Biology I

Of Atoms and Molecules: Chemistry Basics

I. The first job of a biologist is to understand the chemistry of life.

What does chemistry have to do with biology?

Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

Figure 2.0 Bombardier beetle

http://www.bing.com/videos/watch/video/bombardier-beetle-1/7f97013685d6db87a42b7f97013685d6db87a42b-166339149941?q=bombardier%20beetle&FORM=VIRE3

A. AtomThe smallest “piece” of an element

that retains the characteristics of that element.

Composed of 3 subatomic particles:• Protons• Neutrons• Electrons

Characteristics of Subatomic Particles

B. Because of its charges, the atom is neutral!

Draw your Carbon atom using the circle provided

II. Elements

A. An element is a pure substance that consists of one type of atom.

B. Abbreviations for the elements are called symbols.

C. There are 92 naturally occurring elements.

What is this?Turn to the very back of

your book

• How many of these elements are essential to life?

Only 25!!!! Find them on your periodic table H hydrogen C carbon N nitrogen Mo molybdenum F fluorine Na sodium Mg magnesium Si silicon P phosphorus S sulfur Cl chlorine K potassium Ca calcium V vanadium Cr chromium Mn

manganese Fe iron Co cobalt Ni nickel Cu copper Zn zinc Se selenium O oxygen Sn tin I iodine

The most abundant elements in living things are:C (carbon)H (hydrogen)O (oxygen)N (nitrogen)

III. Atomic number• # protons in nucleus of an atom

(establishes identity of the atom)• Since most atoms are electrically

neutral, atomic number indicates # of electrons as well.

IV. Atomic mass• # protons plus # neutrons in

nucleus of an atom

How can we determine the number of neutrons in an atom?• # neutrons = atomic mass - atomic #

• Determine # neutrons in a carbon atom (atomic mass = 12; atomic # = 6).• # neutrons = 12 - 6 = 6

Do all carbon atoms have the same number of protons? Turn to page 36

Do all carbon atoms have the same number of neutrons?

V. Atoms can have different numbers of neutrons. Atoms of the same element that have different numbers of neutrons are called isotopes

Carbon is a great example Draw your 3 carbon atoms

(pg.36)

Some isotopes are radioactive. This means that their nuclei is unstable and breaking down, emitting radiation

Some important uses of radioactive isotopes are

a) carbon dating – determine age of fossils and rocks http://videos.howstuffworks.com/science/carbon-dating-videos-

playlist.htm#video-29401

b)Treat cancerc) Kill bacteria (that cause food to

spoil)d)Labels or “traces” that move

through an organism

VI. Ions: sometimes atoms gain or lose electrons.

This gives them a positive or negative charge.

This is written as Na+ or Cl-

VII. A compound is a substance formed by the chemical combination of two or more elements in definite proportions.

These are represented by chemical formula.

3H2O

How many atoms of oxygen? 1

This is a subscript. It shows the number of Hydrogen atoms

This is the coefficient It shows the number of Water Molecules.

The chemical and physical properties of an element are usually different from the compound.

Examples are:a) H is a gas, O is a gas, H20 is a

liquidb) Na is a silver-colored metal

that is soft enough to cut with a knife

c) Cl is a poisonous greenish gas that was used to kill many soldiers in WWI

d) NaCl is a white solid that dissolves easily with water. (table salt) Sodium chloride is not poisonous, it is

essential for the survival of most living things

Chemical ReactionsThe reactants of a reaction are written to the left of the arrow

Chemical reactionsThe products of a reaction are written to the right of the arrow

ExampleRewrite the equation in your notes so the subscripts are lower

This is the equation for cellular respiration

The process your cells are doing right now!

VIII. Chemical Bonds• Chemical bonds involve the electrons in the last energy level. We call these electrons valence electrons!

• Octet rule!• The goal of chemical bonding is for all atoms involved to complete or eliminate their outer electron shells.

The Octet Rule!!!Atoms can only handle a certain

number of electrons in each energy level!!

2 in the first one They really,8 in the second really want8 in the third EIGHT!!!!

The valence electrons are the electrons in the last shell or energy level of an atom.

A.) Ionic bonds – The attractions between positively charged ions and negatively charged ions

form when oppositely charged ions are attracted to each other.

• atoms with 1, 2 or 3 valence electrons give up electrons to atoms with 7, 6 or 5 valence electrons which forms ions

• Example salt (NaCl) form salt which break apart in water

• Ex. NaCl

B.) Covalent bonds – sometimes electrons are shared rather than transferred.

Covalent bonds form when electrons are shared between atoms.

• Molecules are formed• Covalent bonds are stronger than

ionic bonds!• The same size dogs SHARE the boneAtoms are the same size and share the

electrons equally!

The structure that results when atoms are joined by covalent bonds is called a molecule.

Covalent bonds are stronger than ionic bonds

Nonpolar covalent bonds - electrons are shared equally between atoms.

Ex. methane

Polar covalent bonds - electrons are not shared equally. They are drawn more strongly to 1 atom’s nucleus than the other.

Ex. water

Unequal sharing of the bone!

One dog is larger than the other and hogs the bone, but they are still sharing!!!!

One atom is larger and hogs the electron making one end of the molecule more negative and one end more positive!!

Unequal sharing of the bone!

One dog is larger than the other and hogs the bone, but they are still sharing!!!!

One atom is larger and hogs the electron making one end of the molecule more negative and one end more positive!!

C.) Hydrogen bonds – involve hydrogen and are the weakest type of bond*

Ex. DNA

H2O

The End

VII. Compounds:A compound is a substance formed by

the chemical combination of two or more elements.

These are represented by formulas

3H2OCoefficient

Subscript

Chemical Reactions• The reactants of a reaction are

written to the left of the arrow.• The products of a reaction are

written to the right of the arrow.

Example:6O2 + C6H12O6 6H2O + 6CO2 + energy

Examples:

• CO2

carbon dioxide

• H2Owater

• CH4

methane

• C6H12O6

glucose

Examples:• 4CO2 4 molecules of carbon dioxide

• 2C6H12O6 2 molecules of glucose

• 6O2 6 molecules of oxygen