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Chapter 4 – Atomic Structure
Atom - Greek for “Atomon” means“Indivisible”
- Smallest unit that can exist alone
or in combination with other atoms.
Chapter 4 – Atomic Structure
Atom - Greek for “Atomon” means“Indivisible”
- Smallest unit that can exist alone
or in combination with other atoms.
Structure of an Atom … Things we know
Two main areas of the atom:
Nucleus
Electron cloud
Chapter 4 – Atomic Structure
Atom - Greek for “Atomon” means“Indivisible”
- Smallest unit that can exist alone
or in combination with other atoms.
Structure of an Atom … Things we know
Two main areas of the atom:
Nucleus
- contains protons (+) and neutrons (0)
- dense, small
Electron cloud
- contains electrons (-)
- surrounds nucleus, mostly empty space
- arranged in shells or energy levels
Chapter 4 – Atomic Structure
Atom - Greek for “Atomon” means“Indivisible”
- Smallest unit that can exist alone
or in combination with other atoms.
Structure of an Atom … Things we know
Two main areas of the atom:
Nucleus
- contains protons (+) and neutrons (0)
- dense, small
Electron cloud
- contains electrons (-)
- surrounds nucleus, mostly empty space
- arranged in shells or energy levels
Atom itself is neutral: Why?
Number of
p+ = en0 are neutral - no effect
Ions- atoms or molecules in which the total
number of electrons does NOT equal the total
number of protons. These particles have a
CHARGE.
Cations- positive ions (lose electrons)
Anions- negative ions (gain electrons)
Isotopes
– atoms of the same element with different masses due to a different number of n0
Ex. H has 3 isotopes
1
2
1H
1
1 p+
3
H
1
1 p+
1 e-
1 n0
1 e-
H
1 p+
1 e-
2 n0
The only thing that changes is the neutrons…
…so it is still hydrogen and acts like hydrogen but it is a little heavier with each
additional neutron added…
What if you change the number of neutrons? electrons?
More on Structure of an Atom … Things we know…
Atom is very, very small overall→ we measure it in Angstroms
1 A = 1 x 10-10 m
More on Structure of an Atom … Things we know…
Atom is very, very small overall→ we measure it in Angstroms
1 A = 1 x 10-10 m
Compare size of electron cloud to nucleus
Nucleus is extremely tiny
compared to the electron cloud.
How much smaller?????
More on Structure of an Atom … Things we know…
Atom is very, very small overall→ we measure it in Angstroms
1 A = 1 x 10-10 m (compare to Metric system units)
10 mill A = 1 mm
Compare size of electron cloud to nucleus
Nucleus is extremely tiny
compared to the electron cloud.
Nucleus “marble”
How much smaller?????
Nucleus is a marble in the
middle of a football stadium.
Electron Cloud “football field”
More on Structure of an Atom … Things we know…
Compare size of proton, neutron, and electron
More on Structure of an Atom … Things we know…
Compare size of proton, neutron, and electron
Nucleus
Proton’s mass = 1 amu
Neutron’s mass = 1 amu
More on Structure of an Atom … Things we know…
Compare size of proton, neutron, and electron
Electron’s mass = 0 amu
Electron Cloud
Nucleus
Proton’s mass = 1 amu
Neutron’s mass = 1 amu
More on Structure of an Atom … Things we know…
Compare size of proton, neutron, and electron
Interesting Stuff
… all the mass of the atom is in the nucleus…Wow! What
does that mean about the density of the nucleus?
Electron’s mass = 0 amu
Electron Cloud
Nucleus
Proton’s mass = 1 amu
Neutron’s mass = 1 amu
More on Structure of an Atom … Things we know…
Compare size of proton, neutron, and electron
Interesting Stuff
… all the mass of the atom is in the nucleus…Wow! What
does that mean about the density of the nucleus?
Electron’s mass = 0 amu
Nucleus
Electron Cloud
Proton’s mass = 1 amu
Neutron’s mass = 1 amu
1 amu (atomic mass unit) = 1.673 x 10-24 g
The atomic mass unit is easier to use to
describe something so ridiculously small!
0.000000000000000000000001673 g
Does an electron having “0” amu means it weighs nothing?
Not Exactly … It’s just it is so small it does not matter relatively …
More on Structure of an Atom … Things we know…
A word about the …
amu
*amu – atomic mass unit – special unit for the mass of an atom.
1/12 mass of carbon-12 atom.
(relative to atom)
More on Structure of an Atom … Things we know…
A word about the …
amu
*amu – atomic mass unit – special unit for the mass of an atom.
1/12 mass of carbon-12 atom.
(relative to atom)
Similar to:
2000 lbs. = 1 ton
Easier to say 10 tons than 20,000 lbs.
Just like:
1 amu (atomic mass unit) = 1.673 x 10-24 g
Easier to say 2 amu than 2.346 x 10-24 g
How did we figure out all this stuff about the atom???
Because the atom is so small !!!!!
How did we figure out all this stuff about the atom???
Because the atom is so small !!!!!
Before I start into the history…
…a little bit about Indirect Evidence???
Where to hunt?
Measure thickness of paper or a dollar?
How did we figure out all this stuff about the atom???
Because the atom is so small !!!!!
400 BC
Democritus
The idea of the atom stems back to 400 BC
by a Greek thinker named Democritus
…he called matter “atomon” meaning
“indivisible”
How did we figure out all this stuff about the atom???
400 BC
Because the atom is so small !!!!!
Now, this guy did not have
any proof…he just thought
about it and told people
what he thought …
…Good Guess??
Democritus
The idea of the atom stems back to 400 BC
by this Greek thinker
…he called matter “atomon” meaning
“indivisible”
How did we figure out all this stuff about the atom???
Because the atom is so small !!!!!
1782
Antoine Lavoisier
Law of conservation of mass
matter cannot be created nor
destroyed
How did we figure out all this stuff about the atom???
Because the atom is so small !!!!!
H2O
two H’s
one O
For this compound to be water…
it must have exactly 2 H and 1 O
1799
What is this?
H2O2
Joseph Proust
Law of definite proportions
a chemical compound contains
the same elements in exactly
the same proportions by mass
How did we figure out all this stuff about the atom???
Carbon monoxide CO
Because the atom is so small !!!!!
C = 12 g
O = 16 g
C = 12 g
O = 32 g
Ratio 1 : 1
Carbon dioxide
1803
CO2
Ratio 1 : 2
Same elements but different ratios make different compounds
John Dalton
Law of multiple proportions
If compounds are composed of
the same elements, the masses
of the elements can be
expressed as ratios of small
whole #’s.
How did we figure out all this stuff about the atom???
Because the atom is so small !!!!!
1803
John Dalton
The Atomic Theory
1. All matter is composed of extremely small, indivisible particles,
called atoms.
2. Atoms of the same element are chemically alike. Atoms of
different elements are chemically different. .
3. Atoms combine in whole # ratios to form compounds.
4. Atoms are combined, separated, or rearranged in chemical
reactions.
How did we figure out all this stuff about the atom???
Joseph Thompson
1897
Used a cathod ray tube to prove
there were negative charged
particles (now known as
electrons) in an atom. This
opened the way to the idea that
an atom was not just a solid
sphere not able to be broken
down anymore.
Because the atom is so small !!!!!
How did we figure out all this stuff about the atom???
1911
Because the atom is so small !!!!!
Earnest Rutherford
In the gold foil experiment, he proved that the electron
cloud was huge in volume comparison to the nucleus and
the nucleus was extremely dense.
How did we figure out all this stuff about the atom???
Because the atom is so small !!!!!
1913 Neils Bohr
He proposed a model of the atom that showed that ecircled that nucleus of an atom in only allowed orbits or
paths.
The Evolving Atomic Model Summary
Dalton Model
Thomson Model
Rutherford Model
Bohr Model
1803 – John Dalton
believed that an atom
was an indestructible
particle with no
internal frame.
1897 – J.J. Thomson
discovers the electron.
He believed electrons
were embedded in
positive charge sphere.
1911 – Ernest
Rutherford discovers
that there is a dense,
positively charged
nucleus. Electrons
go around the
nucleus.
1913 – Niels Bohr
enhances Rutherford’s
model by having
electrons move in a
circular orbit at fixed
distances from the
nucleus.
(Billiard Ball Model) (Plum pudding Model)
Atomic Number – number of p+ in the nucleus of an atom (always
equal to number of e-)
Mass Number – number of p+ and n0 in the
nucleus of an atom
Atomic Weight (mass) – the average mass of the isotopes
The mass number is just the atomic weight rounded off to a whole number!!
Atomic Weight
32.065
Shorthand method:
32
16 S
Mass #
(rounded)
32
Put light blue boxes on
your periodic table…as a
reference
Atomic #
(# of p+ or e-)Mass # - Atomic # = n0
Atomic Weight
Atomic #
Mass #
# p+
# e# n0
=
=
=
=
=
=
(Avg. mass of isotopes)
=
(number of protons or electrons) =
(Atomic weight rounded)
=
(same as Atomic #)
=
(same as Atomic #)
=
(Mass # - Atomic #)
=
Try Sodium (Na):
Atomic Weight
Atomic #
Mass #
# p+
# e# n0
=
=
=
=
=
=
(Avg. mass of isotopes)
(number of protons)
(Atomic weight rounded)
(same as Atomic #)
(same as Atomic #)
(Mass # - Atomic #)
32.066
16
32
16 p+
16 e 16 n0 (32 – 16)
= ________
= ________
= ________
= ________
= ________
= ________
Atomic Weight
Atomic #
Mass #
# p+
# e# n0
=
=
=
=
=
=
(Avg. mass of isotopes)
=
(number of protons or electrons) =
(Atomic weight rounded)
=
(same as Atomic #)
=
(same as Atomic #)
=
(Mass # - Atomic #)
=
Try Sodium (Na):
Atomic Weight
Atomic #
Mass #
# p+
# e# n0
=
=
=
=
=
=
(Avg. mass of isotopes)
(number of protons)
(Atomic weight rounded)
(same as Atomic #)
(same as Atomic #)
(Mass # - Atomic #)
32.066
16
32
16 p+
16 e 16 n0 (32 – 16)
= ________
22.99
= ________
11
23
= ________
11
= ________
11
= ________
12
= ________
PRACTICE THESE…………
Au
Atomic Weight
Atomic #
Mass #
Ag
Pb
= (Avg. mass of isotopes)
= _______________
= (number of protons)
= ______________
= (Atomic weight rounded) = ______________
# p+
= (same as Atomic #)
= ______________
# e-
= (same as Atomic #)
= ______________
# n0
= (Mass # - Atomic #)
= ______________
PRACTICE THESE…………
Au
Atomic Weight = (Avg. mass of isotopes)
Atomic # = (number of protons)
Ag
Pb
196.97 107.87 207.2
= __________________
79
47
82
= __________________
197
108
207
Mass # = (Atomic weight rounded) = __________________
# p+ = (same as Atomic #)
79
47
82
= __________________
# e - = (same as Atomic #)
79
47
82
= __________________
# n0 = (Mass # - Atomic #)
118
61
125
= __________________
Shorthand Notation
Mass #
Atomic #
Ions- atoms or molecules in which the total
number of electrons does NOT equal the total
number of protons. These particles have a
CHARGE.
Cations- positive ions (lose electrons)
Anions- negative ions (gain electrons)
Periodic Table
Horizontal Rows are periods.
Indicate how many shells are needed to hold all of the electrons
Vertical columns are Groups or families
Indicate the # of valence electrons
1
2
3
4
5
6
7 8
Ions
NonMetals
Metals
Gain electrons until they
Lose Valence electrons
have 8*
Form Positive Ions
Equal to Group #
Form negative ions
Cations
Equal to how many electrons
they gained
Anions
*Helium has
2 valence e*Silver has
1 valence e-
1 2
3 4 5 6 7 8
*
*
Ions
Metals (regular name)
NonMetals (end in “ide”)
Ca+2
Calcium Ion
F-1
1 2
Fluoride
3 4 5 6 7 8
Isotopes
– atoms of the same element with different masses due to a different number of n0
Ex. H has 3 isotopes
1
2
1H
1
1 p+
3
H
1
1 p+
1 e-
1 n0
1 e-
H
1 p+
1 e-
2 n0
The only thing that changes is the neutrons…
…so it is still hydrogen and acts like hydrogen but it is a little heavier with each
additional neutron added…
If you change the number of neutrons…it is still Carbon but it makes a different isotope.
Carbon –12
Carbon - 14
Different number of neutrons
8
Isotopes?
Which of the following represent isotopes
of the same element? Which element?
What is an Average Atomic Mass (weight)?
Look at our periodic table…why the decimals????
It comes from the isotopes…Let’s look at Oxygen…
16
17
8O
8
8 p+
8
n0
18
O
8
8 p+
8 e-
9 n0
8 e-
0.038%
99.762%
O
8 p+
81 e-
10 n0
.20%
Almost all of Oxygen is Oxygen 16 but there are small amounts of the others…therefore it
makes sense that the average atomic mass would be closest to 16…here is how it is figured …
Oxygen 16
Oxygen 17
Oxygen 18
(15.994915)(0.99762) + (16.999131)(0.00038) + (17.999160)(0.0020)
= 15.9994
average atomic mass
Isotope Calculations
(abundance as a decimal) ( mass of isotope)
+ (abundance as a decimal) ( mass of isotope)
+ (abundance as a decimal) ( mass of isotope)
Answer =
Isotope Calculations
Element X has two natural isotopes. The isotope
with a mass of 10.012 amu has a relative abundance of
19.91%. The isotope with a mass of 11.009 amu has a
relative abundance of 80.09%.
Answer = 10.810 amu
Lewis Dot Structures
1) Find your element on the
periodic table.
2) Determine the number of
valence electrons.
3) This is how many electrons
you will draw
Lewis Dot Structures
1) Write the element symbol.
2) Write down the number of
valence electrons (based of the
group #)
3) Write down the symbol and
draw an imaginary box around
it
4) Draw the valence electrons as
dots on the sides of the box.
 One at a time on each side
until you are out of valence
electrons
Lewis Dot Structures
On an open area on your notes, try these elements on your own:
1) H
2) P
3) Ca
4) Ar
5) Cl
6) Al
Bohr Model of the Atom – …Kinda like concert seating!
Put the number of p+ , n0 , and e- in the diagram as shown…
Lets diagram Sulfur
p+ = Atomic # = 16
e- = Atomic # = 16
n0 = Mass # - Atomic # = 32 – 16 = 16
Remember that mass # is atomic weight rounded
Maximum seats =
2
8
18
32
p+ = 16
e- = 2
n0 = 16
e- = 8
e- = 62
e- =
Bohr Model of the Atom – …Kinda like concert seating!
Put the number of p+ , n0 , and e- in the diagram as shown…
Lets diagram Sulfur
p+ = Atomic # = 16
e- = Atomic # = 16
0 = Mass # - Atomic # = 32 – 16 = 16
n
*NOT
ACTUAL
MODEL*
Remember that mass # is atomic weight rounded
Maximum seats =
2
8
18
2n2
32
p+ = 16
e- = 2
e- = 8
e- = 62
e- =
n0 = 16
1
2
3
4
n = shell number
Bohr Model of the Atom – Try these…
Lithium
Magnesium
Helium
Argon
Maximum seats =
2
8
18
2n2
32
p+ = ?
e- = 2
e- = 8
e- = 62
e- =
n0 = ?
1
2
3
4
n = shell number