ELECTRON CONFIGURATION

Section 5.2

Stability

Lowest possible energy

Energy levels

The maximum number of electrons in the principle energy level (shell) is 2n2.Energy Level (n)

Maximum # of e-

1 2

2 8

3 18

4 32

Electron Configuration

The Electron Configuration tells us how many electrons exist in each principal energy level (n=1-7) Atomic Number-6 Mass Number- 12

6 protons 6 neutrons 6 electrons Electron Configuration- 2-4

Electron Configuration

The electron configuration for the ground state of an atom is given on the Periodic Table of the Elements.

39.0983 +1

K192-8-8-1

Electron Configuration

What is the electron configuration of a sulfur atom in the ground state?

(1) 2-4(2) 2-6(3) 2-8-4(4) 2-8-6

Three Rules

Aufbau principle Pauli exclusion principle Hund’s rule

Aufbau Principle

Electrons occupy the orbital of lowest energy first.

Orbitals

spdf- comes from a now-discredited system of categorizing spectral lines

s- “strong” p- “principal” d- “diffuse” f- “fundamental”

s orbital

spherical

p orbitals

Dumb bell shaped

d orbitals

Double dumb bell shaped

f orbitals

Very complicated Rare earth elements

Energy levels sublevels orbitals

Principal Energy Level

Number of sublevels

Type of sublevel

n=1 1 1s (1 orbital)

n=2 2 2s (1), 2p (3)

n=3 3 3s (1), 3p (3), 3d (5)

n=4 4 4s(1), 4p (3), 4d (5),

4f (7)

Orbitals- Number of electrons

s-1 orbital= 2 e-

p-3 orbitals= 6 e-

d-5 orbitals= 10 e-

f-7 orbitals= 14 e-

Filling Orbitals

1s2s 2p3s 3p 3d4s 4p 4d 4f5s 5p 5d 5f (5g)6s 6p 6d (6f 6g 6h)7s 7p (7d 7f 7g 7h 7i)

Pauli Exclusion Principle

An atomic orbital may describe at most 2 electrons.

Those two electrons must have opposite spins

Spin: a quantum mechanical property of electrons (clockwise/counterclockwise)

Hund’s Rule

Electrons occupy orbitals of the same energy in a way that makes the number of electrons with the same spin direction as large as possible.

Exceptions

Some actual electron configurations differ from those assigned using the Aufbau principle

This leads to variation in chemical behavior

Valence Electrons

Outermost electrons Participate in reactions

Properties of elements Coincides with groups on the Periodic Table

Kernel

The nucleus and inner electrons 2 valence

e-

KERNEL

What is the total number of valence electrons in an atom of electron configuration X?

Which electron configuration represents the excited state of a calcium atom?

Element Electron Configuration

X 2-8-8-2

Y 2-8-7-3

Z 2-8-8

2

2-8-7-3

What is the total number of electrons in the valence shell of an atom of aluminum in the ground state?

(1)8(2)2(3)3(4)10

Lewis Dot Structures

Diagrams that show valence electrons as dots

Lewis (Electron) Dot Structures

C

Your Turn

Draw the Lewis Dot Structures for the following elements: Hg, Mn, K, Au, Cs