Download Unit 2 Atomic Theory

Unit 2
Atomic Theory
Matter
• All matter is made
of atoms
o Alone as elements
• Au, Na, O, He
o In combination of elements
as compounds
• H2O, NaCl, LiO2
Early Theories of Matter
• Democritus (460-370 B.C.)
proposed & believed that
o Matter was not infinitely
divisible
o Made up of tiny particles called
atomos
o Atoms could not be created,
destroyed, or further divided
John Dalton,
th
19
• Dalton revised
Democritus's ideas based
upon the results of
scientific research he
conducted
• Dalton’s atomic theory
o Not totally correct
Century
Dalton’s First Atomic Theory:
o Elements are made up of small indivisible
particles called atoms
o Atoms of the same element are identical, different
elements are different
- (Same size, mass and chemical properties)
o Atoms are not created or destroyed in a chemical
reaction
o A compound always has the same relative
numbers and kinds of atoms
What is an atom?
• An atom is the smallest particle of an element
that retains the properties of the element
Atomic Models
• Thomson:
Plum Pudding Model
• Rutherford:
Electron Cloud
Model
Rutherford: The
Nuclear Atom
• His model consisted of the following ideas:
o an atom consists mostly of empty space through which
electrons move
o electrons are held within the atom by their attraction to
the positively charged nucleus
o small, dense, positive charged nucleus
Bohr Model
• Based on Rutherford’s
model
• Adds idea of “quantized”
energy levels
Inside an atom: subatomic
particles
• These particles have
mass and charge
• Nucleus holds protons &
neutrons
o Protons: + charge
o Neutrons: Ø charge
• Outside of nucleus is the
electron cloud
o Electron: - charge
Parts of the Atom
Name
Symbol
Charge
Mass
Location
proton
p
+1
1 amu
nucleus
neutron
n
0
1 amu
nucleus
electron
e-
-1
~ 0 amu
outside
nucleus
Atomic Mass Unit (amu)
• Small mass #’s are not easy to work with, so the atomic
mass unit (amu) was developed
• The mass of 1 amu is nearly equal to the mass of one
proton or neutron
Reading the Periodic Table
Atomic Number
• The number of protons determine the
element (ALWAYS!!!)
• Number of protons are unique to each
element
• Examples:
o Carbon (C) has 6 protons
• Atomic number is 6
o Copper has 29 protons
• Atomic number is 29
Atomic Number
• In uncharged atoms, atomic number is also the
number of electrons
o Why?
o If an atom is charged, then it is an ion
• Uncharged atom:
Atomic number = # of protons = # of electrons
Charge = # protons - # electrons
Mass Number
• To find the Mass number
# protons + # neutrons = mass number
• To find # neutrons
mass number – proton (or atomic number) = neutrons
• Mass numbers are always WHOLE #’s!!
Symbols for Atoms
X= symbol of element
A= mass number
Z= number of protons
A
Z
X
A
or
X
- Can also be written “element - A”
- i.e. carbon - 12
Mg-25
70
30
Zn
atomic #
12
30
proton
12
30
neutron
13
40
electron
12
30
mass #
25
70
Isotopes and Mass Number
12
6
C
carbon-12
13
6
C
carbon-13
Isotopes are atoms with the same number of protons
but different number of neutrons
Isotopes and Mass Number
• Example:
3 types of Potassium
19 electrons
All 3 types contain 19 protons and __
# of Protons
19
19
19
# of Neutrons
20
21
22
Mass Number
39
40
41
What’s the difference between mass number
and average atomic mass(weight)?
12
6
C
carbon-12
But if you look on the periodic table, the number states
12.01…
Atomic Mass (atomic weight) – a weighted average of
the masses of all of the isotopes of that element. It is not
the same as the mass number.
What’s the difference between mass
number and average atomic mass?
• Mass number- specifically about one isotope
• Average atomic mass- includes the masses of
all the different isotopes for that atom
Mass of Individual Atoms
• Atomic mass:
o The weighted average mass of the isotopes of
an element
o Example: Chlorine
• Mixture of 75.00% chlorine-35 and 25.00%
chlorine-37
Atomic mass = (0.7500)*35.00 + (0.2500)*37.00
= 35.50 amu
Try this one
• 3 isotopes of neon:
o Ne-20 (90.92%)
o Ne-21 (0.25%)
o Ne-22 (8.83%)
What is the atomic mass of Ne? (add .00 to masses)
(20.00)*(0.9092) + (21.00)*(0.0025) + (22.00)*(0.0883) =
20.17 amu
There are two isotopes of magnesium in a
container: Mg-24 and Mg-25. The mass of 121
atoms of magnesium is 2988 amu. How many
of each isotope are present?
X = 37  37 Mg-24 atoms
Y = 84  84 Mg-25 atoms
A container has 10,000. carbon atoms have a mass of
120,110. amu. There are 2 carbon isotopes: C-12 and C-13.
How many of each isotope?
C-12 = 9890.
C-13 = 110.
The atomic weight of lithium is 6.072 amu. There are two
isotopes:Li-6 and Li-7. the mass of 151 atoms is 917 amu?
How many of each isotope?
Li-6 = 140.
Li-7 = 11
The mass of one nickel is 5.13 grams, the mass of one dime is
2.73 grams, the mass of 1 envelope is 4.38 grams. Eight coins
are put into an envelope. The mass of the envelope and coins
is 38.22 grams. How many dimes and nickels are in the
envelope?
Dimes = 3
Nickels = 5
• A container with a mass of 4.13 grams has a
total of 25 dimes and quarters. The mass of a
dime is 2.73 grams, and a quarter is 7.26 grams.
If the total mass of the container and coins is
149.39 grams, how many dimes and how many
quarters are there?
• Dimes = 8
Q = 17
c
f
wl
Energy of light is:
- directly related to the frequency of
the light
- inversely related to the wavelength.
- As frequency
- As wavelength
, energy
Energy has units of Joules (J)
E = hf
E
, energy
h
h = Planck’s constant = 6.626 x 10-34 J. s
f
What is the energy and wavelength of radiation
whose frequency is 6.775 x 1018 s-1?
3.00 x108 m/s = 4.44 x10-11 m
6.775 x1018 s-1
E = hf = (6.626 x10-34 Js) (6.775 x1018 s-1)
= 4.489 x10-15 J
1.What is the wavelength of light that has a
frequency of 2.27 x1017 s-1?
2.What is the frequency of light that has a
wavelength of 9.13 x10-10 m?
3. What is the wavelength of light with a
frequency of 4.27 x1018 s-1?
4.Radiation has an energy of 1.23 x10-16 J.
What is the frequency and wavelength of
the radiation?
1. wavelength = 1.32 x10-9 m
2. frequency = 3.29 x1017 s-1
3. wavelength = 7.03 x10-11 m
4. frequency = 1.86 x1017 s-1
wavelength = 1.62 x10-9 m
Radioactivity – when the nucleus of an atom
is unstable causing it to decompose into
another nucleus
There are three types of radioactive decay:
1.Alpha Decay
2.Beta Decay
3.Gamma Decay
Alpha Decay
• An alpha particle (α ) is produced
• An alpha particle is just a helium nucleus,
4
+2
He
2
Beta Decay
• An e- is kicked out of the nucleus (a neutron
breaks up into a proton and e-), -10 e
Gamma Decay
• energy is released from the nucleus
• the nucleus itself does not change, but almost
always accompanies alpha and beta decay
•Alpha Decay
230
4 He + 226 Ra
Th

90
2
88
222
4 He + 218 Rn
Ra

2
86
88
•Beta Decay
234
0 e + 234 Pa
Th

90
-1
91
131
53I 
0
131 Xe
e
+
-1
54
•Gamma Decay
238
4 He + 234 Th + energy
U

92
2
90
What are the products of Po-218 after it
undergoes alpha decay followed by a beta
decay, followed by beta decay followed by
alpha decay?
218
4 He + 214 Pb
Po

84
2
82
214
0 e + 214 Bi
Pb

82
-1
83
214
0 e + 214 Po
Bi

83
-1
84
214
4 He + 210 Pb
Po

84
2
82
Half-Life (t1/2) - time required for one half of
the original sample of nuclei to decay.
•The half-life of Ra-223 is 12 days. If you start
with 100.0 grams of Ra-223, how much will be
left after 36 days?
100.0 g  50.00 g  25.00 g  12.50 g
•The half life of Ra-225 is 15 minutes. If you
have 10.0 grams now, how much did you start
with 60 minutes ago?
•10.0 g  20.0 g  40.0 g  80.0 g  160.g
Fission – when an atom splits into two or more
smaller atoms in a nuclear reaction.
1n+
235
92
U
92
36
Kr +
141
56
Ba + 3 n + energy
• This is what takes place in a nuclear reactor or
an atomic bomb.
Fusion – when several smaller atoms combine to
make a larger atom
2
1
3
1
4
2
H + H  He + 1n + energy
• This is how all of the elements were created in
nature.