energy and water

ap bio

energy level

areas of energy when electrons can be found
( 1st level holds 2, 2nd holds 8 )

valence shell

outermost electron shell

valence electrons

electrons in outermost shell

( unpaired electrons are unstable and full valence shells are stable )

valence number

number of unpaired electrons in outer shell ( tells how many bonds the atom can form )

electronegativity

attraction of an atom for electrons of a covalent bond

(when this is strong, the atoms pull electrons toward them )

covalent bold

sharing a pair of valence electrons by two atoms H-H

nonpolar covalent bond

bond in which the electrons in covalent bond are shared equally

(H202)

polar covalent bond

bond when electrons in covalent bond are shared equally by the two atoms

(H20)

double covalent bond

bond formed by sharing two pairs of electrons

Ionic bond

results from a transfer of electrons between atoms, and is a chemical bond resulting from the attraction between oppositely charged ions

ion

an atom or group of atoms that have lost or gained an electron

WEAK BONDS

onward

ionic bond

in the presence of water ionic bonds are easily disrupted and are considered weak chemical bonds

hydrogen bond

the interaction between a hydrogen atom of one molecule and a very electronegative atom ( oxygen or nitrogen) of another molecule

van der waals interaction

weak attractions between molecules that occur when molecules are in close proximity and are attracted to each other by charge differences. this happens when electrons are not symmetrically distributed in a molecule

hydrophobic interaction

water is polar molecule

oxygen has a slight negative charge

hydrogen has a slight positive charge

hydrogen bonds form between water molecules

cohesion

bonding together of like molecules to hold a substance together

due to hydrogen bonds

adhesion

clinging of one substance to another

due to hydrogen bonds

surface tension

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

due to hydrogen bonds

specific heat

amount of heat that must be absorbed for 1g of the substance to change temp by 1 degree C

due to hydrogen bonds

heat of vaporization

quantity of heat liquid must absorb for 1g of it to change from liquid to gas

due to hydrogen bonds

evaporative cooling

occurs b/c the molecules with the most kinetic energy(hottest) are most likely to leave a gas

why does ice float

it is less dense than liquid water, due to hydrogen bonds

when is water most dense

at 4 degrees C

why is water a good solvent

because of its polar nature

solution

liquid that is completely homogeneous of two or more substances