INTERMOLECULAR FORCES - Sutherland High School- Robyn Harrison Doc Scientia Grade 11 2018

Interatomic forces Ionic Bonding Metallic Bonding Covalent Bonding 01 Positive ion cores are bound together by a sea of delocalized electrons. : For atoms to forms a compound, one of the following types of bonds must be formed 02 Ionic Bonding Atoms transfer electrons and form positively and negatively charged ions. These oppositely charged ions attract each other with electrostatic forces. 03 Covalent Bonding Electrons of different atoms are shared, and a molecule is formed. TB. pg. 51 & 58

TB. pg. 52 Forces between molecules are called intermolecular forces. In a liquid or solid state, there must be forces between the particles that will hold the particles together. If there were no such forces, the molecules would move apart and become a gas. Ionic and metallic bonds are strong. The intermolecular forces between small covalent molecules is what we will be focusing on. TB. pg. 52 Free PowerPoint Templates

TB. pg. 56 Let’s clarify first: POLAR MOLECULES This is where one side of the molecule has a slightly positive charge and the other side has a slightly negative charge. HOW DOES THIS HAPPEN? When one atom is more electronegative than the other. So it tends to pull a shared pair of electrons more than the other. TB. pg. 56 Free PowerPoint Templates

Types of Intermolecular forces TB. pg. 52 Free PowerPoint Templates

1. Ion-dipole forces TB. pg. 53 Occurs when a dipole approaches a positive or negative ion. The dipole will move so that the side closest to the ion has the opposite charge. When salt is dissolved in water – ions become “hydrated.” ??? 𝑁 𝑎 + 𝑎𝑞 means the 𝑁 𝑎 + ion is hydrated. TB. pg. 53 Free PowerPoint Templates

Ion-induced dipole forces 2. Ion-induced dipole forces This is when an ion affects the electron cloud around an atom or molecule when it is nearby, causing a temporary dipole. Atom with no dipole. Ion responds and the atom develops a dipole. TB. pg. 54 Free PowerPoint Templates

3. Dipole- dipole forces TB. pg. 55 These are attraction forces between the slightly positive pole of one atom in the polar molecule and the slightly negative pole of the other atom in a polar molecule. TB. pg. 55 Free PowerPoint Templates

Dipole-induced forces 4. Dipole-induced forces A polar molecule (permanent dipole) can induce a temporary dipole in a non-polar molecule or atom. This results in an attractive force between the two oppositely charged dipoles. Very weak force. TB. pg. 56 Free PowerPoint Templates

Induced-dipole forces 5. Induced-dipole forces (Dispersed or London forces) When two non-polar molecules or atoms approach each other, there is a slight change in the charge distribution in the electron cloud of both molecules or atoms. The electrons will not be exactly equally arranged around the atom/molecule. These are temporary and will disappear and reform between other particles in different directions. TB. pg. 56 Free PowerPoint Templates

6. Hydrogen Bonds These occur between molecules in which hydrogen is bonded to a small atom with an extremely high electronegativity, as in compounds with oxygen, nitrogen and fluorine. This bond is an electrostatic force between a slightly negative charge on the electronegative atom of one of the molecules and the slightly positive charge on the hydrogen of one of the other molecules. TB. pg. 57 Free PowerPoint Templates

Watch me carefully!!! TB. pg. 57

LIQUID MERCURY!!!!

SODIUM!!!!

MAGNESIUM!

Homework Exercise 5 TB. pg. 59-60

Intermolecular forces influence: State Size Density Boling and Melting points Viscosity Thermal Expansion Thermal Conductors TB. pg. 61 Free PowerPoint Templates

1. State of molecules Solids –strong intermolecular forces. Liquids – weaker Gases - weakest TB. pg. 61 Free PowerPoint Templates

2. Size of molecules Larger molecules – greater tendency towards polarity. More electrons and greater distance over which it can move. Greater molecular mass – greater intermolecular force. E.g. Petrol 𝐶 8 𝐻 18 (liquid) has weaker intermolecular forces than wax 𝐶 23 𝐻 48 (solid). Why? TB. pg. 61 Free PowerPoint Templates

3. Density of molecules Density is the number of particles per unit volume. Higher density – stronger intermolecular forces. Low density Low IMF High density High IMF TB. pg. 62 Free PowerPoint Templates

Waters density decreases when it freezes… EXCEPT WATER!!!! Waters density decreases when it freezes… TB. pg. 62

Boiling and Melting Point 4. Boiling and Melting Point Stronger forces – more energy is needed to overcome forces – higher melting and boiling points. Why so high??? TB. pg. 62 Free PowerPoint Templates

5. Viscosity This is an indication of a liquid’s resistance to flow. Higher the intermolecular forces – higher viscosity. Increase temperature – decrease viscosity as intermolecular forces decrease. TB. pg. 63 Free PowerPoint Templates

6. Thermal expansion This means that the material expands on heating. More energy – IMF weaken – particles move further apart – volume increases. (expands). TB. pg. 66 Free PowerPoint Templates

7. Thermal conductors Covalent structures and molecules (non-metals) are bad conductors as there are no free electrons. Exceptions: diamond, graphite. Metallic bonds (metals) are good thermal conductors as the delocalized electrons are free to move. TB. pg. 66 Free PowerPoint Templates

READ THE EXPERIMENTS…. This is your practical for Term 2. eh..

Homework Exercise 6 TB. pg. 73-75

Chemistry of Water Microscopic Structure of Water O H H Polar Molecule Angular / Bent shape Polar Molecule 𝛿 − O Greenhouse Gas The polar characteristic of water allows it to absorb infrared radiation from the sun. This way, the ocean acts as a heat reservoir and keeps the earth’s climate moderate. Strong intermolecular forces (WHY) H H 𝛿 + 𝛿 + TB. pg. 75-76 Free PowerPoint Templates

Specific Heat Capacity 1. Properties of Water Specific Heat Capacity This is the amount of energy necessary to change the temperature of 1kg of a substance by 1ºC. When a substance changes state, energy is absorbed or released. However, the temperature does not change. This is called “latent heat or latent energy.” Water has a high specific heat capacity (why) and also a high latent energy. Waters specific heat capacity is responsible for: Moderate climate change. Regulates body temperature. Temperature. TB. pg. 77 Free PowerPoint Templates

Melting and Boiling Point 2. Melting and Boiling Point Melting point: 0ºC and Boiling Point: 100ºC. These temperatures are higher than expected. Because of the strong hydrogen bonds – a lot of energy is needed to overcome the IMF. They must be this high – otherwise most of our water would be in a gaseous state. TB. pg. 78 Free PowerPoint Templates

Density of water and ice 3. Density of water and ice As liquid water cools, its density increases until it reaches a maximum at about 4ºC. As it continues to cool, the water expands and the density decreases. The reason for this is that the molecules form strong hydrogen bonds with three other water molecules to form the open hexagonal structure. Ice layers on top of frozen lakes – insulating layer – organisms can still live in the water below. TB. pg. 78 Free PowerPoint Templates

4. Adhesion and Cohesion TB. pg. 78 Cohesive forces – Forces between the same type of molecules. (Water and water) Adhesive force – Forces between two different types of molecules. (water and glass) TB. pg. 78 Free PowerPoint Templates

5. Surface Tension This is due to the cohesive forces of molecules on the surface of a volume of water. Every water molecule is attracted to every other water molecule. Top layer has air molecules above them. Adhesive force between water and air is weaker than the cohesive forces between water. Net force causes a tension force on the top layer. Allows very light objects to rest on the surface, TB. pg. 79 Free PowerPoint Templates

6. Capillary Action The tendency of a liquid to rise in a tube as a result of surface tension and is a result of adhesive properties of water molecules. Straw – water molecules are attracted to the molecules of the straw. TB. pg. 79 Free PowerPoint Templates

A single drop of sea water under a microscope

Homework Exercise 7 TB. pg. 83-84