(WIP) Chapter 2 – The Chemical Basis of Life I: Atoms, Molecules, and Water

BIO 190A

Atoms

the smallest function units of matter that form all chemical substances

Element

a pure substance made up of only on ekind of atim

Molecule

2+ atoms bonded together

Three subatomic particles found within an atom:

protons, neutrons, and electronsProt

Protons

positive charge (+), found in the atomic nucleus

Neutrond

electrically neutral, found in the atomic nucleus

Electrons

negative charge (-), found in orbitals around the nucleus

Protons and electrons are typically present in ___ numbers, giving the atom __ __ charge

equal; no net

The number of neutrons can __ for a given atom

vary

The solar system model for atoms is

over-simplified but convenient

Orbital

3D volumes of space surrounding the atomic nucleus that electrons are found in

Electron shells

the organization of orbitals

Orbitals of a given shell have a characteristic amount of

energy

Valence electrons

Covalent bonds

form when atoms share a pair of electrons

Atoms are more stable then the valence shall is

full

Covalent bonds are ___ and ___ chemical bonds

strong;; stableA

Atoms can potentially share: 1 pair of electrons -

single bond (e.g. H — F)

Atoms can potentially share: 2 pairs of electrons -

double bond (e.g. O == O)

Atoms can potentially share: 3 pairs of electrons -

triple bond (e.g. N ≡≡ N)

Each atom forms a characteristic number of ___ ___, which depends on the ___ of ___ required to ___ the ___ ___.

covalent bonds; number of electrons; fill; outer shell

Carbon can form how many covalent bonds?

4

Carbons’s capacity to simultaneously link multiple atoms tgether is important in forming

biomolecules

Electronegativity of an atom

a measure of an atom’s ability to attract electrons (some “pull” in shared electrons more strongly than others)

Relative eletronegtivity of H

2.20

Relative eletronegtivity of C

2.55

Relative eletronegtivity of N

3.04

Relative eletronegtivity of O

3.44

Relative eletronegtivity of Na

0.93

Relative eletronegtivity of Cl

3.16

Nonpolar covalent bonds

<0.4 difference in electronegativity; electrons shared equally

Polar covalent bond

0.4-1.8 difference in electronegativity; electrons shared unequally

Ionic bond

>1.8 difference in electronegativity; electrons transferred

Due to polar covalent bonds, a water molecule has a ___ ___ charge (δ-) around the ___ and a ___ ___ charge (δ+) around the ___.

partial negative, oxygen; partial positive, hydrogens

Nonpolar molecules contain

predominantly nonpolar bonds

Examples of nonpolar covalent bonds that are important to :remember include:

C—C, C—H

Polar molecules contain

many polar bonds

Examples of polar covalent bonds that are important to remember include

O—H, N—H, O—C

-

Solute concentration

the amount of solute dissolved in a unit of volume of solution

Molarity

another way to quantify solute concentrationMo

Mole

measures the number of particles (atoms, molecules) in a substance

Water exists in what states?

solid (ice), liquid (water), gas (water vapor)W

As a liquid, water is extremely

stable

Specific heat

the amount of heat energy required to raise the temperature of 1g of a substance by 1°C

What contributes to these properties of water?

the hydrogen bonds that form between molecules

In addition to acting as a solent, water serves many other important functions:

participates in chemical reactions, provides force or support, removes toxic waste components, evaporative cooling, cohesion & adhesion, lubrication, surface tension, and insulation form ice

Water spontaneously dissociates to form…

hydroxide ions (OH^-) and hydrogen ions (H⁺): H₂O —> H⁺ + OH^-

When certain substances (___ and ___) dissolve in water, the may ___ or ___ _ or _ , thus altering the ___ ___ of these ___.

acids and bases; release or absorb; H⁺ or OH^-; relative concentrations; ions

What do acids do when added to a solution?

release H⁺

What are acids classified as (2 options)?

strong or weak, based on degree of dissociation and H⁺ production

What do bases do when added to a solution?

accept H⁺

What are bases classified as (2 options)?

strong or weak, based on degree of dissociation and H⁺ acceptance

pH is a measure of

H⁺ concentration

pH and [H⁺] are

inversely related

Pure water is

neutral and has a pH of 7

Acidic solutions have

more H⁺ than OH^-; the pH is less than 7

Basic solutions have

less H⁺ than OH^-; the pH is greater than 7

The pH scale is

logarithmic

The pH of a solution can affect:

the shapes and functions of molecules, the rates of many chemical reactions, the ability of two molecules to bind to each other, and the ability of ions or molecules to dissolve in water

Since pH affects many important biological processes, organisms typically regulate the pH of body fluids to…

maintain pH within a relatively narrow range

Buffer

a substance (or group of substances) that prevents pH changes is either excess acid or base is added to a solution

Acid-base buffer system

can shift to remove or release H⁺ to adjust for changes in pH