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Essential Knowledge TOPIC ONE: ELEMENTS & THE PERIODIC TABLE (PAGE 1) Atoms are made of three types of subatomic particles: protons, neutrons and electrons. Each atom has a nucleus in the center, made of protons and neutrons packed tightly together. An electron cloud surrounds the atomic nucleus. The atomic number for an element is the same as the number of protons. All atoms of the same element have the same number of protons. A proton has a positive charge and a relative mass of one. The number of electrons is the same as the number of protons in a neutral atom. An electron has a negative charge and a relative mass of zero. A neutron has no charge and a relative mass of one. TOPIC TWO: COMPOUNDS & BONDING (PAGE 2) Subscripts in a chemical formula represent the relative number of each type of atom. The subscript always follows the symbol for the element. Example: In a water molecule, H2O, there are 2 hydrogen atoms and one oxygen atom. Parentheses are used when a subscript affects a group of atoms. Example: the formula for magnesium nitrate is written Mg(NO3)2 to show that there is a ratio of one magnesium atom, 2 nitrogen atoms and 6 oxygen atoms in the compound. TOPIC THREE: KINETIC MOLECULAR THEORY (PAGE 3) Solids have a fixed shape. In a solid the particles are closely packed together. Each particle in a solid is held in one position and vibrates around that position. The particles in a liquid stay relatively close together, but they can move around each other. Gas particles are far apart; they move rapidly and collide with each other and with the walls of the container. TOPIC FOUR: THE MOLE & STOICHIMETRY (PAGE 4) The sum of the protons and neutrons in an atom is known as the mass number. Isotopes are atoms of the same element that have different numbers of neutrons. Some isotopes are radioactive, many are not An element’s atomic mass is a weighted average of the masses of all the known isotopes of the element. The mass of one mole of any element is the same as the element’s atomic mass in grams (called molar mass). TOPIC FIVE: CHEMICAL REACTIONS )PAGE 5) The only way to form a compound from elements is by a chemical reaction. Example: Hydrogen gas and oxygen gas react to synthesize water. 2H2 + O2 2H2O The only way to separate a compound into its elements is by a chemical reaction that breaks the chemical bonds, forming new substances. (Example: water decomposes to form hydrogen and oxygen gas. 2H2O 2H2 + O2 In the rearrangement of atoms, chemical bonds are broken and formed. Bond breaking requires energy while bond making releases energy. Physical changes can be written as a “reaction” or equation as well. TOPIC SIX: SOLUTIONS (PAGE 6) A solution is a homogeneous mixture because the separate parts of the mixture cannot be seen. The solvent (usually water) is the part of the solution that is present in largest amount. The solute is the substance that is dissolved. A saturated solution has all the dissolved solute that it can hold, and can be identified by undissolved solute particles on the bottom after mixing. An unsaturated solution can still hold more solute. TOPIC SEVEN: EXPERIMENTATION (PAGE 7) Identify equipment: ring stand, funnel, watch glass, beaker, graduated cylinder and evaporating dish. Demonstrate filtration and evaporation and explain when each can be used to physically separate a mixture. Define filtrate as the liquid that passes through the filter. Measure volume of a liquid in milliliters (mL) using a graduated cylinder and stating measured digits plus the estimated digit. Measure mass in grams (g) using an electronic balance and identifying the estimated digit.