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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 • 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
