CHAPTER 2

The Chemistry of Life

Concept 2.1

Atoms, Ions and Molecules

ELEMENTSElement: pure

substanceCannot be broken down

into other substances by chemical means

25 elements are essential to life

ELEMENTS

4 elements make up 96% of all living matter

Hydrogen (H)Oxygen (O)Nitrogen (N)Carbon (C)

ELEMENTS

Calcium (Ca), phosphorus (P), potassium (K), sulfur (S) most of remaining 4%

Trace elements: less than 0.01 % of body massare essential to lifeE.g.: iodine (I), copper (Cu), fluorine (F),

manganese (Mn), and selenium (Se)

Iodine is a trace element that prevents goiter

COMPOUNDS

COMPOUNDS: substance containing two or more elements combined in a fixed ratio

Compound properties may differ greatly from the elements they contain

H2O – liquid at room temperature, while hydrogen and oxygen are both gases

NaClNaCl – white crystal (table salt), while sodium is a silver-gray metal and chlorine is a yellowish-green gas

Na+ + Cl- NaCl

ATOMS

Atom: smallest possible particle of an element

Made up of 3 subatomic particles:proton: single unit of (+) charge

electron: single unit of (-) charge

neutron: electrically neutral—no charge

ATOMIC NUCLEUS

Forms central core of atom

Made up of tightly packed protons and neutrons

Nucleus has a net (+) charge due to the protons it contains

ATOMIC NUMBERAll the atoms of a particular element

have the same number of protons

Atomic number: the number of protons in the nucleus of an element

Examples: Carbon has 6 protons atomic number is 6

Helium has atomic number of 2 helium has 2 protons

ELECTRONSSmall negatively

charged particles that travel around nucleus

Pictured as traveling

around nucleus in a “cloud”

ELECTRONS & REACTIVITY

Electrons are said to belong to different energy levels

First or lowest level contains 2 electrons and is closest to nucleus

Each of the other energy levels contains 8 electrons.

ELECTRON ENERGY LEVELS

If the outer most shell is not filled, the atom is reactive.

The electrons in the outermost shell are called valence electrons.

Valence Electrons (Bohr Model)

Valence Electrons (Lewis Structure)

Concept 4.3

CHEMICAL BONDS JOIN ATOMS TO ONE ANOTHER

CHEMICAL BONDS

Atoms react with one another to fill their outer energy levels One atom may transfer an electron to another

atom or two atoms may share electrons

Transferring or sharing electrons creates an attraction called a chemical bond that holds atoms together

IONIC BONDS

Ionic bond: one atom transfers an electron to another atom

Ions: atoms that become electrically charged as a result of gaining or losing an electron

Oppositely charged ions are attracted to one another forming a chemical bond an ionic bond

COVALENT BONDS

Formed when atoms share electrons

Electrons may be shared equally or unequally

Molecule: two or more atoms held together by covalent bonds

CHEMICAL REACTIONS

Breaking of old chemical bonds and formation of new chemical bonds resulting in the formation of new substances

Reactants: starting material for a chemical reaction

Products: material created as a result of a chemical reaction

CHEMICAL EQUATION

Concept 4.4

LIFE DEPENDS ON THE UNIQUE

PROPERTIES OF WATER

WATER MOLECULEWater is a polar molecule

Electrons in bond are not shared equally between hydrogen and oxygen

Electrons attracted to oxygen more strongly than to hydrogen

Results in an internal separation of charge

Note: Hydrogen atoms in the water molecule are slightly positive and the oxygen atom slightly negative

POLARITY & HYDROGEN BONDING

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WATER’S LIFE-SUPPORTING PROPERTIES

Polarity of water and effects of hydrogen bonding give water with unique properties:

Cohesion and adhesion

Temperature moderation

Low density of ice compared to water

Ability to dissolve substances

COHESION & ADHESION

Cohesion: an attraction between like moleculesWater’s polarity results in hydrogen bonds forming

between water moleculesAdhesion: an attraction between unlike

moleculesBoth cohesion and adhesion are important forces in

the living world

COHESION & ADHESIONKeep large molecules

organized so they function properly in cells

Help transport water through roots and leaves in plants

Provides surface tension on surfaces of ponds and lakes

TEMPERATURE MODERATION

Hydrogen bonds in water molecules allow water temperatures to change more slowly

Causes oceans and lakes to moderate temperatures of nearby land areas less extreme temperatures in coastal areas

Through evaporation (sweating), water moderates temperature absorbs heat energy from skin cooling the body

LOW DENSITY OF ICE

Density: amount of matter/given volume

For most substances, solids are more dense than liquid state of matter

Due to hydrogen bonding, water is the opposite

Liquid water more dense than solid water

Since less dense substances float in more dense substances, ice floats

LOW DENSITY OF ICE

Why is this important to living things?

If ice sank, bodies of water would freeze from the bottom up

Organisms could NOT get to nutrients on the bottom and would be trapped

Ice insulates the water below, allowing life to persist below the frozen surface

WATER DISSOLVES OTHER SUBSTANCES

Solution: uniform mixture of two or more substances

Solvent: the substance that dissolves the other substance; present in the greater amount

Solute: the substance that is dissolved; present in the lesser amount

Aqueous solution: solution where water is the solvent

SOLUTIONS

Salt Dissolving in Water.url

ACIDS, BASES, & pH

Acid: a compound that donates H+ ions to aqueous solutions

Base: a compound that removes H+ ions from an aqueous solution

pH scale: range of numbers that describes how acidic or how basic a solution is

pH scale ranges from 0 (most acidic) to 14 (most basic); pH of 7 is neutral

ACIDS, BASES, & pH

BUFFERSBuffers: substances that cause a solution to

resist changes in pH

Molecules in cells are very sensitive to even small changes in pH

Many biological fluids such as blood contain buffers that maintain its pH at or very near 7.4

THE END

BUFFERS

Buffers.url

COVALENT BONDS

covalent bond.url

Save Video - ionic bonds.url

STABLE ISOTOPES

Most isotopes are stable—their nuclei do not change over time

Other isotopes contain nuclei that will change or decay over time

ionic and covalent bonds .url

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