Unit 6B: Electron structure in Atoms Bohr model spectra wave mechanical model atomic orbitals electron configurations

Wave Mechanical model of the atom the Bohr model was correct in many ways electron energies are quantized spectra arise from electrons moving between the energy levels the Wave Mechanical model is different in one major way electrons are located in orbitals rather than in distinct circular orbits orbitals are defined by a wave equation

Schröedinger wave equation more details

orbitals orbitals are graphs of the wave equation showing regions or “clouds” in which the electrons are usually located (e.g. 90% probability)

energy levels quantum numbers are solutions to the wave equation each quantum number identifies a different orbital with a different energy there are many different orbitals, thus many different energy levels spectra are still explained the same way: electron absorbs E, moves to higher energy level, then returns to lower level and emits excess E as light (or other radiation)

energy levels least energy more energy even more energy similar to the Bohr model, higher energy orbitals are usually larger

energy sublevels the energy levels are further subdivided the number of subdivisions is equal to the principle quantum number level 1 has 1 sublevel level 2 has 2 sublevels etc. the names of the sublevels, in order, are spdfgh...

energy sublevels the sublevels are further subdivided (i.e. sub-sublevels) the s orbital has 1 spherical region

energy sublevels there are 3 distinct p orbitals probability map

energy sublevels there are five distinct d orbitals

Atomic orbital energies

filling orbitals with electrons # of electrons = atomic # for atoms cations have fewer electrons, anions more electrons fill the lowest energy orbital first, then the next highest orbital, etc. a maximum of two electrons can be in any one orbital

filling orbitals with electrons for p, d, and f orbitals, one unpaired electron goes in each subpart before any electrons are paired represent the first electron in each orbital with  and the second with 

 examples 1 hydrogen  2 helium    3 lithium 

 examples 4 beryllium  5 boron   6 carbon         

examples 7 nitrogen 8 oxygen   9 fluorine               

examples 10 neon 11 sodium 12 magnesium                  

more concise notation 12 magnesium        1s 2 2s 2 2p 6 3s 2

even more concise notation 12 magnesium        [Ne] He Ne 3s 2

periodic “blocks” sp d

1s 2s 3s 4s 5s 3d 2p 3p 4p 5p 4d

periodic “blocks” 1s 2s 3s 4s 5s 3d 2p 3p 4p 5p 4d

extended periodic table 6s4f 5d 6p 7s5f6d7p 82 Pb:[Xe]6s 2 4f 14 5d 10 6p 2 [Rn]7s 2 5f 4 92 U:

PERIODIC TRENDS 1. Atomic size atomic size is the radius of the atom, measured from the center of the nucleus to the outer edge of the electron cloud

PERIODIC TRENDS 1. Atomic size down a family atomic size more electrons are present, and are in larger orbitals, thus producing a larger atom 4s is larger than 3s, 3s is larger than 2s, etc. 5d is larger than 4d, 4d is larger than 3d, etc. INCREASES

PERIODIC TRENDS 1. Atomic size across a period atomic size more protons (in the nucleus) cause a larger attractive force, thus shrinking the orbital common error: “more electrons cause larger orbital.” this logic is incorrect since the added electrons are in the same orbital as those before them, and that orbital isn’t fundamentally bigger with 2 e – than with 1 e – DECREASES

PERIODIC TRENDS 1. Atomic size decreases

PERIODIC TRENDS 1. Atomic size there are some minor exceptions oxygen family elements are sometimes “too big” because paired e – repel each other transition metals also show a slight size increase beginning around d 6 or d 7 or d 8 due to their paired e – repelling each other

PERIODIC TRENDS 2. Ion size (vs. neutral atoms) compared to neutral atoms, cations are cation has same number of protons yet fewer electrons thus there is more attractive force per electron moreover, the largest orbital(s) has been emptied result: smaller electron cloud SMALLER

PERIODIC TRENDS 2. Ion size (vs. neutral atoms) compared to neutral atoms, anions are anion has same number of protons yet more electrons thus there is less attractive force per electron result: larger electron cloud LARGER

PERIODIC TRENDS 2. Ion size (vs. other ions) decrease cations anions decrease

PERIODIC TRENDS 2. Ion size (vs. other ions) what do these ions all have in common? fewer protons attract electron cloud less strongly more protons attract electron cloud more strongly e–e– 10 p+p the same electron configuration as neon: 1s 2 2s 2 2p 6 “isoelectronic”

PERIODIC TRENDS 3. First ionization energy the energy required to remove the outermost electron from a neutral atom increases (mostly) increases

PERIODIC TRENDS 3. First ionization energy down a family I.E. the electron being removed is farther from the nucleus, thus is less strongly attracted and is easier to remove DECREASES across a period I.E. generally each electron is being removed from the same orbital, but each successive element’s nucleus has one more proton, thus its electron is more strongly attracted and is more difficult to remove INCREASES

PERIODIC TRENDS 3. First ionization energy exceptions: boron family is easier to ionize than expected an electron in the p orbital is slightly easier to remove than an electron in the s orbital oxygen family is easier to ionize than expected the first electron being removed is paired the repulsion of the other electron in that orbital helps “push out” the second electron, making it easier to remove

PERIODIC TRENDS 4. Successive ionization E the energy required for each successive ionization the same number of protons attract fewer electrons resulting in more attractive force per electron, making them harder to remove each cation is smaller than the atom or ion before it, thus the electrons are pulled closer to the nucleus and are held more tightly INCREASES energies to remove the 2 nd, 3 rd, etc. electron from an ion

PERIODIC TRENDS 4. Successive ionization E once an atom is ionized to a noble gas electron configuration, the next ionization energy is at this point a core electron (rather than a valence electron) is being removed these core electrons are in orbitals closer to the nucleus and thus are held more tightly note: focus on the factor of the increase (multiplication) rather than the absolute size of the increase (addition) e.g. 100 to 500 (5x) vs. 500 to 1000 (2x) MUCH LARGER

PERIODIC TRENDS 4. Successive ionization E it is possible to determine the family to which an element belongs based on the “easy” ionizations remove the valence e – e.g. three “easy” ionizations (before a much larger increase in ionization energy) suggests three valence electrons, or s 2 p 1, which indicates the boron family e.g. one “easy” ionization indicates an alkali metal how many “easy” ionizations occur

PERIODIC TRENDS 5. Electronegativity An index of an atom’s overall ability to attract electrons. It combines atomic size, ionization energy, etc., into a single summarizing number.

PERIODIC TRENDS 5. Electronegativity increases