SOL 6.4 Matter= anything that has mass and takes up space. Examples: fruit, softballs, tools, animals, rain, flowers and even air. Mass=how much of something you have. Energy is the ability to do work or cause change. Change can mean… 1. motion=moving matter from one place to another. (ex. nail being hammered into something) 2. change in form (ex. water boiling or freezing) The study of the properties of matter and how matter changes is called chemistry. Matter has a variety of characteristics or properties that can differ. They fall into 2 different groups used to identify, describe and classify matter: 1. Physical 2. Chemical A single kind of matter that has distinct physical and chemical properties is called a substance. A physical property can be observed without changing the substance into something else. Odor Taste Hardness Texture Color Temperature at which a solid melts or liquid boils Whether its solid, liquid or gas A chemical property is observed when a substance interacts with another substance. Burning or flammability Rusting Tarnishing Whether an object will explode What is an example of a physical property of a candle? Chemical property? An element is a substance that cannot be broken down into any other substances by chemical or physical means. All elements can be identified by its specific physical and chemical properties. Examples: aluminum foil, copper coatings on pennies, oxygen and nitrogen gas. All of the kinds of elements are found on the periodic table along with their symbols. A compound is a substance made of two or more elements chemically combined in a set ratio or proportion. Examples: Carbon Dioxide gas is a compound made up of Carbon and Oxygen. Water is a compound made up of oxygen and hydrogen. When elements are combined to make a compound, the new substance has properties different from those of the original elements. Example: table sugar is made up of 3 elements- Carbon, Oxygen and Hydrogen. Carbon=found in charcoal Oxygen/hydrogen=colorless gases Do sugar crystals resemble them? Most matter occurs in mixtures. A mixture is made from two or more substances (elements or compounds) that are in the same place but are NOT chemically combined. Mixtures differ from compounds in 2 ways: 1. The substances in a mixture keep their individual properties. 2. The parts of a mixture are not necessarily present in set ratios. Example: soil has particles of sand, tiny bits of clay, and pieces of decaying plants. If you were to grab 2 handfuls of soil would they be made up of the same amount of clay, sand, and decaying plant matter? Which is a mixture and which is a compound? Chex mix Table salt Water Muddy water Carbon dioxide There are 2 types of changes that matter goes through: physical and chemical. Physical change= a change that alters the form or appearance of a material but does NOT make the material into another substance. Examples: chopping wood, bending a copper wire, molding clay. Matter has 3 principal states: solid, liquid and gas. A change in state is an example of a physical change. Why is a change in state considered to be a physical change? A chemical change or reaction is a change in matter that produces new substances with properties different from the original substance. Elements may combine to form a compound or compounds may be broken down into elements. Examples: souring of milk, burning of wood Energy is ALWAYS involved when a chemical or physical change to matter occurs. Think of tearing a sheet of aluminum foil in half and then tearing the halves into quarters and so on… Could you keep tearing forever producing smaller and smaller pieces or would you eventually reach the smallest possible piece? Democritus, a greek philosopher who lived in 440 B.C., thought that you could cut matter into smaller and smaller pieces until you eventually got to its smallest piece. He called this smallest piece atomos meaning “uncuttable”. Look familiar? This is where the word atom comes from which is the smallest particle of an element. In 1802, John Dalton (a British school teacher) proposed an atomic theory. His main conclusions were: 1. Atoms can’t be broken into smaller pieces. 2. In any element, all of the atoms are exactly alike. 3. Atoms of different elements are different. 4. Atoms of two or more elements can combine to form compounds. 5. Atoms of each compound have a unique mass. 6. The masses of the elements in a compound are always in a constant ratio. Today, scientists have identified some important exceptions to Dalton’s statements but his ideas still form the basis of our understanding of atoms. What were two of Dalton’s ideas about atoms? Although atoms are extremely small, they are made of even smaller parts: nucleus, protons, neutrons and electrons. Nucleus= the tiny, central core of the atom, which contains protons and neutrons. Protons=have a positive electric charge (+). Neutrons=have no charge. (they are neutral) Electrons= very energetic particles that move in the space around the nucleus and carry a negative charge (-). All atoms of a particular element have the same number of protons. Because the number of protons is unique to each element, this number is called the element’s atomic number. Example: the atoms that make up the element carbon all have 6 protons so the atomic number for carbon is 6. The force that hold two atoms together is a chemical bond. Two or more atoms that are bonded together form a molecule. Some are made up of only one type of atom but most are made up of two or more different types of atoms bonded together. Scientists can’t study atoms by looking at them. (They are too small to see!) So….How do they study them? They make inferences about them based on observations. They use models to make and test their predictions. How are atoms and molecules related? • • Molecules= Two or more atoms chemically combined Compounds= Two or more different elements chemically combined During the California gold rush, miners needed a way to remove Gold from a mixture that also contained dirt and sand. Gold can be separated from other materials in a mixture because of its density. (It has a higher density than most other materials including fool’s gold.) They used the method of panning using a shallow pan and water. Because gold is more dense, it stays in the bottom of the pan when the less dense materials (water, dirt, sand) are poured off. How could you tell the difference between fools gold and real gold?