GED Study Guide for Chemistry

GED Study Guide for Chemistry The GED, or General Education Development Test, is taken in the U.S. or Canada to demonstrate proficiency in high school-level academic skills. The exam most commonly is taken by people who did not complete high school or receive a high school diploma. Passing the GED grants a General Equivalency Diploma (also called a GED). One section of the GED covers science, including chemistry. The test is multiple choice, drawing on concepts from the following areas: The Structure of MatterThe Chemistry of LifeProperties of MatterChemical Reactions The Structure of Matter All substances consist of  matter.  Matter  is anything which has mass and takes up space. Some important concepts to remember about  matter  are: Matter  is made up of one or more of over 92 naturally-occurring  elements.Each  element  is a pure substance, made up of only one type of  atom.An  atom  consists of three types of particles:  protons,  neutrons, and  electrons. An atom does not need to have all three particles, but will always contain at least protons.Electrons  are  negatively charged  particles,  protons  have a positive charge, and  neutrons  do not have an electrical charge.An atom has an inner core called a  nucleus, which is where the protons and neutrons are located. The electrons orbit around the outside of the nucleus.Two main forces hold atoms together. The  electric force  holds the electrons in orbit around the nucleus. Opposite charges attract, so the electrons are drawn to the protons in the nucleus. The  nuclear force  holds the protons and neutrons together within the nucleus. The Periodic Table The  periodic table  is a chart which organizes the chemical elements. The elements are categorized according to the following attributes: Atomic Number  - number of protons in the nucleusAtomic Mass  - sum of the number of protons plus neutrons in the nucleusGroup  - columns or multiple columns in the periodic table. Elements in a group share similar chemical and physical properties.Period  - rows from left to right in the period table. Elements in a period have the same number of energy shells. Matter can exist in the form of a pure element, but combinations of elements are more common. Molecule  - a molecule is a combination of two or more atoms (could be  from  the same or different elements, such as H2  or H2O)Compound  - a compound is a combination of two or more  chemically-bonded  elements. Generally, compounds are considered to be a subclass of molecules (some people will argue they are determined by the types of chemical bonds). A  chemical formula  is a shorthand way of showing the elements contained in a molecule/compound and their ratio. For example, H2O, the chemical formula for water, shows that two atoms of hydrogen combine with one atom of oxygen to form a molecule of water. Chemical bonds hold atoms together. Ionic Bond  - formed when  an electron transfers  from one atom to anotherCovalent Bond  - formed when two atoms share one or more electrons The Chemistry of Life Life on earth depends on the chemical element  carbon, which is present in every living thing. Carbon is so important, it forms the basis for two branches of chemistry, organic  chemistry  and biochemistry. The GED will expect you to be familiar with the following terms: Hydrocarbons  - molecules that only contain the elements carbon and hydrogen (e.g., CH4  is a hydrocarbon while CO2  is not)Organic  - refers to the chemistry of living things, all of which contain the element carbonOrganic Chemistry  - study of the chemistry of carbon compounds involved in life (so, studying diamond, which is a crystalline form of carbon, isnt included in organic chemistry, but studying how methane is produced is covered by organic chemistry)Organic Molecules  - molecules that have carbon atoms linked together in a straight line (carbon chain) or in a circular ring (carbon ring)Polymer  - hydrocarbons which have chained together Properties of Matter Phases of Matter Each phase of matter has its own chemical and physical properties. The phases of matter you need to know are: Solid  - a solid has a definite shape and volumeLiquid  - a liquid has a definite  volume  but can change shapeGas  - the shape and volume of a gas can change Phase Changes These phases of matter can change from one to another. Remember the definitions of the following phase changes: Melting  - melting occurs when a substance changes from a solid to a liquidBoiling  - boiling is when a substance changes from a liquid to a gasCondensing  - condensation is when  a gas changes  to a liquidFreezing  - freezing is when  a liquid changes  to a solid Physical Chemical Changes The changes that take place in substances may be categorized  in  two classes: Physical Change  - does not produce a new substance (e.g., phase changes, crushing a can)Chemical Change  - produces a new substance (e.g., burning, rusting, photosynthesis) Solutions A solution results from combining two or more substances. Making a solution can produce either a physical or chemical change. You can tell them apart this way: The original substances can be separated from one another if the solution produces only a physical change.The original substances cannot be separated from one another if a chemical change took place. Chemical Reactions A  chemical reaction  is  the process  that occurs when two or more substances combine to produce a chemical change. The important terms to remember are: chemical equation  -  name  was given  to the shorthand used to describe the steps of a chemical reactionreactants  - the starting materials for a chemical reaction; the substances that combine in the reactionproducts  - the substances that are formed as a result of a chemical reactionchemical reaction rate  - the speed at which a chemical reaction occursactivation energy  - the external energy that has to be added in order for a chemical reaction to  occurcatalyst  - a substance that helps a chemical reaction to occur (lowers the activation energy), but does not participate in the reaction itselfLaw of Conservation of Mass  - this Law states that matter is neither created nor destroyed in a chemical reaction. The number of reactant atoms of a chemical reaction will be the same as the number of product atoms.