Science and Technology Material World Periodic Table and Solutions Peridoic table is grouped by broad categories of elements, groups and periods. Broad categories: metals, non-metals and metalloids o Metals are on the left of the staircase o Metalloids are found on either side of the staircase o Non-metals are on the right of the staircase Groups/Families are part of the same columns and have the same number of valence electrons o Valence electrons are electrons found in the outermost shell of an atom Periods are the rows of the periodic table elements in the same period have the same number of electron shells (aka orbitals or energy levels) Each individual box on the periodic table gives the following o Atomic number = # if protons = # of electrons (when the atom is neutral) o Atomic mass = protons + neutrons o Element Name (usually) o Element Symbol
Organization of the Periodic Table Metal Metalloids Non-Metals Alkali Alkaline Earth Properties of metals and non metals Hydrogen Halogens Noble gases group 1A group 2A found in group 1 but not an alkali metal group 7 A group 8 A 1 valence electron 2 valence electrons 1 valence electrons 7 valence electrons full outer shell - 8 valence excep He which has 2 Soft, light metals that melt at low temperatures Grey, metallic solids that are excellent conductors forms acids with non metals Very reactive (in nature they exist only in combined states) Lack of chemical reactivity as they have full outer shell of electrons Found combined with other elements (never found as free elements) Also reactive with air and water, but less vigorously than alkali metals colourless, odourless Toxic and corrosive Do not form compounds with other elements under normal conditions ordinary conditions Excellent conductors Melting points are higher than alkali metals flammable -- makes a popping sound with a flaming splint Form salts when combined with alkali metals Highly reactive with water and air Form strong acids in combination with Hydrogen
Alkali metals Alkaline Earth metals Halogens Noble Gases
Rutherford Bohr Diagrams represents the atom as o Mostly empty space with a very dense, small, positively charged nucleus at the center o Negatively charged electrons moving in defined orbits around the nucleus o Neutrally charged, so that the number of protons in the nucleus is equal to the number of electrons in the orbits Nucleus o Contains protons o Is positively charged (because protons are positively charged) o Contains nearly all of the mass of the atom o The nucleus is much smaller than the atom and very dense o The number of protons determines the type of element the atom makes up o The number of protons in the nucleus is different for each element Electron Orbitals (Shells) o Contains the electrons which are negatively charges Follows the 2-8-8-2 rule 1st shell holds a maximum of 2 electrons 2 nd shell holds a maximum of 8 electrons 3 rd shell holds a maximum of 8 electrons 4 th shell holds a maximum of 2 electrons o Once a shell is full, you fill in the next shell Example: Chlorine, Cl Atomic number = 17 17 protons, 17 electrons Nucleus with the protons inside 1 st shell holds a maximum of 2 electrons 17+ 2 nd shell holds a maximum of 2 electrons Chlorine is in row 3 so has 3 electron orbitals and in group 7 so has 7 electrons in its outer shell
Law of Conservation of Mass law of conservation of mass states that in all chemical reactions the mass of reactants is equal to the mass of products. Example: The chemical equation for the combustion of methane, CH 4, is shown below. CH 4 + 2 O 2 CO 2 + 2 H 2O When 8 grams of methane reacts completely with 32 grams of oxygen, 18 grams of water are produced. How many grams of carbon dioxide are produced in this reaction? mass of reactants = mass of products mass CH 4 + mass O 2 = mass CO 2 + mass H 2O 8g + 32g = mass CO 2 + 18g 40 g = mass CO 2 + 18g 40 g - 18g = mass CO 2 mass CO 2 = 22g the law of conservation of mass is applied to the type and number of atoms in a chemical reaction o the type and number of atoms on the reactant side must be equal to the type and number of atoms on the product side balanced reactions The particle model can be used to visually represent a chemical reaction. This can be applied to the law of conservation of mass to show an equal amount of reactants and an equal amount of products. The reaction of the combustion of methane is represented below using the particle model. Since mass in conserved, the number of particles of each type in the reactants is equal to the number of particles of each type in the products.
Balancing Chemical Reactions Balancing a chemical equation consists of placing a coefficient before each reactant and product so that the number of atoms of each element on the reactant side is equal to the number of atoms of each element on the product side. Coefficients must be whole numbers placed in front of a reactant or product Coefficients must be as small as possible (lowest common denominator) New substances must never be added, nor existing substances removed Subscripts in chemical formulas must never be changed The final equation should always be checked by counting the number of atoms of each element on both sides Using the drawing method H 2SO 4 + KOH K 2SO 4 H 2O Unbalanced H- H S O-O-O-O K-O-H K- K S O-O-O-O H- H O K-O-H H- H O Atom Reactant s Produc ts H 3 2 S 1 1 O 5 5 K 1 2 H 2SO 4 + 2KOH K 2SO 4 2H 2O Balanced Atom Reactant s Produc ts H 4 4 S 1 1 O 6 6 K 2 2
Properties of Solutions Ions Atoms -- protons = electrons no charge positive ion -- lost electrons Negative ion - gained electrons Metals in groups 1, 2 and 3 on the periodic table lose 1, 2, or 3 electrons respectively The non-metals in groups 5, 6 and 7 gain 3, 2, or 1 electrons respectively An atom is neutral equal number of protons and electrons Ions are hen an atoms that have gained or lost electrons to have a full outer shell to be chemically stable o Positive ions electrons lost Metals tend to lose electrons to become positively charged ions. Metals in groups 1, 2 and 3 on the periodic table lose 1, 2, or 3 electrons respectively o Negative ions electrons gained Non-metals tend to gain electrons to become negatively charged ions. The non-metals in groups 5, 6 and 7 gain 3, 2, or 1 electrons respectively ***the number of protons never changes!!!*** Example: Na Na atom 11 Protons (11+) and 11 electrons (11 -) Lost 1 electron Na ion (Na + ) 11 Protons (11+) and 10 electrons (10 -)
Example: S S atom 16 Protons (16 +) and 16 electrons (16 -) Gained 2 electrons Acids, Bases and Salts Acids S ion (S 2- ) 16 Protons (16 +) and 18 electrons (18 -) These are all ionic substances Generally have an H in the front of the formula (e.g. HCl but not H2O = water) followed by non-metals Bases Generally have a metal in the front of the formula and have OH at the end of the formula (e.g. NaOH, Al(OH)3 NH4OH) Salts A metal and a non-metal combine to form a salt (e.g. NaCl, CaF2) Does not have a H in front or OH at the end of the formula The ph scale is a measure of how acidic or basic a substance is. A solution with a ph below 7 is acidic. A solution with a ph above 7 is basic (alkaline). A solution with a ph equal to 7 is neutral
The ph scale is a logarithmic scale Electrical Conductivity When an ionic substance dissolves in water, it dissociates into positive and negative ions. HBr (s) H + (aq) + Br (aq) These ions can move and will move in solution towards electrodes (if they are present) This movement of charged particles produces an electrical current this is how batteries work
Chemical Changes Combustion Rapid combustion is a form of oxidation (a reaction that uses oxygen) that releases a large amount of energy over a short period of time. The energy is released mostly in the form of heat and light e.g., a candle burning. Combustion is a form of oxidation (a reaction that uses oxygen) that releases a large amount of energy. Three conditions must be met for combustion to occur: 1) The presence of an oxidizing agent, a substance that provides oxygen to react with a fuel 2) The ignition temperature has been reached. The ignition temperature is the minimum temperature at which there is enough energy to start the combustion. This varies from one type of fuel to another 3) The presence of a fuel. A fuel is a substance that releases a large amount of energy by reacting with an oxidizing agent. (e.g. Wood) Combustion will only occur if all three conditions are present. If any one of these conditions is removed, then combustion will stop. Examples: Water will extinguish a fire because the water significantly reduces the temperature of the system. (Ignition temperature not reached) A candle will eventually stop burning when all of its wax is consumed. (Fuel no longer present) A frying pan fire is extinguished when a lid is placed on the pan. (Oxidizing agent (oxygen in the air) is prevented from reaching the fuel)
Chemical Changes Photosynthesis and Respiration Photosynthesis Plants make their own food. They use carbon dioxide, water and solar energy during photosynthesis, a chemical change, which produces glucose and oxygen. The photosynthesis reaction can be represented by the balanced chemical equation below. 6 CO2(g) + 6 H2O(l) 6H12O6(s) + 6 O2(g) Carbo Respiration Respiration is the process by which plants and animals release energy stored in glucose. Respiration involves the reaction of glucose with oxygen. Cells will burn this fuel (glucose) for energy and give off waste in the form of carbon dioxide and water. This respiration reaction can be represented by the balanced chemical equation below. C6H12O6(s) + 6 O2(g) 2(g) + 6 H2O(l) + energy Glucos
Chemical Changes: Acid-Base Neutralization Reaction Neutralization is a chemical reaction in which an acid combines with a base to form a salt and water. When an acid and a base combine, they neutralize each other forming a salt and water. Both salt and water have a neutral ph. Ex HCl + NaOH H 2O + NaCl Acid + base water + salt The positive ion, H+, from the acid combines with the negative ion, OH-, from the base to form neutral water. The positive ion of the base combines with the negative ion of the acid to form a salt. Concentration C = m V Units of measurement 1) g/l 2) % m/v ( # g 100 ml 3) ppm ( # mg 1 L ) x 100%)
Converting between units: 1) g/l to ppm g x 1000 L = mg L = ppm Ex. What is 3.2 g/l in ppm? 3.2 g x 1000 L = 3200 mg L = 3200 ppm 2) g/l to % m/v g 1L x 1000 = g x100% = % m/v 1000 ml Ex. What is 3.2 g/l in %m/v? 3.2 g 1L x 1000 = 3.2 g x100% = 0.32 % m/v 1000 ml 3) ppm to g/l Ex. What is 3.2 ppm in g/l? ppm = 3.2 mg 1000 1L mg 1000 L = g L = 0.0032 g/l