The Chemical Basis of LifeEnergy levels of electrons

Electron configuration and chemical properties:

*chemical behavior due to

electrons

Covalent Bonds– A covalent bond forms when two atoms share one or

more pairs of outer-shell electrons.– Atoms held together by covalent bonds form a

molecule.

Namemolecular formula

Hydrogen gas H2

Oxygen gas O2

Methane CH4

Electron configuration Structural formula Space-filling model Ball-and-stick model

Single bonda pair of shared electrons

Double bondtwo pairs of shared electrons

Ionic Bonds– When an atom loses or gains electrons, it becomes

electrically charged.• Charged atoms are called ions.• Ionic bonds are formed between oppositely charged ions.

Outer shellhas 1 electron

Outer shellhas 7 electrons

The outer electron is strippedfrom sodium and completesthe chlorine atom’s outer shell

NaSodium atom

ClChlorine atom

Completeouter shells

The attractionbetween theions—an ionicbond—holdsthem together

Na

Sodium ionCl

Chlorine ion

Sodium chloride (NaCl)

Hydrogen Bonds– Water is a compound in which the electrons in its

covalent bonds are shared unequally.• This causes water to be a polar molecule, one with opposite

charges on opposite ends.

H H

O

slightly slightly

slightly –

Hydrogen bonding• Weak bonds formed

between hydrogen and another atom – Surface tension of water

• Important as intramolecular bonds, giving shape to proteins and other biomolecules

WATER AND LIFE– Life on Earth began in water and evolved there for 3

billion years.• Modern life remains tied to water.• Your cells are composed of 70%–95% water.

Properties of Water• Numerous properties due to the hydrogen bonding

Properties of Water

Microscopic tubesCohesion due tohydrogen bondsbetween watermolecules

Evaporation from the leaves

SEM

Flow

of w

ater

• Cohesion• Adhesion

– Heat and temperature– Water can absorb and store large amounts of heat

while only changing a few degrees in temperature.– Water can moderate temperatures.

Properties of Water

– Surface tension is the measure of how difficult it is to stretch or break the surface of a liquid.

Properties of Water

*solution

*solvent *solute *aqueous solution

Water is the solvent of life

The Chemical Basis of Life

Hydrophilic and hydrophobic substances*hydrophilic *hydrophobic

The dissociation of water molecules

H2O H+ + OH-

Acids and bases*acid

*base

Basicsolution

Neutralsolution

Acidicsolution

Oven cleaner

Householdbleach

Human bloodPure water

Grapefruit juice,soft drinkLemon juice,gastric juice

Household ammonia

Milk of magnesia

Seawater

Tomato juice

Urine

pH scale0

1

2

3

4

5

6

7

8

9

10

11

12

13

14

Incr

easi

ngly

aci

dic

gre

ater

H c

once

ntra

tion

Incr

easi

ngly

bas

iclo

wer

H c

once

ntra

tion

Neutral[H+] [OH–]

Acids, Bases and pH

Carbon and Organic Chemistry– Carbon is a versatile atom.– Carbon forms large, complex, and diverse molecules

necessary for life’s functions.– Organic compounds are carbon-based molecules.

Structuralformula

Ball-and-stickmodel

Space-fillingmodel

• Variations in Carbon skeletons Carbon skeletons vary in length

Carbon skeletons may be unbranched or branched

Carbon skeletons may have double bonds,which can vary in location

Carbon skeletons may be arranged in rings

Carbon and Organic Chemistry

– Larger hydrocarbons form fuels for engines.– Hydrocarbons of fat molecules fuel our bodies.

Hydrocarbons

*structural isomers

*geometric isomers

*enantiomers

Example of enantiomers:

Chemical Components of Cells