Chemistry is… …the study of the composition, structure, and properties of matter and the changes it undergoes
Matter Anything that has mass and occupies space Mass A measure of the amount of matter Weight The measure of the force of gravity acting on an object
Atom The smallest unit of an element that maintains the properties of that element
By asking questions scientists can classify matter into: Mixtures – two or more substances that are not chemically combined with each other and can be separated by physical means. The substances in a mixture retain their individual properties. –Solutions – a special kind of mixture where one substance dissolves in another. Elements – simplest form of pure substance. They cannot be broken into anything else by physical or chemical means. Compounds – pure substances that are the unions of two or more elements. They can be broken into simpler substances by chemical means.
Types of Chemical Formulas An empirical formula gives the relative number of atoms of each element in a compound; i.e., the smallest whole number ratio that is possible. A molecular formula gives the actual number of atoms of each element in a molecule of a compound. Molecular Empirical Hydrogen peroxide H 2 O 2 HO Water H 2 O H 2 O Glucose C 6 H 12 O 6 CH 2 O A structural formula uses lines to represent covalent bonds, and shows how the atoms in a molecule are joined together: H—O—O—H H—O—H O=C=O
Homogeneous – a substance that is the same throughout. Heterogeneous – a substance that is different throughout.
Separation of a Compound Separation of a Compound The Electrolysis of water Water Hydrogen + Oxygen H 2 O H 2 + O 2 Reactant Products Compounds must be separated by chemical means. With the application of electricity, water can be separated into its elements
Properties of Matter Extensive properties Intensive properties Volume Mass depend on the amount of matter that is present. do not depend on the amount of matter present. Melting point Boiling point Density
Physical Change A change in a substance that does not involve a change in the identity of the substance. Example: A change in size, shape color etc. Phase Changes
Phase Differences Solid Solid – definite volume and shape; particles packed in fixed positions. Liquid Liquid – definite volume but indefinite shape; particles close together but not in fixed positions
Gas Gas – neither definite volume nor definite shape; particles are at great distances from one another Plasma – high temperature, ionized phase of matter as found on the sun.
Phase changes occur when a substance changes state from… A solid to liquid…melting A liquid to solid…freezing A liquid to gas…boiling A gas to liquid…condensing A solid to gas…subliming A gas to a solid…deposition
The heat that is being added to a given state that does not result in a temperature increase is being used to overcome the intermolecular forces between the particles. The heat added to a solid to convert it to a liquid is called the heat of fusion. (fusion means melting) You add heat to get a solid to melt. When you condense a liquid back to a solid, you get that heat back! Melting and freezing are only different in which way heat flows in or out of a substance.
The same occurs at the boiling/condensation point. The heat put in to a liquid to convert it to a gas is called the heat of vaporization. When a gas is condensed to a liquid, then that heat is again released. Boiling and condensation are only different in the direction of heat flow in or out of a substance.
Chemical Change A change in which one or more substances are converted into different substances. Something new is created. Heat and light are often evidence of a chemical change.
Catalyst – a substance that increases the rate of a chemical reaction without itself being permanently changed. Entropy – the measure of disorder in a substance.
Physical properties shapesize texturehardness odormass colorstate freezing point magnetism melting point
More physical properties conductivity (conducts electricity) malleability (can be hammered into sheets) ductility (can be drawn into wires) solubility (will dissolve in another substance) density (mass / volume)
Chemical properties Flammibilty Reactivity Combustibility Acidic or basic
Properties of Metals Metals are good conductors of heat and electricity Metals are malleable Metals are ductile Metals have high tensile strength Metals have luster
Examples of Metals Potassium, K reacts with water and must be stored in kerosene Mercury, Hg, is the only metal that exists as a liquid at room temperature
Propertiesof Nonmetals Properties of Nonmetals Carbon, the graphite in “pencil lead” is a great example of a nonmetallic element. Nonmetals are poor conductors of heat and electricity Nonmetals tend to be brittle Many nonmetals are gases at room temperature
Examples of Nonmetals Sulfur, S, was once known as “brimstone” Graphite is not the only pure form of carbon, C. Diamond is also carbon; the color comes from impurities caught within the crystal structure
Properties of Metalloids Metalloids straddle the stairstep. They have properties of both metals and nonmetals. Metalloids are more brittle than metals, less brittle than most nonmetallic solids Metalloids are semiconductors of electricity Some metalloids possess metallic luster
Silicon, Si – A Metalloid Silicon has metallic luster Silicon is brittle like a nonmetal Silicon is a semiconductor of electricity
Number of naturally occuring elements is 90 Sir ramsey discovered the Noble gases, octets, group 8, helium family Accuracy – nearness of a measurement to its accepted value Precision – agreement between numerical values of a set of measurements.