slide 2 Flashcards
elements
There are 92 naturally occurring elements
which cannot be broken down by chemical
reactions into anything else.
essential elements
20-25% of the 92 are essential elements, those
that organism needs to live and reproduce.
The 4 elements that comprise 96% of living matter.
hydrogen, carbon, nitrogen and
oxygen
*
Each element consists of one
kind of atom comprised of
sub-atomic particles:
nucleus:
- protons (positive charge)
- neutrons (no charge)
not:
- electrons (negative charge)
An element’s atomic number
is the number of
protons in its nucleus.
*
An element’s mass number
is the sum of protons
and neutrons in the nucleus and approximates the
atomic mass,
*
atomic mass
the atom’s total mass
Isotopes are
two atoms of an element that differ
in number of neutrons
*
Radioactive isotopes
decay spontaneously,
giving off particles and energy
Energy
is the capacity to cause change.
Potential energy
is the energy that matter has
because of its location or structure.
*
electron shell.
An electron’s state of potential energy is called
its energy level,
(electron shells)
The electrons of an atom
occupy fixed energy levels
The number of electrons
in the outer valence shell
influences the reactivity of
the atom.
Atoms react to acquire
complete valence shells
Shell 1 – holds 2 electrons
Shell 2 – holds 8 electrons
Shell 3 – holds 8 electrons
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an ionic bond.
Transfer of electrons between atoms so that each
has a full outer shell forms an ionic bond
*
covalent bond.
Sharing of electrons between atoms
forms a covalent bond. These bonds
are stronger than ionic bonds
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molecule.
Two or more atoms that form
covalent bonds
Van der Waals interactions
occur when
transiently positive and negative regions of
molecules attract each other.
These are weak bonds, but are the forces that
allow geckos to climb walls!
Water comprises
60 to 90% of most living organisms
Water (H2O) is
a polar molecule
Weak hydrogen bonds
among the
polar water molecules contribute to
important properties of water.
Four of water’s properties that
facilitate life are:
– Cohesive behavior – Ability to moderate temperature – Expansion upon freezing – Versatility as a solvent *
cohesion.
Collectively, hydrogen bonds hold water molecules
together, a phenomenon called cohesion.
*
Adhesion
is an attraction between different
substances, for example, between water and plant
cell walls.
*
Adhesion
is an attraction between different
substances, for example, between water and plant
cell walls.
Surface tension
is related to cohesion and is a measure of how hard it is to break the surface of a liquid.
Temperature Moderation
Water absorbs heat from warmer air and releases
stored heat to cooler air.
Water can absorb or release a large amount of
heat with only a slight change in its own
temperature
specific heat
of a substance is the amount of
heat that must be absorbed or lost for 1 g of that
substance to change its temperature by 1ºC
The specific heat of water
is 1 cal/g/ºC
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– Heat is released when hydrogen bonds form
Heat is absorbed when hydrogen bonds break
*
Water has a high heat of vaporization
which is
the heat a liquid must absorb for 1 g to be
converted to gas
*
evaporative cooling
As a liquid evaporates, its remaining surface
cools, a process called evaporative cooling
Water has its highest density at 4 C
and then
becomes less dense as it becomes a solid at
lower temperatures.
*
Ice: Hydrogen bonds
are stable
Liquid water:
Hydrogen bonds
break and re-form
The Solvent of Life
Water is a versatile solvent due to its polarity – can
form hydrogen bonds with other compounds
When an ionic compound is
dissolved in water
each ion
is surrounded by a sphere
of water molecules
Even large polar
molecules such as
proteins can
dissolve in water
if
they have ionic
and polar regions
*
In aqueous solution most water molecules are
intact, but
some break apart or dissociate into ions,
molecules with a net positive or negative charge.
The correct balance of
H+ and OHions
is
critical
for the proper
chemical functioning
of organisms
The pH scale tells
how acidic or basic a solution is.
pH 6 = 10-6 moles H+ per liter
(acid, more H+
)
*
pH 7 = 10-7 moles H+ per liter
(neutral)
*
pH 8 = 10-8 moles H+ per liter
(basic, less H+
)
*
Acids donate H+ in
aqueous solutions
Bases donate OH- or accept H+ in aqueous solutions *
Ocean Acidification
CO2 dissolved in sea water forms carbonic acid;
this process is called ocean acidification.
*
CO2 is the main product of burning fossil fuels. About 25% of human-generated CO2 is absorbed by the oceans.
Less carbonate ions are available for
marine organisms to use in the
formation of calcium carbonate
Acid precipitation
is rain, fog, or snow with a pH
lower than 5.2
*
Astrobiologists seeking life on other planets are
concentrating their search on planets with water.
More than 3000 planets have been found outside
our solar system; several of them contain water.
