Introduction to Chemistry

This course introduces students (in grade 8, 9, or 10) to key chemistry concepts that provide a foundation for further study in chemistry or other science disciplines. Within the course, there are two main organizing themes from which to develop standards-based learning cycle lessons:

• Nature of matter
• Nature of energy

Nature of Matter

• The atom is the basic unit of an element. Theories about the structure of the atom have changed over time from Democritus’s belief that the atom was the smallest particle in nature to current discoveries of quarks and neutrinos. Scientists such as Dalton, Thomson, Rutherford, Bohr, and Shroedinger contributed to the advancement of such understanding.
• Atomic structure impacts both the chemical and physical properties of matter. Physical properties are those properties that can be changed without changing the chemical composition of the substance. Some physical properties are density, melting point, freezing point, color, and conductivity. Chemical properties are those properties that when changed, result in a change in the chemical composition of the substance. Some chemical properties are flammability, reaction with water, and reaction with acids. Matter can be described by its physical and chemical properties.
• The periodic table can be used to classify elements and to make predictions about elemental properties and behavior. On the periodic table, trends and patterns exist for density, atomic radii, ionic radii, electronegativity, reactivity, and a variety of other properties.
• Bonding explains how elements combine to form various compounds. Bonds can be described as ionic, polar covalent, or nonpolar covalent. The octet rule is useful for illustrating how electrons are arranged in an atom and explaining why certain elements tend to lose, gain, or share electrons.
• In order to write chemical formulas, knowledge of atomic structure, properties, and chemical symbols is required. Chemical formulas represent compounds formed by the sharing or transferring of electrons. These chemical formulas are used to write chemical equations that describe what happens during given chemical reactions.
• Sometimes matter changes without a chemical reaction taking place. This is known as a physical change. One type of physical change occurs when matter changes state. Phase-change diagrams illustrate how matter transforms into liquids, solids, or gases at certain temperatures and pressures.

Nature of Energy

• Energy changes occur as a chemical reaction progresses from reactants to products. This is due to the breaking and forming of bonds that happens during the reaction. If, overall, energy is released in the reaction, the reaction is said to be exothermic. If energy is consumed during the reaction, then the reaction is said to be endothermic.
• Radioactivity is the spontaneous disintegration of an unstable atomic nucleus. The three natural types of nuclear emissions include the alpha particle (helium nucleus), beta particle (an electron-like particle), and energy (gamma radiation). Simple nuclear equations can be written to exemplify how a nuclear change can result in the formation of a new element.
• Radioactivity is used as an energy source in fission reactors. During a fission reaction, a large nucleus is split into at least two smaller nuclei. This reaction releases a substantial amount of energy.
• Fusion reactions involve the joining of two light nuclei to form a more massive one. This reaction releases a large amount of energy.
• Fission and fusion reactions have societal significance in that they are potential sources of energy. However, with these benefits come certain risks.
• Matter and energy are conserved in all chemical reactions. These are explained through two scientific laws: The law of conservation of matter and the law of conservation of energy.