BASIC CONCEPTS OF CHEMISTRY

WHAT IS THE GOAL OF SCIENCE?

HYPOTHESIS, LAW AND THEORY A hypothesis is a tentative explanation based on observations. A hypothesis is a tentative explanation based on observations. If you notice that a particular student tends to get an 88 on tests, you might hypothesize that they will score an 88 on the next test. If you notice that a particular student tends to get an 88 on tests, you might hypothesize that they will score an 88 on the next test. A law can be verbal or mathematical statement that describes something consistently observed in nature without contradiction. A law can be verbal or mathematical statement that describes something consistently observed in nature without contradiction. If the students in fact scores an 88 on each test that year, we can change the hypothesis into a law. If the students in fact scores an 88 on each test that year, we can change the hypothesis into a law. A theory is a unifying principle that explains a body of facts A theory is a unifying principle that explains a body of facts A theory is not just a guess in science. They are based reproducible evidence. They can change if new facts are found. A theory is not just a guess in science. They are based reproducible evidence. They can change if new facts are found.

STATES OF MATTER Kinetic-molecular theory of matter explains the properties of each state of matter. Kinetic-molecular theory of matter explains the properties of each state of matter. All matter is made of tiny particles that are constantly moving. All matter is made of tiny particles that are constantly moving. In solids, the particles are packed close together in a pattern and vibrate back and forth. In solids, the particles are packed close together in a pattern and vibrate back and forth. In liquids, the particles are arranged randomly, and the particles move around. In liquids, the particles are arranged randomly, and the particles move around. In gases, the particles are far apart, move rapidly, and collide with each other. In gases, the particles are far apart, move rapidly, and collide with each other. The kinetic energy of the particles is proportionate to the temperature. The kinetic energy of the particles is proportionate to the temperature. Why is water special in terms of phase changes? Why is water special in terms of phase changes?

MACROSCOPIC AND PARTICULATE LEVELS Chemistry can be viewed in different ways. Chemistry can be viewed in different ways. The macroscopic world is what we can observe with our five senses. The macroscopic world is what we can observe with our five senses. Observing color Observing color Testing conductivity Testing conductivity The particulate world is too small to see. The particulate world is too small to see. We can’t see it, but what know what particles exist. We can’t see it, but what know what particles exist. We use models to represent the particles. We use models to represent the particles.

CLASSIFYING MATTER

TYPES OF MATTER Heterogeneous mixture: made of two or more substances that you can see Heterogeneous mixture: made of two or more substances that you can see Examples: Examples: Homogeneous mixture: made of two or more substances, but looks like one Homogeneous mixture: made of two or more substances, but looks like one Examples: Examples: Element: pure substance made of only one type of atom Element: pure substance made of only one type of atom Examples: Examples: Compound: pure substance made of two or more types of atoms Compound: pure substance made of two or more types of atoms Examples: Examples:

ATOMS AND MOLECULES Atoms are the smallest particles that retains the properties of an element Atoms are the smallest particles that retains the properties of an element Every element has unique atoms Every element has unique atoms Molecules are the smallest unit of a compound Molecules are the smallest unit of a compound Some compounds are made of ions instead. Some compounds are made of ions instead. Ion examples: Ion examples: Molecule examples: Molecule examples:

PHYSICAL CHANGES A physical change doesn’t change the composition of a material so it doesn’t create a new substance A physical change doesn’t change the composition of a material so it doesn’t create a new substance Examples: Examples:

CHEMICAL CHANGES A chemical change changes the composition of a material and creates a new substance. A chemical change changes the composition of a material and creates a new substance. Also called a chemical reaction and can be represented by a chemical equation. Also called a chemical reaction and can be represented by a chemical equation. Examples: Examples:

PROPERTIES Assessing physical and chemical properties is the same as for changes. Assessing physical and chemical properties is the same as for changes. A property that can be observed without changing the composition is physical. A property that can be observed without changing the composition is physical. Examples: Examples: A property that can only be observed by changing the composition is chemical. A property that can only be observed by changing the composition is chemical. Examples: Examples:

DENSITY How is density calculated? How is density calculated? What happens when two substances of differing densities are mixed? What happens when two substances of differing densities are mixed?

EXTENSIVE AND INTENSIVE Extensive properties depend on the amount present. Extensive properties depend on the amount present. For example, mass and volume are extensive. For example, mass and volume are extensive. Intensive properties do not depend on the amount present. Intensive properties do not depend on the amount present. For example, density and boiling point are intensice. For example, density and boiling point are intensice.

ASSIGNMENT: PAGE , 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 14, 16, 18, 20, 22, 24, 25, 26, 28, 29, 31, 35, 37 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 14, 16, 18, 20, 22, 24, 25, 26, 28, 29, 31, 35, 37