The Electron Structure of the Atom

The quantum model emphasizes the wave nature of electrons.

Quantum Numbers Quantum numbers are solutions to the wave equations of electrons. Scientists use a set of 4 quantum numbers to determine an electron’s location around an atom.

Where are the Electrons? Electrons exist in principal energy levels that correspond to Bohr’s orbits: 1, 2, 3, 4, 5, … Principal energy levels are divided into 4 types of sublevels: s, p, d, and f.

Where are the Electrons? The sublevels contain orbitals. Each orbital can hold up to two electrons.

Principal Quantum Number (n) Identifies the principal energy level Correlates to Bohr’s orbits n = 1, 2, 3, 4, 5, 6, or 7 for the ground state e−. The total number of e− in a level is 2n2.

Level Total # e− 1 2 8 3 18 4 32 5 50 (32) 6 72 (18) 7 98 (8)

Azimuthal Quantum Number (l) Identifies the sublevel Different sublevels have different shapes. 4 types of sublevels: s, p, d, f

Principal energy levels are divided into four types of sublevels: The Quantum Model Principal energy levels are divided into four types of sublevels: s s, p, d, and f. p d f S Silly, p people d don’t f fly.

The Quantum Model The sublevels contain orbitals. The orbitals contain the electrons. Each orbital can hold up to two electrons.

The Quantum Model s = 0 p = 1 d = 2 f = 3 A number is associated with each type of sublevel. s = 0 p = 1 d = 2 f = 3

The Quantum Model No. Do all levels have all four sublevels? Which levels have which sublevels?

The Quantum Model Levels & Sublevels 1st ……… s 2nd ……… s, p 3rd ……… s, p, d 4th ……… s, p, d, f 5th ……… s, p, d, f 6th ……… s, p, d 7th ……… s, p

Allowed Azimuthal Quantum Numbers for Each Principal Energy Level Possible azimuthal quantum numbers (l) 1 2 0, 1 3 0, 1, 2 4 0, 1, 2, 3 5 0, 1, 2, 3, 4 6 0, 1, 2, 3, 4, 5 7 0, 1, 2, 3, 4, 5, 6

Magnetic Quantum Number (m) Identifies the orbital Describes how the e− responds to magnetic fields Each sublevel has 2l + 1 orbitals.

Electron-Spin Quantum Number (ms) Identifies the spin Each orbital can hold only 2 e−. Each e− in an orbital has an opposite reaction to a magnetic field.

Electron-Spin Quantum Number (ms) Scientists call this property “spin.” The values for the electron-spin quantum numbers are +½ or −½.

Pauli Exclusion Principle Electrons can occupy the same orbital only if they have opposite spins.

Pauli Exclusion Principle Said to be “spin-paired” Represented by the direction of an arrow

Pauli Exclusion Principle Because of this principle, the MAXIMUM number of electrons that can occupy any orbital is 2. MAXIMUM 2

So, it can hold only 2 electrons. Sublevels & Orbitals The “s” Sublevel It has only 1 orbital. Chemistry textbook, p. 85 So, it can hold only 2 electrons.

So, it can hold 6 electrons. Sublevels & Orbitals The “p” Sublevel It has 3 orbitals. + + = Chemistry textbook, p. 85 So, it can hold 6 electrons.

So, it can hold 10 electrons. Sublevels & Orbitals The “d” Sublevel It has 5 orbitals. Chemistry textbook, p. 85 So, it can hold 10 electrons.

So, it can hold 14 electrons. Sublevels & Orbitals The “f” Sublevel It has 7 orbitals. Chemistry textbook, p. 86 So, it can hold 14 electrons.

Sublevel # orbitals # e− p 3 6 d 5 10 f 7 14

The Sublevels Remember that their shapes are only mathematical representations of electron behavior. They help visualize the electrons and account for their properties.

Question What are the four sublevels named? a, b, c, d w, x, y, z s, p, d, f e, f, g, h

The Quantum Model Levels & Sublevels No. Do all levels have all four sublevels? No. Which levels have which sublevels?

The Quantum Model Levels & Sublevels 1st ……… s 2nd ……… s, p 3rd ……… s, p, d 4th ……… s, p, d, f 5th ……… s, p, d, f 6th ……… s, p, d 7th ……… s, p

In what order do the sublevels fill? Energies of Sublevels In what order do the sublevels fill? 1s, 2s, 3s, 4s, 5s, … ? 1s, 2s, 2p, 3s, 3p, 3d, 4s, … ? Some other order?

Order of Filling Electrons fill the sublevels in order of increasing energy. Whichever sublevel is lowest in energy receives electrons first, then the next lowest sublevel, and so on.

1s 2s 3s 4s 5s 6s 7s 2p 3p 4p 5p 6p 7p 3d 4d 5d 6d 4f 5f

1s 2s 2p 3s 3p 3d 4s 4p 4d 4f 5s 5p 5d 5f 6s 6p 6d 7s 7p

Question Which sublevel fills after 3p? 4s 3d 4p 3s 2p

Question Which sublevel fills after 6s? 6p 7s 4f 5s 5p

Question Which sublevel fills after 7p? 7s 6p 6d 3f There is no next sublevel.

Periodic Table & Electron Configuration Atomic numbers increase from left to right. Each row corresponds to the next principal energy level. Certain regions correspond to sublevels.

Chemistry textbook, p. 88

The Aufbau Principle: How to Build an Atom The arrangement of electrons in an atom may be determined by the addition of electrons to a smaller atom.

The Aufbau Principle: How to Build an Atom In the progression from hydrogen up to larger elements, each successive element has one additional electron and one additional proton.

Electron Configuration It is a shortcut to show the location of an electron in an atom. Write 1s followed by a superscript 1 or 2 to denote how many electrons are in the 1s sublevel.

E− Configuration of Elements H 1s1 He 1s2 Li 1s2 2s1 Be 1s2 2s2 B 1s2 2s2 2p1 C 1s2 2s2 2p2 N 1s2 2s2 2p3 O 1s2 2s2 2p4 F 1s2 2s2 2p5 Ne 1s2 2s2 2p6

Question Which sublevel holds the first electron? 1s 2s 2p

Question Which sublevel holds the second electron? 1s 2s 2p

Question Which sublevel holds the third electron? 1s 2s 2p

Question Which sublevel holds the fourth electron? 1s 2s 2p

Question Which sublevel holds the fifth electron? 1s 2s 2p

Question What comes after 2p6 in electron configuration? 2p7 3s1 3p1 2d1 No more e− can be added.

Another method of showing the location of an electron in an atom Orbital Notation Another method of showing the location of an electron in an atom Write 1s, 3p, etc. for each level and sublevel containing electrons. Use lines to represent orbitals. Use arrows to show the e− in the orbitals.

Orbital Notation H 1s He 1s Li 1s 2s Be 1s 2s

Orbital Notation B 1s 2s 2p ? ? C 1s 2s 2p

Hund’s Rule When electrons fill a sublevel, all orbitals receive one electron before any receive two.

Orbital Notation B 1s 2s 2p ? ? C 1s 2s 2p N 1s 2s 2p O 1s 2s 2p

Orbital Notation F 1s 2s 2p Ne 1s 2s 2p

Summary The Aufbau principle tells the order in which electrons fill the sublevels. Hund’s rule tells whether electrons in the same sublevel will be paired or unpaired. Transition elements may be exceptions.

Question What is the main difference between orbital notation and e− configuration? E− config. does not show sublevels. E− config. looks better. Hund’s rule does not apply to orbital notation. Only orbital notation shows the orbitals.

6d 5f 7s 6p 5d 4f 6s 5p 4d 5s 4p 3d 4s 3p 3s 2p 2s 1s 6d 5f 6d 7s 5f Chemistry textbook, p. 91 1s

Application MRI (Magnetic Resonance Imaging) Developed by Raymond Damadian Based on the magnetic fields produced by atoms