What is Chemistry?
 Study of composition, structure, and properties of
matter
 Chemicals are the substances that make up everything
on Earth
 Inorganic Chemistry studies every kind of substance
that does not require a living organism to exist
 Organic chemistry is only substances that can be made
by living organisms and must have a carbon (C)
backbone
What is an Atom?
 Resembles a solar system
 Largely emptiness
 Building blocks of matter
 Smallest unit of matter
 Radioactive decay transforms original atom
to another atom
 Smallest particle of an element that keeps
all properties of that element
Mass vs. Weight
 Mass = quantity of matter of an object
 Weight = force of gravity on an object
Elements in Living Things
Elements = pure substances that
cannot be broken down
The four most abundant elements in
living things are carbon, hydrogen,
oxygen, and nitrogen or C, H, O, & N,
respectively
Parts of an Atom and Charge
 Nucleus
 Made up of protons (+) and neutrons (neutral)
 Makes up most of the mass of an atom
 The # of protons = atomic number
 # protons + # neutrons = atomic mass number
 Electrons (e‾ ) make up most of the volume of an
atom; have a negative charge
Compounds and Molecules
 Compound = 2 or more elements chemically combined
 Chemical combination is accomplished by bonding
 Covalent Bond = sharing of 2 or more pairs of e‾
 Ionic Bond = transfer of e‾ ; based on electrical charge
 Molecule = simplest part of a substance that can exist
in a free state
 Ion = atom/molecule with an electrical charge; if an element
has lost e‾ , the atom is positively charged, while if an
elements has gained an e‾ , then it is electrically charged
More about Bonding
 A chemical bond is the energy required to hold atoms
together (union of atoms)
 Bonds are created by the activity of electrons
 Bonds broken release energy
 Bonds formed store energy
 Electrons farther away from the nucleus have the greatest
potential energy (stored energy); kinetic is energy of motion
Types of Chemical Bonds
Nonpolar
covalent
Polar covalent
Ionic
Electrons are shared Electrons are shared Electrons are
equally
unequally
transferred
No difference in
electronegativity
Increasing
difference of
electronegativity
The Four Types of Bonds
 Covalent – sharing electrons
 Ionic – transferring electrons
 Hydrogen – weak bonds between molecules
 Polar molecules, such as water and DNA
 The H⁺ of one molecule bonds with the O¯ of another water
molecule (H₂O)
 van der Waals forces – weak attractions between
nonpolar molecules
Electronegativity
The force that an atom exerts on its
electrons
Honors Biology:
Chapter 3 – Biochemistry
 Water, water everywhere! – that aqueous molecule that is one of
the most crucial compounds of life . Mickey Mouse ――›

 Water: is neutral; however, it is polar because there are uneven
charges. The area where O is has a somewhat (-) charge &
 ‹―― where the 2 H atoms bind O have a slightly (+)
charge――›

 is the universal solvent – Consider an ionic compound (cmpd)
like NaCl: the (+) end of a water molec attracts the (-) end of the
Cl ‾ and the (-) end of water attracts the (+) end of Na+, so NaCl
breaks apart (dissociates)