Chapter 2

AtomElement

= the smallest unit of matter that cannot be broken down

= a pure substance made of only one kind of atom

Protons = positive electric charge (1+)

Neutrons = neutral charge (0)Electrons = negative charge (1-)

Atoms are composed of even smaller parts, called subatomic particles.

Each element has a unique number of protons = atomic number.

• Atoms have equal numbers of P and e- – The atomic number = tells the number of

protons and the number of electrons

•Mass number = the sum of the number of protons

and neutrons in the nucleus of an atom.

# Neutrons = Mass # - Atomic #

# protons?# electrons?# neutrons?

Carbon =

• Atoms of a given element may differ in the number of neutrons = isotopes.

• In nature, an element occurs as a mixture of isotopes.– For example, 99% of carbon atoms have 6

neutrons (12C).– Most of the remaining 1% of carbon atoms

have 7 neutrons (13C) while the rarest isotope, with 8 neutrons is 14C.

• YouTube - The element song

6 C Carbon 12.01

Electron ShellsEnergy Levels

1st Shell = 2 electrons2nd Shell = 8 electrons3rd Shell = 8 electrons (stable)

PN

e-

Atoms are mostly “empty space”

If Nucleus= golf ball ----------------------------------------------------- e-

1km (10 football fields)

Electron ShellsEnergy Levels

Valence Electrons = electrons in outer energy shell

Valence Electrons do the interaction during chemical reactions.The nuclei do not come close enough to interact.

Groups/Families

Periods (+ Protons/electrons)

(Reactivity/Valence e-)

? ? ? ? ? ?

?1 2 3 4 5 6 7

2/8Valence Electrons?

Atom Interaction?

~ 50 trillion cellsEach cell 1,000’s atoms

Valence Electrons

• Atoms want to be “stable” = full valence shell.

• Share or transfer electrons.

• To become stable, atoms will hold together by chemical bonds.– The strongest chemical bonds are covalent

bonds and ionic bonds.

Chemical bonds

ChemicalBond

SingleAtoms

• A covalent bond is the sharing of a pair of electrons by two atoms.

Hydrogen

H H

H2 Subscript (2 atoms)

“Hydrogen Molecule” (H2)

Single Covalent

Double Covalent

Two or more atoms held together by covalent bonds constitute a molecule

“Oxygen Molecule” (O2)

• Ionic bond = one atom strips an electron completely from the other.

NaCl

Ions = charged atoms or molecule

• YouTube - Carl Sagan on the chemical elements

BalloonVan de Graff Machine

Top 4 Atoms found in Organisms?

O = 65%C = 18.5%H = 9.5%N = 3.3%

AstronomersLife evolved in water

~75% Earth Cells 70-95% Water

H2O

Polar Covalent Bond = electrons not shared equally

-

+

“Polar Molecule”

• Hydrogen bonds = a weak chemical attraction between polar molecules.

H+ O-

Up to 4 per water molecule

Cohesion = water molecules bonding to each other.

“Surface tension” prevents

stretch or break the surface

Adhesion = clinging of one substance to another (polar polar).

Solution = homogenous mixture.

Solute = Solvent =

Water is the “solvent” of life

dissolving agentsubstance dissolved

Forms hydrogen bonds with charged and polar covalent molecules.

Solvent?Solute?

“Dissolve”

pHHydrogen Ion

H+

“Dissociation”

H2O <=> H+ + OH-

Acid = any compound that forms hydrogen ions (H+) ions in solution

Base = any compound that forms hydroxide ions (OH-) in solution

pH scale = concentration of H+ in a solution

Buffers = weak acids or bases that prevent sudden changes in pH

“Homeostasis”

pH

Hydrogen Ion

H+

• Dissociation

H2O <=> H+ + OH-

• In pure water only one water molecule in every 554 million is dissociated.

pH scale = concentration of H+ in a solution

0 - 14

7 = neutral (H+ = OH-)

0-6 = acidic (H+)8-14 = basic (OH-)

Base = any compound that forms hydroxide ions (OH-) in solution

Acid = any compound that forms hydrogen ions (H+) ions in solution

Factor of 10

Cell pH = 6.5 – 7.5

“Homeostasis”

Buffers = weak acids or bases that prevent sudden changes in pH

CARBON COMPOUNDS“ORGANIC CHEMISTRY”

96%

-------------------

-------------------

4%

-------------------

Life dependson 25 elements

“Trace elements”

• Although cells are 70-95% water, the rest consists mostly of carbon-based compounds.

• Proteins, DNA, carbohydrates, and other molecules are all composed of carbon atoms bonded to each other and to atoms of other elements.

“CARBON COMPOUNDS”

Organic chemistry = the study of carbon

compounds (organic compounds).

HONSP

C bonds with:

3-D

Hydrocarbons “Petroleum”

Functional groups unique properties

Macromolecules

Form

MONOMERS

POLYMERS

“Single”

“Multiple”

Large Carbon Based Molecules

B

ond

MACROMOLECULES

Elements Monomers Example

Carbohy-drates

C,H,O

1:2:1

Monosac-

carhides

Starch

Glucose

Sucrose

Lipids C,H,O Glycerol

Fatty Acids

Fats

Oils

Cholesterol

Proteins C,H,O,N Amino

Acids

Insulin

Hemoglobin

Nucleic

Acids

C,H,O,

N, P

Nucleotides DNA

RNA

1. CARBOHYDRATES

“Sugar”

Main source of energy

GlucoseC6H1206

Monomer =

“Monosaccharide”

1:2:1

“Polysaccharide”

Starch Glucose Glucose

Polymer =

Monomers:

2. LIPIDS (fats, oils, waxes)

Glycerol

Fatty Acid

Monomer

Polymer

Straight

Kinked

Solid at room Temp (Bad)

Liquid at Room Temp (Good)

Double bond prevents “packing”

Store energy

Steroids

Cholesterol

3. PROTEINS

AA—AA—AA—AA

Monomer =Amino Acids

“Peptide” Bond

Polymer =“Polypeptide”

20 different Amino Acids

“R Group”

Proteins:Control rate of reactionsRegulate cell processesForm bone and muscleTransport substances into and out of the cellFight disease

4. NUCLEIC ACIDS

Monomers =Nucleotides

Monomer

Monomer

Polymer =Nucleic Acids (DNA/RNA)

• YouTube - Carl Sagan on the chemistry of life on Earth/ other planets

CHEMICAL REACTIONS AND ENZYMES

Energy = the ability to move or change mater

Chemical reactions = chemical bonds between atoms are broken and new ones formed

Chemical equations: Reactants ProductsNaCl Na+ + Cl-

Metabolism = all the chemical reactions that occur in an organism

Activation energy = the energy needed to start a chemical reaction

Enzyme = a substance that increases the speed of chemical reactions

Speeds-up reaction by reducing activation energy

Chemical reactions = chemical bonds between atoms are broken and new ones formed

Reactants Products

NaCl Na+ + Cl-

Chemical equations:

Energy is released or stored

Na + Cl Na+Cl-

Energy Releasing Reaction

“Bonds Broken”

NaCl Na+ + Cl-

Energy Absorbing Reaction

“Bonds Formed”

Na + Cl Na+Cl-

Metabolism = all the chemical reactions that occur in an organism

Activation energy = the energy needed to start a chemical reaction

“Push” needed

Cells require activation energy

Enzyme = a substance that increases the speed of chemical reactions

“catalyst”

Speeds-up reaction by reducing activation energy

1. Substrate binds to enzyme

2. Substrate is converted toproducts

3. Productsare released

4. Active siteis availablefor anothersubstrate

active sitesubstrate

induced fit

Enzymes are unaffected by the reaction and arereusable

Reaction rate issubstrate concentrationdependant

denature

End in “-ase” AmylaseCatalase