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Elementary, My Dear Watson Exam Review 2013 Matter All matter is made up of tiny particles called atoms. These atoms are made up of even smaller particles: electrons (which have a negative charge) protons (which have a positive charge) neutrons (which have not charge) Electron Neutron Proton in the nucleus The Periodic Table The rows are called periods and they are arranged by atomic number. We use numbers to identify them. The columns are called families. Each column contains elements that have similar properties. The elements are metals, non-metals or metalloids (having both properties of metals and non-metals). Each square in the Periodic Table tells us something about the element. The atomic number is equal to the number of protons. atomic number 1 H Hydrogen chemical symbol element’s name If the chemical symbol is made up of one letter, it is always a capital. For example: H is hydrogen C is carbon If the chemical symbol is made up of two letters, the first is a capital letter and the second is a minuscule (small) letter. For example: Cl is chlorine He is helium How Many? The number of protons = atomic number Protons are found in the nucleus The number under the chemical symbol is the atomic mass (the mass of one atom of that element) 4 9.012182 atomic number Be Berylium atomic mass chemical symbol element’s name To find the number of neutrons, you need to round the atomic mass to the nearest whole number. Then subtract the number of protons from the atomic number and you will get the number of neutrons found in the nucleus of the atom, intermingled with the protons. 4 9.012182 Be Berylium Step 1. Round atomic mass: 9 amu Step 2: 9 - 4 Step 3: 5 neutrons Mysterious Molecules When two or more atoms join together, they form molecules. A molecule could be made up of atoms of the same kind. For example: O2 (oxygen) and 03 (ozone). A molecule could also be made up of different atoms. We often call these compounds. Here are some examples: CO2, H20, C6H1206 The letters represent the elements that are involved and the numbers tell us how many atoms of each kind are involved. For example, water (H20) is made up of 2 atoms of hydrogen and 1 atom of oxygen. For example, carbon dioxide (CO2) is made up of 1 atom of carbon and two atoms of oxygen. Whereas sulphur dioxide (SO2) is made up of 1 atom of sulphur and 2 atoms of oxygen. We can draw molecules using Dalton’s model. For example, if = Carbon = Oxygen then we can draw CO2 as and we can draw H2O as = Hydrogen Physical Changes No new substances are being formed. The product has the same chemical formula as the reactants. A physical change could involving separating a mixture into its components. Physical Changes Physical changes involve a change in the physical properties of the substances: state of matter, shape, temperature, particles. Physical changes are often (but not necessarily) reversible. Chemical Changes In a chemical change, a new substance is made. The product has a different chemical formula from the reactants. A chemical change is usually accompanied by one of the following signs: Colour Change Light Effervescence (Bubbles) Precipitate Temperature Change Conservation of Matter Lavoisier’s law states that the mass of the reactors equals the mass of the products Examples: a) CH4 + 2 O2 ---> CO2 + 2 H2O 5 g + 8 g ----> 7 g + ? b) C3H8 + 5O2 ---> 3 CO2 + 4 H2O 10g + 4 g ---> ? + 9g Answer: 6 g Answer: 5 g Conservation of Matter Remember the vinegar and baking soda lab we did: the mass of the reactors (baking soda and vinegar) was equal to the mass of the product (fizz!) only when we placed a balloon on top of the Erlenmeyer Flask to catch the gas (CO2) that was produced. Otherwise, the mass after the reaction would have decreased because the produced CO2 could have escaped. Electrolysis Water can be decomposed into its original elements using electrolysis. When water is split apart, there is twice as much hydrogen as there is oxygen, since the molecular formula for water is H2O. For example: if we get 20 ml of hydrogen we should get 10 ml of oxygen Electrolysis When you test the gases after decomposing water, they produce the following results: oxygen bursts in flame (glowing splint test) hydrogen makes a small pop (flaming splint test)