2ElementA substance that cannot be broken down into simpler substances.Each element is identified by a one or two letter symbol.Ca = CalciumC = CarbonTrace ElementPresent in living things in very small amounts.
3AtomSmallest particle of an element that has all the characteristics of that element.
4Structure of the Atom Nucleus Protons (positive) Neutrons (neutral) Each element has a different number of protons.The number of protons determines the characteristics of each elementDetermines the atomic number.Neutrons (neutral)Atomic mass – atomic number = average number of neutrons
5Structure of the Atom Electron Cloud Electrons (negative) Electrons surround the nucleus because of the attraction between the opposite charges.All the electrons occupy distinct energy levels.
6Structure of the AtomAll atoms have the same number of protons and electrons, so the atoms have a neutral charge.
7IsotopeAtoms of the same element which vary in the number of neutrons they contain are called isotopes.Isotopes are named by the total number of neutrons and protons in the atom.Example: Carbon-12 and Carbon-14Some isotopes can be radioactive.
8CompoundA substance composed of atoms of two or more different elements that are chemically combined.Atoms combine with other atoms only when the resulting compound is more stable than the individual atoms.Atoms become stable when their outermost energy level is full.
9How do atoms fill their outermost energy level? Form a covalent bond and share their electrons with another atom.A molecule is a group of atoms held together by covalent bonds.
10How do atoms fill their outermost energy level? Form ions by giving away electrons or take electrons from other atoms.When atoms do this they gain either a positive or a negative charge.Ions with opposite charges can form compounds through ionic bonding.
11Chemical ReactionsOccur when bonds are formed or broken, causing substances to recombine into different substances.The substances that undergo the chemical reactions are called the reactants.The substances formed by the chemical reaction are called the products.
12Chemical ReactionsThe substance created by a chemical reaction has different properties than the reactants that formed it.Atoms are never created or destroyed in chemical reactions, but simply rearranged.Represented by writing chemical equations.
13Chemical ReactionsIn organisms, chemical reactions occur inside cells.All the chemical reactions occurring within an organism are referred to as the organism’s metabolism.
14MixtureA combination of substances in which the individual components retain their own properties.A solution is a mixture in which one or more substances (solutes) are distributed evenly in another substance (solvent).The more solute dissolved in a solvent, the greater the concentration of the solution.
15pH A measure of how acidic or basic a solution is. Measured on a scale of 0 to 14.A substance with a pH of 7 is considered neutral.
16AcidAny substance that forms hydrogen (H+) ions in water.pH below 7.
17Base Any substance which forms hydroxide ions (OH-) in water. pH above 7.