually happens with gas elements**. *(Oxygen and Nitrogen Bond them)*

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**EXAMPLES:**

Cl2 *(made up of one element)*

*CH4* *(made of up only two elements = nonpolar)*

CO2 *(made up of 2 elements = nonpolar)*

KCl *(made up of 2 elements = nonpolar)*

separate

**How do intermolecular forces affect the properties of a substance?**

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molecules with weak IMF are easy to __________

Energy

**How do intermolecular forces affect the properties of a substance?**

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the rule of thumb is that the stronger the intermolecular forces of attraction, the more ______ is required to break those forces. *(related to Melting Point)*

Melting Point

This is the temperature at which a solid substance turns into a liquid.

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This measures at what temperature something will the substance change states of matter.

Strong

**Question about Melting Point**

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A high melting point indicates a ______ Intermolecular Force. Molecules are difficult to separate.

Boiling Point

It is the temperature at which a liquid substance turns into gas.

Separate

**Questions about Boiling Point**

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Molecules with weak IMF are easier to _________.

Strong

A high melting point indicates _____ IMF. Molecules are difficult to separate.

Viscosity

A measure of a substance’s resistance to flow.

Strong

______ IMF = Higher Viscocity

Surface Tension

A measure of the toughness of the surface of a liquid to resist increasing its surface area.

Higher

Strong IMF = ________ Surface Tension

Vapor Pressure

Pressure exerted by gas above its liquid form

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; indicates the amount of substance that transformed into gas

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; higher pressure means more gas about its liquid form.

Lesser

Stronger IMF = _______ tendency to become a gas, lower vapor pressure.

KCl

It has the highest boiling point of the elements.

H2

It has the lowest boiling point.

Weaker

Oil has _____ intermolecular forces than mayonnaise.

Higher

Salt has a _______ melting point than butter.