General Biology

Inorganic Chemistry

I. Chemical Elements and Compounds

A. Elements

• Consist of only one kind of atom, cannot be decomposed into a simpler substance.

• The planet is made up of some 90 elements.

• Only 25 or so are used to build living things.

• All matter is made of elements.

• Consider the following chart.

Elemental composition of the lithosphere and the human body. Each number represents the percent of the total number of atoms present.

Composition of Lithosphere Composition of the Human Body

Oxygen 47 Hydrogen 63

Silicon 28 Oxygen 25.5

Aluminum 7.9 Carbon 9.5

Iron 4.5 Nitrogen 1.4

Calcium 3.5 Calcium 0.31

Sodium 2.5 Phosphorous 0.22

Potassium 2.5 Chlorine 0.08

Magnesium 2.2 Potassium 0.06

Titanium 0.46 Sulfur 0.05

Hydrogen 0.22 Sodium 0.03

Carbon 0.19 Magnesium 0.01

All others <0.1 All others <0.01

• Living Matter

• Uses only a fraction of the elements available to it.

• The relative proportions of those it does acquire from its surroundings are quite different from the proportions in the environment.

• One of the properties of life is to take up certain elements that are scarce in the nonliving world and concentrate them within living cells.

• C, O, H, & N make up 96% of living matter

B. Atoms consist of protons, neutrons, and electrons

Drawing Atoms

Draw the following atoms, showing all subatomic particles.

Helium (He)

Lithium (Li)

Fluorine (F)

II. Isotopes

• Atoms of an element that have the same atomic number but different mass number.

• Elements occur as mixtures of isotopes.

• Different isotopes of the same element react chemically in the same way. Why?

• Some isotopes are radioactive.

• Unstable isotope in which the nucleus spontaneously decays, emitting subatomic particles and/or energy as radioactivity.

• Biological applications of radioactive isotopes:

1. Dating geological strata and fossils (Radioactive decay is at a fixed rate)

http://earthsci.org/geotime/radate/radate.html#RadiocarbonJanuary 12, 2004

2. Radioactive tracers (Used to study biological pathways)

3. P, N, and H were used to determine DNA structure

4. Treatment for some cancers (Cobalt)

5. Can be extremely hazardous to cell molecules

6. Used to diagnose disease (PETscanner)

http://www.triumf.ca/welcome/petscan.htmlJanuary 12, 2004

III. Compounds

• A pure substance composed of two or more elements combined in a fixed ratio.

• Example: NaCl (sodium chloride)

IV. Electron Configuration

• An atom’s electron configuration determines its chemical behavior.

• Chemical properties of an atom depend upon the number of valence electrons.

• The valence electrons are responsible for the atom’s bonding capacity (Octet Rule)

V. Bonding

• Chemical Bonds – Attractions that hold molecules together.

• Molecules – Two or more atoms held together by chemical bonds.

A. Covalent Bonds

• Chemical bond between atoms formed by sharing a pair of valence electrons.

• Strong chemical bond

Illustrate covalent bonding;

Hydrogen and Hydrogen

Covalent Bonding Continued

• Two types, nonpolar covalent and polar covalent bonds.

• The electronegativity is the atoms ability to attract and hold electrons.

• The more electronegative an atom, the more strongly it attracts shared electrons.

• Notice that Fluorine is the most electronegative, but it is Oxygen that is exploited by life.

• The relative electronegativity of two interacting atoms plays a major part in determining what kind of chemical bond forms between them.

1. Nonpolar Covalent Bond – Covalent bond formed by an equal sharing of electrons between atoms.

• Occurs when electronegativity of both atoms is about the same.

• Molecules made of one element.

Illustrate Nonpolar Covalent Bonding;

Carbon and Hydrogen

2. Polar Covalent Bond – Covalent bond formed by an unequal sharing of electrons between atoms.

• Occurs when the atoms involved have different electronegativities.

• Shared electrons spend more time around the more electronegative atom.

• Think of it as a Tug-Of-War

Oxygen e Hydrogen

Oxygen e Hydrogen

B. Ionic Bonds

• Bonds formed by the electrostatic attraction after the complete transfer of an electron(s) from one atom to another.

• Ion – Charged atom or molecule

• Anion – An atom that has gained one or more electrons from another atom and has become negatively charged.

• Cation – An atom that has lost one or more electrons and has become positively charged.

• Ionic Compounds are called salts.

• A strong chemical bond.

C. Weak Chemical Bonds

1. Hydrogen Bonds – bond formed by the charged attraction when a hydrogen atom covalently bonded to one electronegative atom is attracted to another electronegative atom.

• About 20 times easier to break than a covalent bond.

2. Van der Waals Interactions – weak interactions that occur between atoms and molecules that are very close together and results from charge asymetry in electron clouds.

3. Weak Bonds play important roles in the chemistry of life.

• Make chemical signaling possible in living organisms (short lived responses)

• Help stabilize the three-dimensional shape of large molecules.

VI. Structure and Function

• A molecule has a characteristic size and shape.

• The function of a molecule is dependent upon the shape of the molecule.

• Example: Insulin causes glucose uptake into liver and muscle cells of vertebrates because the shape of the insulin molecule is recognized by specific receptors on the target cell.

VII. Chemical Reactions

• Process of making and breaking chemical bonds leading to changes in the composition of matter.

• Reactants undergo changes to become products.

• Most reactions are reversible.

• Chemical equilibrium – equilibrium established when the rate of forward reaction equals the rate of reverse reaction.