Ch 4 – Atomic Structure
History:
1. Democritus- (400 BC) What’s the smallest possible particle? Break a rock into pieces…
eventually get to smallest possible pieces → call those “atomis” (invisible)
2. Aristotle- Everything is made of a substance called “hyle.” Re-arrange hyle to make
different substances. Aristotle's philosophies accepted by Roman Catholic church
- Western science in dark ages until ~ 1500’s.
3. Dalton- (1800’s) father of atomic theory
1. All elements composed of tiny, invisible particles →atoms
2. All atoms of same element are identical atoms of different elements are different
3. Atoms of diff. elements combine in whole # ratios.
4. Chem. occur when atoms separate from each other, join with others, but the atoms
themselves never change.
4. JJ Thompson (~1900) uses cathode ray tube & discovers the electron
5. Millikan (~1900) his oil drop experiment discovered mass/charge of electron
6. Rutherford- (1905)- Gold Foil Experiment – discovered the nucleus →(+) charged core of
the atom
7. Neils Bohr- (~1910’s)- Planetary model of the atom
8. Chadwick- (1932)- discovered neutron
Subatomic particles
Particle
Symbol
Charge
Mass in
grams
Mass in amu
Proton
p+
+1
1.67x10-24
1
Electron
e-
-1
9.11x10-28
1/1840
Neutron
no
0
1.67x10-24
1
500,000,000,000,000,000,000,000,000,000,000 electrons equals 1pound
2,500,000,000,000 protons side by side = 1 inch
Ch. 4 HW #1 1-5
1. Explain how Democritus came up with his theory every made of atoms:
2. Which statement would Dalton Agree with:
a) Atoms are the smallest particles of matter.
b) Mass of an iron atom is different from mass of a copper atom.
c) Every atom of silver is Identical to every other atom of silver.
d) A compound is composed of atoms of two or more different elements.
3. Since all atoms have negatively charged electrons shouldn’t every sample of
matter have a negative charge? Explain.
4. Now did the results of Rutherford's Gold Foil Experiment differ from his
expectations?
5. What is the charge of every nucleus (+ or -)?
Ch 4 HW #2
6. (in class)
7. (in class)
8. An atom is identified as platinum- 195.
a) What is the number 195 called?
b) What is the symbol with #’s?
9. Determine the number of neutrons:
a) Carbon - 13
b) Nitrogen- 15
c) Radium - 226
Ch 1 – XC Clock
Suppose a metric clock used the following system:
1 day = 10 metric hours
1metric hour = 10 metric minutes
1 metric minute = 10 metric seconds
1 metric second = 10 metric mini-seconds
If the metric clock reads 4hrs, 5min, 6 sec, 7 mini-sec,
What time is it in the real world?
Ch 4- The Periodic Table
6
2
4
C
Carbon
12.011
Atomic # - # of protons
- the periodic table is arranged in increasing atomic #.
- since all atoms are electrically neutral # protons = #of electrons
Mass # - total mass of atom mass = protons and neutron
- do not count electrons → too small!
HW # 6) (copy to separate paper!)
Element
Symbol
Atomic #
# of protons
Potassium
5
16
Y
HW # 7)
Atomic #
Mass #
# Protons
9
# Neutrons #Electrons
10
14
47
55
15
22
25
Symbol
Writing symbols:
16
← mass # (prots & nuets)
ex:
8
← Atomic # (prots)
Neutrons = mass- atomic
= 16 – 8 = 8 Neutrons
ex:
108
Ag
Neutrons = 108 – 47 = 61 N
47
Sometimes written is this form :
ex: Carbon – 12
↖ mass # Look at P.T. to find atomic #
Neutrons = Mass – Atomic
= 12 – 6 = 6 neutrons
ex: Uranium – 238
Neutrons = 238 – 92 = 146
Back to P.T.
6
2
4
C
Carbon
12.011
Average Atomic Mass
H – 1.0079 ( Over 99% of all hydrogen's are H – 1)
( A few are H – 2, or H – 3)
C – 12.011 ( Almost all are C – 12)
Cl – 35.435 - only 2 isotopes → Cl – 35 & Cl – 37
75% in nature are Cl – 35
25% are Cl – 37
So these are weighted averages
14) Cu had 2 isotopes: Cu – 63 , Cu – 65. Given that the ave atomic mass is 63.546 amu,
which isotope is more abundant?
(finish for HW)
Calculating
Ex) Element x has 2 natural isotopes. One isotope with mass 10.012 amu has a relative
abundance of 80.09%. Calculate the atomic mass and the name of the element.
10X:
10.012 amu x 0.1991 =
“X: 11.009 amu x 0.8009 =
Ch 4 HW # 4 10-15
Isotopes
Isotopes of the SAME ELEMENT obviously have the same # of protons, differ in # of
Neutrons
Ex. Write the chemical symbol and find # of Neutrons for:
Carbon-12 and Carbon-13
12 C
13 C
6
6
HW #12) Determine # of prots, elects, Neuts for the 5 isotopes of zinc
p+ e- N
Zn-64 30 30 34
Zn-66 30 30 36
Zn-67 30 30 37
Zn-68 30 30 38
Zn-70 30 30 40
Atomic Mass
↓
.00000000000000000000003g
1 Flourine atom-3.155x10-23 g
1 arsenic atom-1.244x10-22 g
Not practical!
Decide to call the mass of 1 proton=1 atomic mass unit
-since prots and Neuts are close, but slightly different, decide to take Carbon-12
(6 prots, 6 Neuts) ÷ by 12 = 1 amu
Element
Symbol # Protons
# Neutrons
Row (period)
C5olumn (Group)
Aluminum
Al
13
14
3
13
Carbon
C
6
6
2
14
Chlorine
Cl
17
18
3
17
Chromium
Cr
24
28
4
6
Cobalt
Co
27
32
4
9
Copper
Cu
29
35
4
11
Gold
Au
79
119
0
11
Helium
He
2
2
1
18
Hydrogen
H
1
0
1
1
Iron
Re
26
30
4
8
Krypton
Kr
30
47
4
18
Lead
Pb
82
125
6
14
Mercury
Hg
80
121
7
12
Nitrogen
N
7
7
2
15
Potassium
K
19
20
4
1
Element
Symbol # Protons
# Neutrons
Row (period)
Column (Group)
Silver
Ag
47
61
5
11
Sodium
Nu
11
12
3
1
Sulfur
S
16
16
3
16
Uranium
U
92
146
7
-
Zinc
Zn
30
35
4
12
Electron Shells Worksheet
1.
1
1 Electron
1
H
1p
0n
Hydrogen
1.0074
2.
2
1
3
Li
2.
2
1
Lithium
6.941
3
Li
Lithium
6.941
3p
4n
3.
2
3
_
__
_p
_n
Boron
______
4.
_
_
_
__
Nitrogen
______
_p
_n
5.
2
8
2
12
12p
18n
Mg
Magnesium
24.3
6.
_
_
_
__
Aluminum
______
_p
_n
7.
2
8
7
_
_p
_n
__
Chlorine
______
8.
2
8
8
_
__
Argon
______
_p
_n
2
8
8
1
9.
_
K
_p
_n
Potassium
______
10.
30
Zn
Zinc
65
30p
35n
Ch 4 HW #3
10) How are isotopes of the same element alike?
How are they different?
11) Three isotopes of oxygen are Oxygen – 16, Oxygen – 17, and Oxygen – 18,
write the chemical symbol.
12) ( in class )
13) There are 3 isotopes of silicon with mass #’s 28, 29, 30.
The atomic mass of silicon is 28.086 amu. Which is most abundant?
14) The element copper has 2 naturally occurring isotopes : 6329 Cu, 6529 Cu.
The relative abundances and atomic masses are:
Calculate the average atomic mass.
Cu – 63 .692 x 63 = 43.47
Cu – 65 .308 x 65 = 20.02
63.49
15) List the # of protons, neutrons, electrons
a) 2713Al
p+
no
e-
b) 4420Ca
c) 31H
d) 188O
e) 7834Se
Chapter 25 Nuclear Chemistry
Ex: Carbon – 14
6
8PN
Radioisotopes – isotopes that are radioactive
because they have unstable
nuclei.
They undergo radioactive decay
- give up energy from the nuclei
( some nuclei break apart. )
Types of Radiation
Alpha radiation – a helium nucleus is emitted from a radioactive source
224 Th +
4 He
(α emission)
Ex) 23892 U
→
90
2
Uranium – 238
Thorium – 234
Alpha particle
4
Low Energy
Low Penetrating
Power
2 He
238
92U
224
90
Th
Beta radiation – an unstoppable nucleus decays, releases a beta particle
- a neutron decomposes into a proton and an electron
1
0N
→
Neutron
Ex)
14
6C
Radioactive
Carbon – 14
→
1
1H
Proton
14
7N
+
Stable
Nitrogen – 14
+
0
-1e
Electron
(beta particle)
0 e
-1
Beta
Particle
↑
↑
p=6
p=7
N=8
N=7
Gamma radiation – an unstable nucleus decays, releasing high energy electromagnetic
radiation.
230 Th
226 Ra
4 He
Ex)
→
+
+
Y
90
88
2
Thorium – 230
Radon – 226
Alpha
Gamma
Particle
Ray
Name the emitted particle and find the new nuclei created:
218 fr
214 At
4 He
Ex)
→
+
87
85
2
241
95Am
→
4
235
92U
→
90
1
0N
+
239
2He
94Pu
38Sr
→
+
237
93Np
+
144
58Ce
144
58Ce
+
1
+
90
38Sr
+
0N
4 0-1e
+
6 10 N
+
2 0-1e
Ch 25 HW#1
1) What part of the atom changes during radioactive decay?
2) Tell how alpha beta and gamma radiation are distinguished based on:
a) mass
b) charge
c) penetrating power
4
0
2
-1
β
4
+2
Low
0 (negligible)
-1
Mid
No mass
No charge
high
3) The disintegration of the radioisotope radium-226 produces an isotope of the element
radon and alpha radiation
write eqn: 226 88 Ra → 222 88 Rn + 4 2
4) Write nuclear eqns:
a) 30 15 P to 30 14 Si
b) 13 6 C to
12
6
C
(positron)
30
30
0
15 P →
14 Si + 1 β
13
6
C → 12 6 C + 1 0 n
a) 3015P → ____ + 0-1e
b) ___ →147N + 0-1e
c) 23892U → 23490Th + ___
d) 14156BA → ___ + 0-1e
6) Beta decay the following:
a) 9038Sr →
b) 146C →
c) 13755Cs →
d) 23993Np →
5) Complete:
Half Life (t ½)
-The time required for ½ the atoms of a radioisotope to decay.
Ex 1) Nitrogen – 13 emits beta radiation and decays to Carbon – 13 with a half life of 10 min.
with a starting mass of 2.00gof N – 13,
a) how long is 4 half lives?
b) how many grams of N – 13 still exist after 3 half lives?
Carbon Dating
- developed in 1940’s
- 146C → 147N + 0-1e
- t1/2 = 5730 years
- fairly accurately dates non-living things 200-50,000 yrs
How do we date the dinos?
Use a radioisotope with a longer ½ life
- uranium – 238 → t1/2 = 4.5 x109 yrs ( 4,500,000,000,) ( 4.5 billion yrs )
- use this to age certain rocks, all the back to beginning of
our solar system 4.6 billion years.
Ex 2) What is the ½ life of this radioisotope ? 5 yrs
If you had 20.0 g of it, how much
remains after 10 years?
1002 half-lives
5g
50amt
%
25-
5
10
15
20
t(yrs)
25
Nuclear Fission and Fusion
Fission-the splitting of a nucleus into smaller fragments caused by bombarding it
with neutrons
-releases enormous amounts of energy
( 1 kg of U-235 = 20000 tons of TNT)
→
235
1
0
92
U
↗
↘
236
92
U
91
36
Kr
N + 235 92 U → 236 92 U → 91 36 Kr + ___ + 3 1 0 N
Fusion – 2 nuclei combine to produce a nucleus of heavier mass
In the sun:
4 11H + 2 0-1e → 42He + energy
- fusion releases more energy than fission but requires high
temps → 40,000,000 0C
Cold fusion
2 H + 3 H →
1
1
4
2He
+
1
0N
+ energy
Ch 25 HW #2
7) A sample of thorium – 234 has a half-life of 25 days. Will all the thorium undergo
radioactive decay in 50 days?
10g → 5g → 2.5g
9) Explain nuclear chain reaction.
10) How is the chain reaction uncontrolled in a reactor?
11) Name a natural nuclear fusion reactor
12) What are advantages of producing electricity in a fusion reactor?
13) write: a) a radon emits an alpha particle to form polonium – 218
Rn → He + Po
b) Radium – 230 is produced when thorium 234 emits alpha
c) When polonium – 210 emits alpha particle, product is Pb – 206
Po → Ne + Pb
Graph the decay of Thorium 234
a) What percent after 60 days?
b) How many grams of a 250g sample remain
after 40 days?
c) How many days would pass while 44g decayed
to 11g?
d) What is half-life?
100
80
60
Remaining %
40
20
20
40
60
Days
80
100
Ch 3, 4, 25 Reviews
Ch 3 – how many seconds are in 3.7 days?
3.7 days 24hrs
60 min 60sec
1days
1hrs
1min
=
sec
-What values does 5.0g of Al occupy ( density of Al is 2.80g/Dm3 )
Ch 6 – 30)
Element
# of
Protons
Mass
Number
# of
Atomic #
Electrons
Si
Number
Neutrons
15
1
2
50
88
24
38
32) List the # of Protons, Neutrons, Electrons for each
a) 2713Al
b) 4420Ca
c) 31H
43) What is the average mass of lead?
204 Pb @ 1.37%
82
206
82Pb
@ 26.26%
207
82Pb
@ 20.82%
208
82Pb
@ 51.55%
Ch 25 – 24 ) Write the symbol and state the charge for each:
a) alpha particle
b) beta particle
c) gamma ray
34) A patient is administered 20mg of iodine – 131, How much of the isotope will remain
In the body after 40 days id the half-life of I – 131 is 8 days?
1
2
3
4
5
20mg
→
10mg
→
5mg
→
2.5mg →
1.25mg
↙
.625mg