Chemistry Review Notes

In general, all the reactions that occur in your cells are collectively called metabolism and are divided into two categories

            1. catabolic reactions - those in which complex molecules are broken into simpler ones.

            2. anabolic reactions - those in which complex molecules are constructed out of simpler ones.


I.         Atoms

            A.        small particles of matter

            B.        composed of three types smaller particles

                        1.         electrons - negatively charged

                        2.         protons - positively charged

                        3.         neutrons - neutral in charge

            C.        the center of the atom is called the nucleus and is where the protons and neutrons are found. The electrons “orbit” the nucleus in an “electron cloud.”

            D.        Protons and neutrons together make up about 99.9% of the mass of an atom but most of volume is occupied by the electron cloud.


II.        Elements

            A.        pure substances that cannot be broken down into simpler substances by chemical means. The elements are the “chemicals” you see on the periodic table.


III.       Molecules

            A.        in biology we talk mostly about molecules

            B.        a molecule is a unit consisting of two or more atoms of the same or different elements bonded together.


IV.      Chemical bonds - Atoms form chemical bonds with one another by sharing or by losing or gaining electrons.

            A.        Ionic bonds

                        1.         when atoms lose or gain electrons they are called ions

                        2.         an atom that loses one or more electrons becomes a positive ion

                        3.         an atom that gains one or more electrons becomes a negative ion

                        4.         ions of opposite charge are attracted to one another and form an ionic bond

            B.        Covalent bonds

                        1.         some atoms share electrons rather than gain or lose them

                        2.         atoms that share electrons form covalent bonds

                        3.         a molecule is formed when two or more atoms are joined together by covalent bonds

            C.        Polar molecules

                        1.         in a covalent bond (found in a molecule) when electrons are shared between atoms the sharing is not always equal

                        2.         the atom that has a larger share of the electrons is slightly negative

                        3.         the atom that has a smaller share of the electrons is slightly positive

                        4.         this results in one end of the molecule being negative and the other end being positive

                        5.         such a molecule is said to be polar

            D.        Hydrogen bonds

                        1.         the negative end (in biology, usually a nitrogen or oxygen atom) of one molecule can be attracted to the positive end (in biology, usually a hydrogen atom) of another

                        2.         this weak attraction is called a hydrogen bond


V.        Acids, Bases, and Buffers

            A.        acid - a substance that releases hydrogen ions in solution

            B.        base - a substance that releases hydroxide ions in solution

            C.        pH

                        1.         the scale that is used to measure the acidity or basicity of a solution

                        2.         the scale goes from 0 to 14

                                    a.         pH < 7 is acidic

                                    b.         pH > 7 is basic

                                    c.         pH = 7 is neutral

            D.        buffer - a chemical that neutralizes excess acid or base, thereby preventing a significant change in pH