Chapter 4

Chapter 4
Atomic Structure
Chemical History covered Ch 4,
sections 1&2 and Ch 5, section 1
S Has anyone been to a
professional football stadium or
a major college football stadium?
S If the nucleus of an atom was
So then, most of the atom is
just “empty space.”
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.
Just how small is an atom?
S Let’s use a penny as an example (picture, in slide
show, is approximately life-size). A penny, if made
of pure Cu (copper) would have 2.4 x 1022 atoms.
That’s 24,000,000,000,000,000,000,000 atoms, btw.
Approx. 1 cm
from arrow to
arrow (in slide
show mode)
S If you lined up 100,000,000 atoms, they would
make up a line of approximately 1 cm. So, 2.4 x
1022 atoms, if lined up would make a line that was
approximately 2.4 x 109 KILOMETERS long.
What does an atom look like?
S In your notes, draw a
simple picture of an atom.
How about Lithium.
S What did you draw?
AAA baseball club Albuquerque Isotopes logo
(you need to know what isotopes are!)
S Most people probably drew a
nucleus of some type with
electrons orbiting around it.
S Possibly it looks a little like a
mini solar system.
S Atoms are composed of
S Protons (in the nucleus).
S Mass of 1 amu; charge = +1
S Neutrons (in the nucleus).
S Mass of 1 amu; charge = 0
S Electrons (moving around the nucleus).
S Mass of 0 amu; charge = -1
Subatomic Particles: Hint, you
need to know this!
Relative mass Actual Mass of
& charge
(1 amu = mass of a
+1.6 x 10-19
1 amu / +1
1.67 x 10-24g
1 amu / 0
1.67 x 10-24g
-1.6 x 10-19
0 amu / -1
9.11 x 10-28g
S Atoms can gain or lose electrons.
S Atoms can NEVER gain or lose protons!
S If an atom loses an electron, it becomes a positive
S Atoms can lose 1, 2 or 3 electrons
S If an atom gains an electron, it becomes a negative ion.
S Atoms can gain 1, 2, or 3 electrons
Atomic Number
S Protons determine the “identity”
of an atom.
S The number of protons is a
property called “atomic number.”
S Atomic numbers are on the
periodic table.
S C has 6 protons
S Ca has 20 protons
# Protons = # Electrons
If it is not an ion!
S Atoms are NEUTRAL (have the same number of
protons and electrons).
S If the charges don’t balance each other out, then
you have an ion.
S Protons MUST equal electrons if the atom has no
S Neutrons are also located in the nucleus
of the atom.
S The neutron was the last particle
Ooops, wrong
discovered, by James Chadwick, a former
student of Rutherford (who discovered
S He used paraffin wax to discover
neutrons. This was done in 1932.
S Atoms can have different numbers of
neutrons. These are called ISOTOPES.
The Nucleus
S Since the neutrons are located in the nucleus,
with the protons, substantially ALL of the
mass of the atom is contained within the
S Mass of nucleus in diagram
0.0000000000000000000000651 g
S Mass of electrons
0.0000000000000000000000000173 g
S In other words, if electrons (all 19 of them)
weighed as much as a piece of notebook
paper, the nucleus’ weight would be equal to
3,763 pieces of paper.
Strong Nuclear Force
S Positively charged things repel other positively charged
things, right?
S Why do all the protons stick together in the nucleus? Why
doesn’t it just spontaneously break apart? The answer is
strong nuclear force.
S It’s the strongest force in the universe.
S It is far, far stronger than gravity. It only can be felt
when the particles are extremely close together, like
when they are packed together in the nucleus.
S Protons and neutrons are made of quarks.
S It is thought that the quarks in neutrons are different
from the quarks in potons, so we think that the
neutrons actually help to hold the nucleus together.
Models of the Atom
S Scientists, starting with Dalton,
came up with models of the
atom, to help understand it and
help to predict its behavior.
S Solid Sphere Model
S Plum Pudding Model
S Nuclear Model
S Planetary Model
S Quantum Mechanics
S Do you remember who did each
S The “atomic number” is the
number of protons.
S We sometimes use a Z to represent
atomic number.
S Z does NOT equal the number of
So, if “ProtonMan”
was a superhero,
he’d have a “Z” on
his suit??
S Sometimes it does, but that is
S But Z is always the number of
Do Not Assume the Atom has a
S Unless you are TOLD that the atom has a charge, you
should assume it has no charge, and therefore, # of
protons = # of electrons.
S The number of protons cannot change.
S If the number of protons changes, it’s no longer the same
S Atoms can gain or lose electrons, but they can NOT
gain or lose protons in any chemical reaction. This is
part of Daltons’s Atomic Theory.
Schwartz’s Law
(a law I made up…hey, it’s my class)
S To calculate the number of electrons, use this little formula.
S # of Electrons = Z – IC
S Where Z = atomic number and IC = ionic charge
S Ex: Suppose we have a sodium ion with a + 1 charge. How many
electrons does it have?
S Atomic number (Z) is 11 (find this on Periodic Table) and ionic charge is 1.
S # electrons = 11 - 1 = 10
S Ex: Suppose we have a sulfur ion with a - 2 charge.
S How many electrons does it have? Atomic number (Z) is 16 and ionic charge
is -2.
S # electrons = 16 - (-2) = 16 + 2 = 18
6 neutrons
Finding Neutrons
8 neutrons
S How do we calculate how many
neutrons we have?
S In order to do that, we need to look at
another property, called mass number.
S The mass number of an isotope =
THE SUM of protons and neutrons.
Hey these are isotopes
again. Isotope = same #
of protons but a different #
of neutrons.
S We will use another formula
S # Neutrons = A – Z
S A = Mass Number
S So, what is Z again?
Finding Neutrons
S Let’s look at an example.
S 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
S # Neutrons = Mass Number - Atomic
S # Neutrons = 80 - 35 = 45
Special note
Hydrogen’s Isotopes
Isotopes of hydrogen:
= hydrogen
1 proton, 0 neutron
= deuterium
1 proton, 1 neutron
= tritium
1 proton, 2 neutrons
Hydrogen is the only
element with special
names for isotopes.
S An atom of Deuterium has Z = 1, and Mass
Number = 2. How many neutrons does it
S Since Z = 1, deuterium must be some type of
S We use the symbol D to represent H-2.
S We also use the symbol T to represent H-3.
S Deuterium is a form of hydrogen. When
deuterium reacts with oxygen it forms
something called “heavy water.”
S Heavy water is represented with the formula
D2O. It is still water, but it has different
PHYSICAL properties
S # of Neutrons = Mass Number - Z = 2 - 1 = 1
Heavy Water
S Here’s an interesting fact…
S Ice cubes made out of “heavy
water” will not float. They
sink to the bottom. So it has
different physical properties.
S Although it PROBABLY tastes
the same, you should NOT
drink it though. Too much of
it can really mess up your
system (and probably kill you).
Isotopes of Gold
S Look at gold (Au) on the periodic table.
It says that the mass = 196.967.
S Since mass number and atomic number
are ALWAYS whole numbers, how do
we get .967?
S The answer is that the atomic masses on
the periodic table are averages.
S 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.
Carats of Gold
S 10K and 14K gold are not different
isotopes of gold.
S They are different ALLOYS.
S 10K and 14K are homogeneous
mixtures of copper and gold.
K = 24 x (Massgold / Massalloy)
10K = 41.67% gold
14K = 58.33% gold
24K = 100% gold
Current price = $42.60/g
Math Alert
Average Atomic Mass
S How do we calculate the average atomic
S To do so, you need to know 2 things:
S All possible isotopes for an element
S The percent abundance for each (in other
words, how much of the whole is
represented by each isotope).
Math Alert
Average Atomic Mass
S Let’s look at an example:
S Chlorine has 2 isotopes
S 35Cl which is 75.77% of the total amount
of chlorine.
S 37Cl which is 24.23% of the total amount
of chlorine.
S What is the average atomic mass of
Proper Rounding of Atomic
Masses on Periodic Table
S In our class, we are always going to round
average atomic masses to 1 decimal place.
S So, we’ll round 35.49 to 35.5 and that’s the
average atomic mass of Chlorine that we’ll use.
S Why can’t you just average 35 and 37 (the two
isotopes) and get 36 as the average atomic
S Why is that wrong?
The End
Next you should look at the Chapter 5 power point.
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