Chapter 2

Basic Chemistry and Cells

Matter is composed of atoms

• Six types of atoms are basic to life = 95% of body weight– C carbon– H hydrogen– N nitrogen– O oxygen– P phosphorus– S sulfur

• Element– Substance that cannot be broken down by chemical means into

a simpler substance (periodic table of elements shows all known elements)

• Atom– Smallest unit of an element that still retains the chemical and

physical properties of the element

• Atomic symbol– One or two letters that represent the name of an

element (Au, C, O, N)

• Subatomic particles– Protons

• Positively charged (+)• Within nucleus

– Neutrons (0)• Uncharged• Within nucleus

– Electrons (-)• Negatively charged• Orbit about nucleus

• Electron shells– Inner shell

• Lowest energy level• Holds 2 electrons

– All shells beyond inner shell

• Holds 8 electrons

– Outer shell• Highest energy level• Holds 8 electrons

• Atomic number– Number of protons of an element– Also tells number of electrons when electronically

neutral

• Mass number– Number of protons plus neutrons

• Isotopes– Atoms of a single element that differ in their number

of neutrons

• Atomic mass– Average mass of all isotopes

The many medical uses of radioactive isotopes

• Low levels of radiation– Tracer to detect tumors

• High levels of radiation– Sterilize medical and dental products– Sterilize mail to free it of possible pathogens

(anthrax)– Treatment for cancer

Atoms react with one another to form molecules

• After atoms react, they have a completed outer shell

• Periodic table– Arranges elements based on characteristics

• Periods– Horizontal row– How many shells an atom has

• Groups– Vertical column– How many electrons an atom has in its outer shell

Periods – how many shellsGroups – how many electrons in outer shell

• Octet rule– Atoms will give up, accept, or share electrons in order to have 8

electrons in the outer shell• Group 8

– Stable– All other groups readily react

• Compound– When atoms of two or more elements bond together in fixed

proportions• Molecule

– Smallest part of a compound that still has the properties of that compound

– Molecule is union of two or more atoms of the same or different elements

• Naturally occurring molecules– O2, H2, N2, H2O

• Naturally occurring compound– H2O

An ionic bond occurs when electrons are transferred

• One atom can take electron(s) from another atom

• Ions result– Ions that lost electrons are

positively charged– Ions that gained electrons

are negatively charged

• Ionic bonds result– An attraction between

negatively and positively charged ions

A covalent bond occurs when electrons are shared

• Atoms want to fill their outer shell• Bond notations

– H – H share one pair of electrons– O = O share two pairs of electrons– N = N share three pairs of electrons

• Molecular – omits the bond line– H2

– O2

– N2

• Common bonds required– H – 1 bond– O – 2 bonds– C – 4 bonds

Chemical reactions

• Some bonds are broken while others are formed• Reactants

– Participate in reaction

• Products– Formed by reaction

• Photosynthesis– Balanced equation– Same number of each type of atom occurs on both sides of

arrow

A covalent bond can be nonpolar or polar

• Nonpolar– Sharing of electrons between two atoms is fairly

equal

• Electronegativity– Attraction of an atom for the electrons in a covalent

bond• H2O

– O • Larger atom• more electronegative• Slightly negative

– H• Smaller atom• Less electronegative• Slightly positive

• Polar– Unequal sharing of electrons in a covalent bond

The polarity of water molecules leads to the formation of hydrogen bonds

Hydrogen bonds can occur between polar molecules

• Hydrogen atoms in one molecule are attracted to oxygen atoms in another molecule

• Weaker than ionic or covalent bonds

• Hydrogen bonds also hold the two strands of DNA together

The properties of water benefit life

Water molecules stick together and to other materials

• Due to hydrogen bonding– Water can be liquid at most temperatures found on

earth– Water molecules exhibit cohesion (stick together)– Water molecules exhibit adhesion (stick to other polar

material)• Cohesion and adhesion

– Create surface tension– Allows water to rise to the top of plants– Allows blood to flow through a body

Water warms up and cools down slowly

• This allows organisms to maintain internal temperatures (homeostasis)

• Cooling slowly aids organisms in winter

• To vaporize water, hydrogen bonds must be broken, this requires a large amount of energy

Water dissolves other polar substances

• Solutions are composed of– Solute

• What is being dissolved

– Solvent• What does the dissolving

Creating sugar watersolute – sugarsolvent – water

• When ionic salt (NaCl) is put in water, the atoms dissociate and the Na+ and Cl- dissolve into the water

Hydrophilic – molecule that can attract water

Hydrophobic – molecule that canon attract water (oil and water do not mix)

Frozen water is less dense than liquid

Water expands as it freezes

Ice floats, allowing bodies of water to freeze from the surface down and they usually do not freeze solid, allowing organisms to survive the winter

Living things require a narrow pH range

• When water dissociates, hydrogen ions (H+) and hydroxide ions (OH-) result in equal concentrations

• Acids– Excess hydrogen (H+) ions

• Bases– Excess hydroxide (OH-) ions

• The pH scale measures acidity and basicity• pH scale ranges from 0 to 14• Neutral = 7

– This is when H+ concentration equals OH- concentration

• Acidic <7• Basic >7

Buffers help keep the pH of the body fluids relatively constant

• Buffer– Resists changes in pH

• Blood pH needs to stay between 7.35 and 7.45• Carbonic acid (H2CO3) and bicarbonate (HCO3) are present in blood• Carbonic acid can dissociate to release bicarbonate and H+

– This lowers pH

• When a base is added (OH-) the carbonic acid dissociates and releases H+, these combine to form water (H2O)

• When there is excess H+, carbonic acid reforms

• Breathing releases CO2, which reduces the amount of carbonic acid in the blood

• Kidneys also filter acids and bases from the body but act more slowly, although powerfully. A malfunction of the kidneys could cause blood pH to go higher or lower than required levels.

Harmful effects of acid rain

• Rainwater pH = 5.6– Low due to CO2 in the air forming carbonic

acid

• Acid rain pH < 5– Contains sulfuric and/or nitric acid– Sulfur dioxide and nitrogen oxides come from

burning fossil fuels

• Acid rain affects lakes in areas with little to no limestone (a buffer) CaCO3

• Acid rain– Causes mercury to accumulate in fish– Can make bodies of water lifeless– Damages plants– Increases respiratory illness in humans– Breaks down limestone and marble buildings

and monuments– Degrades paint on homes and cars