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Electron Configurations & Quantum Numbers. Atomic structure defined by electron levels Principal Quantum Number “N” Small integer numbers allowed (e.g. 1, 2, 3 …) N defines effective size (radius) of the electron orbit The radius determines the energy (larger = more)

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## Electron Configurations & Quantum Numbers

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**Electron Configurations & Quantum Numbers**• Atomic structure defined by electron levels • Principal Quantum Number “N” • Small integer numbers allowed (e.g. 1, 2, 3 …) • N defines effective size (radius) of the electron orbit • The radius determines the energy (larger = more) • N defines shells, groups of electron s with same radius • Energy of the electron increases with larger values of “N”**Quantum Numbers**• Angular Momentum Quantum Number “L” • Defines the shape or path of the orbiting electron • Provides 3-D perspective • “S” is spherical • “P” is dumbbell shape • Also has small integer numbers, 0 to (N-1) allowed • NO negative values • Historical identification by letters as well as numbers • O “s”, 1 “p”, 2 “d”, 3 “f”, etc. • Chemical structures are a direct result**Quantum Numbers**• Magnetic Quantum Number “m” • Also a set of small integers, negative values ARE allowed • Range of values “- L” to “+ L” (momentum numbers) • The + and – values relate to “spin” • Spin conceptually like current creating a magnetic field • Electron orbits usually have paired electrons opposite spin • Net magnetic moment is zero • Most materials are non-magnetic (spins cancelled) • Magnetic materials have unpaired spins • Fe, Co, Ni • Gives rise to permanent and reversible magnets**Another way to look at electronsorganized by increasing**element number, not properties**A few examples**• Helium, element 2 1s2 • Boron, element 5 1s2 2s2 2p • Alternative description [He]2s2 2p • Neon, element 10 1s2 2s2 2p6 • Sodium, element 11 1s2 2s2 2p6 3s • Alternative description [Ne] 3s • Chlorine, element 17 1s2 2s2 2p6 3s23p5 • Alternate description [Ne] 3s23p5**As electrons are added, the quantum numbers to build up**orbitals and create new elements (see text table 3.2)**Writing Electron Configurations**• Use the alphabetic abbreviation for shells (e.g. s, p, d, f) • List shells in numerical order 1, 2, 3 …. • List number of shell electrons in superscript • S shell ≤2, p shell ≤6, d shell ≤10, f shell ≤14 • Keep going until all electrons accounted for • Example • Sodium metal, Na0 Z=11 (protons = electrons) • 1s2 2s2 2p6 3s1 • Sodium ion, Na1+ Z=11 (11 protons + 10 electrons) • 1s2 2s2 2p6 • Alternative to utilize nearest (lower) inert gas shell • [Ne]3s1 for sodium metal, [Ne]1+ for sodium ion • A handy abbreviation for large atoms and ions • Electron shells of identical configurations are ISOELECTRONIC • Neon gas (1s2 2s2 2p6 ) &Sodium ion (1s2 2s2 2p6 )are Isoelectronic • A favorite exam question !**Hund’s RuleElectrons add with same spin until all orbit**positions have 1 electron, then pair up until shells are full.Gives rise to magnetic properties of transition elements**Valence Electrons**• Outer electrons undergo transfer • Outer electrons are most loosely held • Oxidation = loss of available electrons • Fe0 Fe++ + 2e- • Octet rule favors complete shell of 8 • Reduction of Chlorine = gain of electrons • Cl0 + e- Cl-**Another way to look at electronsorganized by increasing**element number, not properties**Electron Configurations by groupwhere n is principal quantum**numbersum of superscripts is available electrons**Another way to look at electronsorganized by increasing**element number, not properties**Another way to look at electronsorganized by increasing**element number, not properties

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