The Chemistry of Life

E. coli vs. E. coli

Atoms

• Submicroscopic units of matter

• Smallest unit of all physical material

Structure of Atoms

• Proton– In nucleus– Positive charge

• Neutron– In nucleus– No charge

• Electron– Surround nucleus– Negative charge

Atomic Mass

• Combined mass of protons & neutrons

• Electron mass is too small to matter

Atomic Mass = 14

Elements

• Made of a single kind of atom

• Type determined by its number of protons

7 Protons = Nitrogen

Atoms & Isotopes• Atoms

– protons = electrons– Electrically neutral

• Isotopes– Same number of protons,

different number of neutrons– Differ in atomic mass

Electrons• Could be found anywhere around nucleus

• Most likely location is its shell

Electrons• Shells correspond to energy levels

• Energy increases away from the nucleus

• Number of protons also increases energy

Molecules

• Combinations of atoms

– Same elements or different elements

– Methods atoms combine

• Share electrons

• Attract via opposing electron charges

Compounds

• Molecules with different atoms

• Methods of combining– Sharing electrons– Atoms lose & gain electrons

(Ions)

Chemical Formula

• Method to describe molecule composition

H2O = Water

2 Parts Hydrogen

1Part Oxygen

Factors that Influence Interaction Among Atoms

1. Tendency of electrons to occur in pairs

2. Tendency of atoms to balance charges

3. Tendency of outer shell to be full

(Octet Rule)

Octet Rule

• Refers to 8 as stable number of electrons in outer shell

• First energy level is exception (2 electrons)

• Atoms with unfilled shells tend to interact

Noble Gases

• Equal numbers of protons & electrons

• Outer energy shell full

• Do not readily react with other elements

Helium Neon

Argon Krypton

Xenon Radon

Chemical Bonds Form Molecules• Ways atoms can satisfy octet rule

– Gain electrons from other atoms– Lose electrons to other atoms– Share electrons with other atoms

Covalent Bonds

• Atoms share outer electrons

Ionic Bonds• One atom donates electron to other atom

Oxidation

• Process where addition of Oxygen, lose Hydrogen or lose electron

from element or compound

• Oxygen

– Strong electron receptor

– Most frequent receptor in biological systems

Reduction

• Process where an atom gains an electron

• Changes charge by -1

• Oxidation and reduction occur together

Called redox reactions

Diatomic Molecules

• Paired atoms that form a molecule

• Share electrons with covalent bond

H2 = Hydrogen Gas

O2 = Oxygen Gas

Cl2 = Chlorine Gas

N2 = Nitrogen Gas

Covalent Bond Strength

• Can be weak or strong

• Single bond (example Hydrogen gas)

• Double bond (example Oxygen gas)

• Triple bond (example Nitrogen gas)

Bonding in Carbon

• Can form four covalent bonds

• Can bond to more than one atom

• Basis for many biological molecules

Energy and Covalent Bonds

• Bonds act as storage place for energy

• Breaking bonds releases energy

• Allows organisms to store & use energy

Water

• Most abundant molecule in your body

• Vital to life

Frog Eggs in Water Environment

Chemical Properties of Water

• Hydrogen’s electrons usually near Oxygen

• Molecule has polarity (polar molecule)

Polarity of Water

• Allows it to attract other molecules

• Forms hydrogen bonds– Weak attraction– Easily made &

broken

Specific Heat

• Heat needed to raise or lower temperature

• Water has high specific heat

– Modulates temperature in living bodies

– As water absorbs heat, hydrogen bonds break

Water, Temperature & Hydrogen Bonds

Cohesion & Adhesion

• Cohesion– Hydrogen bonds make molecules “stick

together”– Aids water movement in plants

• Adhesion– Weak electrical attraction of molecules– Capillary action

Surface Tension

Cohesion of water molecules at its surface

Water as a Solvent

• Solution = homogeneous mixture of substances

• Solvent = substance in greatest amount

• Solute = dissolves in solvent

• Water is a powerful solvent

• Ions break away in presence of water

How Salt Dissolves in Water

Water &Nonpolar Molecules

• Nonpolar molecules– Do not form hydrogen bonds– Not dissolved in water

Oil is Hydrophobic

Ionized Water

• Water can Accept or donate protons

H2O OH- + H+

Acids & Bases

• Acid– Dissociates to form H+ ions in water– pH less than 7

• Base– Accepts H+ ions in water– pH greater than 7

pH scale

• Indicates concentration of H+ ions

• Neutral is at 7

• Determined by taking negative value of exponents of its H+ ions concentration

End Chapter 3