Download + mass isotope 2

Laboratory Outline
•
•
•
•
•
Objective/Purpose
Procedure
Data/Observations
Results
Conclusion
Lab 1 – Developing
Observation Skills
• Objective: Develop a
hypothesis from observations
• Procedure:
1.
2.
3.
4.
5.
6.
Add water to a petri dish to a height of 0.5
cm. Measure 1 mL of oil using a graduated
cylinder or a graduated plastic pipette, then
add it to the petri dish.
Dip one end of a toothpick into liquid
dishwashing detergent.
Touch the tip of the toothpick to the center
of the petri dish. Records your detailed
observations.
Add whole milk to a second petri dish to a
height of 0.5 cm.
Place one drop of four different food
colorings in four different locations on the
surface of the milk. Do not put a drop of
food coloring in the center.
Repeat steps 3 and 4.
Elements &
Atoms
Matter and The Ancient Greeks
 Ancient Greek Philosopher
Democritus (460-370 BC)
 Matter is composed of atoms
moving through empty space
 Atoms are solid and indivisible
 Different kinds of atoms have
different sizes and shapes
John Dalton Atomic Theory
•
•
•
•
All matter is made of atoms.
Atoms of an element are identical.
Each element has different atoms.
Atoms of different elements combine
in constant ratios to form compounds.
• Atoms are rearranged in reactions.
• His ideas account for the law of conservation of mass (atoms
are neither created nor destroyed) and the law of constant
composition (elements combine in fixed ratios).
Law of Conservation of
Mass
Blue
2(2)
4
+
+
+
White
6(2) = 4 + 12
12 = 16
Four molecules – each with 1 blue
and 3 white
Blue
4(1)
4
+
+
+
White
4(3) = 4+12
12 = 16
A Cathode Ray
Tube
J.J. Thomson (1856–1940)
• Identified the first
subatomic particle –
the electron
• Received Nobel Prize in
1906
• Determined the mass
to charge ratio of
electrons through
cathode ray tube
experiments
J.J. Thomson
Cathode Ray Experiment
•
•
1897 Experimentation
Using a cathode ray tube, Thomson was able to deflect cathode rays
with an electrical field.
The rays bent towards the positive pole, indicating that they are
negatively charged.
High
voltage
cathode
source of
high voltage
negative
plate
_
+
anode
positive
plate
Oil Drop Experiment
• Robert Milliken (1860–1953)
o Determined the mass of the
electron using the oil-drop
apparatus
• Mass of an electron:
Masse- = 9.1 x 10-28 g
• This is
the mass of a
Hydrogen Atom
Plum-Pudding Model
α–particle path
Zumdahl, Zumdahl, DeCoste, World of Chemistry 2002, page 56
Rutherford’s Gold Foil Experiment
• Ernest Rutherford (1871–1937)
o
o
o
o
Thin Gold foil bombarded by a beam of α–particles
Detecting screen showed the final position of a particle
This experiment disproved the plum pudding model
This experiment also led to the discovery of the nucleus
The Atom
• An atom has three parts:
Subatomic
Particle
Symbol
Location
Charge
Relative
Mass
Actual mass
(g)
9.11 x 10-28
Electron
e-
Electron
cloud
–1
Proton
p+
Nucleus
+1
1 amu
1.673 x 10-24
Neutron
n0
Nucleus
0
1 amu
1.675 x 10-24
Periodic Table
Atomic Number:
Number of protons and
number of electrons in
an atom of an element.
Element’s Symbol:
An abbreviation for
the element.
8
O
Oxygen
Elements Name
Atomic Mass/Weight:
Number of protons +
neutrons.
16
Review
Protons = 3
3
-
Li
+
+
+
-
-
Lithium
7
Electrons = 3
Neutrons = 4
(7-3=4)
Zinc problem
An atom of zinc has a mass number of 65.
A. Number of protons in the zinc atom
1) 30
2) 35
3) 65
B. Number of neutrons in the zinc atom
1) 30
2) 35
3) 65
C. What is the mass number of a zinc isotope
with 37 neutrons?
1) 37
2) 65
3) 67
Calculating Atomic Mass
 Percent(%) abundance of isotopes
 Mass of each isotope of that element
 Weighted average =
mass isotope1(%) + mass isotope2(%) + …
100
100
Atomic Mass of Magnesium
Isotopes
Mass of Isotope
Abundance
24Mg
=
24.0 amu
78.70%
25Mg
=
25.0 amu
10.13%
26Mg
=
26.0 amu
11.17%
(24)(.787) + (25)(.1013) + 26(.1117) =
18.888 + 2.5325 + 2.9042 = 24.3 amu
Bohr Model
• The Bohr Model shows
all of the particles in
the atom.
• In the center is circles.
Each circle represents
a single neutron or
proton. Protons should
have a plus or P
written on them.
Neutrons should be
blank or have an N.
• In a circle around the
nucleus are the
electrons. Electrons
should have a minus
sign or an e.
-
+
+
-
Nuclear
Chemistry
21
Radioactivity
• Emission of subatomic particles or high-energy
electromagnetic radiation by nuclei
• Radioactivity characterized by a nuclear reaction
• Radiation:
o Rays and particles emitted by the radioactive material
• What causes radiation?
o The instability in an atom nucleus
o To gain instability, the nucleus emits radiation spontaneously
• Such atoms/isotopes said to be radioactive
22
History
• Discovered in 1896 by Becquerel working
working with uranium salts
• Marie Curie & her husband discovered two new
elements
o Polonium & Radium
• Curie and Becquerel shared the 1903 Nobel Prize in
Physics
• Curie also won the 1911 Nobel Prize in Physics
23
Types of radioactivity
• Alpha decay
• Beta decay
• Gamma ray emission
24
Alpha decay
• Alpha () particle:
o helium-4 nuclei minus 2e-= 42He
• Parent nuclide  daughter nuclide + He-4
238 U  234 Th + 4 He
92
90
2
• Daughter nuclide = parent nuclide atomic #
minus 2
• Sum of atomic #’s & mass #’s must be
equal on both sides of nuclear equation!
25
26
Alpha decay
• Has largest ionizing power
• = ability to ionize molecules & atoms due to
largeness of -particle
• But has lowest penetrating power
• = ability to penetrate matter
• Skin, even air, protect against -particle radiation
27
Beta decay
•
•
•
•
•
Beta () particle = eHow does nucleus emit an e-?
 neutron changes into proton & emits e 10n  11p + 0-1e
Daughter nuclide = parent nuclide atomic number
plus 1
137 Cs  137 Ba + 0 e55
56
-1
28
Beta decay
• Lower ionizing power than alpha particle
• But higher penetration power
• Requires sheet of metal or thick piece of wood to
arrest penetration
29
30
Gamma Decay
Electromagnetic radiation
High-energy photons
0 
0
No charge, no mass
Usually emitted in conjunction with other
radiation types…why?
• Lowest ionizing power, highest penetrating
power  requires several inches lead
shielding
•
•
•
•
•
31
Problems
• Write a nuclear equation for each of the following:
1. beta decay in Bk-249
249
97Bk
249
Cf
+
e
98
2. alpha decay of Ra-224
224
88Ra
4
2He
+
220
86Rn
Calculate the neutron to proton ratio of each species
32
Band of Stability
• In determining nuclear
stability, ratio of neutrons
to protons (N/Z)
important
• Notice lower part of
valley (N/Z = 1)
• Bi last stable (nonradioactive) isotopes
• N/Z too high: above
valley, too many n,
convert n to p, betadecay
• N/Z too low: below valley,
too many p, convert p to
n
33
Magic numbers
• Actual # of n & p affects
nuclear stability
• Even #’s of both n & p give
stability
• Similar to noble gas electron
configurations: 2, 10, 18, 36,
etc.
• Since nucleons (= n+p)
occupy energy levels within
nucleus
• N or Z = 2, 8, 20, 28, 50, 82,
and N = 126
• Magic numbers
34
Radioactive decay series
35