Chapter Outline

Chemistry

Chemistry: the study of the phases and behavior of matter

The Structure of Matter

Matter is anything that has weight and takes up space. Some of the current theories about the structure of matter are listed below:

• All matter is formed from one or more of 92 naturally occurring elements.
• An element is a pure substance made up of one kind of atom.
• An atom contains three types of particles: one or more electrons in orbit around a central nucleus that contains protons and neutrons.
• Electrons are negatively charged particles. Protons are positively charged particles. Neutrons carry no charge and are said to be electrically neutral.
• Atoms are held together by two main forces: electric force holds electrons in orbit around the nucleus; nuclear force holds protons and neutrons together within the nucleus.

The periodic table is an ordered listing of the known elements. Each element is characterized by the following attributes:

• atomic mass—the sum of the protons plus the neutrons in the nucleus
• atomic number—the number of protons in the nucleus
• period—each row read from left to right in the periodic table; contains elements with the same number of energy shells
• group—each column read from top to bottom in the periodic table; contains elements with similar physical and chemical properties

Most objects are made up of a combination of elements:

• molecule—a combination of two or more atoms
• compound—a substance that is made up of molecules containing the atoms of two or more elements

A chemical formula is a shorthand way of showing which elements are contained in a molecule.

• An ionic bond is formed when an electron transfers from one atom to another.
• A covalent bond is formed when two atoms share one or more electrons.

The Chemistry of Life

One of the chemical characteristics of all living things is the presence of the element carbon. Carbon is considered to be so important to the life process that scientists refer to the study of carbon as the study of life.

• organic—refers to compounds produced by living things
• organic chemistry—the study of substances that contain the element carbon
• organic molecules—molecules characterized by carbon atoms that link together in a straight line (carbon chain) or in a circular ring (carbon ring)
• hydrocarbons—compounds composed of molecules that contain only the elements hydrogen and carbon
• polymer—a long chain hydrocarbon

Behavior of Matter

Each phase of matter has its own physical and chemical properties:

• solid—characterized by definite shape and definite volume
• liquid—characterized by a definite volume, but not a definite shape
• gas—characterized by neither definite volume, nor definite shape

Matter can change from one phase to another:

• A substance melts when it changes from a solid to a liquid.
• A substance boils when it changes from a liquid to a gas.
• A substance condenses when it changes from a gas to a liquid.
• A substance freezes when it changes from a liquid to a solid.

Changes in substances are characterized in two ways:

• physical change—does not produce a new substance
• chemical change—produces a new substance

A solution is a combination of two or more substances. A solution can be either a physical or a chemical change:

• In a solution that is a physical change, the original substances can be separated from one another.
• In a solution that is a chemical change, the original substances cannot be separated from one another.

Chemical Reactions

When two or more substances combine during a chemical change, the steps of the process are called a chemical reaction.

• chemical equation—the shorthand used by chemists to describe a chemical reaction
• reactants—the substances that are combining in a chemical reaction
• products—the substances formed in a chemical reaction
• Law of Conservation of Matter—a law that states that matter is neither created nor destroyed during a chemical reaction
• chemical reaction rate—the speed at which a chemical reaction takes place
• catalyst—a substance that causes a chemical reaction to occur but does not itself take place in the reaction
• activation energy—an external source of energy needed to cause a chemical reaction to take place