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Chemistry Essentials Unit 2 Matter – A Central Idea in Chemistry Unit Warm-Up 1. What do chemists study? 2. How do atoms differ from molecules? 3. Describe a chemical change (chemical reaction) you have witnessed outside of school. How did you know that it was a chemical change? Section 1: The Nature of Matter Chemists study matter What it is How it changes Matter is the physical “stuff” the Universe is made of Examples: a tree, your body, atoms, water, air All matter has two characteristics Mass Volume (takes up space) Humans have studied matter forever We ask the question “What is everything made of?” The simple answer is ---- MATTER So…. What is matter made of? Since ancient times two schools of thought: Aristotle (300’s BCE) Fundamental set of substances that can be combined to form all other substances Called elements Earth, air, fire, and water Democritus (400’s BCE) There is a fundamental particle all matter is made of Called the atom Who was right? BOTH! Matter is made of elements and elements are made of atoms Atoms Fundamental particle from which elements are made ~ 92 different types of atoms that occur naturally in the Universe Microscopic -- invisible to the naked eye Elements Substance that contains only 1 type of atom Cannot be broken down into other substances Macroscopic – can see with naked eye Section 2: Pure Substances Is all matter the same? Of course not!!!!! We can find similarities to create types of matter Can be classified into 2 broad categories pure substances mixtures Pure Substances Composition is the same throughout (contains only 1 type of matter) Can be an element or a compound Examples: gold, water, baking soda, oxygen Elements Contains only 1 type of atom ~ 92 naturally occurring elements Cannot be broken down by ordinary means; must use nuclear reaction Symbol has only 1 capital letter Examples copper (Cu), carbon (C), lithium (Li), tungsten(W) Macroscopic idea (microscopic is atom) Compounds Contain two or more types of atoms that are hooked together by a chemical bond Infinite number of compounds possible Ratio of atoms is always the same Cannot be separated into elements by physical means; must use chemical means Properties are very different from properties of elements that it is made of Formula has more than 1 capital letter Macroscopic idea (microscopic is molecule) Examples CH3OH -- methanol H2O – water NaCl – sodium chloride (table salt) Examples Identify the following as an element or a compound a)Mg element b) CuSO4 compound c) Zr element d) P element e) I2 element f) C6H5OH compound Separating Compounds Must be separated by chemical means (break the chemical bonds) Example Electrolysis Passing an electric current through the compound will break the bonds Water – H2O will be broken down into H2(g) and O2(g) Practice Identify each of the following as an element or a compound: a) Au element b) C6H12O6 compound c) KMnO4 compound d) Pb element Section 3: Mixtures Two or more substances that occupy the same container without interacting with each other No chemical bonds between components of the mixture Variable composition from sample to sample or within a sample Properties are usually a blend of the properties of the components in the mixture No definite formula May contain elements, compounds, or both May contain solids, liquids, &/or gases Can be separated by physical means (sorting, filtration, chromatography, etc.) Examples; soda, dirt, sand, coffee, air Types of mixtures Mixtures can be classified as either homogenous mixtures or heterogeneous mixtures Homogeneous Mixtures Same throughout – cannot see the different substances that make up the mixture May also be called solutions or alloys Examples: chocolate milk, brewed tea, salt water, air, brass Heterogeneous Mixtures Not the same throughout – can see at least two substances in the mixture May have different properties in different regions of the mixture Examples: a bag of M&M’s, sand and water, iced tea Examples Identify each of the following as a homogeneous mixture or a heterogeneous mixture a) brewed coffee homogeneous mixture b) a glass of Coke with ice heterogeneous mixture c) a bag of Skittles heterogeneous mixture d) Gatorade homogeneous mixture Practice Identify each of the following as a homogeneous mixture or a heterogeneous mixture. a) Gasoline homogeneous mixture b) A stream with gravel at the bottom heterogeneous mixture c) Air homogeneous mixture d) A bowl of Lucky Charms cereal with milk heterogeneous mixture Section 4: Properties of Matter and Changes in Matter Chemistry is about Matter and its changes Describing Matter How to describe matter? List its properties Property—an observable characteristic of matter Properties are either microscopic or macroscopic Two types of macroscopic properties Physical properties and chemical properties Physical Properties Describe matter on its own Does not require matter be changed into a different type of matter Still the same substance after determining the property Examples: color, odor, texture, shape, state at a given temperature, density, melting point, boiling point States of Matter Substances can exist in one of three states of matter under normal conditions Solid Liquid Gas States are temperature and pressure dependent Macroscopic reflection of microscopic particle movement and relative position Solids Low temperature &/or high pressure Microscopically: Particles are close together Minimal movement – only vibrations Lots of inter-particle interactions Macroscopically Observed as having fixed shape and volume Ice (solid form of water) Liquids Higher temperatures &/or lower pressure Microscopically Particles slightly apart from each other Some movement present – sliding Some inter-particle interactions Macroscopically Observed as having definite volume but not shape – will take shape of container Liquid water Gases High temperature &/or low pressure Microscopically Particles are very far apart from each other Lots of particle movement – all directions Almost no inter-particle interactions Macroscopically Observed as having no definite shape or volume – will fill the container Water vapor Chemical Properties Describe how matter interacts with other matter to form new substances What happens when it combines with____? Examples: Does it combine with oxygen to form a new substance? The matter is a different substance after observing the property How to tell if it’s a physical or chemical property? Ask question Is this the same substance as before I observed it? If yes – it’s a physical property If no – it’s a chemical property Example Classify each of the following as a physical or a chemical property: a) a certain solid melts at 2000ºC Physical Property b) when combined sodium metal and chlorine gas turn into sodium chloride (table salt) Chemical property Practice Classify each of the following as a physical or a chemical property: a) The boiling point of a certain alcohol is 78C physical b) Diamonds are very hard physical c) Sugar ferments to become alcohol chemical d) A metal wire conducts electric current physical Changes in Matter There are two types of changes Physical changes Do not involve the matter changing into a new substance Chemical changes Require the matter to change into something new with different properties Physical Changes Do not involve the matter changing into a new substance Microscopically: No bonds are broken or formed. Indicators ( Macroscopically) Change in size or shape Change in state Dissolving and recrystallization Expected color change If only 1 substance involved – physical change Chemical Changes Require the matter to change into something new with different properties Microscopically: Bonds are broken &/or formed) Indicators(Macroscopically) Unexpected color change Formation of a solid from two or more liquids or gases Formation of a gas, not due to boiling Production or absorption of heat Production of light Must be at least two substances involved Examples Classify each of the following as a physical change or a chemical change and give a reason for your answer a) A white crystalline solid is crushed to a fine white powder. Physical change – change in size b) Two clear colorless liquids are mixed and the resulting mixture is orange. Chemical change – unexpected color change c) A piece of paper is crumpled. Physical change – change in shape Practice Classify each of the following as a physical change or a chemical change and give a reason for your answer. a) A green crystalline substance is placed in a mortar and ground to a fine green powder. physical change – change in size or shape b) A clear blue liquid and clear yellow liquid are mixed. The resulting liquid is clear and green. physical change – expected color change c) A small piece of a white solid is placed in a flask and a clear colorless liquid is added. The white solid bubbles vigorously and eventually disappears, leaving a colorless liquid in the flask. chemical change – formation of a gas, not due to boiling d) Two clear colorless liquids are mixed in a flask and the flask becomes cool to the touch. chemical change – absorption of heat e) A blue solid is mixed with a clear colorless liquid until no solid remains. The liquid is then heated and the blue solid reappears. physical change – dissolving and recrystallization