Chemistry
of
Life
•Composition of Matter
Matter
anything that occupies space and has mass
Mass
is the quantity of matter an object has
Mass vs. Weight
• Weight
is determined by the force of gravity
acting on a mass
• Example:
The same mass would have less weight on
the moon than on the Earth
Elements and Atoms
Elements are substances that cannot be
broken down chemically into simpler kinds
of matter
.
Over 100
elements exist.
Fewer than 30 are
important for life
90% of the mass of all living
things are composed of just
four elements:
Carbon
Hydrogen
Oxygen
Nitrogen
ELEMENTS – organized in Periodic Table
•chemical
symbol- consists of 1,2,or 3
letters
•derived from first letter or other
letters in the name
•Ex: Chlorine-Cl
•Most other names are derived from
Latin names
•ATOMS – simplest particles of an
element that retains all the properties of
that element
Consist of 3 SUBATOMIC PARTICLES
n
Protons
Neutrons
Inside Nucleus
Electrons
Outside
Nucleus
# electrons = # protons
in a NEUTRAL ATOM
NUCLEUS -
the central part
of an atom
and makes up
the bulk of the
mass of an
atom
ELECTRONS- are negatively charged particles
found orbiting the nucleus of an atom
 high energy –fast orbit
 very little mass
 located in orbitals or energy
levels
 Electrons in outer orbitals have
more energy
 1st energy level can only hold 2
electrons
 2nd energy level can hold up to
8 electrons
Isotopes-atoms of the same element
that have a different number of neutrons
Compounds - made up of atoms
of two or more elements in fixed proportions
Chemical Formula
•
shows the kinds and proportions of atoms of each
element that forms a particular compound
H2O
2 Hydrogen Atoms
1 Oxygen Atom
So,when does
bonding occur?
o Elements will combine to form molecules or
compounds if their outer energy level or orbital
is NOT FILLED.
o An atom is chemically stable when its highest
energy level is filled with the maximum
number of electrons.
 These elements are called noble or inert
elements (gases) and do not react with
other elements under normal conditions.
(Ex: Helium, Neon)
CHEMICAL BONDS – attractive
forces that hold atoms together
Ionic
Covalent
Hydrogen
Covalent Bonding form when
two atoms
share one or
more pairs
of electrons
electrons in an atom’s outermost
energy level = valence electrons
When outer shell is filled – atom is
stable
Hydrogen has ______electron so it
needs __________more to fill its
first energy level to achieve
stability
•Ionic Bonds- form from the
attractive force between oppositely charged
ions (charged particle)
•
Atoms gain or lose electrons to achieve stability
•
they become either positively charged or negatively charged
•
NaCl is table salt and forms from a Na+ ion bonding with a Cl- ion