Chemistry of Life:
Atoms, Ions, Molecules, and
Water
August 13 & 14
Lecture and Lab Rotations
Atoms
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Matter- any substance that has mass
Matter is composed of small particles called atoms.
Difference between
mass and weight:
Mass refers to the
amount of a substance,
whereas weight refers
to the force of gravity on
the substance.
EX: walking on the
moon
Example of an atom: Carbon
Carbon is an essential atom for life.
 It can assemble into DNA, proteins,
carbohydrates and lipids, making complex
life possible.

Carbon
Atomic mass is the number of protons and
neutrons in the nucleus of the atom. Carbon is 12.
Atomic number is the number of protons in the
nucleus. Carbon is 6.
Carbon is a neutral atom.
Element
Atoms with the same atomic number (same
number of protons) have the same
chemical properties and belong to the
same element.
Energy: the ability to do work

Electrons are negatively charged and carry the
ability to be attracted to the positively charged
nucleus, and repelled by the negative charge of
other electrons.
When
an electron
moves toward the
nucleus it releases
energy, and absorbs
energy when it
moves away from
the nucleus.
Electron Shells


Electron shells are where the energy of the atom is
stored.
Orbital is the volume of space around a nucleus where
an electron is most likely to be found. Each electron shell
has a specific number of orbitals, and each orbital can
only hold up to two electrons.
Since carbon has 6 electrons, how many shells (and
electrons on each shell) does it have?
Ions


An atom can gain or loose electrons from its outer shell.
An ion is when the number of electrons and the number
of protons is not equal because the atom has gained or
lost an electron.
A sodium atom becomes a sodium ion when it looses an
electron because the nucleus is left unbalanced and
becomes positively charged.
Isotopes
An isotope is an atom that has the same
number of protons but different number of
neutrons.
 The number of neutrons in an atom of a
particular element can vary without
changing the properties of the element.
 Isotopes have the same atomic number,
but different atomic mass.

Molecules
A molecule is a group of atoms held
together by energy.
 A chemical bond is the energy or force
that holds two atoms together.

Ionic Bond
When atoms are attracted to each other by
opposite electrical charges.
2 key properties: strong and non-directional
Covalent Bond


A strong chemical bond when that forms between two
atoms when they share electrons.
Why do atoms in molecules share electrons?
Single, double (two pairs of electrons are shared), triple
covalent bonds.
Carbon has 4 electrons in outer shell and can form as many
as 4 covalent bonds.
Hydrogen Bonds


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Form when the positive end of
one polar molecule is attracted
to the negative end of another
polar molecule.
Are weak chemical bonds and
one nucleus may be better at
attracting the shared electron
than the other and spend more
time in the vicinity of the more
strongly attracted atom.
Characteristics: highly
directional and create tight
bonds through the effect of
many weak interactions.
Hydrogen bonds give water unique
properties:
Heat storage- it takes water a long time to boil
and cool
 Ice formation- Why is ice less dense than
water?
 High heat of vaporization- water can
evaporate
 Cohesion (ability to bind to other polar molecules
that are water; when this polar substance is not
water, it is adhesion)
 High polarity- hydrophilic and hydrophobic
