Electron Configuration and Basic Quantum Model NC Essential Standard Quantum mechanics and it relation to electron configuration

Quantum Model The quantum model describes the probability of locating an electron at any place. Heisenberg Uncertainty Principle – it is impossible to know both the velocity (momentum) and the position of an electron at the same time. –The impact of a photon of light alters the motion of the electron in unpredictable ways, so measuring position changes velocity Each electron is assigned four quantum numbers that describe it. No two electrons of an atom can have the same four quantum numbers.

Principle Energy Level, n Indicates main energy level occupied by e- Always a whole number (1, 2, …) To calculated the number of electrons that a given energy level can have. Simpley use the formula 2n 2 1 st level can hold 2(1) 2 = 2 e- 2 nd level can hold 2(2) 2 = 8 e- 3 rd level can hold 2(3) 2 = 18 e- 4 th level can hold 2(4) 2 = 32 e- The period indicates the # of principle energy levels

Sublevels, l Main energy levels are then divided into sublevels Indicates the shape or type of orbital –s, p, d, f –s sublevel is spherical and holds 2 e- –p sublevel is shaped like a dumbbell and holds 6 e- –d holds 10 e- –f holds 14 e-

Orbitals, m Represents the orbital within the sublevel where the electron is located Each orbital holds a pair of electrons therefore: –1 s orbital –3 p orbitals –5 d orbitals –7 f orbitals

Spin, s Each orbital holds 2 electrons that will always spin in opposite directions the electrons are represented by +1/2 and -1/2. Note arrows are used in the orbital notation for example ↑↓.

The s orbital is spherically shaped. There is one s orbital for each value n = 1,2,3,…, of the principle number.

P Orbitals

For each of the values n = 3, 4, 5,…, there are five d orbitals. Four of the five have similar shapes, but differ in orientation.

Electron Configurations Shows the electron arrangement in an atom, always represents the lowest possible energies Aufbau Principle (German for “building up”) – electrons fill orbitals that have the lowest energies first

Explanation of configuration 1s 2 Energy level sublevel Number of electrons

Practice Write electron configurations –Pb: 1s 2 2s 2 2p 6 3s 2 3p 6 Note All the superscripts should add up to the number of electrons

Electron Configurations H: 1s 1 Be: 1s 2 Li: 1s 2 2s 1 Be: 1s 2 2s 2 B:1s 2 2s 2 2p 1 Cl: 1s 2 2s 2 2p 6 3s 2 3p 5 We just need to account for all the electrons and their locations Since they fill up the lower levels first, only the last shell (Valence) varies from the previous element’s configuration Notice 3s2 and 3p5 add together to produce the valence (outer most electrons) electrons in the atom. This atom has7 valence electrons.

Practice Write the electron configuration for C N O F Ne Na Mg Al

Practice Write the electron configuration for C: 1s 2 2s 2 2p 2 N: 1s 2 2s 2 2p 3 O: 1s 2 2s 2 2p 4 F: 1s 2 2s 2 2p 5 Ne: 1s 2 2s 2 2p 6 Na: 1s 2 2s 2 2p 6 3s 1 Mg: 1s 2 2s 2 2p 6 3s 2 Al: 1s 2 2s 2 2p 6 3s 2 3p 1

Refer to this Periodic Table when writing electron configurations The numbers in front of the “s” and “p” are the same as the row # 1A are s 1 and 2A are s 2

Shorthand Notation Shorthand notation uses the noble gases as a reference point, for example – Na: »[Ne]3s 2 Noble Gas Highest energy level / period Sublevel / block Number of valence electrons / group number

Shorthand Notation Samples Li[He] 2s 1 He1s 2 K[Ar] 4s 1 P[Ne] 3s 2 3p 3 Cl[Ne] 3s 2 3p 5 Al[Ne] 3s 2 3p 1

Shorthand Notation Practice B Ar K Ca H Mg

Shorthand Notation Practice Answers B[He] 2s 2 Ar[Ne] 3s 2 3p 6 K[Ar] 4s 1 Ca[Ar] 4s 2 H1s 1 Mg[Ne] 3s 2

Orbital notation Orbital notation uses lines to represent orbits and arrows to represent the spin of each electron. 1s Energy level and sublevel Electron spinning clockwise Electron spinning counter clockwise

Orbital Notation Orbital notation uses lines to represent orbits and arrows to represent the spin of each electron. oxygen has a total of 8 e- The e- configuration for O: 1s 2 2s 2 2p 4 Hund’s Rule: e- spread out within equivalent orbitals ↑↓ ↑↓ ↑↓ ↑ ↑ 1s 2s 3s 3s 3p

Sample Orbital Notation He Be N F

Practice Orbital Notation Practice ElementOrbital Notation Li C Al O

ElementOrbital Notation Li C Al O 1s 2 2s 1 1s 2 2s 2 3s 2 3p 1 3p 1 1s 2 2s 2 2p 2 2p 2 2p 2 3s 2 3p 1 1s 2 2s 2 2p 2 2p 2 2p 2

SymbolGroup#Valence e- PeriodS,p,d,f block Highest energy level [Ar]4s 2 [Ne]3s 2 3p 3 [He]2s 2 2p 5 1s 2 2s 2 1s 2 2s 2 2p 3 1s 2 2s 2 2p 6 3s 2 3p 1 Mixed practice

SymbolGroup#Valence e- PeriodS,p,d,f block Highest energy level [Ar]4s 2 Ca224s4 [Ne]3s 2 3p 3 P5A /1553p3 [He]2s 2 2p 5 O6A /1672p4 1s 2 2s 2 Be222s2 1s 2 2s 2 2p 3 N5A /1552p2 1s 2 2s 2 2p 6 3s 2 3p 1 Al3A /1333p3