Definition of Chemistry Chemistry is a physical science that deals with the composition, structure and properties of substances and the reactions they undergo. As a science, chemistry involves the intuitive and creative application of knowledge gained from experiment observation and theoretical descriptions. Matter The term matter could replace the word substance in the definition of chemistry. The two distinguishing characteristics of matter is that matter is classified as anything that has mass and occupies space. While it is possible to list examples of matter, we might also say pretty much everything meets the criteria for matter, except, for example, energy and light. Video 1 and video 2 Look at PLE#1 1
Composition of Matter For a chemist matter is either pure or it is a mixture. If the sample is a pure substance that means it has a fixed composition and distinct physical and chemical properties. If the sample is not pure then the sample is a mixture. What are some examples of matter? Pure substances? Mixture? Composition of Matter For a chemist matter is either pure or it is a mixture. If the sample is a pure substance that means it has a fixed composition and distinct physical and chemical properties. If the sample is not pure then the sample is a mixture. What are some examples of pure substances? Elements and compounds 2
Pure Substance - Elements An element is an example of matter which consists of only one kind of atom, either individually or combined into larger units. Atoms are the smallest particles of an element (that retain the chemical properties of the element). When we think of an atom I'd like you to think of a spherical shaped object (like a ball). Since an element contains only one kind of atom it is classified as a pure substance. Pure Substance - Compounds A compound is a pure substance composed of two or more different elements combined in fixed ratio. Chemists have a list of elements and a much, much longer list of compounds. The list of elements is found in the periodic table. The list of compounds is too long to even think about listing here. Composition of Matter Work on Activity 3
Summary Elements Do you know any elements? Names Symbols Formulas Elements Do you know any elements? Names Symbols Formulas hydrogen Carbon Iron Oxygen Sulfur Mercury 4
Elements Do you know any elements? Names Symbols Formulas hydrogen H Carbon C Iron Fe Oxygen Sulfur Mercury O S Hg Elements Do you know any elements? Names Symbols Formulas hydrogen H H 2 Carbon C C Iron Fe Fe Oxygen O O 2 Sulfur S S 8 Mercury Hg Hg Molecules Molecules are units of matter consisting of two or more atoms combined in a definite ratio. When the atoms in a molecule are the same, the substance is an element. 5
Elements Molecules are units of matter consisting of two or more atoms combined in a definite ratio. When the atoms in a molecule are the same, the substance is an element. Names Symbol Formula Hydrogen H H 2 Nitrogen N N 2 Oxygen O O 2 Fluorine F F 2 Chlorine Cl Cl 2 Bromine Br Br 2 Iodine I I 2 Phosphorus P P 4 Sulfur S S 8 Pure Substance - Compounds A compound is a pure substance composed of two or more different elements combined in fixed ratio. Chemists have a list of elements and a much, much longer list of compounds. The list of elements is found in the periodic table. The list of compounds is too long to even think about listing here. So Far Elements Atoms/Molecules Compounds Molecules/formula units Know the name, symbol and formula for the first 20 elements and 20 additional common elements. 6
So Far Know the name, symbol and formula for the first 20 elements and 20 additional common elements. Hydrogen, nitrogen, oxygen, fluorine, chlorine, bromine and iodine are all diatomic molecules.. X 2 Phosphorus is a tetra-atomic molecule, P 4. Sulfur is octa-atomic S 8. Mixtures A mixture is a combination of two or more substances (element and/or compound) where each substances retains its chemical identity (its physical and chemical properties). Mixtures are either heterogeneous or homogeneous. heterogeneous mixtures do not have the same composition, properties or appearance. homogeneous mixtures do have the same composition, properties or appearance. Examples.look at movies. Physical Properties Matter is either a pure substance or a mixture. With all the different pure substances and mixtures how to we characterize the differences so we can know what is what. How is the element sulfur different from the element mercury? One way is to record the physical properties of the material. Physical properties are properties that can be measured and observed without changing the identity of the substance. 7
Physical Properties 1 State(gas, liquid and solid) another example using water 2 Color 3 Melting Point (Important to note that a change in phase, which occurs at the boiling point or melting point of a substance does not necessarily mean a chemical change has occurred.) 4 Boiling Point 5 Density 6 Texture 7 Hardness Examples of Physical Properties Sulfur Mercury Iodine Nitrogen Dioxide Here are some additional pictures of these elements. Chemical Properties Let s look at some chemical properties of elements and compounds. Show movies 8