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• Matter is anything that takes up space and has mass. • All matter is made of atoms • Atoms are the building blocks of matter, sort of how bricks are the building blocks of houses. • What is an atom? • Atom: the smallest unit of matter that retains the identity of the substance Three Laws Supporting the existence of Atoms • Law of definite proportions – states that a chemical compound always contains the same elements in exactly the same proportions by weight or mass • Law of multiple proportions – states that when two elements combine to form two or more compounds, the mass of one element that combines with a given mass of the other is in the ratio of small whole numbers • Law of conservation of mass – states that mass cannot be created or destroyed in ordinary chemical and physical changes Dalton’s Theory 1. All matter is composed of extremely small particles called atoms, which cannot be subdivided, created, or destroyed. 2. Atoms of a given element are identical in their physical and chemical properties. 3. Atoms of different elements differ in their physical and chemical properties. 4. Atoms of different elements combine in simple, whole-number ratios to form compounds. 5. In chemical reactions, atoms are combined, separated, or rearranged but never created, destroyed, or changed. Discovery of the Subatomic Particles • Electrons – Discovered using Cathode Rays by English Physicist J.J. Thomson. • Nucleus – Discovered by Ernest Rutherford using Goldfoil experiment Atomic Structure • Atoms are composed of 2 regions: Nucleus: the center of the atom that contains the mass of the atom Electron cloud: region that surrounds the nucleus that contains most of the space in the atom Electron Cloud Nucleus What’s in the Nucleus? • The nucleus contains 2 of the 3 subatomic particles: Protons: positively charged subatomic particles Neutrons: neutrally charged subatomic particles What’s in the Electron Cloud? • The 3rd subatomic particle resides outside of the nucleus in the electron cloud Electron: the subatomic particle with a negative charge and relatively no mass How do these particles interact? • Protons and neutrons live compacted in the tiny positively charged nucleus accounting for most of the mass of the atom • The negatively charged electrons are small and have a relatively small mass but occupy a large volume of space outside the nucleus How do the subatomic particles balance each other? In an atom: The protons = the electrons • If 20 protons are present in an atom then 20 electrons are there to balance the overall charge of the atom—atoms are neutral The neutrons have no charge; therefore they do not have to equal the number of protons or electrons Periodic Table Atomic Number: Number of protons and it is also the number of electrons in an atom of an element. Element’s Symbol: An abbreviation for the element. Elements Name Atomic Mass/Weight: Number of protons + neutrons. 8 O Oxygen 15.999 How do we know the number of subatomic particles in an atom? • Atomic number: this number indicates the number of protons in an atom Ex: Hydrogen’s atomic number is 1 • So hydrogen has 1 proton Ex: Carbon’s atomic number is 6 • So carbon has 6 protons **The number of protons identifies the atom. Ex. 2 protons = He, 29 protons = Cu Learning Check State the number of protons in each. 1. A nitrogen atom A. 5 protons B. 7 protons C. 14 protons 1. A sulfur atom A. 32 protons B. 16 protons C. 6 protons 12 How do we know the number of subatomic particles in an atom? • Mass number: the number of protons and neutrons in the nucleus Ex: hydrogen can have a mass of 3. Since it has 1 proton it must have 2 neutrons # of neutrons = mass # - atomic # Determining the number of protons and neutrons Li has a mass number of 7 and an atomic number of 3 Protons = 3 (same as atomic #) Neutrons= 7-3 = 4 (mass # - atomic #) • Ne has a mass number of 20 and an atomic number of 10 Protons = Neutrons = What about the electrons? • The electrons are equal to the number of protons So e- = p = atomic # • Ex: He has a mass # of 4 and an atomic # of 2 p+ = 2 no = 2 e- = 2 Determine the number of subatomic particles in the following: • Cl has a mass # of 35 and an atomic # of 17 p+ = no = e- = • K has a mass # of 39 and an atomic # of 19 P+ = no = e- = An atom refresher • An atom has three parts: • Proton = positive • Neutron = no charge • Electron = negative • The proton & neutron are found in the center of the atom, a place called the nucleus. • The electrons orbit the nucleus. Picture from http://education.jlab.org/qa/atom_model_03.gif Element Name Atomic Number Number of Number of Protons Neutrons 45 24 Mass Number 80 52 89 silver 152 107 76 114 States of Matter • The Kinetic Theory 1. All matter is composed of small particles (atoms, molecules, or ions). 2. They are in constant, random motion. 3. They constantly collide with each other and with the walls of their container. Phase Liquid Proximity close close Gas far apart Solid Particle Properties Volume Energy little definite moderate definite a lot indefinite Shape definite indefinite indefinite What is a Physical Change? • A physical change alters the form of a substance, but does not change it to another substance. Example: Making Orange Juice What is a Chemical Change? • When a substance undergoes a chemical change, it is changed into a different substance with different properties. Example: Baking a Cake 5 Signs of a Chemical Change 1. Color Change 2. Precipitation Precipitation – the solid that forms from a solution during a chemical reaction. It looks like a cloudy solid in an otherwise clear solution. 5 Signs of a Chemical Change 3. Gas Production 4. Temperature Change 5. Changes in Characteristic Properties (odor, light given off) Chemical or Physical Change? • Cutting paper? • Physical Chemical or Physical Change? • Ice melting? • Physical Chemical or Physical Change? • Toast burning? • Chemical Chemical or Physical Change? • Rocket fuel burning? • Chemical Chemical or Physical Change? • Sawing wood? • Physical Chemical or Physical Change? • Metal rusting? • Chemical Chemical or Physical Change? • Disappearing puddle? • Physical Chemical or Physical Change? • Candle burning? • Chemical Chemical or Physical Change? • Dry ice? • Physical Physical or Chemical Property? • Ability of gun powder and fire to explode. Chemical Property Physical or Chemical Property? • The color of a sunset. Physical Property Physical or Chemical Property? • The ability of a nail to rust. Chemical Property Physical or Chemical Property? • The shape of a leaf. Physical Property Physical or Chemical Property? • The ability of wood to burn. Chemical Property Physical or Chemical Property? • The hardness of a diamond. Physical Property Physical or Chemical Property? • The volume of your coke. Physical Property Physical or Chemical Property? • The mass of two camels. Physical Property Physical or Chemical Change? • Water evaporates from the ocean. Physical or Chemical Change? • The yolk of an egg, which contains sulfur, causes tarnish to form on silver. Physical or Chemical Change? • The ice on a lake melts to become water in the lake. Physical or Chemical Change? • Charcoal in a fire turns to ash after several hours. Physical or Chemical Change? • A pencil is sharpened in a pencil sharpener, leaving behind shavings. Physical or Chemical Change? • A battery makes electricity to turn on a flashlight. Physical or Chemical Change? • A bicycle rusts when left in the rain. Physical or Chemical Change? • A shirt is accidentally torn in the washing machine. Physical or Chemical Change? • A log is split in two by an axe. Properties - Pure Substances Matter can either be found in nature as a pure substance or a mixture. • Pure substance - a substance that contains a single type of matter. When the substance is pure, it has a unique set of properties Example: pure water contains ONLY molecules of water (H2O) and NOTHING else!! Properties of Matter - Mixtures • Mixture - two or more substances mixed together, but not chemically combined. Each component in a mixture keeps its individual properties. Example: salt water contains water molecules (H2O) and sodium chloride (NaCl) molecules. The mixture will behave differently than the two materials separate. Salt water will have a different boiling point than pure water! Types of Mixtures: The prefix “homo” – indicate sameness Homogeneous – A homogeneous mixture has the same uniform appearance throughout. Many homogeneous mixtures are commonly referred to as solutions. The prefix “hetero” – indicate difference Heterogeneous - A heterogeneous mixture consists of visibly different substances or phases. The three phases or states of matter are gas, liquid, and solid. YES Uniform properties? If not, it’s a heterogeneous mixture YES Fixed composition? Can be broken down chemically? If not, it’s a homogeneous mixture If not, it’s an element If so it’s a compound What is it? Homogeneous Cheerios What is it? Homogeneous Kool - Aid What is it? Heterogeneous Trail Mix What is it? Homogeneous Water What is it? Heterogeneous Italian Salad Dressing What is it? Heterogeneous Raisin Bran What is it? Homogeneous White Vinegar An element is a substance that is made from one kind of atom only. It cannot be broken down into simpler substances. atom An element atom An element A compound is a substance that is made from more than one element. atom A compound made up of 2 different elements atom A compound made up of 7 different elements A compound can be broken down into elements An element An element A compound made up of 3 different elements An element Material Made up of: Water Hydrogen and Oxygen Carbon Coal Carbon dioxide Oxygen Carbon and Oxygen Chalk Calcium, Carbon & Oxygen Sodium & Chlorine Table salt Caffeine Oxygen Carbon, Hydrogen, Nitrogen & Oxygen Element or compound