THE CHEMISTRY OF LIFEChapter 2

Biology – Miller • Levine

ATOMS

Basic unit of matterFrom the Greek word atomos, which means “unable to be cut”

Subatomic particles:Protons – positive charge (p+)Neutrons – neutral, no charge (n0)

Electrons – negative charge (e-)

ATOMS

Nucleus – contains protons & neutrons

Electron cloud – area where electrons are located around the nucleus1st level holds 2 e-2nd level holds 8 e-3rd level holds 18 e-

Atoms are neutral because p+ = e-

ATOMS

ELEMENT

A pure substance that consists entirely of one type of atom

92 naturally occurring elementsPeriodic Table of Elements:

Represented by a 1 or 2 letter symbol

Atomic number – # of protonsMass number – protons + neutronsHorizontal rows are called periodsVertical columns are called groups

ELEMENTS

ISOTOPES

Atoms of the same element that have a different number of neutrons

Radioactive isotopes – isotopes that are unstable and give off radiationCan be used in geological dating, to

treat cancer, to kill bacteria in food, & as “tracers” in medical diagnosis

ISOTOPES

CHEMICAL COMPOUNDS

Compound – a substance formed by two or more different elementsAlways found in a fixed ratioChemically and physically different

from the elements that they include

Chemical formula – shows the number of each element in a compoundEx. H2O

CHEMICAL BONDS

Atoms in compounds are held together by chemical bonds

Valence electrons – electrons that are available to form bondsAn atom is stable when its outer

(valence) shell contains 8 e- (except H and He which are stable with 2 e-)

3 major types of bonds – ionic, covalent, and hydrogen

IONIC BONDS An ion is formed when one or more

electrons are transferred from one atom to another

Oppositely charged ions are attracted to each other forming an ionic bond

Ex. NaCl

COVALENT BONDS

Form when electrons are shared between atoms

Molecule – when atoms are joined together by a covalent bond

Ex. H2O

VAN DER WAALS FORCES

The random movement of electrons creates temporary areas of slightly positive and slightly negative charges

When molecules come close together, these positive and negative regions form a weak attraction known as van der Waals forces

THE WATER MOLECULE

Water is a polar molecule, where the electrons are not shared equallyThere is a – charge near the O and a +

charge near the HHydrogen bonds – attraction

between the H of one water to the O of anotherWeaker than covalent or ionic

HYDROGEN BONDS

COHESION & ADHESION

Cohesion – the attraction between molecules of the same substance

Adhesion – the attraction between molecules of different substances

MIXTURES

When two or more elements or compounds are physically mixed together but not chemically combined

Heterogeneous mixture – the components remain distinctSuspension – a mixture of water and

nondissolved materialsWill settle back out over time

Colloid – the particles will not settle out

MIXTURES

Homogeneous mixture – uniform composition throughoutSolution – a mixture in which all

the components are evenly distributedSolute – the substance that is dissolved

Solvent – the substance in which the solute dissolvesWater is the greatest solvent

SOLUTIONS

ACIDS, BASES, AND PH

A water molecule can react to form hydrogen (H+) and hydroxide (OH-) ions

Acid – any compound that forms H+ ions in solution (pH less than 7)

Base – any compound that forms OH- ions in solution (pH greater than 7)

ACIDS, BASES, AND PH

pH scale – a measurement system that indicates the concentration of H+ ions in a solution (0-14)

Buffer – weak acids or bases that react with strong acids or bases to prevent sudden changes in pH

CHEMICAL REACTIONS

Process that changes one set of chemicals into another set of chemicalsFe + O2 → Fe2O3

Reactants – in front of the arrowProducts – after the arrow

Law of Conservation of Matter – matter can be neither created nor destroyedEquations must be balanced

ENERGY IN REACTIONS

Endergonic – reactions that require an input of energy or store energy

Exergonic – reactions that release energy

Activation energy – the energy needed to start a reaction

ENZYMES

Some chemical reactions are too slow or have too high an activation energy

Catalyst – a substance that speeds up the rate of a chemical reaction by lowering the activation energy

Enzymes – proteins that are catalysts

EFFECT OF ENZYMES

ENZYME ACTION

The enzyme-substrate complexSubstrates – the reactantsActive site – the place where the

substrates bind to the enzymeWhen the substrates bind to the

active site they form the enzyme-substrate complex

Enzymes are specific to the substrate that they act upon (lock and key mechanism)

ENZYME-SUBSTRATE COMPLEX

REGULATION OF ENZYME ACTIVITY

Can be affected by pH and temperatureMost enzymes have an optimal pH

and temperatureCan be turned “on” or “off”Can be used over and over again