Intro to Chemistry
Periodic Table tidbits
Period table organization – organized by
increasing atomic number
 Split into metals (left side of stair step line)
and nonmetals (right side of stair step line)

 ONE


EXCEPTION
Hydrogen!
vertical columns (#1-18)
 Groups

horizontal rows (#1-7)
 Periods
Atomic Structure

Nucleus- center of an atom
-contains protons
(which are positive)
-contains neutrons
(which are neutral)
Ex- Sodium:
Atomic Structure
Outside the Nucleus:
 Electrons (which are negative) surround the
nucleus in energy levels
1st energy level = holds 2e
2nd energy level = holds 8e
3rd energy level =
SAVE
4th energy level =
FOR
CHEMISTRY!!
Subatomic Particles Organized
Charge
Protons
Neutrons
Electrons
Location
Mass
Try it out!
Read pp 104-108
then do #3, 4, 5 on page 110
Subatomic Particle Organized
Protons
Charge
Location
Mass
Positive
In nucleus
1 amu
Neutrons
Neutral
In nucleus
1 amu
Electrons
Negative
Outside of
0 amu
nucleus/ in
energy levels
Atomic
Mass
An atom is defined by the
number of PROTONS IT HAS!!!
Chemistry tidbits

Chemical Symbol- letter representing the
atom (sometimes from Latin)
Chemistry tidbits
Atomic number = number of protons
 Mass number = # protons + # neutrons

 Don’t

bother to weigh the air inside the box
So how can you calculate NEUTRONS??
Calculating Neutrons is a simple
algebraic problem…
Mass Number = protons + neutrons
 Atomic Number = protons
 Write the equation…

Mass Number= Atomic Number + neutrons
 #Neutrons = (mass number – atomic number)

Chemistry tidbits

Usually can assume:
#
protons = # electrons

ONLY true for NEUTRAL ATOMS!
And remember…

Don’t mess with the
PROTONS!!!
So what CAN we “mess with?”

Neutrons…
 Changes
the MASS
 Get an ISOTOPE

Electrons…
 Changes
the CHARGE
 Get an ION
Atomic Mass Mystery…

Look at the atomic mass for Oxygen.
What does it say (exactly?)
 15.9999

What is the atomic mass?
P

+N
So what the heck!?!?!
 Average
of the actual isotopes on Earth!!!
Isotopes
Isotopes are different atoms of the same
element that contain the same number of
protons but different number of neutrons.
 Examples

Cl-35
vs.
Cl-37
17P
17P
18N
20N

How to write isotopes…

Mass/Hyphen Notation:
 Especially
important for a form of the isotope
that is NOT the “usual”
 Write the symbol, a dash, and the mass # for
that isotope
 Ex’s
C-14
 C-12

How to write isotopes…

Nuclear Symbol Notation
 Includes
the symbol, atomic #, and the mass
# for that isotope
 Ex’s
14
6
C
What else CAN we “mess with?”

Neutrons…
 Get

an ISOTOPE
Electrons…
 Get
an ION
IONS
If you mess with the electrons you change
the overall charge of the atom…an atom
that is no longer neutral is called an ION.
 WE WILL LEARN ABOUT IONS LATER
WHEN WE DO BONDING!!

How do we Draw Atoms
Bohr Models
 Lewis Dot Structures

Look at the many things in your classroom or at home: desks, chairs,
windows, shoes, etc. If all of these things are made from atoms and all
atoms are made of only a few kinds of particles, what accounts for the
variety of things that you see?
Atoms of different elements have different atomic numbers. The atomic
number tells us the number of protons (+ charge). If the atom is neutral, the
number of electrons (-charge) equals the number of protons.
The mass number is the number of protons + the number of neutrons
(0 charge). In the following, C-14, the 14 is the mass number. The atomic
number for C can be found on the periodic table. C’s atomic number is 6, so
it has 6 protons and 6 electrons. To find the neutrons, take the mass
number minus the protons (14-6 = 8 neutrons).
In the Bohr Model, the protons and the neutrons are placed in the
atomic nucleus while the electrons orbit around the nucleus in stationary
levels. Each level can hold only a certain maximum number. The 1st up to 2
electrons, the 2nd up to 8 electrons, and the 3rd, 4th, etc. hold even more
electrons
Complete the table below using the information given for each atom.
Atom A has 3 protons and 4 neutrons.
Atom B has 11 protons and 12 neutrons.
Atom C has an atomic number of 19 and a mass number of 39.
Atom D has an atomic number of 17 and a mass number of 35.
Atom
A
B
C
D
# of
protons
# of
neutrons
Atomic # Mass #
# of
electrons
Complete the table below using the information given for each atom.
Atom A has 3 protons and 4 neutrons.
Atom B has 11 protons and 12 neutrons.
Atom C has an atomic number of 19 and a mass number of 39.
Atom D has an atomic number of 17 and a mass number of 35.
Atom
# of protons # of
neutrons
Atomic # Mass #
# of electrons
A
3
4
3
7
3
B
11
12
11
23
11
C
19
20
19
39
19
D
17
18
17
35
17
Let’s Draw some Bohr Models!
But…that can be a pain…
Most of the time we only really care about
the valence electrons
 Valence Electrons- electrons in the
outermost shell

 Also
the GROUP NUMBER!!!
Valence Electrons are what
react!
Lewis Dot Structures
 Lewis
dot diagrams- display the
number of valence electrons
(outermost electrons) around the
element symbol
 Used to show how atoms of different
elements bond and form compounds
 Hint- use group number to find
valence electrons
Octet Rule
Most atoms want to have 8 electrons in
their outer shell
How to draw a Lewis Dot
Structure
1.
2.
3.
Find the group # (top of the row on the
PT)
Write the symbol.
Draw dots around the symbol equal to the
group number (if group 2- draw two dots)
1.
Place dots one at a time around the top,
right, bottom and left side of the atom before
you double any up.
How to draw a Lewis Dot Structure
1.
2.
3.
Find the group # (top of the row on the PT)
Let’s do Phosphorus
Write the symbol. P
Draw dots around the symbol equal to the
group number (if group 2- draw two dots)
1.
Place dots one at a time around the top, right,
bottom and left side of the atom before you double
any up.
EXCEPTIONS!!!

Helium What
is its group number?
 Why doesn’t it make sense to draw that many
dots?

Because it is easier for it to fill that first shell which
only needs two electrons
Electron configurations (Bohr Models)

Lewis Dot Structures