Photoelectron Spectroscopy PES PES Provides explanation for shells
- Slides: 44
Photoelectron Spectroscopy (PES)
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
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
Example 1: Na
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) B) C) D) Aluminum Boron Carbon Sodium
Example 3: Aluminum has the following electron configuration: 1 s 22 p 63 s 23 p 1 A) How many peaks should be expected in a PES spectrum for Al? B) Which electrons will show the highest energies? Why?
Example 3: (cont. ) Aluminum has the following electron configuration: 1 s 22 p 63 s 23 p 1 C) Which peak on the spectrum will be the most intense/largest? Why? D) Explain why the peaks for the 3 s and 3 p electrons would be closely grouped and why they are different than electrons in the 2 s and 2 p orbitals.
Periodic Trends Elemental Properties and Patterns
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.
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.
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.
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
Periodic Trends There are several important atomic characteristics that show predictable trends that you should know. Atomic properties— Deal with only single atoms
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.
1. Covalent Radius Half the distance between the nuclei of 2 bonded atoms. Radius of nonmetallic atoms Ex. Br 2. 86 Å 1. 43 Å
2. Metallic Radius Half the distance between nuclei of adjacent atoms in a metal Radius of metallic atoms
Atomic Radius Trend Decreases Increases
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.
Identify the atom with the largest radii 1) Ca, F 2) Cl, O 3) N, P
Ionic Radii 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: 1) Anions Larger size than original neutral atom Generally nonmetals Electrons repel as increase in number, causes size to increase
Ionic Radii: 2) Cations Smaller size than original neutral atom Generally metals Less electrons, more attractive force from nucleus
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
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.
Ionization Energy (cont. ) 1 st ionization energy Energy required to remove 1 st electron from atom Taken from highest energy level Easiest to remove Energy increases as more electrons are removed
Ionization Energy Trend Increases Decreases
Ionization Energy
Identify the highest ionization energy 1) F, Mg 2) Na, Rb 3) P, O
What does affinity mean?
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
Electron Affinity Trend Increases Decreases
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?
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.
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
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
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.
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
Noble Gases Group 18 Do NOT react with other elements Atomspheric gases Naturally in elemental form , single atoms Not completely unreactive
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
Metallic Character Decreases Increases
Nonmetallic Character Atoms with a tendency to GAIN electrons Increases Decrease s
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
Classwork: Metal Identity Identify each element as a nonmetal, or metalloid 1) Na 6) Cl 2) P 7) Mg 3) Se 8) Al 4) Ge 9) Sb 5) N 10) Si
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