This document discusses atomic structure and properties. It begins by reviewing the basic atomic model including protons, neutrons, and electrons. It then discusses atomic number, mass number, isotopes, ions, and electron configuration. The document also covers average atomic mass and mass spectrometry. It concludes by discussing the Bohr model of the atom and how this helped explain emission spectra of elements. In summary, the key topics covered are the fundamental particles of atoms, atomic notation, isotopes, ions, electron configuration, and early atomic structure models.

1. Atomic
Structure
IB Chemistry Power Points
Topic 02
Atomic Structure
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2. Review – Basic Atomic Structure
ELECTRONS
ELECTRONS
NEUTRONS
NEUTRONS
PROTONS
POSITIVE
CHARGE
ATOM
POSITIVE
CHARGE
NEUTRAL
CHARGE
NUCLEUS
NEGATIVE CHARGE

3. Review – Basic Atomic Model
Subatomic
components
Relative
Mass
Charge
Proton
1 +1
Neutron
1 0
Electron
5 x 10-4 -1

4. A-Z notation
element symbol
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12
6C
mass number A
atomic number Z
The atomic number
equals the number of
protons. Each element
has a unique atomic
number.

5. Mass Number
• mass number A = protons + neutrons
• always a whole number
• NOT the value given on
the Periodic Table!
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6. Practice: determine the required values and
write the chemical symbol in A-Z notation.
• Chlorine-37
– atomic #:
– mass #:
– # of protons:
– # of electrons:
– # of neutrons:
17
37
17
17
20
Cl 37
17

7. Ions
• ions are electrically charged atoms
Neutral atom
lose electrons gain electrons
positive ion negative ion
p+ > e- p+ < e-cation
anion

8. Practice: determine the required values for
the negative chloride ion 37 Cl -1
37 Cl-1
– atomic #:
– mass #:
– # of protons:
– # of electrons:
– # of neutrons:
17
37
17
18
20

9. Practice: determine the required values for
the positive calcium ion 40 Ca +2
40 Ca+2
– atomic #:
– mass #:
– # of protons:
– # of electrons:
– # of neutrons:
20
40
20
18
20

10. Isotopes: Atoms of the same element with different
mass numbers.
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carbon-12 and
carbon-14 are
isotopes
stable
similar chemical properties
radioactive

11. Radioisotopes and Their Uses
Radioisotopes are unstable isotopes that undergo
radioactive decay. Radioisotopes have a number
of uses:
U-235 is used as fuel in nuclear reactors
Co-60 is used in cancer radiation therapy
C-14 is used as a tracer and for archeological
dating
Am-241 is used in smoke detectors

12. Mass Spectrometer
A mass spectrometer is used to detect, identify and
measure the abundance of different atoms,
molecules or molecular fragments.
Mass spectrometer studies are used to determine
the average atomic mass for an element. The
operation of a mass spectrometer can be divided
into 5 steps:
1. Vaporization
2. Ionization
3. Acceleration
4. Deflection
5. Detection

13. Vaporization: the element to be analyzed is heated and vaporized
(gaseous form).
Chapter 12 13=>
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14. Ionization: the gaseous element is injected slowly into a vacuum
chamber where the atoms are bombarded by electrons. This
-  +
-
forms ions positive ions X (g) + e
X
(g) + 2 e
Chapter 12 14=>
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15. Acceleration: the gaseous ions are accelerated through an
electric field (towards a negative plate)
Chapter 12 15=>
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16. Deflection: Ions are deflected in an adjustable magnetic field
oriented at right angles to the path. Heavier ions are deflected
less.
Chapter 12 16=>
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17. Detection: ions of a specific mass are counted
Chapter 12 17=>
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18. A sample mass spectrograph
Output provides
the abundances of
the elemental
isotopes of
different relative
mass

19. Atomic Mass is Relative
• 12C atom = 1.992 × 10-23 g
• atomic mass unit (amu)
• 1 amu = 1/12 the mass of a 12C atom
• 1 p = 1.007276 amu
1 n = 1.008665 amu
1 e- = 0.0005486 amu
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20. Average Relative Atomic Mass AR
• a weighted average of
all isotopes of an
element
• based on the %
abundance data from
mass spectrometer
• this value is found on the Periodic Table
(mass)(%) (mass)(%)

100
Avg.
Atomic
Mass

21. Average Relative Atomic Mass AR
• EXAMPLE: Calculate the average atomic mass of
chlorine if its abundance in nature is 75.77%
35Cl, and 24.23% 37Cl.
Avg.
Atomic
Mass
(35)(75.77) (37)(24.23)

 
100
35.48
amu

22. Average Relative Atomic Mass AR
Gallium has two naturally occurring isotopes, Ga-
69 and Ga-71, with masses of 68.9257 amu and
70.9249 amu, respectively. Calculate the percent
abundances of these isotopes
Average relative mass of Ga 69.7231 amu
equation 1
equation 2
(68.9257)(x)  (70.9249)(y)
69.7231=
100
x + y = 100
Solve to get 60.1% Ga-69 and 39.9% Ga-71

24. All EM radiation is fundamentally the same. The
only difference between a gamma ray and a
radio wave is the frequency/wavelength/energy.

25. Visible light is one category of EM radiation. The
visible light spectrum is subdivided into six
“colors”.
White Light
Prism
RED
ORANGE
YELLOW
GREEN
BLUE
VIOLET

26. A continuous spectrum includes all wavelengths
of radiation in a given range.
When white light is passed through a prism a
continuous spectrum is produced.

27. Colored lights do not emit all the wavelengths of the
visible light spectrum. For example, a red light emits
mostly wavelengths from the red end of the spectrum.
An energized gas sample will emit light of specific
wavelengths characteristic of the gas. This is called a line
spectrum

28. Emission spectra are unique for each element
Balmer Lyman

30. The Bohr model of the atom was developed
using information from hydrogen emission
spectrum studies. Bohr envisioned an atomic
model with:
• a central dense positive
nucleus composed of protons
and neutrons.
• negative electrons at specific
energies orbit the nucleus
• mostly empty space. Nucleus
is 10-5 times smaller than
atom.

31. Bohr further stated that the orbiting electrons
occupy discrete energy levels. Electrons can only
“jump” between energy levels if they absorb or
emit a specific amount of energy.

32. Bohr saw the line spectrum of hydrogen as a
direct result of energized electrons releasing a
specific amount of energy by emitting a photon
of light at a certain wavelength.
The different lines in the hydrogen spectrum
were evidence for a number of different energy
levels.

33. lower energy
longer wavelength
higher energy
shorter wavelength
Visible spectrum
for
hydrogen atom
convergence

34. Lower energy = more stable electron orbit
Electrons will first occupy the lowest energy level
orbital (Aufbau principle).
Each energy level has a maximum possible
number of electrons.
As you should recall:
1st energy level (ground state) = 2 electrons
2nd energy level = 8 electrons
3rd energy level = 8 electrons

35. A carbon atom has six electrons
1st energy level holds 2
2nd energy level takes the remaining 4
The electron configuration for carbon would be
written as 2,4
The electrons in the outermost energy level
are called valence electrons. Carbon has 4
valence electrons.

36. Try writing the electron configuration for calcium
A calcium atom has 20 electrons
1st energy level holds 2
2nd energy level holds 8
3rd energy level holds 8
4th energy level holds last 2
The electron configuration for calcium would be
written as 2,8,8,2

37. Connect to Periodic Table
Energy
Level
1
2
3
4