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Atomic Structure
IB Chemistry Power Points
Topic 02
Atomic Structure
www.pedagogics.ca
Review – Basic Atomic Structure
NUCLEUS ELECTRONS
PROTONS NEUTRONS
POSITIVE
CHARGE
ATOM
POSITIVECHARGE
PROTONS
NEUTRALCHARGE
NEUTRONS
NUCLEUS
NEGATIVE CHARGE
ELECTRONS
ATOM
Subatomic components
Relative
Mass
Charge
Proton 1 +1
Neutron 1 0
Electron 5 x 10-4 -1
Review – Basic Atomic Model
A-Z notation
© Addison-Wesley Publishing Company, Inc.
126C
mass number A
atomic number Z
element symbol
The atomic number equals the number of protons. Each element has a unique atomic number.
Mass Number• mass number A = protons +
neutrons• always a whole number
© Addison-Wesley Publishing Company, Inc.
• NOT the value given on the Periodic Table!
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
Cl3717
Ions
• ions are electrically charged atoms
Neutral atom
negative ionpositive ion
lose electrons
gain electrons
p+ > e- p+ < e-
cation anion
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
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
© Addison-Wesley Publishing Company, Inc.
Isotopes: Atoms of the same element with different mass numbers.
carbon-12 and carbon-14 are
isotopes
similar chemical properties
stable
radioactive
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 reactorsCo-60 is used in cancer radiation therapyC-14 is used as a tracer and for archeological datingAm-241 is used in smoke detectors
Mass SpectrometerA 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. Vaporization2. Ionization3. Acceleration4. Deflection5. Detection
Chapter 12 13=>
Vaporization: the element to be analyzed is heated and vaporized (gaseous form).
http://www.magnet.fsu.edu/education/tutorials/java/singlesector2/index.html
Chapter 12 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-
http://www.magnet.fsu.edu/education/tutorials/java/singlesector2/index.html
Chapter 12 15=>
Acceleration: the gaseous ions are accelerated through an electric field (towards a negative plate)
http://www.magnet.fsu.edu/education/tutorials/java/singlesector2/index.html
Chapter 12 16=>
Deflection: Ions are deflected in an adjustable magnetic field oriented at right angles to the path. Heavier ions are deflected less.
http://www.magnet.fsu.edu/education/tutorials/java/singlesector2/index.html
Chapter 12 17=>
Detection: ions of a specific mass are counted
http://www.magnet.fsu.edu/education/tutorials/java/singlesector2/index.html
A sample mass spectrograph
Output provides the abundances of the elemental isotopes of different relative mass
Atomic Mass is Relative
• 12C atom = 1.992 × 10-23 g
• 1 p = 1.007276 amu1 n = 1.008665 amu1 e- = 0.0005486 amu
© Addison-Wesley Publishing Company, Inc.
• atomic mass unit (amu)
• 1 amu = 1/12 the mass of a 12C atom
Average Atomic Mass• a weighted average
of all isotopes of an element
100
(%)(mass(mass)(%) )
Avg.AtomicMass
• this value is found on the Periodic Table
• based on the % abundance data from mass spectrometer
Avg.AtomicMass
Average Atomic Mass
• EXAMPLE: Calculate the average atomic mass of chlorine if its abundance in nature is 75.77% 35Cl, and 24.23% 37Cl.
(35)(75.77) (37)(24.23)
10035.48amu
Average Atomic Mass
equation 1
equation 2
(68.9257)(x) (70.9249)(y)69.7231=
100x + y = 100
Average relative mass of Ga 69.7231 amu
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
Solve to get 60.1% Ga-69 and 39.9% Ga-71
All EM radiation is fundamentally the same. The only difference between a gamma ray and a radio wave is the frequency/wavelength/energy.
Visible light is one category of EM radiation. The visible light spectrum is subdivided into six “colors”.
White LightPrism
REDORANGEYELLOWGREENBLUE
VIOLET
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.
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
Emission spectra are unique for each element
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.
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.
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.
lower energylonger
wavelength
higher energyshorter
wavelength
Visible spectrum for
hydrogen atom convergence
Lower energy = more stable electron orbit
Electrons fill the lowest energy orbitals first.
Each orbital 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
The electronic structure of an atom
A carbon atom has six electrons
1st energy level holds 2
2nd energy level takes the remaining 4
The electron structure for carbon would be written as 2,4
The electrons in the outermost energy level are called valence electrons. Carbon has 4 valence electrons.
Try writing the electron structure for calciumA 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 structure for calcium would be written as 2,8,8,2
Connect to Periodic Table
1234
EnergyLevel