Chapter 5
Atomic Structure and The Periodic Table
Objective B: Just how
small is an atom?
http://imagecache5.art.com/p/LRG/6/667/USYC000Z/fedex-field--washington-d-c-.jpg
 Has anyone been to a
professional football
stadium or a major college
football stadium?
So then, most of the atom is
just “empty space.”
 If the nucleus of an atom
was the size of a marble,
sitting at the 50 yard line, the
electrons would be about the
size of really little gnats
(bugs) whizzing around the
top rows of the upper deck.
Angstoms (Å)
http://intro.chem.okstate.edu/1314F00/Lecture/Chapter7/ATRADIID.DIR_PICT0003.gif

Even the largest atoms are very small. The diameter of a uranium atom is only about
0.345 nanometers.

A special unit is sometimes used to describe atomic dimensions, such as atomic radius
or atomic diameter. Note the trend as you go across a row and down a column.

That is the Angstrom. We use a Å to represent Angstroms (if you want to type that it’s
shift-alt-A on a Mac and control-shift-2, shift-A on a bogus, inferior, Windows or
Vista based machine).
What does an atom look like?
http://www.lanl.gov/orgs/pa/newsbulletin/images/Isotopes_logo.jpg
 In your notes, draw a
simple picture of an
atom. How about
Lithium.
 What did you draw?
AAA baseball club Albuquerque Isotopes logo
(you need to know what isotopes are!)
Atoms
http://upload.wikimedia.org/wikipedia/commons/thumb/e/e1/Stylised_Lithium_Atom.svg/270pxStylised_Lithium_Atom.svg.png
http://www.solarsystempictures.net/
Neutron
Proton
Electron
 Most people probably drew a
nucleus of some type with
electrons orbiting around it.
Lithium
Planets=Electrons
Sun=Nucleus
 Possibly it looks a little like a
mini solar system.
 Atoms are composed of
 Protons
 Neutrons
 Electrons
Subatomic Particles: Hint,
you need to know this!
Particle
Relative charge Relative mass Actual Mass of
(1 amu = mass of a Particle
proton)
Proton
Neutron
+1
1 amu
1.67 x 10-24g
0
1 amu
1.67 x 10-24g
-1
0 amu
9.11 x 10-28g
Electron
Electrons
 Atoms can gain or lose electrons.
 Atoms can NEVER gain or lose protons!
 If an atom loses an electron, it becomes a positive
ION.
 Atoms can lose 1, 2 or 3 electrons
 If an atom gains an electron, it becomes a negative
ion.
 Atoms can gain 1, 2, or 3 electrons
Protons
http://www.periodictable.com/Items/020.6/index.html
Atomic Number
 Protons determine the “identity”
of an atom. The number of
protons is a property called
“atomic number.” Atomic
numbers are on the periodic
table.
 H has 1 proton
 C has 6 protons
 U has 92 protons
# Protons = # Electrons
 Well yes, most of the time. Atoms are
NEUTRAL (have the same number of protons
and electrons).
 If the charges don’t balance each other out, then
you have an ion.
 Protons are located in the nucleus of the atom.
(Where are the electrons?)
Neutrons
http://www.ct.infn.it/~rivel/Archivio/chadwick.jpg
http://kwisp.files.wordpress.com/2009/05/adventures-jimmy-neutron-300-032707.jpg
 Neutrons are also located in the nucleus
of the atom.
Ooops, wrong
neutron!
 The neutron was the last particle
discovered, by James Chadwick, a
former student of Rutherford.
 He used paraffin wax to discover
neutrons. This was done in 1932.
 Atoms can have different numbers of
neutrons. These are called ISOTOPES.
Chadwick
The Nucleus
http://www.chemicalelements.com/bohr/b0019.gif
 Since the neutrons are located in the
nucleus, with the protons, substantially
ALL of the mass of the atom is contained
within the nucleus.
 Mass of nucleus in diagram
0.0000000000000000000000651 g
 Mass of electrons
0.0000000000000000000000000173 g
What element
is this??
 In other words, if the nucleus weighed 651
pounds, the electrons (combined) would
weigh less than a McD’s quarter-pounder
patty.
Models of the Atom
http://www.fiu.edu/~zhangj/cartoon_quantum3.gif
 Scientists, starting with
Dalton, came up with models
of the atom, to help
understand it and help to
predict its behavior.





Solid Sphere Model
Plum Pudding Model
Nuclear Model
Planetary Model
Quantum Mechanics
 Do you remember who did each
one?
Objective E
 We already know that the number of
protons is what makes an atom unique.
 Hydrogen has 1 proton.
 Carbon has 6 protons.
 Uranium has 92 protons.
So, if “ProtonMan”
 The “atomic number” is the number of
was a superhero,
protons. We sometimes use a Z to
he’d have a “Z” on
represent atomic number.
his suit??
Objective E
 So, for hydrogen, Z = 1
Don’t memorize
these…they are on the
Periodic Table
 For carbon, Z = 6
 For uranium, Z = 92.
 What is the atomic number for
 Aluminum
 Zinc
 Chlorine
Find THEM!!
Objective F
 So, Z (atomic number) tells us how many protons an
atom has. It does NOT tell you how many
ELECTRONS you have (accurately) all the
time!
 Unless you are TOLD that the atom has a charge, you
should assume it has no charge, and therefore, # of
protons = # of electrons.
 The number of protons cannot change. If the number
of protons changes, it’s no longer the same element.
Atoms can gain or lose electrons, but they can NOT
gain or lose protons in any chemical reaction.
Schwartz’s Law
(a law I made up…hey, it’s my class)
 To calculate the number of electrons, use
 # of Electrons = Z – IC
 Where Z = atomic number and IC = ionic charge.
 Ex: Suppose we have a sodium ion with a + 1 charge. How
many electrons does it have? Atomic number (Z) is 11 (find
this on Periodic Table) and ionic charge is 1.
 # electrons = 11 - 1 = 10
 Ex: Suppose we have a sulfur ion with a - 2 charge. How many
electrons does it have? Atomic number (Z) is 16 and ionic
charge is -2.
 # electrons = 16 - (-2) = 16 + 2 = 18
6 neutrons
Objective F
http://www.atomicarchive.com/Physics/Images/isotopes.jpg
8 neutrons
 How do we calculate how many
neutrons we have?
 In order to do that, we need to
look at another property, called
atomic mass. The atomic mass of
an atom = THE SUM of protons
and neutrons.
 We will use another formula
Hey these are isotopes
again. Isotope = same #
of protons but a different
# of neutrons.
 # Neutrons = A – Z
 A = Mass Number
 So, what is Z again?
Objective F
http://www.lbl.gov/abc/Basic.html#Nuclearstructure
 Let’s look at an example. An atom of
Bromine (Br-80) has Z = 35 and Mass
Number = 80. How many neutrons does it
have? (Br-80 doesn’t mean bromine with a charge
of -80. When they write it like that, it’s a DASH
and 80 is the mass number)
 # Neutrons = Mass Number - Atomic
Number
 # Neutrons = 80 - 35 = 45
Objective G
http://www.usagold.com/images/gold-coins-images.jpeg
http://finestimaginary.com/shop/images/medium/jewellery/au_MED.jpg
 How do isotopes differ from each other?
(You should know this by now).
 Look at gold (Au) on the periodic table. It
says that the mass = 196.967. Since mass
number and atomic number are ALWAYS
whole numbers, how do we get .967?
 The answer is that the atomic masses on the
periodic table are averages.
 They get that average atomic mass for
Au by taking into account ALL of gold’s
isotopes.
 Isotopes differ from each other in the
number of neutrons. They behave the
same CHEMICALLY because all
isotopes of the same element have the
same number of protons.
Math Alert
Objective H
 How do we calculate the average
atomic mass?
 To do so, you need to know 2 things:
 All possible isotopes for an element
 The percent abundance for each (in
other words, how much of the whole is
represented by each isotope).
Objective H
 Let’s look at an example:
 Chlorine has 2 isotopes
 35Cl which is 75.77% of the total
amount of chlorine.
 37Cl which is 24.23% of the total
amount of chlorine.
 What is the average atomic mass of
Chlorine?
Objective H
 Cl-35 accounts for 75.77% of the total chlorine. CL-37
accounts for the rest.
 Remember to convert percents into decimals, you have to
move the decimal point 2 places to the left.
 You then mutiply the percentage (in decimal form) times the
mass number for that isotope. You do that for the other
isotope too, and then add the answers together.
 Avg Atomic Mass = 35 (0.7577) + 37 (0.2423).
 Avg Atomic Mass = 26.52 + 8.97 = 35.49
Objective H
 In our class, we are always going to round
average atomic masses to 1 decimal place.
 So, we’ll round 35.49 to 35.5 and that’s the
average atomic mass of Chlorine that we’ll
use.
 Why can’t you just average 35 and 37 (the
two isotopes) and get 36 as the average
atomic mass? Why is that wrong?
Alkali Metals
 Sodium and potassium and all the rest of the
elements in that group are alkali metals.
 The alkali metals all have one valence electron. That
similarity is what makes them behave the same
chemically.
 They are very reactive. Reactivity is highest on the
outer edges of the table and elements get less
reactive the closer they are to the center of the table.
Lithium is the least reactive alkali metal and
reactivity increases as you go down the group.
Noble Gases
 The noble gases are very stable. They are unreactive
because they are so stable.
 The noble gases all have 8 valence electrons.
Helium is an exception in that it only has 2.
 The noble gases are obviously gases at STP
 STP = Standard Temperature and Pressure
Alkaline Earth Metals
& Halogens
 Group IIA or Group 2 are called “the alkaline earth
metals.” They have 2 valence electrons.
 Group VIIA or Group 17 are called “the halogens.”
The halogens all have 7 valence electrons, and like
the alkali metals, they are very reactive (fluorine is
most reactive and reactivity decreases as you go
down the group).
 Iron is one of the least reactive elements known. It
can take literally years for it to react.
Lewis Structures
http://www.ausetute.com.au/lewisstr.html
 A Lewis structure can have a maximum of 8 dots.
 You put one dot on each side of the symbol (top,
bottom, left and right), until each side has a dot.
 Then you can start pairing them up, until every
side has 2 dots.
Oxygen
Lewis
structure
 When every side has two dots, you can’t put any
more dots on the structure. If you need to, you did
something wrong.
The End
Next you should look at the Chemical History power point.
Then…
Advanced Chemistry should go to Chapter 28
powerpoint.
Chemistry should go to the Special Topics for SOL 2
powerpoint.