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Biology Made Simple 2

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Atomic structure and characteristics of solids, liquids, and gases.

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Biology Made Simple 2

  1. 1. CHAPTER 2 BASIC MATTER CONCEPTS BIOLOGY MADE SIMPLE “If you can’t explain it simply enough, you didn’t understand it well enough” (Albert Einstein)
  2. 2. What is “The Matter”? 1 Matter is everything in and around you, from the air that you – ideally - cannot see to anything else that you can see or touch. REMEMBER: If you chop something (like a can of soft drink) many, many, maaany times, there will come a time when you cannot make it any smaller and this is called “atom”. Atom means “not divisible” [or “can’t be made any smaller”]. That was true for a long time until someone spoiled it with the development of the electron microscope that showed that atoms are actually made of 3 particles: a nucleus made of protons (+) and neutrons (O), and tiny orbiting particles called electrons (-). An atom pretty much looks like the Earth with several Moons. Imagine you are chopping off a can of soft drink and a gold ring. The can is made of aluminium and the gold ring, well..., of gold. Aluminium and gold are atoms that have a tendency to join together with each other to form substances (more fancily known as “elements”). The smallest you could make the can would be an atom of aluminium and the smallest you could make the ring would be an atom of gold. Put differently, an atom is the smallest possible piece of an element that retains all the properties of that element. Now imagine that you want to know what something else is made of, for example a piece of paper. You chop it many, many times and when you cannot chop it any smaller you look at it under a microscope (a powerful electron microscope) and to your surprise you see that the piece of paper is not made of just one atom or element but of several of them, namely: carbon, hydrogen, oxygen, calcium, potassium, sulfur, nitrogen, and magnesium. You could do the same with a rock, a piece of wood, a piece of body tissue, a plant, anything. What you will notice is that 95% of everything is made of only 6 elements: Carbon, Hydrogen, Nitrogen, Oxygen, Phosphorus, and Sulfur (CHyNOPS) [Mnemonic: Almost everything is Made in Chynops]. The acronym goes from most to least common of the most common elements]. You can also go the other way, instead of chopping off a piece of something you can create something by putting together several elements and you’ll have a compound (molecule). Examples of quite simple compounds (or molecules) are water (2 hydrogens + 1 oxygen) and salt (1 sodium + 1 chloride). Having said that, you should know that there are in fact a bit over 100 elements.
  3. 3. What is “The Matter”? 2 The Atom
  4. 4. States of the Matter The matter, just like people, can change or go through “phases” or “states”. The classic example of a substance that can be in different phases/states is water (H2O). As you can see, the water molecule is made of 2 atoms of hydrogen and 1 atom of oxygen, abbreviated as H and O for convenience. Water is often in liquid form/state/phase. Very intelligently, in very cold temperatures, the water molecules tend to get closer together and turn into solid ice. Also very intelligently, in very hot temperatures, the water molecules tend to want to be as far as possible from each other and turn into gas. So there you are: The 3 states of the matter are solid, liquid, and gas depending on how close together the molecules are. The water molecule remains a water molecule (H2O) regardless of whether it is in ice, liquid or gas form. That is, the chemical composition is the same, the only thing that changed here is the physical aspect. Physical changes mean different distances between the molecules, chemical changes mean destruction of the molecule into smaller, simpler components. Temperature, pressure, and chopping can produce physical changes. Taking or adding a substance to another substance often results in a chemical change. An example of chemical change is rusting: It happens when a piece of metal (like an iron nail) is left in contact with air or water, both of which contain lots of oxygen. When a metal is in contact with oxygen, the oxygen becomes a part of that metal and changes its chemical composition making it brittle and reddish. Removing oxygen has similar effects. When a brain/heart artery gets clogged, the oxygen-carrying blood cannot reach the brain/heart tissue resulting in the death of the tissue. The scientific explanation for chemical changes is the gain or loss of electrons = making or breaking of bonds between the atoms of the substance. All matter can move from one state to another. It may require extreme temperatures, pressures, or mixing with other substances, but it can be done.
  5. 5. Physical vs. Chemical Changes 1 PHYSICAL CHANGES CHEMICAL CHANGES No change in composition or properties Change in composition and properties No new substance is needed to produce it A new substance needs to be added to produce it Easily reversible Often not reversible Examples of physical change: • Liquid water turning into solid water (ice) by decreasing the temperature • Wood being turned into sawdust through sanding Examples of chemical change: • Iron nail rusting because adding / contact with Oxygen in the air/water • Wood turned into ashes mainly through adding / contact with Oxygen
  6. 6. Physical vs. Chemical Changes 2 PHYSICAL CHANGE CHEMICAL CHANGE Source: Pearson Education Inc., 2010
  7. 7. A Name for Each Physical State When a substance goes from solid to liquid, the process is called melting (or fusion). When a substance goes from liquid to gas, the process is called boiling (or vaporization). How about going the other way around? When a substance goes from gas to liquid, the process is called condensation. When a substance goes from liquid to solid, the process is called freezing (or solidification). Note that some substances can go from solid to gas (match) and the process is called sublimation. Going from gas to solid is called deposition.
  8. 8. A Special Type of Chemical Change 1 We now know that if we add or subtract a substance (like oxygen, but also any other element) to another substance, we can produce a chemical change. Another way to create a chemical change is to rearrange the atoms of a substance. For this, you need to think in 3D. Imagine you have 6 green balls, 12 yellow balls, and 6 red balls. You could arrange them in a considerable number of positions but you still would have the same number and type of balls. This is what happens with sugars (or carbohydrates). The chemical composition of sugar is 6 carbons, 12 hydrogens, and 6 oxygens or C6H12O6 . Glucose, fructose, and galactose are 3 types of sugar/s from different natural origin. They have exactly the same type and number of atoms but they are put together differently. The result is that they have different properties and react differently in different situations (!). These types of substances are called isomers and are a special type of chemical change of the matter that consists of a rearrangement of the same type and number of elements.
  9. 9. A Special Type of Chemical Change 2
  10. 10. SOLIDS 1 A chair, a piece of paper, an ice cube, a bone, and a rock are all solids. Solids are hard, but some are harder than others. Another characteristic of solids is that they hold their shape and don't flow like a liquid because the atoms of a solid substance are very compact, very close together. Solids can be made of just one element (gold nugget, diamond) or – more often – of several elements (most rocks). The gold nugget is made exclusively of gold (Au) which means that a gold nugget has a homogeneous composition. A rock, however, often has different colours which often means that it is made of several elements. It will not have exactly the same amount (or concentration) of each element in it, which means that rocks are a mixture of elements, i.e., rocks have a heterogeneous composition.
  11. 11. SOLIDS 2 - CRYSTALS Another type of solid are crystals. Most crystals are heterogeneous mixtures of elements. Crystals are solids where all the atoms are arranged in an orderly fashion, in a geometric shape. Salt (NaCl) and sugar (C6H12O6) are crystals. Salt crystals are cubes and sugar crystals are oblong. They are so small that they can dissolve in water. Diamonds, rubies, emeralds, sapphires, etc., are all crystals but only diamonds are made of only just one element: Carbon (C). Charcoal and graphite (pencil leads) are also made of just carbon. But why do diamonds look so different from pencil leads (graphite)? The reason is called “allotropy”, i.e.: different geometrical arrangement of the atoms. In the case of graphite C atoms join in groups of 3 (C-C-C) in a flat fashion (2D). Diamonds are made of C atoms geometrically arranged in groups of 4 in 3D. The difference in the way C atoms are arranged means that graphite and diamonds look and behave very differently.
  12. 12. SOLIDS 3 – CRYSTAL ALLOTROPY Source: http://www.ausetute.com.au/allotropy.html
  13. 13. LIQUIDS 1 Water (H2O), blood, wine, honey, and even lava are all liquids. Most liquids are made of more than one element, meaning they have a heterogeneous composition. When you mix 2 or more liquids together or if you add a soluble substance (salt, sugar) into a liquid it is called a solution. When bees combine water, sugar, and other substances they create a solution called honey. Liquids fill the shape of any container they are in. If you pour enough water in a cup it will fill up the cup. If you freeze that cup of water and then break the cup, the ice will be in the shape of the cup. The top of a liquid will usually have a flat surface, which is mostly the result of gravity pulling on the liquid molecules.
  14. 14. LIQUIDS 2 SOLID LIQUID GAS - Space between atoms +
  15. 15. LIQUIDS 3 Because the atoms in liquids are quite far apart from each other, if you apply a lot of pressure to a liquid you can compress it and make it fit into a smaller space/volume/container. You can find compressed air in SCUBA air tanks. Most solids are very difficult to compress while gases are easier because the distance between the atoms/molecules affect the strength of the intermolecular (or cohesive) forces. Closer molecules = stronger bonds between molecules = stronger intermolecular forces When you place a drop of water on a hard surface or when you see it at the tip of a faucet, you will see it stay together in the shape of a drop. This is because of the action of 3 forces: the atmospheric pressure around the drop, the intermolecular forces, and gravity.
  16. 16. GASES 1 Gases are everywhere. The atmosphere is a mixture of gases that surrounds the Earth. As we have already seen, in solids atoms are very close together, very compact. Atoms in liquids are spread out a little more. In gases, atoms are really spread out and constantly moving around in every direction which means that gases can completely fill a container of any size or shape, no matter how big it is. It also means that gases are very easy to compress (think of a fire extinguisher or an air freshener). The molecules spread out to fill the whole space equally. Think about a balloon of any shape. No matter what shape you make the balloon, it will be evenly filled with the gas molecules. The shape of liquids is very dependent on gravity (pour a liquid and it will fall onto the ground), while most gases are light enough to go in every direction up, down, right, and left.
  17. 17. GASES 2 Vapor and gas mean the same thing. The word vapor is used to describe the gas resulting from making a liquid (which is a liquid at room temperature) turn into a gas. Examples of these types of liquids include water (H2O) and mercury (Hg). The term “water vapor” means water in a gas state. Molecules that are naturally a gas at room temperature are called simply a gas, not vapor. Compounds such as carbon dioxide (CO2) are usually gases at room temperature and scientists never refer to it as carbon dioxide vapor but as carbon dioxide gas.

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