Atoms

Report
BELL RINGER
What subatomic
particle is not
located in the
nucleus?
Atomic History Research
Chapter 3
Review Book – Topic 1
Chapter 1
BELL RINGER
What are the
nucleons (things in
the nucleus)?
1. Who did the gold foil experiment?
2. Who first named an atom?
3. According to Bohr, where are
electrons located?
4. Draw an atom according to
Democritus.
5. Who discovered the electron?
A. Ancient Greece (2000+ years ago)
Democritus - believed that matter could not be
continuously divided
- Matter consists of small indivisible
particles
“Atomos” = Atom  indivisible
- Aristotle did not agree  his teacher
Particles are in continuous motion
Four elements make up all matter and energy
Earth, Wind, Water, Fire!
No scientific evidence to show this.
 by


1700s
(scientific revolution),
all chemists agreed:
on the existence of atoms
that atoms combined to make
compounds
B. Dalton’s Atomic Theory - 1803
1. All matter is composed of small particles which cannot
be broken down (atoms)  same as Democritus
2. All atoms of the same element are identical in size, mass
and properties. Atoms of different elements are different in
size, mass and properties
Hydrogen
Sulfur
3.Atoms of different element combine in simple ratios to make
PbO2
compounds
H2S
4. In chemical reactions, atoms are combined, separated, or
rearranged (No atoms are created or destroyed)
So at this point, we believe that an atom is like a small solid
ball of matter that cannot be split up
 Some
parts of Dalton’s theory were
wrong:  AMENDMENTS



atoms are divisible into smaller particles
(subatomic particles)
atoms of the same element can have
different masses (isotopes)
Matter can be lost - Nuclear
C. J.J. Thomson - 1897
Experimented with cathode rays
Used electric field to show that cathode rays
are negatively charged particles
DISCOVORED THE ELECTRON
After discovery of the proton, Thomson assumed an atom was a
mixture of + and – charged particles, all mixed up
Plum-Pudding Model
+- + - + -+ - +
D. Rutherford
Ernest Rutherford wanted to determine what an atom looked like.
Fired (+) charged alpha particles at a very thin piece of gold (Gold foil)
Put a screen behind the foil to determine what happens to the rays
Gold foil
Radioactive source
Most of the rays went straight through the foil
Some rays deflected
A very few rays came straight back
Screen
Click on me!!!
Rutherford explained this by stating that
a. Atoms have mostly empty space
This is why most rays went straight through
b. There must be a dense positive center to an atom
This is why the positive rays deflected. (Positive rays
are repelled by positive charged objects)
-
+
-
-
-
Rutherford
model
Later experiments showed that electrons exist in the space between nuclei
 includes



all particles inside atom
proton
electron
neutron
 charge
on protons and electrons are
equal but opposite
 to make an atom neutral, need equal
numbers of protons and electrons
number
of protons
identifies the atom as a
certain element
protons and neutrons are
about same size
electrons are much smaller
#
protons = atomic number
 # electrons = # of protons (for now)
 # neutrons =
mass number– atomic number
p
n
e
3
4
3
23
Na
11
11
12
11
9
4
4
5
4
26
30
26
7
Li
3
Be
56
Fe
26
BELL RINGER
Give the p, n, and e
in a neutral atom of
Silver.
p
n
e
17
18
17
Hg
80
121
80
Xe
54
77
54
22
26
22
Cl
17
201
X
22

Nucleus:



contains protons
and neutrons
takes up very little
space
Electron Cloud:


contains electrons
takes up most of
space
E. Bohr - looked at the arrangement of electrons
Electrons exist in definite areas around the nucleus
Energy levels
e-
e-
Further from the nucleus, an electron has more energy
ee-
Electrons can gain energy and “jump” to higher levels
nucleus
They can then give off the energy as they jump back down
Energy levels are numbered 1,2,3,4,5,6,7
•With 1 being closest to the nucleus and
having the least amount of energy
All atoms have the same types of energy levels
+
- -
-
-
Planetary model
F. Wave Mechanical Model
Aka – ‘Electron Cloud’
Dr. Wave Mechanical
Modified Bohr’s model
Electrons are not in circular orbits,
but exist in specific spaces around
the nucleus
Pattern is random, unpredictable
•most dense near nucleus
level
Energy levels contain sublevels
nucleus
level
Review of Atoms
Dalton
Bohr
Thompson
Rutherford
Democritus
Wave Mechanical
Electron Location
• Located in energy levels outside of the nucleus
• The closer to the nucleus = less energy
• The farther away from the nucleus = more energy
Electron Location
Electrons are located in energy levels or shells.
There are a bunch of energy levels and each level can
“fit” only a limited number of electrons.
2
2n
Where ‘n’ represents
the energy level
Energy level 1 can have Energy level 2 can have Energy level 3 can have Energy level 4 can have -
2 e8 e18 e32 e-
Bohr Diagrams
Gives the location and the number of the p, n, and e.
Draw the Bohr diagram for Oxygen:
p= 8
n= 8
Valence e- = 6
Answer
p= 9
n= 10
Valence e- = 7
BELL RINGER
What did Rutherford
contribute to the
development of the
atom?
Ge
6. Sodium
2. Manganese
7. Cr
3. As
8. Krypton
4. Phosphorus 9. Be
5. Ti
10.Boron
1.
The above is an example of a ground
state electron configuration
(=the configuration on your R.T.’s)
Each electron in an atom has its own
distinct amount of energy. Electrons in
the first energy level have the lowest
potential energy since they are located
closest to the nucleus.
As an electron gains a specific bunch
of energy, the electron “jumps” to a
higher energy state (excited state).
p= 10
p= 10
n= 10
n= 10
Ground State
e- Configuration for Ne
2-8
Excited State
e- Configuration for Ne
2-7-1
How is light produced?
Absorbs nrg
p= 10
n= 10
n= 10
Gives off
Ground State
Releases nrg
p= 10
e- Configuration for Ne
Excited State
2-8
e- Configuration for Ne
2-7-1
When an electron
returns from a higher
energy state to a
lower energy state, a
specific amount of
energy is given off -->
RELEASED
Each element gives off a
certain color or spectrum
of colors.
You can identify unknown elements by
the color of light that they give off.
Bohr Animation
Ions
 So
far we have only talked about electrically
neutral atoms, atoms with no positive or negative
charge on them.
 Atoms, however, can have electrical charges –
They can gain/lose e-. Some atoms can either gain
or lose electrons
The
number of protons never
changes in an atom.
Ions

If an atom gains electrons, the atom becomes
negatively charged.
the atom loses electrons, the atom becomes
positively charged (because the number of
positively charged protons will exceed the number
of electrons).
 An atom that carries an electrical charge is called
an ion.
 If
Ions

Listed below are three forms of hydrogen; 2
ions and the electrically neutral form.
H+ : a positively
charged
hydrogen ion
H- : a negatively
charged
H : the
hydrogen
ion
hydrogen atom
Ions

Neither the number of protons nor neutrons changes
in any of these ions, therefore both the atomic
number and the atomic mass remain the same.
H+ : a positively
charged
hydrogen ion
H- : a negatively
charged
H : the
hydrogen atom hydrogen ion
Ions
Identify the number of subatomic
particles in the following ions:
A.)
+
Na
B.)
F
C.)
-2
O
p
11
9
8
n
12
10
8
e
10
10
10
BELL RINGER
Which is the electron configuration
of an atom in the excited state?
1)2-8-2
2)2-8-1
3)2-7-1
4)2-8-3
When subjected to a flame, solutions containing certain
metals have characteristic colors corresponding to the energy
released when excited electrons return to lower energy levels.
Ions
Identify the number of subatomic
particles in the following ions:
A.)
+2
Mg
B.)
Br
C.)
+
K
p
12
35
19
n
12
45
20
e
10
36
18
BELL RINGER
Draw the Bohr
-1
diagram for a F ion.



atoms of the same element with different numbers
of neutrons
most elements exist as a mixture of isotopes
Disproves Dalton’s theory
What
do the Carbon isotopes below have in common?
What is different about them?



sum of the particles in nucleus
= #p + #n
This is a whole number!!!
How many protons do each of the
hydrogen atoms below have?
Ions/Isotopes
PRACTICE
PROBLEMS
 since
masses of atoms are so small, it
is more convenient to use relative
atomic masses instead of real masses
 to set up a scale, we have to pick one
atom to be the standard
 since 1961, the carbon-12 nuclide is
the standard and is assigned a mass of
exactly 12 amu (=atomic mass unit)
REFERENCE TABLES
 atomic
mass unit (amu)- one is exactly
1/12th of the mass of a carbon-12 atom
 mass
of proton= 1.007276 amu = 1 amu
 mass of neutron= 1.008665 amu = 1amu
 mass of electron= 0.0005486 amu = 0 amu
 weighted
relative atomic masses of the
isotopes of each element
 each
isotope has a known natural
occurrence (percentage of that
elements’ atoms)
 An
element has three main isotopes
with the following percent occurances:



#1: 19.99244 amu, 90.51%
#2: 20.99395 amu, 0.27%
#3: 21.99138 amu, 9.22%
 Find
the average atomic mass and
determine the element.
=20.179 amu
 Naturally
occurring copper consists of:
Cu-63
Cu-65
Actual Mass
62.929amu
64.927amu
Percent
Abundance
69.71%
30.83%
100.54
Relative
abundance
.6971
.3083
1.0054
Relative
Mass
43.87
20.02
63.89
BELL RINGER
Isotope
AMU
32S
31.97
32.97
33.97
35.97
33S
34S
36S
Natural
Abundance
94.93%
0.76%
4.29%
0.02%
Calculate the average atomic mass of
Sulfur.
32.06 amu
There are two isotopes of Silver, Ag-107
and Ag-109. 52% of the isotopes are Ag107, what is the average atomic mass of
silver?
Ag-107
52% = 5564
Ag-109
48% = 5232
10796 ÷100 =107.96
BELL RINGER
Identify the number of p, n, and e
in the following:
37
17
Cl
1
Spectroscopy
The energy emitted is in the form of
radiant or light energy which
corresponds to a bright-line spectrum.
Each element has its own signature or
bright-line spectrum.
There are several kinds of spectra,
such as: continuous & bright line.
A continuous spectrum is, as the name
implies, a parade of all the colors from
the deepest red to the ultraviolet - of
which the rainbow in the sky is a good
example.
In the laboratory, a continuous
spectrum can be produced by
heating a solid - Light from the
electric lamp filament, for example,
produces such a spectrum.
When light emitted by a gas through
which an electrical discharge is passing
produces a spectrum consisting of a
few isolated parallel lines, it is known
as a "bright line spectrum"
The characteristic color of neon signs
is due to bright red and orange lines in
its spectrum. The typical color of neon
signs is due to the great intensity of the
red and orange lines.
A group of elements would create a combination of spectral lines
Element X
Element Y
3 different
electron jumps
Elements X and
Y combined
Notice how the combination of X and Y is just a combination of
the individual spectral lines?
Some Atomic Emission
Spectra

Hydrogen
Mercury
Argon
Helium
It should be carefully noted that each
element always gives the same pattern
of lines. Each element, so to speak, has
its own fingerprints, possessed by no
other element. This fact is utilized in
chemical analysis and in many other
applied fields.
BELL RINGER
Identify the number of electrons
and neutrons in the following:
1)Ti
+3
-2
2)S
What element is the unknown?
Unknown
Atomic History
DEMOCRITUS
named the most
basic particle
 atom- means
“indivisible

Atomic History
DALTON
1.
2.
3.
4.
Atoms of same element have the same
size, mass, and properties
Atoms can’t be subdivided, created or
destroyed
Atoms of different element combine in
whole number ratios to make compounds
In chemical reactions, atoms are
combined, separated, and rearranged.
Atomic History
DALTON

Some parts of Dalton’s theory were wrong:



atoms are divisible into smaller particles
(subatomic particles)
atoms of the same element can have different
masses (isotopes)
Most important parts of atomic theory:


all matter is made of atoms
atoms of different elements have different
properties
Atomic History
RUTHERFORD

‘Gold
Foil Experiment’
Atom is mostly empty space
Small, hard, dense positive
part = NUCLEUS

Atomic History
JJ THOMSON

discovered the e-
Atomic History
NEILS BOHR
Electons in
‘orbit’
 protons in
nucleus

Atomic History
MODERN MODEL
protons in nucleus
Electrons in an orbital – most
probable location

Atomic History
SUMMARY
What we know about the
atom has been the work
of many scientists over
thousands of years!
WHITE
BOARD
REVIEW
BELL RINGER
How much heat energy in joules is released
by 25.0 grams of water when it is cooled from
75.2ºC to 31.9 ºC?
Get the formula from Reference Tables
q = mcΔT
q = 25.0g (4.18J/g•ºC) 43.3ºC
q = 4525 J

similar documents