structure of water and hydrogen bonding Flashcards
matter
anything that takes up space and has mass
element
a substance that cannot be broken down into other substances by chemical reactions
compound
a substance consisting of two or more different elements combined in a fixed ratio
essential elements
of the 92 naturally occurring elements, 20-25% are essential to survive and reproduce
CHON make up 96% of living matter
trace elements
of the 92 naturally occurring elements, these are required by an organism in very small quantities
atomic number
number of protons in an element
atomic mass
number of protons and neutrons averaged all over isotopes
group
elements in the same vertical column have the same number of valence electrons
period
elements in the same horizontal row have the same total number of electron shells
bohr model
shows electrons orbiting the nucleus of an atom
electrons are placed on shells around the nucleus
each shell is a different energy level and can hold up to a certain number of electrons
lewis dot model
does not show energy levels
only shows electrons in the valence shell (outermost shell)
electrons are placed around the element symbol
elements want to be blank
stable
how do elements achieve stability?
by forming chemical bonds with other elements
octet rule
elements will gain, lose, or share electrons to complete their valence shell and become stable (like noble gases)
chemical bonds
an attraction between two atoms, resulting from the sharing or transferring of valence electrons
electronegativity
the measure of an atom’s ability to attract electrons to itself
covalent bonds
when two or more atoms share electrons (usually between two nonmetals)
forms molecules and compounds
two types of covalent bonds
nonpolar and polar
nonpolar covalent bonds
electrons are shared equally between two atoms
ex: O2
polar covalent bonds
electrons are not shared equally between two atoms
ex: H2O
ionic bonds
the attraction between oppositely charged atoms (ions)
usually between a metal and nonmetal (metal transfers electrons to nonmetal)
occurs when there is a transfer of electrons from one atom to another atom forming ions
cation
positively charged ion
anion
negatively charged ion
hydrogen bonds
the partially positive hydrogen atom i one polar covalent molecule will be attracted to an electronegative atom in another covalent molecule
intermolecular bond
bond that forms between molecules
why does hydrogen bonding happen?
when a hydrogen atom is bonded to an electronegative atom (usually O, N, or F), the electrons are not being shared equally between atoms (remember: this is a polar covalent bond)
this causes hydrogen to have a partial positive charge and the electronegative atom to have a partial negative charge
properties of water:
polarity
unequal sharing of the electrons make water a polar molecule
properties of water:
cohesion
attraction of molecules for other molecules of the same kind
allows for the transport of water and nutrients against gravity in plants
responsible for surface tension, a property allowing liquid to resist external force
H2O molecules stick together
what increases cohesive forces in water?
hydrogen bonds between H2O molecules
what does cohesion allow for?
the transport of water and nutrients against gravity in plants
what is responsible for surface tension?
cohesion
properties of water:
adhesion
the clinging of one molecule to a different molecule
due to polarity of H2O
what does adhesion allow for in plants?
for water to cling to the cell walls to resist the downward pull of gravity
properties of water:
capillary action
the upward movement of water due to forces of cohesion, adhesion, and surface tension
when does capillary action occur?
when adhesion is greater than cohesion
properties of water:
temp control:
high specific heat
H2O resists changes in temp
how does water resist changes in temp?
hydrogen bonds
heat must be absorbed to break hydrogen bonds, but heat is released when hydrogen bonds form
importance of high specific heat
moderates air temp:
large bodies of water can absorb heat in the daytime and release heat at night
stabilizes ocean temp:
benefits marine life
organisms can resist changes in their own internal temp
properties of water:
temp control:
evaporative cooling
water has a high heat of vaporization
the molecules with the highest KE leave as gas
importance of evaporative cooling
moderates earth’s climate
stabilizes temp in lakes and ponds
prevents terrestrial organisms from overheating (think sweating in humans)
prevents leaves from becoming too warm in the sun
properties of water:
density (floating ice)
as water solidifies, it expands and becomes less dense
due to hydrogen bonds
when cooled, water molecules move too slowly to beak the bonds; allows marine life to survive under floating ice sheets
properties of water:
solvent
dissolving agent in a solution
solution
homogenous mix of 2+ substances
solute
substance that is dissolved
