Essential Chemistry for Biology

Chapter 2

Tracing Life Down to the Chemical Level

Basic Chemistry

Matter Anything that takes up

space and has mass Can exist as a liquid,

solid, or gas Elements

Basic building block of matter

92 naturally occurring elements

Basic Chemistry

Only 6 elements that make up most of the body weight of organisms C CarbonH HydrogenN NitrogenO OxygenP PhosphorusS Sulfur

Trace Elements

Trace elements make up 0.01% of human body weight, but still very important

Each Element Consists of ONE Kind of Atom

Smallest unit that retains the properties of a given element And to enter a chemical reaction

Composed of subatomic particles: Protons (p+) Neutrons Electrons (e-)

Move @ atomic nucleus Usually (e-) = (p+)

Electrically neutral

Atomic Symbol

Atomic Mass = Number of Protons + Number of Neutrons

Atomic Number = The Number of Protons in the Nucleus

Valence Shell

Molecules and Compounds

Molecules Chemical bonding that joins atoms Some contain atoms of only one element

N2

Compounds Atoms of two or more different elements

H2O Mixture

Two or more molecules mingling together

Chemical Bonds

Atoms are held together by bonds 3 main types:

Ionic bond Accept or donate electrons

Covalent bond Share one or more electrons

Hydrogen bond

Ionic Bond

Atoms gain and lose electrons Balance between protons

and electrons shifts Become “ionized”

Ion Atom that has a charge Losing an electron results

in a net positive Gaining an electron results

in a net negative charge Ionic bond

Association of two ions that have opposing charges

Which will form an ionic bond?

Potassium (K)

Chlorine (Cl)

Helium (He)

Argon (Ar)

Can Mg and Cl form an ionic bond?

Magnesium (Mg)Chlorine (Cl)

Covalent Bond

Covalent bond Stable and stronger

than ionic bonds Atoms share

electrons Each atom will

have a completed outer shell

Bond Notation Single covalent

bonds are written as H-H

Double covalent bonds are written as O=O

A covalent bond can be nonpolar or polar

Nonpolar covalent bond Sharing of electrons

between atoms is fairly equal

Polar covalent bond Unequal sharing of

electrons

Hydrogen Bond

Hydrogen bond Weak attraction

Form and break easily

Occurs between polar molecules

Polar bonds have charges on either end and often attract to each other

Chemical Reactions

Cells constantly rearrange molecules by breaking existing chemical bonds and forming new ones

Reactants Starting materials

Products End materials

Chemical reactions cannot create or destroy matter, They only rearrange it

Solvent of life

Water dissolves other polar substances

Solvent Ions and polar molecules

easily dissolve in it Solute

A dissolved substance Hydrophilic

water-loving molecules form hydrogen bonds with

water Hydrophobic

water-fearing molecules do not form hydrogen

bonds with water

Acids and Bases

When water ionizes, it releases an equal number of hydrogen ions (H+) and hydroxide ions (OH-)

Some substances release more or fewer or each Acids - Excess hydrogen ions Bases - Excess hydroxide ions

Acidic and Basic Solutions

Acidic Solutions Sharp, sour taste Molecules that

dissociate in water Release

hydrogen ions (H+)

Basic Solutions Bitter taste Molecules that

either take up hydrogen ions (H+) or release hydroxide ions (OH-)

pH Scale

The pH Scale Ranges from 0 - 14

pH below 7 is acidic [H+] > [OH-]pH above 7 is alkaline [OH-] > [H+]pH of 7 is neutral [H+] = [OH-]

Buffer Chemical or combination of chemicals that

keeps pH within normal limits