4. What Are Atoms?
• Smallest particles that retain
properties of an element
• Made up of subatomic particles:
– Protons (+) located in the nucleus
– Neutrons (no charge) located in
the nucleus
– Electrons (-) located in space
around the nucleus
5. Atomic Number
(whole # on the periodic table)
• = the # of protons
• All atoms of a specific element have
the same atomic #
• Atomic # of hydrogen = 1
• Atomic # of carbon = 6
• Atomic # of helium = 2
• If you change the # of protons, you
change the atom into a different
element
6. Atomic Mass
(decimal # on the periodic table)
Number of protons
+
Number of neutrons
So why is it a decimal
number? You’ll soon
find out….
7. What is the role of neutrons?
• Since protons have a +
charge, they repel
each other
• Neutrons are neutral
and help to stabilize
the nucleus – think
police
9. Why Electrons Matter
• Atoms acquire, share, and
donate electrons
• Whether an atom will
interact with other atoms
depends on how many
electrons it has
10. Electrons
• Carry a negative charge
• Also repel one another
• Attracted to protons in the
nucleus
• Move in volumes of space
that surround the nucleus
11. Shell Model
• The shell model of electron orbitals
diagrams electron vacancies, filled from
inside out
• Each shell represents an energy level:
– 1st shell: (2 electrons)
– 2nd shell: (8 electrons)
– 3rd shell: (8 electrons)
• Atoms with vacancies in their outer shell CALCIUM
tend to give up, acquire, or share electrons 20p+ , 20e-
12. Electron Vacancies
• Unfilled levels make
atoms more likely to
react with other atoms
CARBON NITROGEN
• Hydrogen, carbon, and 6p+ , 6e- 7p+ , 7e-
nitrogen are examples of
elements with vacancies
in their outer levels
HYDROGEN
1p+ , 1e-
13. Ion Formation
• Atoms that lose electron(s),
become positively charged ions
(cations)
• Atoms that gain electron(s),
become negatively charged
ions (anions)
• Electronegativity:
– A measure of an atom’s
ability to pull electrons from
another atom
17. Isotopes: What are They?
• Atoms of an element with the SAME # of
protons, but a DIFFERENT # of neutrons
• The atomic mass # on the periodic table is
an avg. mass of all the different isotopes
possible for the element
“Carbon 12” has 6
protons, 6 neutrons
• How do you figure out the number of
“Carbon 14” has 6
neutrons in an atom? protons, 8 neutrons
Atomic mass – atomic number = #
neutrons
18. Special Isotopes: Radioactive Isotopes
• Have an unstable nucleus
that emits energy or some
of the subatomic particles
(protons or neutrons)
• Some are used in research
and medical applications
(pacemakers, radiation
therapy, MRI)
19. Radioactive Isotopes Can be Used
as Tracers
• A tracer is a substance with a radioactive isotope attached
to it
• Emissions from the tracer can be detected with special
devices
• Following the movement of tracers is useful in many areas
of biology and medicine
21. Lab 3: Making Conversions Between Various
Measuring Systems
• Purpose of this lab:
To become familiar
with several systems of
measurement and
make conversions from
one unit to another as
well as learn to read
syringes and graduated
cylinders
