1. 2.7 – Intermolecular &Intramolecular Forces

2. The difference between the prefixes
Inter – between
Intermolecular forces are forces between different molecules
Intra – inside
Intramolecular forces are forces within a molecule
Intramolecular forces keep a molecule together
We usually talk about these as types of bonding

3. Intermolecular forces
Inter – between
Intermolecular forces are forces between different molecules
Intermolecular forces are weaker than intramolecular forces
We will look at 4 different intermolecular forces
Ion-Dipole
Dipole-Dipole
Hydrogen Bonding
London (dispersion) Forces

4. Ion-dipole Forces
An attraction between a polar molecule (a dipole) and an ion
The greater the charge, the greater the interaction
Negative ions attract the partial positive of the polar molecule
Vice versa for positive ions
These are very strong interactions
Example
When Na+ is in water (a polar molecule) it experiences ion-dipole forces

5. Dipole-Dipole A permanent attraction of polar molecules to each other
The partial positive pole will be attracted to the partial negative pole
Example
Iodine monochloride, the partially negative chlorine is attracted to the partially positive iodine

6. Hydrogen Bonding
Hydrogen bonding is a special dipole-dipole interaction
This happens when hydrogens are bonded to very electronegative elements
F, O, Cl or N
H-bonds are very strong intermolecular forces

7. London Forces
London forces, sometimes called Dispersion forces, are weak forces that exist in ALL compounds
London forces are the weakest intermolecular force
London forces happen for only an instant in a molecule
The larger the molecule or the more surface area, the greater this force acts

8. London Forces
At any moment, electrons around a compound may be localized in a single area
This creates an instantaneous dipole
This will cause a dipole by pushing/pulling electrons to create a brief induced-dipole
London forces are the only force a non- polar molecule experiences
All of the properties of non-polar materials come from the amount of London Forces they experience

9. Intermolecular Forces
Below is a list of intermolecular forces by strength
Ion-Dipole
H-bonding
Dipole-Dipole
London Forces
The forces a molecule experiences determine the properties of that material

10. Examples What IMF’s will the following elements experience? POCl3 HNO
Na+ and Water

11. Intramolecular Forces
We will look at several types of intramolecular forces
Ionic Bonding
Covalent Bonding
Non-Polar Covalent Bonding
Polar Covalent Bonding
Metallic Bonding

12. Ionic Bonding
An ionic bond is formed if 2 elements with an electronegativity difference greater than 1.7 come together
This causes a complete transfer of electrons
The opposite charges attract forming an extremely strong bond between the ions formed
The easiest way to think about it is 1 metal and 1 non-metal

13. Ionic Bonding
Ionic compounds fit into a crystal structure to attract to each other in the most efficient way
These structures are different depending on what ions are in the compound

14. Intramolecular Forces
This crystal lattice give ionic compounds their properties:
Crystals are formed in regular shapes based on the shape of the crystal lattice (a square lattice makes a square crystal, etc)
Break easily and when broken, crystals break along specific lines
Brittle and fracture is specific patterns
They do not form liquids easily as the ions do not want to ‘slide past’ each other
High melting and boiling points
The charges allow easy dissolving in water
Soluble in polar compounds
Can have electrical properties because of charges

15. Covalent Compound Covalent compounds are when 2 atoms share electrons
Co – together/share
Valence – outer orbital
Covalent – share the outer orbital
There are no ions in a covalent compound
Covalent compounds always have 2 non-metals

16. Non-polar Covalent Bond
With an electronegativity difference less than 0.5 a non-polar covalent bond is formed
Non-Polar Covalent Bond – An equal sharing of electrons
Electrons are distributed totally even around each atom

17. Polar Covalent Bond
An electronegativity difference of creates a polar covalent bond
Polar Covalent Bond – UNEQUAL sharing of electrons.
The more electronegative element has more electrons around it
More electrons makes that side of the bond partially negative
The less electronegative element is partially positive

18. Ionic vs. Non-Polar Covalent vs. polar Covalent
NOTE – WE COVERED THIS SLIDE YESTERDAY, NO NEED TO RE-COPY!
Ionic vs. Non-Polar Covalent vs. polar Covalent

19. Covalent Compound Properties
Covalent compounds have varying properties
In general:
Low melting points and boiling points
Molecules are only held together by weak attractions so they can break away from each other easily
Usually soft or brittle as solids
Weak forces between molecules makes them easy to break or deform as solids
Poor electrical and thermal conductors
No charges and molecules are typically not close together

20. Metallic Bonding Metals bond by arranging in an array of atoms
The valence orbitals of all the atoms then touch and overlap
This allows valence electrons to move freely from atom to atom
This is called delocalized electrons
They do not have a central location to stay at

21. Metallic Bonding
Because of metallic bonding and delocalized electrons, metals behave differently
A small voltage (energy for electrons) easily causes them to move from atom to atom in a single direction (current)
High conductivity
Metals have good thermal conductivity as the atoms are arranged close together
Metals are not held together with rigid overlap
flexible and bendable
Malleable (can be flattened into a sheet) and ductile (can be made into a wire)
LOTS of orbital overlap
Metals have high melting and boiling points