2. Symbols
Contain the symbol of the element, the mass number and the atomic number X
Mass
number
Atomic
# protons
+ # neutrons
mass number
# protons

3. F Symbols 19 9 Find the number of protons number of neutrons
number of electrons
Atomic number
Mass number
= 9 + F 19 9
= 10
= 9
= 9
= 19

4. Br Symbols 80 35 Find the number of protons number of neutrons
number of electrons
Atomic number
Mass number
= 35
= 45 Br 80 35
= 35
= 35
= 80

5. Na Symbols 23 11 Find the number of protons number of neutrons
number of electrons
Atomic number
Mass number
= 11
= 12 Na 23
= 11
= 11 11
= 23
Sodium atom

6. Na Symbols 23 11 Find the 1+ number of protons number of neutrons
number of electrons
Atomic number
Mass number
= 11 Na
= 12 23 1+
= 10 11
= 11
= 23
Sodium ion

7. Symbols
If an element has an atomic number of 23 and a mass number of 51 what is the
number of protons
number of neutrons
number of electrons
Complete symbol
= 23
= 28
= 23 V 51 23

8. Symbols
If an element has 60 protons and 84 neutrons what is the
Atomic number
Mass number
number of electrons
Complete symbol
= 60
= 144
= 60 Nd
144 60

9. Symbols
If a neutral atom of an element has 78 electrons and 117 neutrons what is the
Atomic number
Mass number
number of protons
Complete symbol
= 78
= 195
= 78
Platinum is even more rare than gold. In fact, 50 tons of ore is required to produce just 50 grams of platinum.
Platinum is a grayish-white metal that is malleable yet, like gold, is resistant to attack by air, moisture, and most solutions.
Its melting point is even higher than gold, at just over 3,000°F. It ranks 72 in abundance among the elements. Pt
195 78

11. C Isotopes Mass # Atomic # 12 6
Atoms of the same element with different mass numbers.
Nuclear symbol: 12 6 C
Mass #
Each isotope has a different number of neutrons.
Atomic #
Hyphen notation: carbon-12
Courtesy Christy Johannesson

12. Isotopes Neutron + Electrons Nucleus Nucleus Proton Proton Nucleus
Carbon-12
Neutrons 6
Protons 6
Electrons 6
Electrons
The chemistry of each element is determined by its number of protons and electrons.
In a neutral atom, the number of electrons equals the number of protons.
Symbols for elements are derived directly from the element’s name.
Nuclei of atoms contain neutrons as well as protons.
The number of neutrons is not fixed for most elements, unlike protons.
Atoms that have the same number of protons, and hence the same atomic number, but different numbers of neutrons are called isotopes.
Carbon-14
Neutrons 8
Protons 6
Electrons 6
Nucleus

13. 6Li 7Li 3 p+ 3 n0 3 p+ 4 n0 2e– 1e– 2e– 1e– Nucleus Neutron Proton
Electrons +
Electrons +
Nucleus
Nucleus
Lithium-6
Lithium-7
Neutrons 3
Protons 3
Electrons 3
Neutrons 4
Protons 3
Electrons 3

14. Cl Isotopes 37 17 Cl Chlorine-37 atomic #: mass #: # of protons:
# of electrons:
# of neutrons: 17 37 20 37 17 Cl
Atoms that have the same number of protons, and hence the same atomic number, but different numbers of neutrons are called isotopes.
Courtesy Christy Johannesson

15. Relative Atomic Mass 12C atom = 1.992 × 10-23 g atomic mass unit (amu)
1 amu = 1/12 the mass of a 12C atom
Neutron +
1 p = amu 1 n = amu 1 e- = amu
Electrons
Atomic mass
1. The mass of any given atom is not simply the sum of the masses of its electrons, protons, and neutrons.
2. Atoms are too small to measure individually and do not have a charge.
3. The arbitrary standard that has been established for describing atomic mass is the atomic mass unit (amu), defined as one-twelfth of the mass of one atom of 12C.
4. Most elements exist as mixtures of several stable isotopes. The weighted average is of the masses of the isotopes is called the atomic mass.
5. Electrons added or removed from an atom produce a charged particle called an ion, whose charge is indicated by a superscript after the symbol for the element.
Nucleus
Proton
Nucleus
Carbon-12
Neutrons 6
Protons 6
Electrons 6

16. Average Atomic Mass Avg. (mass)(%) + (mass)(%) Atomic Mass 100
weighted average of all isotopes
on the Periodic Table
round to 2 decimal places
Avg.
Atomic
Mass
(mass)(%) + (mass)(%) =
100
Courtesy Christy Johannesson

17. Average Atomic Mass
EX: Calculate the avg. atomic mass of oxygen if its abundance in nature is 99.76% 16O, 0.04% 17O, and 0.20% 18O.
Avg.
Atomic
Mass
(16)(99.76) + (17)(0.04) + (18)(0.20)
16.00
amu = =
100
Courtesy Christy Johannesson

18. Average Atomic Mass (35)(8) + (37)(2) 10 Avg. Atomic = = Mass
EX: Find chlorine’s average atomic mass if approximately 8 of every 10 atoms are chlorine-35 and 2 are chlorine-37.
Avg.
Atomic
Mass
(35)(8) + (37)(2) = =
35.40 amu 10
Courtesy Christy Johannesson

19. Cl 17
100
Mass spectrum of chlorine. Elemental chlorine (Cl2) contains
only two isotopes: amu (75.53%) and (24.47%) 90 80
Cl-35 70
AAM = (34.97 amu)(0.7553) + (36.97 amu)(0.2447) 60
AAM = ( amu) ( amu)
AAM = amu 50
Abundance 40 30
Cl-37
Mass spectrum of chlorine. Elemental chlorine (Cl2) contains
only two isotopes: amu (75.53%) and (24.47%) 20 10 34 35 36 37
Mass

20. Mass Spectrophotometer
magnetic field
heaviest
ions
stream
of ions of
different
masses
lightest
ions
electron
beam
gas
Dorin, Demmin, Gabel, Chemistry The Study of Matter 3rd Edition, page 138

21. Weighing atoms ions accelerate towards charged magnetic field
gas sample
enters here
filament current
ionizes the gas
ions accelerate
towards charged
slit
magnetic field
deflects lightest ions
most
ions separated by mass
expose film .
                                                                                                                                                                                                                         
The first mass spectrograph was built in 1919 by F. W. Aston, who received the 1922 Nobel Prize for this accomplishment
mass spectrometry is used to experimentally determine isotopic masses
and abundances
interpreting mass spectra      
average atomic weights
- computed from isotopic masses and abundances
- significant figures of tabulated atomic weights gives some idea
of natural variation in isotopic abundances
Copyright © by Fred Senese

22. Mass Spectrometry 198 200 202 Photographic plate 196 199 201 204 - +
Mass spectrum of mercury vapor
Photographic plate
A gaseous sample is ionized by bombarding it with electrons in the lower part of the apparatus (not shown), producing positive ions.
The ions pass through an electric field in which they are brought to a particular velocity. The ions then pass through a narrow slit
into a curved chamber. A magnetic field is applied perpendicular to the beam of ions. All the ions with the same mass-to-charge ratio
are deflected into the same circular path. (In most cases, the ionic charge is 1+ and the mass-to-charge ratio is the same as the mass.)
Modern spectrophotometers use electronic detection devices (TOF = time of flight detectors) rather than photographic plates or film to
establish mass-to-charge ratios and relative number of ions. - +
Stream of positive ions
Hill, Petrucci, General Chemistry An Integrated Approach 1999, page 320

23. Mass Spectrum for Mercury
(The photographic record has been converted to a scale of relative number of atoms)
The percent natural abundances
for mercury isotopes are:
Hg %
Hg %
Hg %
Hg %
Hg %
Hg %
Hg % 30 25 20 15 10 5
Mass spectrum of mercury vapor
Relative number of atoms
Mass number

24. The percent natural abundances
for mercury isotopes are:
Hg %
Hg %
Hg %
Hg %
Hg %
Hg %
Hg % A B C D E F G Hg
200.59 80
(% "A")(mass "A") + (% "B")(mass "B") + (% "C")(mass "C") + (% "D")(mass "D") +
(% "E")(mass "E") + (% F)(mass F) + (% G)(mass G) = AAM
( )(196) + (0.1002)(198) + (0.1684)(199) + (0.2313)(200) + (0.1322)(201) + (0.2980)(202) + (0.0685)(204) = x
= x
x = amu

26. Isotopes, cont. Objectives:
To draw a diagram of an atom given its atomic notation.
To explain and illustrate the concept of isotopes.
To explain the concept of relative atomic mass.
To calculate the atomic mass for an element given the mass and abundance of the naturally occurring isotopes.

27. Isotopes Dalton was wrong.
Atoms of the same element can have different numbers of neutrons
different mass numbers
called isotopes
The word isotope comes from the Greek words isos, meaning "equal," and topos, meaning "place."
C vs C-14
California WEB

28. Naming Isotopes Put the mass number after the name of the element
carbon- 12
carbon -14
uranium-235
California WEB

29. Using a periodic table and what you know about atomic number, mass, isotopes, and electrons, fill in the chart:
Element
Symbol
Atomic
Number
Mass
# of protons
# of neutron
# of electron
charge 8
Potassium 39 +1 Br 45 -1 30 35
Atomic Number = Number of Protons
Number of Protons + Number of Neutrons = Atomic Mass
Atom (no charge) : Protons = Electrons
Ion (cation) : Protons > Electrons
Ion (anion) : Electrons > Protons

30. Using a periodic table and what you know about atomic number, mass, isotopes, and electrons, fill in the chart:
A N S W E R K E Y
Element
Symbol
Atomic
Number
Mass
# of protons
# of neutron
# of electron
charge 8
Potassium 39 +1 Br 45 -1 30 65
Oxygen O 8 16 K 19 19 20 18
Bromine 35 80 35 36
Zinc Zn 30 35
Atomic Number = Number of Protons
Number of Protons + Number of Neutrons = Atomic Mass
Atom (no charge) : Protons = Electrons
Ion (cation) : Protons > Electrons
Ion (anion) : Electrons > Protons

31. Isotopes
Because of the existence of isotopes, the mass of a collection of atoms has an average value.
Average mass = ATOMIC WEIGHT
Boron is 20% B-10 and 80% B-11. That is, B-11 is 80 percent abundant on earth.
For boron atomic weight
0.20 (10 amu) (11 amu) = amu

32. Atomic Mass
Magnesium has three isotopes % magnesium 24 with a mass of amu, 10.00% magnesium 25 with a mass of amu, and the rest magnesium 26 with a mass of amu. What is the atomic mass of magnesium?
If not told otherwise,
the mass of the isotope is the mass number in amu.
Isotope
Percent
Abundance
Mass
Mg-24
78.99
Mg-25
10.00
Mg-26
Atomic mass is not a whole number because it is an average.
This is why their are the decimal numbers on the periodic table.
11.01
amu
California WEB

33. Atomic Mass
Calculate the atomic mass of copper if copper has two isotopes % has a mass of amu and the rest has a mass of amu.
Isotope
Percent
Abundance
Mass
Cu-63
69.1
62.93
Cu-65
64.93
30.9
63.548 Cu 29
63.548

34. Isotopes of Magnesium Atomic symbol Mg Mg Mg24 12 25 12 26 12
Number of protons
Number of electrons
Mass number
Number of neutrons
Isotope Notation Mg-24 Mg Mg-26
Timberlake, Chemistry 7th Edition, page 64

35. Isotopes of Hydrogen Protium Deuterium Tritium 1 p+ 1 e- 1 p+ 1 n 1 e-
(ordinary hydrogen)
(heavy hydrogen)
(radioactive hydrogen)
H-2
H-3
H-1
Ralph A. Burns, Fundamentals of Chemistry 1999, page 100

36. Isotopes of Hydrogen Protium (H-1) Deuterium (H-2) Tritium (H-3)
1 proton, 0 neutrons, 1 electron
most abundant isotope
Deuterium (H-2)
1 proton, 1 neutron, 1 electron
used in “heavy water”
Tritium (H-3)
1 proton, 2 neutrons, 1 electron
radioactive
1 p+
1 n
1 e-
1 p+
2 n
1 e-

37. Isotopes of Three Common Elements
Symbol
Fractional Abundance
Average Atomic Mass
Carbon
Chlorine
Silicon Si 28 29 30
27.977
28.976
29.974
92.21%
4.70%
3.09%
Mass
Number
Mass (amu) 12 6 C 12
12 (exactly)
99.89%
12.01 13 6 C
13.003
1.11% 13 35 17 Cl 35
34.969
75.53%
35.45 37 17 Cl 37
36.966
24.47% 28 14 29 14
28.09 30 14
LeMay Jr, Beall, Robblee, Brower, Chemistry Connections to Our Changing World , 1996, page 110

38. Radioisotopes Radioactive isotopes Many uses Medical diagnostics
Optimal composition of fertilizers
Abrasion studies in engines and tires
Radioisotope is injected
into the bloodstream to
observe circulation.

39. Half-Life of Isotopes
Half-Lives and Radiation of Some Naturally Occurring Radioisotopes
Isotope Half-Life Radiation emitted
Carbon-14
5.73 x 103 years b
Potassium-40
1.25 x 109 years
b, g
Radon-222
3.8 days a
Radium-226
1.6 x 103 years
a, g
Thorium-230
7.54 x 104 years
a, g
Thorium-234
24.1 days
b, g
Uranium-235
7.0 x 108 years
a, g
Uranium-238
4.46 x 109 years a

40. Atomic Structure ATOMS IONS ISOTOPES Differ by number of protons
Differ by number of electrons
ISOTOPES
Differ by number of neutrons

41. Island of Stability, (13:10)