Lecture Notes-08 Biology 1004

North Arkansas College

Topic: Chemical Basis of Life

1. Anything that has mass and occupies space.
2. Mass; quantity of matter.
3. Matter is composed of chemical elements.

1. Smallest unit of matter that retains the chemical properties.
2. Over 110 elements of which 93 are naturally occurring.
3. On Earth, oxygen and silicon are the 2 most common elements.
4. In humans, carbon, hydrogen and oxygen are the most common elements.
5. Elements are made up of atoms.

1. The smallest unit of element that retains properties of element.
2. Atoms contain over 100 sub-atomic particles of which three are the most understood in relationship to activity of the atom.
3. Sub-atomic particle

1. Protons; positively charged particles located in atom’s nucleus.
2. Neutrons; no charge; located in atom’s nucleus.
3. Electrons; negatively charged particles that form "clouds" around the nucleus.

4. In an electrically neutral atom, the number of protons (positive) and electrons (negative) are equal.
5. The number of protons in an atom is the atomic number of the element. Hydrogen has one proton, and it’s atomic number if ₁H.
6. The total number of protons and neutrons is the atomic mass. If you know the atomic mass and the number of protons, you could determine the number of neutrons. The number of neutrons = mass minus the number of protons.

1. The number of electrons in the outermost energy shell (level).
2. Electrons can exist in several energy levels (shells). An electron may absorb energy, become "excited" and jump from one energy level to others. If an electron loses energy, it "falls back" to the original energy level.
3. The number of electrons in a particular energy level can be determined by the formula 2(n)² where n = energy level.

1. First level; 2 electrons
2. Second level; 8 electrons
3. Third level; 18 electrons
4. Fourth level; 32 electrons

4. The outermost or valence energy shell must contain 8 electrons to be stable; the octet rule.
5. The valence electron is the outermost energy level. It must have 8 electrons to be stable (octet rule). If 8 electrons are not present, the atom becomes reactive and gains, loses or shares electrons. These reactions produce compounds and macromolecules. Of course, the first energy level only needs 2 electrons to be stable (H & He).

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