Post on 14-Dec-2015
Electron Configuration and Basic Quantum Model
NC Essential Standard1.3.2
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 2n2
• 1st level can hold 2(1)2 = 2 e-• 2nd level can hold 2(2)2 = 8 e-• 3rd level can hold 2(3)2 = 18 e-• 4th 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.
• 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
1s2Energy levelEnergy level
subl
evel
subl
evel
Number of electronsNumber of electrons
Practice Write electron configurations
– Pb: • 1s22s22p63s23p6
Note All the superscripts should add up to the number of electrons
Electron Configurations• H: 1s1
• Be: 1s2
• Li: 1s2 2s1
• Be: 1s2 2s2
• B:1s2 2s2 2p1
• Cl: 1s2 2s2 2p6 3s2 3p5
• 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: 1s2 2s2 2p2
• N: 1s2 2s2 2p3
• O: 1s2 2s2 2p4
• F: 1s2 2s2 2p5
• Ne: 1s2 2s2 2p6
• Na: 1s2 2s2 2p6 3s1
• Mg: 1s2 2s2 2p6 3s2
• Al: 1s2 2s2 2p6 3s2 3p1
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]3s2
Noble GasHighest energy level / period
Sublevel / block
Number of valence electrons / group number
Shorthand Notation Samples
Li [He] 2s1
He 1s2
K [Ar] 4s1
P [Ne] 3s2 3p3
Cl [Ne] 3s2 3p5
Al [Ne] 3s2 3p1
Shorthand Notation Practice Answers
B [He] 2s2
Ar [Ne] 3s2 3p6
K [Ar] 4s1
Ca [Ar] 4s2
H 1s1
Mg [Ne] 3s2
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:
1s2 2s2 2p4
Hund’s Rule: e- spread out within equivalent orbitals
↑↓ ↑↓ ↑↓ ↑ ↑1s 2s 3s 3s 3p
Element Orbital Notation
Li
C
Al
O
1s2 2s1
1s2 2s2 3s2 3p13p1
1s2 2s2 2p2 2p2 2p2 3s2 3p1
1s2 2s2 2p2 2p2 2p2
Symbol Group# Valence e-
Period S,p,d,f block
Highest energy level
[Ar]4s2
[Ne]3s23p3
[He]2s22p5
1s22s2
1s22s22p3
1s22s22p63s23p1
Mixed practice