Bio 178 Lecture 2 The Nature of Molecules

Reading Chapter 2 Quiz Material Questions on P 34 Chapter 2 Quiz on Text Website (

Outline Atoms Chemical Bonds Water Acids, Bases, and Buffers

The Chemistry of Life - Definitions Matter Any substance that has mass and occupies space. Mass Amount of a substance. Weight How strongly mass is pulled by gravity. Example of Mass Vs. Weight: Astronauts in space and on earth.

The Structure of Atoms What are Atoms? The smallest particle into which a substance can be divided and still retain its chemical properties.

Atomic Number The number of PROTONS an atom possesses. Eg. Oxygen Atomic number = 8 Atomic Mass Sum of the masses of protons and neutrons. Masses: Protons = Da, Neutrons = Da, Electrons = 1/1840 Da Eg. O 2 Atomic Mass = 16 Da

Elements and Isotopes Element Atoms with the same atomic number have the same chemical properties. Isotopes Atoms of an element that have the same number of protons but a different number of neutrons C 13 6 C 14 6 C

Radioactive Isotopes Unstable isotopes - the nucleus of the isotope has a tendency to break into elements with different atomic numbers. Eg. 14 C decays to 14 N (1 neutron in 14 6 C  1 proton  14 7 N) Half-Life Time taken for 1/2 the atoms in a sample to decay. Example: The half-life of 14 6 C is 5,600 yrs. How old is a fossil that contains 1/8 the proportion of 14 6 C in the atmosphere?

Electrons Determine the chemical behavior of atoms. Neutral Atoms Have no net charge. Ions Atoms in which: # electrons  # protons  Electrical charge Cation Ion with > # protons than electrons. Anion Ion with > # electrons than protons.

Electron Orbitals Orbital The area around an atom’s nucleus where an electron is most likely to be found. Potential Energy of Electrons (Energy of Position) Negative charge of electrons  Attraction to Nucleus  Keeping electrons in orbit  work

Which requires more energy of position? Orbitals close to or far away from the nucleus? Eg. Photosynthesis

Electron Energy Levels

Electron Orbitals

Electron Energy Levels

Redox Oxidation-Reduction occurs when an electron is transferred from one atom to another (OILRIG).

The Periodic Table

Chemical Bonds Molecule Compound A molecule that contains atoms of more than one element. Types of Chemical Bond Ionic Covalent Hydrogen Two or more atoms held together by chemical bonds.

Ionic Bonds *Not important in most biological molecules. When do they occur? When 2 atoms are so unequal in their attraction for electrons that an electron is transferred from one atom to the other and ions are formed.

Ionic Bonds CRYSTALS are formed - each ion is attracted to ions of opposite charge (NOT between particular ions, so DISCRETE NaCl molecules do not form). Properties Strong (not as strong as covalent) Non-directional

Covalent Bonds *Important in biological molecules. When do they occur? When electrons are SHARED between 2 atoms so that their outer energy level is completed. Properties Strong (important for bonding within molecules) Directional (bonds between 2 specific atoms, resulting in specific SHAPE)

Strength of Covalent Bonds Dependent on the number of shared electrons. Double Bonds 2 pairs of shared electrons. Eg. O=O Triple Bonds Strongest covalent bonds.

Polar Covalent Bonds Occur when the nucleus of one atom (involved in a covalent bond) is more electronegative than the other atom(s). This results in partial charges (  ) on the atoms. Example Water

Hydrogen bonds *Important in biological molecules When do they occur? When a hydrogen atom is covalently bonded to an electronegative atom it will have a partial positive charge and will  also be attracted to another electronegative atom.