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Chemistry Matter and Classification Purpose of classification: To gain a better understanding and appreciate the similarities and differences. Matter: Has mass and occupies space. We can divide matter into 2 categories: Matter Mixtures Pure Substances Heterogeneous Elements Metals Nonmetals Alloy Compounds Ionic Molecular Homogeneous Solutions Pure Substances Substances that are the same or consistent throughout. Can be a single element or a combination of elements. Elements Substance composed of only one kind of atom. 109 on the periodic table. Each has a unique international symbol. Can be combined to make other pure substances. Compounds Combination of two or more elements in specific proportions. Once combined the compound acts as one, with consistent chemical and physical properties. Mixtures A combination of two or more compounds. Homogeneous A mixture in which all regions are consistent (the same) Ex. Sugar water (a solution) brass (an alloy - mixture of 2 metals; copper and zinc) air (gas solution) Heterogeneous A mixture that can be easily separated, not consistent. Regions of differing properties. Ex. Sand and water. Chemical vs Physical Properties Chemical Describes the reactivity of a substance Physical Properties that describe the appearance or the composition of a substance. In a physical change no new substance is being formed. Chemical Reactions The process that occurs when a substance or substances reacts to create a different substance Indicators of a Chemical Reactions 1. Involve the production of a new substance 2. Involve the flow of energy (exothermic and endothermic) Exothermic - Release of energy in the form of heat, light, sound etc ex. Cellular Respiration, combustion DEMO Endothermic - Absorption of energy (It cools, uses light etc.) ex. Photosynthesis, Ba(OH)2(s) + NH4SCN(s) DEMO 3. Involve the formation of a gas ex. Hydrogen gas formation when Mg(s) is placed in HCl(aq) DEMO 4. Involves the formation of a solid in a liquid (precipitate) ex. KI(aq) + PbNO3(aq) DEMO Read Pages 12 to 17 and answer the following questions: Pg 17 #1 to 9 The Development of an Atomic Model As theories developed old ideas were not discarded, they were modified and expanded upon. Democritus 460BC Democritus develops the idea of atoms he pounded up materials in his pestle and mortar until he had reduced them to smaller and smaller particles which he called ATOMA (greek for indivisible) 1808 John Dalton - Billiard Ball Model Atom is in the shape of a billiard ball and acts as a single, indestructible and indivisible particle. The larger the atomic number the larger the atom or “billiard ball” Observations that supported this theory: Law of Conservation of mass: The masses of the reactants always equals the masses of the products. Example: 2 g of hydrogen and 16 g of oxygen would react to produce 18 g of water. J.J Thomson "Raisin Bun" Model Atoms have negatively charged particles embedded in them like raisins in a bun. Observations that supported theory: -electricity passed through a gas in a vacuum tube produced a stream of negatively charged particles. Rutherford “Nuclear” Model An atom’s mass is concentrated in a very small,dense and positively charged nucleus. Electrons orbit the nucleus at a distance. Observations that supported theory: Gold foil experiment- large positively charged particles should go right through the gold foil. Most did but some came right back towards the particle emitter. Bohr “Orbits” Model Electrons are located in specific orbits, each having a specific energy level, around the nucleus. It is the electrons in the outermost orbit that react with neighboring atoms to form compounds. Observations that supported theory: electricity passed through a gaseous element emits only certain wavelengths of light. Quantum Mechanical Model “Electron Cloud Model” Electrons are in a cloud moving very quickly around a nucleus forming an electron cloud. Read pages 18 to 25 and answer the following questions: Pg 25: #1 to 8, 10 and 11. 2. Metals vs Non-metals separated by the staircase line Staircase line Metals Non-metals 3. Groups (or families) vertical columns that have similar properties 4. Periods Horizontal rows with repeated trends of reactivity. Example: Calcium Atomic Number: _____ metal/nonmetal: _____ group: period: _____ _____ The periodic table can also list the physical state (phase) of the element at SATP (room temperature). Regular Print - Solid Clear Print - Gas Bold - liquid (There are only 2, Mercury and Bromine) Other physical properties such as electronegativity and molar mass can also be determined by using the key on your periodic table. Families of the Periodic Table Group IA: Alkali Metals Elements are highly reactive. Contain most reactive metal: Francium. Silver colored Very ductile React with air or water As you move from top to bottom they become more reactive Group II A: Alkaline Earth Metals Similar to alkalies but not as reactive in air. Oxidize with air to form a protective coating When mixed in solution are likely to form a compound with a pH greater than 7. Group VIIA or 17: Halogens - “Salt Formers” Reacts well with metals to form compounds similar to salts. Most diverse Group. Contains all phases. Contains most reactive non-metal: Fluorine As you move up the column they become more reactive. Group VIIIA or 18: Noble Gases. Seldom reacts to form compounds. formerly called the “Inert Gases” Group B elements: Transition Metals typical metals such as copper, iron, zinc and silver wide variety of characteristics Metal Non-Metal Staircase: Metal vs Non-Metal Properties Metals Non-Metals -solid (except Hg) -s, l, g -silver(except: copper, gold) -all colors -ductile & malleable -brittle/inflexible -conduct heat/electricity -poor conductors of heat and electricity -reacts with acid to form hydrogen gas Metalloids Nonmetals along the staircase line that have some of the properties of metals, mainly they can conduct electricity. (semiconductors) Lanthanides and Actinides Last Two Groups - found at the bottom of the periodic table Rare Earths / Lanthanide Series: Name says it all, atomic #’s 58 - 71 Trans Uranium /Actinide Series: Made in nuclear reactors, #’s 90-103 Atom Atomic Structure The basic unit of matter. Smallest unit of matter that retains the properties of the element. Consists of subatomic particles. Subatomic Particles 1. Proton: symbol “p+” -Positively charged particle located in the center of an atom (nucleus). Makes up a large portion of the mass of an atom. 2. Neutron: symbol “n°” -Neutral charged particle located in the center of the atom (nucleus). Also makes up a large portion of the mass of the atom ***Atomic mass of any element is determined by the number of protons and neutrons. 3. Electron: symbol “e-” -Negatively charged particle surrounding an atom. -Has very little mass. Moves about the nucleus in an electron cloud. Cloud consists of mostly space. If the nucleus was the size of a ping pong ball the first electron would be about 0.5 km away! Finding Numbers of Subatomic Particles Protons = Atomic Number *Proton number can never, never, never change. Electrons = Atomic Number (neutral atom only!) *Electron number can change if an ion. Neutrons = Mass number - Atomic number. Isotopes: Atoms that have a different number of neutrons from another atom of the same element. U 235 is a light isotope having 3 fewer neutrons than the most common form of uranium U 239 is a heavy isotope having 1 more neutron than the most common form of uranium Periodic Table Elements on the periodic table are classified and arranged according to four basic patterns. 1. Atomic Number the number of protons (positively charged particle) in the nucleus of an element.