AP Biology Unit 1 Chapter 2

Ap Biology Unit 1

The Chemical Context of Life

This behavior of element, which makes up all living things, starts with the same structure of individual atoms

________ is anything that takes up _____ & has ______

Matter…..space…..volume

Matter cannot be ______ or______

Created….Destroyed

_______ are substances that cannot be broken down into other substances by chemical reactions

Elements

The elements ____, ____, ____, and ____ make up ~96% of living matter

Carbon, Hydrogen, Oxygen, and Nitrogen

______ elements are required for organisms to survive

Essential

_______ elements are required by organisms in small quantitites (ex. iron, iodine, fluoride —> ion)

Trace

Atoms

The smallest unit of matter that retains properties of an element (building blocks of matter)

Charge ( + or - )

• Electrical property

• Attracts or repels other properties

Electrons

• Negative charge (e-)

• Move around nucleus

Nucleus

• Dense core of an atom made of

  • Protons (p+) —> positive charge

  • Neutrons (n⁰) —> no charge

Atomic Number

• #P+ (thus #e-)

• Determines element type

Atomic Mass/Mass Number

• Total mass of an atom

• Sum of p⁺ + n⁰

• 1 atomic mass unit (amu) or dalton = 1.7 × 10^-24 g

Isotopes

Same element(s) with different number(s) of n⁰

Radioisotopes

• Isotopes used spontaneously-decaying nuclei

• Used in research and medical applications

• Drawback: Radiation can damage cellular molecules, and severity depends on type & amount absorbed

Radioactive Decay

Radioisotopes emit subatomic particles of energy when their nucleus breaks down, at a constant rate, transforming from one element to another (ex. ¹⁴C—>¹⁴N)

Isotopic Tracers

• Molecules with a detachable substance attached

Electron Shell

• Levels e- are found in

• Electrons can change shells by absorbing or released energy amounts equal to differences in potential energy btwn old and new shells

1st electron shell

Can hold 2e-

2nd electron shell

Can hold 8e-

3rd electron shell

Can hold 8e-

Valance electrons

• Bonding capacity corresponding to the number of covalent bonds an atom can form

• The number of unpaired e- required to fill an atoms outer shell

• Atoms with full outer shells are unreactive

Chemical Reactions

The making and breaking of bonds to change the composition (rearranging molecules)

Reactants

Starting materials

Products

Ending materials

Law of Conservation of Matter

There are always equal amounts of the same atoms on both sides of chemical equations

Only _____ are directly involved in chemical reactions between atoms

electrons

Chemical Bonds

Attractions that had atoms together (sharing or transferring e-)

Chemical reactions are____

irreversable

Reaction Rate

Impacted by the reactants (more reactants = more collisions = faster reaction)

Chemical Equilibrium

The forward and reverse reactions occur at the same rate (relative concentrations of produts and reactants stop changing)

Compounds

• Substances formed by chemical reactions

• Consists of two or more different elements in a fixed ratio (ex. NaCl, H2O)

Ions

Atoms with positive or negative charges due to the loss or gain of e- in their outer/valence shells (ex. Na⁺, Cl^-)

Anion

Negatively charged ion

Cation

Positively charged ion

Ionic Bonding

• Transfer of e-

• Form ionic compounds (salts) ex. NaCl

Covalent Bonding

• Sharing of a pair of valence e- by two atoms

• Can be stronger than ionic bonds

Molecules

Two or more atoms joined with chemical bonds (Ex. O2, H2O)

Electronegativity

Measure of an atom’s ability to pull e-

Nonpolar Covalent Bond

• Atoms share e- EQUALLY

• Formed between atoms with same electronegativity

Polar Covalent Bond

• Atoms share e- UNEQUALLY

• Formed between atoms with different electronegativity

• Results in one atom having a slightly more negative charge and the other atom a slightly more positive

Polarity

Separation of charges into distinct positive and negative regions in polar covalent molecules

Van Der Waals Interactions (London Dispersion, Dipole-Dipole)

• Electrons always move and may accumulate in one part of a molecule, creating changing regions of positive and negative charges

• Enables atoms and molecules to “stick” together

• Forms individually “weak” attractions which can be “strong” if many occur simutaneously

Hydrogen Bonding

• A weak attraction between a highly electronegative atom of one molecule and a hydrogen atom of another molecule that is taking part in a separate polar covalent bond

• Hydrogen (H) bonds do not form molecules and are not chemical bonds

• H-Bonds stabilize the structures of large biological molecules

Water’s Unique Life Supporting Properties

• Organims are mostly water

• All chemical reactions involving life are carried out in weater

• Water makes life possible on earth

• The properties of water are a result of extensive hydrogen bonding between water molcules

Polarity of Water

• Water is polar

• Its overall charge is unequally distributed

• The oxygen atom is slightly negative

• Thhe hydrogen atoms are slightly positive

• Hydrogen bonds form between water miolecules (| | | | | | |)

Cohesion of Water

• Hydrogen bonding allows water molecules to “stick” together

• Provies surface tension

Surface Tension

A measure of how difficult it is to stretch or break the surface of a liquid

Adhesion of Water

Hydrogen bonding allows water molecules to “stick” to other surfaces

Temperature Moderation of Water

Compared with other molecules, water absorbs more heat before it becomes measurable hotter

Kinetic Energy (KE)

Energy of movement

Heat

energy from movement of molecules

Temperature

Measures the energy of heat intensity that represents average KE of molecules

• Molecules move faster as they absorb heat

Celsius Scale

Indicates Temperature

Calorie

The amount of heat required to raise the temperature of water by 1 degree celsius (°C)

Specific Heat

The amount of heat that must be absorbed or lost for 1 gram of that substance to change its temeprature by 1°C

• The heat in weater is used to disrupt bonds first before it is used to move the water molecules

Heat of Vaporization

Quantity of heat a lioquid must absorb for 1g to be converted to gas state

• Water has a high heat of vaporization —>580 cal, resulting from the H bond that must be broken

Evaporization

Convservation of a liquid to ag as by the addition of heat energy

Evaporative Cooling

As liquid evaporates, the surface of the liquid that remains cools down

Density of Water

• Ice is less dense than liquid water

• Water expands as it cools and contracts as it warms

• Hydrogen bonds form a crystalline lattice during freezing

  • H-bonds frozen at “arm’s length”

  • Prevents bodies of water from freezing solid

Solution

Liquidb that is a completetly homogeneous mix of two or more substances

Solvent

Dissolving agent

Solute

Substance(s) that are dissolved

In aqueous solutions…

Water is alwaus the solvent

Water dissolved polar molecules

• Polar molecules dissolved by water are hydrophillic (water-loving)

• Nonpolar (hydrophobic [water-repelling]) molecules are NOT dissolved by water

Molecular Mass

The sum of the masses of all atoms in a molecule

Mole

Exact number of “something”

• Equal to Avogadro’s number:" 6.02 × 10²3 daltons

Molarity

Number of moles of solute per liter of solution

Biological Reactions occur in Water

Molecules in water can separate into hydrogen ions (H+) and hydroxide ions (OH-)

pH

A measure of the number of H+ in a solution (pH = -log [H+])

• More H+ = lower pH

pH > 7

Basic

pH < 7

Acidic

pH = 7

Neutral

Acid

Subtances that increases the concentration of Hydrogen ion (H+) in a solution by “donating” H+ ions to the solution

• Can be weak or strong

Base

Substances that reduces the concentration of Hydrogen ions (H+) in a solution by “accepting” or dissociating into Hydroxide ions (OH-)

• Can be weak or strong

Salt

A compound that dissolves easily in water and releases ions other than H+ and OH-

Buffers

Substances (a weak acid or base and its salt) that minimize changes in concentration of H+ and OH- in a solution

• Accept OH- from solution in excess and donate H+ when depleted

Buffering Carbon Dioxide in Blood

Carbon dioxide in blood forms carbonic acid, which separetes into H+ and bicarbonate ions

Ocean Acidification

• 20% of CO2 generated by humans is absorbed by coeans

• CO2 dissolves in seawater and lowers its pH

Acid Precipiation

• Can be snow, rain, or fog with a pH < 5.2

• Sulfur dioxide dissolveas in water vapor to form an acidic solution

• Damages soil and water health