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Photoelectron Spectroscopy (PES)
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PES
Provides explanation for shells and orbitals in quantum theory
Photoelectric effect— Utilization of photons to remove electrons from atoms Photons have been energized, analyzing the energy
needed to remove electrons from an atom/compound
Photoelectric spectrum— Energy on x-axis Number of electrons in a subshell on y axis
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Photoelectric Spectrum
Peaks— Number of subshells/orbitals
Peak heights— Number of electrons in subshell
Electrons within the same subshell have similar energy values but different orbital energies, energy values vary among subshells
Shells with high energies indicate electrons located close to nucleus
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Example 1: Na
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Example 2:
A third period element in the periodic table forms a PES spectrum with three peaks, in the ratio 2:2:1. Name this element. A) Aluminum
B) Boron
C) Carbon
D) Sodium
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Example 3:
Aluminum has the following electron configuration: 1s22s22p63s23p1
A) How many peaks should be expected in a PES spectrum for Al?
B) Which electrons will show the highest energies? Why?
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Example 3: (cont.)
Aluminum has the following electron configuration: 1s22s22p63s23p1
C) Which peak on the spectrum will be the most intense/largest? Why?
D) Explain why the peaks for the 3s and 3p electrons would be closely grouped and why they are different than electrons in the 2s and 2p orbitals.
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Periodic Trends
Elemental Properties and Patterns
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The Periodic Law
Dimitri Mendeleev (1869/1871) was the first scientist to publish an organized periodic table of the known elements.
He was taking a chemistry course in Russia and tried to find a way to organize the periodic table.
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The Periodic Law
Mendeleev even went out on a limb and predicted the properties of 2 at the time undiscovered elements.
He was very accurate in his predictions, which led the world to accept his ideas about periodicity and a logical periodic table.
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The Periodic Law
Mendeleev understood the ‘Periodic Law’ which states:
When arranged by increasing atomic number, the chemical elements display a regular and repeating pattern of chemical and physical properties.
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The Periodic Law
Atoms with similar chemical properties and behavior appear in groups or families (vertical columns named by Roman numerals with A or B) on the periodic table.
They are similar because they all have the same number of valence (outer shell) electrons, which governs their chemical behavior.
Periods– horizontal rows on periodic table
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Periodic Trends
There are several important atomic characteristics that show predictable trends that you should know.
Atomic properties— Deal with only single atoms
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Atomic Radius
Enables us to gain information on atom’s size Outer electrons hard to locate
Radius is the distance from the center of the nucleus to the “edge” of the electron cloud. Measurement of distance between nuclei of 2 atoms
Since a cloud’s edge is difficult to define, scientists use define covalent radius, or half the distance between the nuclei of 2 bonded atoms.
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1. Covalent Radius
Half the distance between the nuclei of 2 bonded atoms.
Radius of nonmetallic atoms
Ex. Br 2.86 Å1.43 Å 1.43 Å
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Half the distance between nuclei of adjacent atoms in a metal
Radius of metallic atoms
2. Metallic Radius
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Atomic Radius Trend
Decreases
Increases
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Atomic Radius
The effect is that the more positive nucleus has a greater pull on the electron cloud.
The nucleus is more positive and the electron cloud is more negative.
The increased attraction pulls the cloud in, making atoms smaller as we move from left to right across a period.
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Identify the atom with the largest radii
1) Ca, F
2) Cl, O
3) N, P
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Affected by distance between nuclei of 2 ions
Defined by the distance between the nuclei occupied by the particular ion Studies with crystal structures
Radii related to original atomic radii
Isoelectronic— Atoms/ions with SAME number of electrons SO ------ electron
configuration same as well
Ionic Radii
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Larger size than original neutral atom Generally nonmetals Electrons repel as increase in number, causes
size to increase
Ionic Radii: 1) Anions
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Smaller size than original neutral atom
Generally metals
Less electrons, more attractive force from nucleus
Ionic Radii: 2) Cations
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Ionization Energy If an electron is given enough energy (in the
form of a photon) to overcome the effective nuclear charge holding the electron in the cloud, it can leave the atom completely.
Amount of energy needed to remove ONE electron from a neutral atom Removal from ground state in neutral atom of
gaseous state to form positive ion
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Ionization Energy (cont.)
The energy required to remove an electron from an atom is ionization energy.
The larger the atom is, the easier its electrons are to remove.
Ionization energy and atomic radius are inversely proportional.
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1st ionization energy Energy required to remove 1st electron from
atom Taken from highest energy level Easiest to remove
Energy increases as more electrons are removed
Ionization Energy (cont.)
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Ionization Energy Trend
Increases
Decreases
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Ionization Energy
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Identify the highest ionization energy
1) F, Mg
2) Na, Rb
3) P, O
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What does affinity mean?
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Electron Affinity
energy change that occurs when electrons added to gaseous atom
Greater value with smaller atoms
Energy released when electron added Exothermic, negative value
An atom’s “desire/affinity” for more electrons, wants to get more electrons ! ! !
Metals—decrease electron affinity. Nonmetals—increase electron affinity, more reactive Stable atoms—full octet
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Electron Affinity Trend
Increases
Decreases
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Metals, Nonmetals, Metalloids
How can you identify a metal?
What are its properties?
What about the less common nonmetals?
What are their properties?
And what the heck is a metalloid?
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A Different Type of Grouping
Besides the 4 blocks of the table, there is another way of classifying element:
Metals
Nonmetals
Metalloids or Semi-metals.
The following slide shows where each group is found.
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Metals Metals are shiny, malleable, ductile, and are good conductors of heat and electricity.
They are mostly solids at room temp.
Want to LOSE valence electrons
Form positive ions
s block (not H and He), d/f blocks, some p block elements
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Nonmetals
Nonmetals are the opposite.
No color, no shine
They are dull, brittle, nonconductors (insulators).
Gases at room temperature
Want to GAIN electrons
Form negative ions
p block elements, H and He
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Transition Metals Middle of the periodic table
Forms positive ions, multiple types
Shine, malleable, ductile, good conductors
s/d orbitals—electrons lost from these subshells.
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Metalloids/Semi-Metals Metalloids, aka semi-metals are just
that.
They have characteristics of both metals and nonmetals.
They are shiny (like metals) but brittle.
And they are semiconductors.
“on the fence, middle of the road”
B, Si, As, Te, At, Ge, Sb, Po
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Noble Gases Group 18
Do NOT react with other elements
Atomspheric gases
Naturally in elemental form , single atoms
Not completely unreactive
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Metallic Character
This is simply a relative measure of how easily atoms lose or give up electrons.
Tendency to LOSE electrons
Related to atomic radius/ionization energy, how easy to remove electrons
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Metallic Character
Decreases
Increases
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Atoms with a tendency to GAIN electrons
Nonmetallic Character
Increases
Decreases
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Classwork: Ionization Energy
Circle the atom with the highest first ionization energy.
1) Al, B 5) Fr, Li 9) Se, Cl
2) Mg, Na 6) Mg, Al 10) Rb, Mg
3) P, As 7) C, F
4) I, At 8) K, Sc
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Classwork: Metal IdentityIdentify each element as a nonmetal, metal, or
metalloid
1) Na 6) Cl
2) P 7) Mg
3) Se 8) Al
4) Ge 9) Sb
5) N 10) Si