Physics in Everyday Life. The Washing Up and the Laundry. Molecules. Structure of the Atom 30/09/2013. Atom: Basic Building Block of Chemistry

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Superior Mirage, Svalbard, Northern Norway, June 2013 Physics in Everyday Life Physics in the Home 1: Washing-up,

with why we use detergent in the bowl, dish washer and washing machine when we wash things To show how this works,

nucleus in black is composed of protons and neutrons The electrons orbit around the nucleus This is the Rutherford

it orbiting Structure of the Atom The shapes of the orbitals are much more complicated than the simple picture These

Because of the Uncertainty Principle, we can never determine the exact position of the electron Molecules Collection

1 Superior Mirage, Svalbard, Northern Norway, June 2013 Physics in Everyday Life Physics in the Home 1: Washing-up, Temperature and Microwaves Andrew Robinson Photo: Pamela and Jamey Burr The Washing Up and the Laundry We ll start with why we use detergent in the bowl, dish washer and washing machine when we wash things To show how this works, first we need to look at the nature of matter (the building blocks) Atom: Basic Building Block of Chemistry The nucleus in black is composed of protons and neutrons The electrons orbit around the nucleus This is the Rutherford Model: the electrons do not actually follow circular orbitals, but they do move around the nucleus, so we still call it orbiting Structure of the Atom The shapes of the orbitals are much more complicated than the simple picture These shapes represent high probabilities of find the electron somewhere within the shape. Because of the Uncertainty Principle, we can never determine the exact position of the electron Molecules Collection of atoms Bonded together The chemical bond is an exchange or sharing of electrons Water molecule H 2 O Oxygen gas O 2 Nitrogen gas N 2 Carbon Dioxide CO 2 1

Protons and Neutrons Electrons Protons and neutrons are about the same mass, and they cluster together in the nucleus.

It is more mobile and can leave the atom, or be shared by neighbouring atoms.

chlorine This is called an ionic bond Ionic bonds tend to be broken up in water salt dissolves Gypsum crystals in the Cueva de los Cristales (Cave of the Crystals), Naica, Chihuahua, Mexico Gypsum:

2 Protons and Neutrons Electrons Protons and neutrons are about the same mass, and they cluster together in the nucleus. The proton has a property known as positive electric charge The neutron has no charge The electron has a much lower mass than the proton ( 1/2000th as much) and orbits at a distance from the nucleus. It is more mobile and can leave the atom, or be shared by neighbouring atoms. This bonds the two atoms together with a chemical bond + We often represent a proton with a + sign Crystals Table Salt Sodium Chloride An electron is transferred from the sodium completely to the chlorine This is called an ionic bond Ionic bonds tend to be broken up in water salt dissolves Gypsum crystals in the Cueva de los Cristales (Cave of the Crystals), Naica, Chihuahua, Mexico Gypsum: Calcium sulphate dihydrate Chemical formula CaSO 4 2H 2 O. Amorphous Materials: Glass Glass has the formula SiO 2 (Silicon Dioxide) The crystal structure is not regular Hydrocarbons Molecules made of hydrogen and carbon. The hydrogen and carbon share their electrons in covalent bonds. Hydrocarbons with additional atoms like oxygen or sulphur (sulfur!) in them are generally known as organic molecules 2

Octane Octane is an additive put in fuel to help give more efficient combustion.

Each of these isomers is a different chemical, with different properties n-octane n signifies normal the linear chain 24 Isomers of Octane!

bonds. These are due to electric attraction and repulsion between atoms.

3 Octane Octane is an additive put in fuel to help give more efficient combustion. It has a chemical formula of C 4 H 8 Four carbon and eight hydrogen atoms The carbons are arranged in a chain There are lots of ways of arranging 4 carbons and 8 hydrogen atoms. Each of these isomers is a different chemical, with different properties n-octane n signifies normal the linear chain 24 Isomers of Octane! Also represented as a ball and stick model, to give more information about the structure Weaker Bonds Between Atoms and Molecules Water There are other bonds, which are much weaker than chemical bonds. These are due to electric attraction and repulsion between atoms. Chemists call them Van der Waals forces Carbon Monoxide CO δ+ C δ- O Slightly positive δ+ C δ- Slightly negative O The water molecule has a strong charge distribution It is a strongly polarised molecule The space filled model δ+ δ- δ+ Since water is highly polarised, it tries to organise itself to maximize attraction between molecules Surface Tension The strong electrical interactions between water molecules gives a high surface tension effect Liquid Water random ordering (almost) Ice: Solid Water highly ordered crystals 3

At the surface, there is a strong sideways interaction between the water molecules, and this provides the

Water Strider Hydrophilic Molecules and Surfaces Water, as a polar solvent, dissolves other things which

Molecules which dissolve well in water are called hydrophilic Surfaces of objects which attract water are

water, such as most oils (hydrocarbons) are called hydrophobic Surfaces which repel water are called

Oil and water do not mix the oil is hydrophobic! Red wine (with extra red dye!

4 At the surface, there is a strong sideways interaction between the water molecules, and this provides the surface tension force Supported by surface tension think of the surface of the water as a rubber sheet Water Strider Hydrophilic Molecules and Surfaces Water, as a polar solvent, dissolves other things which are also polar, such as salt (NaCl), or sugars. Molecules which dissolve well in water are called hydrophilic Surfaces of objects which attract water are called hydrophilic surfaces Hydrophobic Molecules and Surfaces Molecules which do not dissolve well in water, such as most oils (hydrocarbons) are called hydrophobic Surfaces which repel water are called hydrophobic Waterproof clothing prevents the water from spreading on the surface (hydrophobic) Olive oil Oil and water do not mix the oil is hydrophobic! Red wine (with extra red dye!) Detergent Molecules Soaps and detergents are designed so that the molecules have hydrophobic parts and hydrophilic parts Washing up liquid (dish soap) Maple syrup Hydrophobic tail Hydrophilic head 4

5 The detergent molecules tend to lower the effect of the strong water to water interactions (because they get in the way!) This lowers surface tension The detergent molecule can also remove grease/oil The hydrophilic heads of the detergent pull the grease off the surface grease The hydrophobic tails of the soap molecule can dissolve in the grease, but not in the water When the grease/oil comes off the surface, it is surrounded by detergent molecules in a large droplet called a micelle Surface Tension and Water Water wants to arrange itself with a minimum surface area This minimizes the number of molecules at the surface and maximizes the number which are completely surrounded by other water molecules. The natural shape for this is a sphere (cutting a water drop video Droplets Spreading Dew Drop Total Wetting Water Spreads out over whole surface Almost no wetting Partial Wetting Hydrophilic Surface Hydrophobic Surface (Greasy or oily) No Wetting 5

Water on glass partial wetting This glass surface is mixed hydrophilic and hydrophobic (so it s dirty!

Temperature and Energy We use temperature in the home all the time Air conditioning Heating Cooking Air temperature outside But what is temperature?

vibrating solid http://www.youtube.com/watch?

energy of vibration, so all molecular and atomic motion stops.

6 Water on glass partial wetting This glass surface is mixed hydrophilic and hydrophobic (so it s dirty!) Take a Break Bakewell Bridge, Derbyshire, England What is Temperature? Temperature and Energy We use temperature in the home all the time Air conditioning Heating Cooking Air temperature outside But what is temperature? Temperature is a number on a scale It is a measure of the average vibrational and rotational energy of molecules or atoms Vibrating water molecules Video of vibrating solid Temperature Scales The most fundamental scale is know as the Kelvin Scale (K) Absolute zero (0 K) is the temperature at which there is no energy of vibration, so all molecular and atomic motion stops. This is important in the sciences, but does not give a very useful scale for everyday use (since absolute zero is -273 o C (Celsius) The Celsius Scale Sometimes called the centigrade scale (because there are 100 degrees C between the two fixed standard points) The freezing point of water is defined as 0 o C The boiling point of water is defined as 100 o C Anders Celsius Swedish Astronomer and Scientist He originally defined 100 o C as freeing point and 0 o as boiling point, but everyone ignored this 6

The Fahrenheit Scale Thermometers Fahrenheit invented the mercury in glass thermometer and defined a temperature scale with 180 o between the fixed points 32 o F is the freezing

(born in Danzig/Gdansk, lived in the Netherlands) Bimetal thermometer Metals tend to expand when heated, so the strips get longer at higher temperature If one strip gets longer

mercury, a liquid metal at room temperature, expands as it gets hotter The bimetallic switch is often used as a cut-off when water gets hot in an electric kettle General purpose

Europe 2013 Microwave Ovens Banned Unknown Not a National priority The microwave oven generates microwave radiation Electromagnetic radiation with a wavelength of around 10 cm.

7 The Fahrenheit Scale Thermometers Fahrenheit invented the mercury in glass thermometer and defined a temperature scale with 180 o between the fixed points 32 o F is the freezing point of water 212F is the boiling point of water In his original proposal, body temperature was defined as 96 o F Daniel Gabriel Fahrenheit ( ) Dutch- German-Polish (born in Danzig/Gdansk, lived in the Netherlands) Bimetal thermometer Metals tend to expand when heated, so the strips get longer at higher temperature If one strip gets longer than the other, then the strip will curl The thermometers use a bimetallic spiral which twists as the temperature increases Mercury in glass thermometers These work because mercury, a liquid metal at room temperature, expands as it gets hotter The bimetallic switch is often used as a cut-off when water gets hot in an electric kettle General purpose thermometer, typically -10 o C to +110 o C Clinical thermometers can be shorter, because they only have to measure a limited range of temperatures Mercury thermometer ban in Europe 2013 Microwave Ovens Banned Unknown Not a National priority The microwave oven generates microwave radiation Electromagnetic radiation with a wavelength of around 10 cm. The radiation has to be exactly the right wavelength, so that it excites water molecules in the food, and heats them up 7

Standing Waves The microwaves bounce around inside the oven, reflecting back on themselves. They form a standing wave inside the oven. antinode node What Does Microwave Energy do to Water Molecules?

8 Standing Waves The microwaves bounce around inside the oven, reflecting back on themselves. They form a standing wave inside the oven. antinode node What Does Microwave Energy do to Water Molecules? Water in the food which is at the antinode absorbs microwave radiation strongly. It vibrates more and so becomes hotter. It collides with molecules in the food itself and makes them vibrate more too, so the whole object gets hotter. The oven usually has a turntable so that different parts of the food goes through the node Consequences of physics on microwave cooking 1. It is difficult to heat up frozen objects, because ice crystals do not absorb microwave radiation as much as free water molecules 2. You can t have metal objects in the microwave because they will absorb the radiation AND disrupt the standing wave patterns 3. A turntable is needed to spread the heat out 4. You are cooking by steaming, so getting food to brown/crisp requires an infra red heater as well The microwave oven can also be used as a mailbox Danby, North Yorkshire, UK. (Wikimedia) 8

We have considered how Coulombic attractions and repulsions help to organize electrons in atoms and ions.

CHEM 2060 Lecture 10: Electrostatics L10-1 Electrostatics of Atoms & Molecules We have considered how Coulombic attractions and repulsions help to organize electrons in atoms and ions. We now look at Coulombic