Atom – the smallest particle of an element that ____________________________
___________________________________________________________________
•
•
•
Electron – negatively charged, fast moving particle
with an extremely small mass that moves through
the empty space surrounding the atom’s nucleus.
Proton – positively charged particle that exists
inside an atom’s nucleus.
Neutron – a neutral particle that exists inside the
atom’s nucleus.
How to obtain information about an atom from the Periodic Table:
•
Atomic Number – gives an atom its identity; tells you…
___________________________________________________________________________
•
Atomic Mass/Weight – the mass of the nucleus of an atom; measured in amu (atomic mass
units); equal to...
___________________________________________________________________________
o To determine # of neutrons:

____________________________________________________________
(round to the nearest whole number!)
* Worksheet – The Atoms Family: Atomic Math Challenge
1
Isotopes & Atomic Mass
Atoms of the same element must have the same atomic number, but they can have different
atomic masses.
•
Isotopes – __________________________________________________________________
___________________________________________________________________________
How does the existence of isotopes disprove part of Dalton’s Atomic Theory?
___________________________________________________________________________
___________________________________________________________________________
___________________________________________________________________________
___________________________________________________________________________
o Example: Lithium has 3 naturally occurring isotopes (shown below).
o The periodic table reports that Lithium has an atomic mass 6.941 amu. What
does that number represent?
__________________________________________________________________
__________________________________________________________________
__________________________________________________________________
o So what do we call the numbers 6, 7 and 8 in the picture above?
__________________________________________________________________
2
o If Lithium’s atomic mass is 6.941 amu, which form do you think most lithium
atoms take? Li-6, Li-7 or Li-8? Why?
__________________________________________________________________
__________________________________________________________________
__________________________________________________________________
How to calculate an element’s atomic mass from information about its isotopes:
• First, you are provided with the mass of each isotope and its percent abundance.
o Example: 2 isotopes of chlorine
 Chlorine-35 (75.77%)
 Chlorine-37 (24.23%)
• Next, you must determine the mass contribution from each isotope by multiplying the mass
of the isotope by its percent abundance:
•
Finally, you will add up the mass contributions of all isotopes of an element to determine
the average atomic mass for the element (your answer should be very close to the mass of
the element reported on the periodic table!):
* Worksheet – Isotope Practice Problems
3
Internal Structure of the Electron “Cloud”
As you well know, the atom consists of a small, dense, positively charged nucleus that contains
the protons and neutrons. You also know that surrounding the nucleus, there is a “cloud” of
electrons.
•
Believe it or not, there is actually some order to the madness of the electron cloud!
o Each electron within the cloud can be said to have its own “address.” Like our
addresses at home, the address of an electron has 4 main parts.
Your Address
Electron’s Address
(Quantum Numbers)
Principal Q. # - tells you which of the 7 main
energy levels the electron is in.
Angular Momentum Q. # - shows you which
sublevel (s, p, d, or f) the electron is in within the
main energy level.
Magnetic Q. # - indicates which orbital of the
sublevel the electron is in.
Spin Q. # - tells you which direction the electron
is spinning (up or down).
o Orbital – region of space where an electron is most likely to be found; 1 orbital
can hold 2 electrons spinning in opposite directions.
o Pauli Exclusion Principle – ____________________________________________
__________________________________________________________________
__________________________________________________________________
•
So...quantum numbers are useful for locating 1 electron in an atom, but it’s very rare that
we need to do that AND quantum numbers can get confusing!
4
Electron Configuration – _________________________________________________________
______________________________________________________________________________
o Before you can try to write an electron configuration for an atom, you need to
make sure you understand a few things.
Main
Maximum # of
# of Orbitals
Energy Sublevels
e- held
(1 orbital = 2 e-)
Levels
by Sublevel
1
s
1
2
2
3
4-7
s
1
2
p
3
6
s
1
2
p
3
6
d
5
10
s
1
2
p
3
6
d
5
10
f
7
14
Max # of e- in
Energy Level
What Do “Orbitals” Look Like?
Remember that an orbital is a region of
space where electrons are likely to be
found. This means that electrons can
move around anywhere within the
boundaries of space you see to the right.
Imagine that the nucleus is at the center of
the coordinate system. If you put all of
these shapes on the same grid, you can
imagine why the atom might look like a
cloudy mess!
5
How to Write an Electron Configuration:
•
An electron configuration uses a combination of coefficients, letters, and superscripts.
o Example: 1s2 = energy level 1, sublevel s, 2 electrons
 Which element has the electron configuration 1s2?
Answer: ___________________
•
To Begin…
Step 1: Determine the number of electrons an atom has.
Example: Aluminum has _______electrons.
Step 2: Place electrons in energy levels and sublevels by using the maximum number of
electrons each time until you get to the end.
Order for Placing Electrons in Energy Levels: start at the beginning of the top
arrow and work your way to the point. Then move to the beginning of the arrow
below and so on...
Aufbau Principle –
_________________________
_________________________
_________________________
_________________________
Example: Aluminum = _______ electrons
__________________________________________________________________
Step 3: Add up the exponents to be sure that you have represented the correct number
of electrons.
Note: The final piece of the electron configuration may NOT have the maximum #
of electrons.
* Worksheet – Writing Electron Configurations
6
•
Orbital Diagram – shows the arrangement of electrons within their orbitals inside the
sublevels s, p, d, and f.
o Instead of using exponents, an orbital diagram uses dashes (___) to represent
orbitals and arrows (↑↓) to represent electrons spinning in opposite directions.
How to Draw an Orbital Diagram
•
To Begin...
Step 1: Write the complete electron configuration for the atom.
Example: Chlorine _________________________________________________
Step 2: Rewrite the electron configuration, step-by-step, but instead of using
exponents, draw a dash above the number and letter to represent the # of orbitals in
that sublevel (s=1, p=3, d=5, f=7)
Example: Chlorine _________________________________________________
__________________________________________________________________
Step 3: Next, place electrons in orbitals. Each orbital should receive 1 up arrow and 1
down arrow.
Hund’s Rule - ______________________________________________________
__________________________________________________________________
__________________________________________________________________
Example: Chlorine _________________________________________________
__________________________________________________________________
* Worksheet – Drawing Orbital Diagrams
7
Shorthand Electron Configuration - each electron configuration builds on the electron
configuration of the element that comes before it on the periodic table.
o Example:
Ne = ______________________________________
Mg = ______________________________________
o To save yourself some time, you can use the symbol of one element to represent
its electron configuration and then simply write whatever is left over in the
configuration of the second element.

Example: Mg = _________________________________
o For standardization purposes (to make sure everyone writes shorthand electron
configurations the same way), ONLY noble gases (helium, neon, argon, krypton,
xenon, radon) can be used inside the brackets to shorten an electron
configuration.
* Worksheet – Writing Shorthand Electron Configurations
8
Are electrons stuck in the same energy level all of the time?
ABSOLUTELY NOT! And it’s pretty exciting when they change energy levels!
 ___________________________________________________________________________
______________________________________________________________________________
 ___________________________________________________________________________
______________________________________________________________________________
 ___________________________________________________________________________
______________________________________________________________________________
•
__________________________________________________________________
__________________________________________________________________
__________________________________________________________________
•
Ground State – when an electron is in its lowest energy state (in its original energy level)
•
Excited State – when an electron has absorbed extra energy and has moved into a higher
energy level.
9
Why is it important to know that elements emit different colors of light when their electrons
are excited?
•
The light emitted by an element can be used as a means for identifying that element.
o Flame Tests – substances are held inside a flame and the color of the flame is
observed.
 If there is an unknown substance, the color of its flame can be compared
to the flame colors of known substances.
* Lab – Flame Tests
10