Matter and Energy in the Matter and Energy in the Web of LifeWeb of Life

Chapter 4Chapter 4

What Are Atoms?What Are Atoms?

1) Smallest particles that retain properties 1) Smallest particles that retain properties

of an elementof an element

2) Made up of subatomic particles:2) Made up of subatomic particles:a) Protons (+)a) Protons (+)

b) Electrons (-) b) Electrons (-)

c) Neutrons (no charge)` c) Neutrons (no charge)`

Atomic ParticlesAtomic Particles

Atomic NumberAtomic Number

1) Number of protons1) Number of protonsa) All atoms of an element have the same a) All atoms of an element have the same

atomic numberatomic number1. Atomic number of hydrogen = 11. Atomic number of hydrogen = 12. Atomic number of carbon = 6`2. Atomic number of carbon = 6`

Mass NumberMass Number

Number of protonsNumber of protons

++

Number of neutronsNumber of neutrons

Isotopes vary in mass numberIsotopes vary in mass number

Mass NumberMass Number

IsotopesIsotopes

1) Atoms of an element with different 1) Atoms of an element with different numbers of neutrons (different mass numbers of neutrons (different mass numbers)numbers)a) Carbon 12 has 6 protons, 6 neutronsa) Carbon 12 has 6 protons, 6 neutronsb) Carbon 14 has 6 protons, 8 neutrons`b) Carbon 14 has 6 protons, 8 neutrons`

RadioisotopesRadioisotopes

1) Have an unstable nucleus that 1) Have an unstable nucleus that emits energy and particlesemits energy and particles

2) Radioactive decay transforms 2) Radioactive decay transforms radioisotope into a different elementradioisotope into a different elementa) Decay occurs at a fixed rate`a) Decay occurs at a fixed rate`

Radioisotopes as TracersRadioisotopes as Tracers

1) A Tracer is a substance with a 1) A Tracer is a substance with a radioisotope attached to itradioisotope attached to ita) Emissions from the tracer can be a) Emissions from the tracer can be

detected with special devices detected with special devices b) Following movement of tracers is b) Following movement of tracers is

useful in many areas of biology`useful in many areas of biology`

Thyroid ScanThyroid Scan

1) Measures health of thyroid by 1) Measures health of thyroid by detecting radioactive iodine taken up by detecting radioactive iodine taken up by thyroid gland`thyroid gland`

normal thyroid enlarged cancerous

PET ScanPET Scan

What Determines Whether What Determines Whether Atoms Will Interact?Atoms Will Interact?

The number and arrangement of their The number and arrangement of their electronselectrons

Electron OrbitalsElectron Orbitals

1) Orbitals can hold up to two 1) Orbitals can hold up to two electronselectronsa) Atoms differ in the number of a) Atoms differ in the number of

occupied orbitalsoccupied orbitals2) Orbitals closest to nucleus 2) Orbitals closest to nucleus

are lower energy and are filled are lower energy and are filled first`first`

Shell ModelShell Model

1) First shell 1) First shell a) Lowest energya) Lowest energy

b) Holds 1 orbital with up b) Holds 1 orbital with up

to 2 electronsto 2 electrons

2) Second shell2) Second shella) 4 orbitals hold up to 8 a) 4 orbitals hold up to 8

electrons`electrons`

CALCIUM20p+ , 20e-

Shell ModelShell Model

ShellsShells

Chemical Bonds, Molecules, Chemical Bonds, Molecules, & Compounds& Compounds

1) Bond is union between electron structures of 1) Bond is union between electron structures of atomsatomsa) Atoms bond to form moleculesa) Atoms bond to form molecules

1. Molecules may contain atoms of only 1. Molecules may contain atoms of only one element one element

a. Oa. O22

2. Molecules of compounds contain more 2. Molecules of compounds contain more than one element than one element

a. Ha. H22O`O`

Chemical BookkeepingChemical Bookkeeping

1) Use symbols for elements when writing 1) Use symbols for elements when writing formulasformulas

a) Formula for glucose is Ca) Formula for glucose is C66HH1212OO66

a) 6 carbons a) 6 carbons

b) 12 hydrogensb) 12 hydrogens

c) 6 oxygens`c) 6 oxygens`

Chemical BookkeepingChemical Bookkeeping

1) Chemical equation shows reaction1) Chemical equation shows reaction

Reactants ---> ProductsReactants ---> Products

2) Equation for photosynthesis:2) Equation for photosynthesis:

6CO6CO22 + 6H + 6H22O ---> + CO ---> + C66HH1212OO6 6 + 6O + 6O22

Chemical EquationChemical Equation

Important Bonds in Important Bonds in Biological MoleculesBiological Molecules

Ionic BondsIonic Bonds

Covalent BondsCovalent Bonds

Hydrogen BondsHydrogen Bonds

Ion FormationIon Formation

1) Atom has equal number of 1) Atom has equal number of electrons and protons - no net electrons and protons - no net chargecharge

2) Atom loses electron(s), becomes 2) Atom loses electron(s), becomes positively charged ionpositively charged ion

3) Atom gains electron(s), 3) Atom gains electron(s), becomes negatively charged ion`becomes negatively charged ion`

Ionic BondingIonic Bonding

1) One atom loses electrons, 1) One atom loses electrons, becomes positively charged ionbecomes positively charged ion

2) Another atom gains these 2) Another atom gains these electrons, becomes negatively electrons, becomes negatively charged ioncharged ion

3) Charge difference attracts the 3) Charge difference attracts the two ions to each other`two ions to each other`

Ionic BondIonic Bond

Covalent BondingCovalent Bonding

1) Atoms share a pair or pairs of 1) Atoms share a pair or pairs of electrons to fill outermost shellelectrons to fill outermost shell

•Single covalent bond

•Double covalent bond

•Triple covalent bond`

Hydrogen BondingHydrogen Bonding

1) Molecule held together by polar 1) Molecule held together by polar covalent bonds has no NET charge covalent bonds has no NET charge a) However, atoms of the molecule carry a) However, atoms of the molecule carry

different chargesdifferent chargesb) Atom in one polar covalent molecule can b) Atom in one polar covalent molecule can

be attracted to oppositely charged atom in be attracted to oppositely charged atom in another such molecule`another such molecule`

Hydrogen BondingHydrogen Bonding

Hydrogen Bond StabilityHydrogen Bond Stability

Properties of WaterProperties of Water

PolarityPolarity

Temperature-StabilizingTemperature-Stabilizing

CohesiveCohesive

SolventSolvent

Water Is a Polar Water Is a Polar Covalent MoleculeCovalent Molecule

1) Molecule has no net 1) Molecule has no net chargecharge

2) Oxygen end has a 2) Oxygen end has a slight negative chargeslight negative charge

3) Hydrogen end has a 3) Hydrogen end has a slight positive charge`slight positive charge`

O

H H

Water PolarityWater Polarity

Hydrophilic & HydrophobicHydrophilic & HydrophobicSubstancesSubstances

1) Hydrophilic substances1) Hydrophilic substancesa) Polara) Polarb) Hydrogen bond with water b) Hydrogen bond with water

1. Example: sugar1. Example: sugar

2) Hydrophobic substances2) Hydrophobic substancesa) Nonpolara) Nonpolarb) Repelled by waterb) Repelled by water

1. Example: oil`1. Example: oil`

Temperature-Stabilizing EffectsTemperature-Stabilizing Effects

1) Liquid water can absorb much heat 1) Liquid water can absorb much heat before its temperature risesbefore its temperature rises

a) Why? a) Why?

2) Much of the added energy disrupts 2) Much of the added energy disrupts hydrogen bonding rather than hydrogen bonding rather than increasing the movement of molecules`increasing the movement of molecules`

Why Ice FloatsWhy Ice Floats

1) In ice, hydrogen bonds lock molecules 1) In ice, hydrogen bonds lock molecules in a lattice in a lattice

a) Water molecules in lattice are spaced a) Water molecules in lattice are spaced farther apart then those in liquid waterfarther apart then those in liquid water

b) Ice is less dense than water`b) Ice is less dense than water`

Water Is a Good SolventWater Is a Good Solvent

The pH ScaleThe pH Scale

1) Measures H1) Measures H++ concentration of fluid concentration of fluid2) Change of 1 on scale means 10X 2) Change of 1 on scale means 10X

change in Hchange in H++ concentration` concentration`