Download I. Atom - New York Science Teacher

UNIT I
The Atom
CHEMISTRY:
** Matter:
I. Atom: ______________________
______________________
______________________________
______________________________
A. History of the Atom
1. Democritus (460 – 370 B.C.)
a. “Atomos”
b. Nature of Matter
- Ignis
- Aer
- Terra
- Aqua
2. John Dalton’s Atomic Theory (1803)
a. All elements are composed
of hard and indivisible spheres
called atoms.
b. All atoms of a given element
are identical.
c. Atoms of different
elements are different;
that is, they have different
masses.
d. Compounds are formed
by the combination of
atoms of different elements.
3. J.J. Thomson (1890’s)
a. Cathode ray tube experiment
b. identified the electron
c. “plum pudding model”
1)
2)
-Experiment passes an electric current through a gas
-Sealed the gas in a glass tube with metal disks (electrodes)
-Electrodes are connected to a source of electricity.
-One electrode, the anode, became positively charged.
-The cathode, became negatively charged.
-The result was a glowing beam, or cathode ray, that traveled from
cathode to anode
Electrical/
Magnetic
Field
Cathode ray is deflected (repelled) by a metal plate that has a
negative charge and attracted to a metal plate that has a
positive charge.
* Opposite charges attract and like charges repel
“Plum pudding model”
1) Atoms contain small, negatively,
charged particles called electrons.
2) Electrons were seen as being
randomly distributed in a sphere of
positive charge.
4. Ernest Rutherford (1909)
“gold foil experiment”
a. Rutherford’s observation
b. Rutherford’s proposal
c. Rutherford’s conclusion
Rutherford’s observation
1) Alpha particles passed
through gold foil with
slight deflections
(bounced back).
Rutherford’s proposal & conclusion
2) The atom is mostly
empty space.
3) The atom has a dense
central core called a
nucleus.
**NUCLEUS:
(write this under nucleus)
i. 3 Parts of the Atom
a. proton:
b. neutron:
c. electron:
Subatomic Particles
Particle
Charge
Mass
Location
Symbol
Proton
+1
1 amu
Nucleus
-
Neutron
0
1 amu
Nucleus
-
Electron
-1
1/1840 amu
Outside
-
ii. Definitions
a. ATOMIC NUMBER:
** The number of protons
equals the number of
electrons.
Element
Helium
Oxygen
Sodium
Argon
Atomic #
Protons
Electrons
iii. Mass Number:
MASS NUMBER = # PROTONS + # NEUTRONS
# OF NEUTRONS = MASS NUMBER – ATOMIC NUMBER
(Why?)
MASS NUMBER = # PROTONS + # NEUTRONS
# OF NEUTRONS = MASS NUMBER – ATOMIC NUMBER
Element
Lithium
Atomic
#
3
Carbon
6
Potassiu
m
Fluorine
Protons Neutrons
2
7
6
20
9
Mass #
10
39
Electrons
Representing the composition of an atom
Isotopic
Notation
197
79
Au
Top #: Mass number
Bottom #: Atomic number
If you subtract the bottom # from the top #, what number do
you get?
Standard notation: Gold - 197.
12
6
C
1. What is the standard notation?
2. What is the mass number?
3. How many protons?
4. How many neutrons?
5. How many electrons?
Practice
How many protons, electrons and neutrons are
in each atom?
1.
9
2.
20 Ne
10
4Be
iv. Isotopes:
Diamonds are a naturally occurring form of elemental carbon. Two
stable isotopes of carbon are carbon - 12 and carbon – 13.
Carbon - 12
# of Protons
# of Neutrons
# of Electrons
Chemical Symbol
Top: Mass #
Bottom: Atomic #
Carbon - 13
42
Mass #
Atomic #
# of Protons
# of Neutrons
# of Electrons
Standard Notation
20Ca
44
20Ca
v. Atomic Mass:
Examine the table of student test scores
for 5 tests, and calculate their average
grades.
Test
Student A
Student B
1
95
76
2
74
88
3
82
90
4
92
81
5
81
72
Average Grade
If you know the student’s average grade, can
you tell what the student’s individual test scores
were? Explain
Test
Student A
Student B
1
95
76
2
74
88
3
82
90
4
92
81
5
81
72
Average Grade
84.8
81.4
Suppose student C had an average of 83%. On each of
his five tests he scored either 65% or 95%.
Which score occurred more often? Explain.
• Find the average of 95 and 65.
• Is 83% greater than this average?
• Which score occurred more often?
What if the teacher decided that test five would count for 40%
of the final grade and test four would count for 30% of the
final grade and each of the other tests would count for 10%.
Calculate the new average for each student. Note: this is
called the weighted average.
Test
Student A
Student B
1
95 x 10% =
76 x 10% =
2
74 x 10% =
88 x 10% =
3
82 x 10% =
90 x 10% =
4
92 x 30% =
81 x 30% =
5
81 x 40% =
72 x 40% =
**Weighted Average
Solve for the weighted average for student A -
Solve for the weighted average for student B -
A sample of cesium is 75% 133Cs, 20% 132Cs
and 5% 134Cs. What is the average atomic
mass?
0.75 x 133 = 99.75
0.20 x 132 = 26.4
0.05 x 134 = 6.7_______
Total = 132.85 amu = average atomic mass
WHICH ISOTOPE OF CESIUM IS THE MOST
ABUNDANT?
Determine the average atomic mass of the
following mixtures of isotopes.
1. 50% 197Au, 50% 198Au
1. 15% 55Fe, 85% 56Fe
1. 98% 12C, 2% 14C
1. 95% 14N, 3% 15N, 2% 16N
1. 99% 1H, 0.8% 2H, 0.2% 3H
e. Niels Bohr (1915)
“Bohr model or Planetary
model”
shells; orbits;
Principle Energy Levels (n)
1) Orbit, shell, principle energy level:
* Each level (n) can hold a specific #
of electrons (2n2).
Orbits
PEL (n)
Max e- (2n2)
K
L
M
N
O
P
Q
1
2
3
4
5
6
7
2
8
18
32
50
72
98
a) Bohr’s atomic model
(shell diagram)
i) Electron shell (1st)
closest to nucleus
contains least amount
of energy.
ii) Electron shell farthest from nucleus
contains electrons with most amount of energy.
iii) Electron configuration found in the periodic
table shows the arrangement of electrons in
these
electron shells.
Oxygen
Electron Configuration:
2) Ground State:
**LOOK for an electron configuration that is same as on
the Periodic Table for that atom:
Example: Find the ground state electron
configuration for sodium and draw Bohr’s shell
diagram.
•
•
•
•
•
•
•
•
Symbol?
Atomic #?
Mass #?
# of protons?
# of neutrons?
# of electrons?
Electron configuration?
Draw Bohr’s shell diagram
Practice # 1: Find the ground state electron
configuration for HELIUM and draw Bohr’s shell
diagram.
•
•
•
•
•
•
•
•
Symbol?
Atomic #?
Mass #?
# of protons?
# of neutrons?
# of electrons?
Electron configuration?
Draw Bohr’s shell diagram
Practice #2: Find the ground state electron
configuration for LITHIUM and draw Bohr’s shell
diagram.
•
•
•
•
•
•
•
•
Symbol?
Atomic #?
Mass #?
# of protons?
# of neutrons?
# of electrons?
Electron configuration?
Draw Bohr’s shell diagram
Practice # 3: Find the ground state electron
configuration for Phosphorous and draw Bohr’s
shell diagram.
•
•
•
•
•
•
•
•
Symbol?
Atomic #?
Mass #?
# of protons?
# of neutrons?
# of electrons?
Electron configuration?
Draw Bohr’s shell diagram
Practice # 4
1. What is the total number of electrons in the
configuration 2 – 8 – 18 – 5?
2. How many electrons are in the fourth shell of
an Iodine atom?
3) Excited State:
a) Occurs when electrons are subjected to a
stimuli (heat, light, electricity).
b) An excited state – electron quickly returns
to a lower available energy level,
emitting (releasing) the same amount
of energy.
Example: Sodium in the excited state is 2 – 7 – 2
Excited state:
LOOK for a configuration that has the same
total number of electrons as of the element
given, BUT, different arrangement on Periodic
Table
What is the ground state and excited state
configuration for phosphorous?
Ground state:
Excited state:
Sulfur
Selenium
Ground state:
Ground state:
Excited state:
Excited state:
Which is an excited state electron configuration
for an atom with 16 protons and 18 neutrons?
1) 2 – 8 – 5 – 1
2) 2 – 8 – 6
3) 2 – 8 – 6 – 2
4) 2 – 8 – 7
4) Valence electrons:
Example: How many valence electrons are in the
element with the atomic number 15?
Draw the electron – dot (Lewis) diagram.
Chlorine
1. Find the electron configuration.
2. Find the number of valence electrons
3. Draw the electron – dot diagram.
Draw the electron dot diagram for:
1. Oxygen
2. Helium
5) Ions:
– Cations
• Have a positive charge
• Have lost electrons
– Anions
• Have a negative charge
• Have gained electrons
– Ion symbol
• To write the ion symbol, you must write the element symbol
with the net charge written on the top right.
• Example: Ca2+, Zn2+, Ag1+, Cl1-
sodium and sodium ion
# of protons ____
# of electrons ____
net charge _____
cation
# of protons ____
# of electrons __10__
net charge ____
chlorine and chlorine ion
# of protons ____
# of electrons ____
net charge _____
anion
# of protons ____
# of electrons ___18_
net charge ____
Determine the ions for these atoms.
Potassium
Cation
# of protons ____
# of electrons __18__
net charge _____
Oxygen
Anion
# of protons ____
# of electrons __10__
net charge _____
f. Wave mechanical model (Schrödinger):
“Quantum Theory”
1. Electron cloud:
a.) Quantum: The specific amount
of energy absorbed by an
electron.
b.) Photons: A bundle of light
being emitted as an electron
jumps down to ground state.
c.) Spectroscope: An
instrument that separates
light into its various
wavelengths
and displays
them as colored
lines of bands.
d.) Bright Line Spectrum: The
particular set of colored
bands produced by a given element.
Your Bright Line Spectrum
400 nm
500 nm
600 nm
700 nm
Which elements are present in this mixture?
Which elements are present in this mixture?
Below are the bright line spectra of four elements and the
spectrum of an unknown gas.
a) Which elements are in the unknown?
b) Why are you able to exclude the other elements?
c) Young stars are mostly hydrogen with a small abundance of
helium and other elements. Is the unknown a likely
spectrum for a young star?
Below are the bright line spectra of four elements and the spectrum of an unknown
gas.
a) Which elements are in the unknown? Hydrogen and Helium
b) Why are you able to exclude the other elements? Because only hydrogen and
helium give out bands of light in those wavelengths similar to the unknown.
c) Young stars are mostly hydrogen with a small abundance of helium and other
elements. Is the unknown a likely spectrum for a young star? Yes, because the
unknown has hydrogen and helium.
g. Werner Heisenberg
Heisenberg Uncertainty Principle:
scientist
ideas
model diagram
Dalton
“PlumPudding”
Thomson
Rutherford
A dense nucleus
at center and
empty space
surrounding it
Planetary
model
Bohr
Schrodinger
Wave
Mechanical
Model
Cloud
Model
problems
1. The atomic number tells you the number of
____________ in one atom of an element. It
also tells you the number of _____________
in a neutral atom of that element.
2. The _______________ of an element is the
total number of protons & neutrons in the
__________ of the atom.
1. The atomic number tells you the number of
protons in one atom of an element. It also
tells you the number of electrons in a neutral
atom of that element.
2. The mass number of an element is the total
number of protons & neutrons in the nucleus
of the atom.
2. Quantum Numbers
A. Principle Quantum Number (n):
* Each PEL contains sublevels
Principal
Energy Level
Type of
Sublevel
# of Orbitals
in a Sublevel
Total Orbitals
per level
Max # of
electrons
1
s
1
1
2
s
p
1
3
4
3
s
p
d
1
3
5
2
(2 electrons)
2
6
(8 electrons)
2
6
10
(18 electrons)
s
p
d
f
1
3
5
7
4
Level n
n types
(n=1, 2, 3, …) (s, p, d, f, etc.)
9
16
2
6
10
14
(32 electrons)
n2 orbitals
2n2 electrons
In the 1st Principle Energy LEVEL, there is one
sub-LEVEL, it’s name is “s”, which has 1 orbital
with two electrons of opposite spin.
In the 2nd Principle Energy LEVEL, there are 2
sub-LEVELs, whose names are “s” and “p”.
S has 1 orbital, which holds 2 electrons.
P has 3 orbitals, which holds 2 electrons each.
B. Electron Configuration:
4
Principal Energy
3p
Level
Type of
sublevel
Number of electrons in
sublevel
Rules for filling sublevels
1. Each added electron is placed in the sublevel of
lowest energy available (*Aufbau Principle).
2. No more than 2 electrons, with opposite spins can
placed in any orbital (*Pauli Exclusion).
3. Before a second electron can be placed in any orbital,
all the orbitals of that sublevel must contain at least
one electron with same spin (*Hunds Rule).
4. No more than four orbitals (one s and three p
orbitals) can be occupied in the outermost principle
energy level. The next electron must enter the next
principle energy level.
Write the electron configurations for:
(and draw the orbital filling diagram)
1. Neon
2. Aluminum
3. Titanium
4. Gallium
Practice
1. What is the total number of electrons needed to
complete fill all the orbitals in an atom's second principal
energy level?
(1) 16
(2) 2
(3) 8
(4) 4
2. What is the total number of sublevels in the fourth
principal energy level?
(1) 1
(2) 2
(3) 3
(4) 4
3. Which sublevel contains a total of five orbitals?
(1) s
(2) p
(3) d
(4) f
Practice
1. What is the total number of electrons needed to
complete fill all the orbitals in an atom's second principal
energy level?
(1) 16
(2) 2
(3) 8
(4) 4
2. What is the total number of sublevels in the fourth
principal energy level?
(1) 1
(2) 2
(3) 3
(4) 4
3. Which sublevel contains a total of five orbitals?
(1) s
(2) p
(3) d
(4) f
Practice
4. What is the maximum number of electrons that can occupy
the fourth principal energy level of an atom?
(1) 6
(2) 8
(3) 18
(4) 32
5. Which of the following sublevels has the highest energy?
(1) 2p
(2) 3p
(3) 2s
(4) 3s
6. What is the maximum number of electrons in an orbital of
any atom?
(1) 1
(2) 2
(3) 6
(4) 10
Practice
4. What is the maximum number of electrons that can occupy
the fourth principal energy level of an atom?
(1) 6
(2) 8
(3) 18
(4) 32
5. Which of the following sublevels has the highest energy?
(1) 2p
(2) 3p
(3) 2s
(4) 3s
3. What is the maximum number of electrons in an orbital of
any atom?
(1) 1
(2) 2
(3) 6
(4) 10
Practice
1.
2.
3.
4.
1s2 2s22p6 3s23p63d104s24p5
In this electron configuration, what do the
coefficients represent? Letters? Exponents?
How many energy levels are shown?
What is the atomic number of this element?
What would this electron configuration look
like in the excited state?
Answers
1s2 2s22p6 3s23p63d104s24p5
1. Coefficients represent principal energy levels
1. Letters represent sublevels
2. Exponents represent number of electrons
2. Four energy levels are shown
3. Atomic Number for this element is 35 (Bromine)
4. 1s2 2s22p6 3s23p63d104s24p4 4d1
g. Werner Heisenberg
Heisenberg Uncertainty Principle: