Bio lesson 3

atom

-composed of protons, neutrons, electrons

-Bohr model (electrons orbit the nucleus at fixed energy levels)

element

-substance consisting of one type of atom w/ the same number of protons

atomic number

number of protons in an atom

mass

amt. of a substance

weight

force exerted by gravity on a substance

atomic mass

sum of masses of protons/neutrons in an atom

Dalton

unit of mass

most abundant elements in living systems

-compromise majority of weight of living systems

-carbon is the basis for most biological molecules “organic molecules”

-trace elements are critical for life (chemical elements that are present in small amounts in living organisms, plants, and soils)

isotopes

atoms of the same element that have a different number of neutrons

energy levels

-atoms contain discrete energy levels

-electrons that are in levels/shells farther from the nucleus have greater potential energy

-potential energy is directly related to distance from nucleus

-electrons in outermost energy level= valence

-octet rule: atoms tend to completely fill outermost energy levels

electrons

determine an atoms chemical behavior

ions

atoms that gain/lose electrons

cations

positively charged ions

anions

negatively charged ions

chemical bonds

-atoms form molecules via chemical bonds

-Bohr model, ball-and-stick model, space-filling model

molecule

a group of atoms held together in a stable association

compound

a molecule that contains atoms of 2 or more different elements

covalent bond

-sharing of electrons

-in water, O shares an electron with each H

-electrons may not be shared equally in the covalent bond because atoms differ in their affinity for electrons (electronegativity)

-some atoms form multiple covalent bonds with another atom

-strongest bond

polar

-covalent bonds where the charge distribution is unequal= polar covalent bonds

-molecules that contain these bonds= polar molecules

-water is polar (H atoms have partial positive charge, O atoms have partial negative)

ionic

-attraction of opposite charges

-second strongest bond

-not directly formed btwn two atoms, but are formed btwn any one atom and all neighboring atoms of the opposite charge

hydrogen bond

-sharing of a H atom

-weakest bond

-water readily forms H bonds

-ex: water is polar because of unequal charge distribution in covalent bonds btwn H and O, meaning that water can interact with other water molecules and polar molecules due to the attraction of opposite partial charges. with other water molecules, the partial positive charge in H of one water is attracted to the partial negative charge in O of the other water. with polar organic molecules, an organic molecule that contains a H bonded to an O is also able to form an H bond with water (this is possible when H is bonded to a more electroneg. atom)

the chemistry of all life is…

based on water

living cells are…

comprised mostly of water (70% water, 4% small molecules, 26% macromolecules)

cohesion

-refers to the attraction of molecules for other molecules of the same kind, and water molecules have strong cohesive forces thanks to their ability to form hydrogen bonds with one another

-the polarity of water promotes the attraction of water molecules for other water molecules

-individual H bonds are weak/short lived but the combined effect of many H bonds is substantial

-means that water is liquid at most temps on Earth and created surface tension (allowing small orgs. to walk/move on surface of water)

adhesion

-the tendency of dissimilar particles or surfaces to cling to one another

-the polarity of water promotes the attraction of water and other polar molecules

-adhesion of water to charged surfaces drives capillary action (ex: cup of water w/ a straw: cup carries a neg. charge, so water rises. Here, adhesion is providing sufficient force to overcome gravity)

high specific heat

-specific heat= amt of heat required to change 1 gram worth of something by 1 degree C

-reflects extent to which a substance resists changing temp. when it absorbs/loses heat

-water has a “high” specific heat bc of its tendency to form H bonds (water heats up slowly and holds temp. longer)

-helps orgs. to maintain temp by absorbing heat from chem. reactions

high heat of vaporization

-heat of vaporization: amt. of energy required to change 1 gram of substance from liquid to gas

-reflects that energy is needed to break H bonds to allow conversion to gas

-helps orgs. maintain temp through evaporative cooling (ex: sweating)

solid water is less dense than liquid water

-ice is less dense bc molecules are more spaced out

-means that ice floats on the surface of water and rogs. can survive in winter in the liquid water below ice

water is the universal solvent

-water clustered around charged and polar molecules

-molecules that interact w/ water are soluble in water

-hydration shells prevent solute from interacting w/ other solute molecules

organization of non polar molecules

-nonpolar, hydrophobic molecules cluster in water (hydrophobic exclusion) bc they don’t form H-bonds w/ water

-amphipathic molecules contaain hydrophilic and hydrophobic regions. They associate into highly organized structures in water

ionization

-water rarely and spontaneously forms ions (one of its covalent bonds may break)

-ex: H2) yields OH- +H+

-important bc the concentration of H ions greatly impacts the function of living systems

why is water essential?

-cohesion

-adhesion

-high specific heat capacity

-high heat of vaporization

-solid water is less dense than liquid

-universal solvent

-organization of non polar molecules

-ionization

pH

-1 is most acidic, 14 is most baisc

-pH= -log[H+]

-7 is neutral/pH of water

acid

substance that dissociates in water to increase the [H+]

base

dissociates in water to decrease the [H+]

buffer

-resists changes in pH

-ex. buffer system: blood

acid/base pair= carbonic acid (H2CO3)/bicarbonate (HCO3-)

works as a pair of reversible reactions