Quantum Model & Configurations

Bohr’s Energy Levels:

Bohr was able to tell us the electrons are

found in layers around the nucleus based on

the following:

Each element gives off a unique emission

spectrum after it absorbs energy.

Each emission is a partial spectrum that shows

bands of visible light with distinct wavelengths

Bohr proposed that each band of light in the

spectrum represented an energy change for the

electrons in the space surrounding the nucleus.

Bohr’s Energy Levels:

Bohr was able to construct the planetary

model of the atom based on the following:

Using Planck’s energy equation and constant we

can determine the electrons can only experience

certain energy changes

In other words, electrons jump back and forth,

between energy levels in the “cloud”

From these observations and calculations we end

up with electrons rotating around the nucleus like

the planets around the sun.

Bohr’s Energy Levels:

In summary, Bohr was able to prove that

electrons exist in layers and that the electrons

move from one energy level to the next by

absorbing or releasing energy.

The electrons can only jump in whole level

increments.

Bohr’s Energy Levels:

The energy level where an electron is found in

its non-excited state is called its ground state

The higher energy level that the electron exists

in once it has absorbed energy is called its

excited state

Light is given off by an atom when the electron

returns to the ground state from the excited state

So how do we know where the electrons go? Electrons in an atom are arranged by:

Energy Levels

Sublevels

Orbitals

We will explore how this system and the atomic number can tell us where the electrons belong in the cloud.

Energy Levels

If you look at the periodic table you will see

there are 7 rows that correspond to the seven

ground state energy levels.

The row on the table where the element is

found tells us how many layers/energy levels

are in the electron cloud of that element’s

atoms.

Capacities of Energy Levels

Here is a quick formula to determine the # of

electrons that each energy level can hold…

# e- in an EL = 2(EL#)2

From Energy levels to Orbitals

Before we can go to the next level (sublevels) we need to look at what ideas proposed by:

Heisenberg: determined that it is not possible to know an electron’s location and speed/direction simultaneously…”the uncertainty principle”

Schrödinger: Though we can’t know the exact location of an electron in the cloud, there are areas where you are more likely to find them…they are referred to as orbitals

Sublevels = Types of Orbitals

According to Schrödinger, there are four types of orbitals: s, p, d & f

Each sublevel contains a different # of orbitals

s has 1 orbital

p has 3 orbitals

d has 5 orbitals

f has 7 orbitals

In order of lowest to highest energy they fill up

s, p, d, f.

Each orbital can hold 2 electrons

To determine the number of

electrons each sublevel can

hold multiply the # orbitals by 2

The “s” sublevel/orbital

The s orbitals are spherical in shape

whose center is the nucleus.

Every energy level contains one s-orbital

s-orbitals from higher energy levels encapsulate

the lower energy level s-orbitals

The “p” sublevel/orbital

The p orbitals align themselves with

the x, y and z axis with a “node” or

area of zero probability at the origin

(aka the nucleus)

There are 3 p orbitals

in the p sublevel

Px (along the x axis)

Py (along the y axis)

Pz (along the z axis)

The “p” orbitals

The “d” sublevel/orbitals The d sublevel has 5 orbitals that typically fall

between the x/y, x/z and y/z axis

The d sublevel can hold 10 electrons in its 5 orbitals

The “f” sublevel/orbitals

The f orbitals are the next highest energy

There are 7 orbitals

that can hold 14 e-

in this sublevel…

orientations are here

These shapes are very

complex and thus require

high energy

s sublevel d sublevel

Number of

orbitals

Total # of

electrons in

each

sublevel

p sublevel f sublevel

How many electrons can be in a sublevel?

Remember: A maximum of two electrons can be placed in

an orbital.

Filling Order of Sublevels

Use the Diagonal Rule

to help you determine

the order in which

electrons are placed in

each sublevel.

The Aufbau principle states electrons must fill

the lowest available energy orbital first.

Diagonal Rules

s 3p 3d

s 2p

s 4p 4d 4f

s 5p 5d 5f 5g?

s 6p 6d 6f 6g? 6h?

s 7p 7d 7f 7g? 7h? 7i?

1

2

3

4

5

6

7

Steps:

1. Write the energy levels top to bottom.

2. Write the orbitals in s, p, d, f order. Write the

same number of orbitals as the energy level.

3. Draw diagonal lines from the top right to the

bottom left.

4. To get the correct order,

follow the arrows!

After 7p, we are past

the current periodic

table so we can stop.

Why are d and f orbitals always in lower energy levels? d and f orbitals require LARGE amounts of

energy

It’s better to skip a d or f sublevel that requires a

large amount of energy for a lower energy s or p

from a higher energy level

This is the reason for the diagonal rule! BE SURE

TO FOLLOW THE ARROWS IN ORDER!

Electron Configurations

A list of all the electrons in an atom (or ion)

Must go in order (Aufbau principle)

2 electrons per orbital, maximum

We need electron configurations so that we can

determine the number of electrons in the outermost

energy level. These are called valence electrons

The number of valence electrons determines how

many and what this atom (or ion) can bond to in order

to make a molecule

1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p6 5s2 4d10 5p6 6s2 4f14… etc.

Electron Configurations

2p4

Energy Level

Sublevel

Number of

electrons in the

sublevel

1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p6 5s2 4d10 5p6 6s2 4f14… etc.

Orbital Diagrams

Graphical representation of an electron

configuration

One arrow represents one electron

Shows spin and which orbital within a

sublevel

Same rules as before (Aufbau principle,

d4 and d9 exceptions, two electrons in

each orbital, etc. etc.)

Orbital Diagrams

One additional rule: Hund’s Rule

In orbitals of EQUAL ENERGY (p, d, and f),

place one electron in each orbital before making

any pairs

All single electrons must spin the same way

I nickname this rule the “Monopoly Rule”

In Monopoly, you have to build houses EVENLY.

You can not put 2 houses on a property until all the

properties has at least 1 house.

Lithium

Group 1A

Atomic number = 3

1s22s1 ---> 3 total electrons

1s

2s

3s

3p

2p

Carbon

Group 4A

Atomic number = 6

1s2 2s2 2p2 --->

6 total electrons

Here we see for the first time

HUND’S RULE.

When placing electrons in a set of

orbitals having the same energy, we

place them singly as long as possible.1s

2s

3s

3p

2p

Lanthanide Element Configurations

4f orbitals used for Ce - Lu and 5f for Th - Lr

The Shape of the Periodic Table

The PT is shaped the way it is because there

are four major regions that are placed relative

to one another.

We call these regions “Blocks” but they

actually help us determine the type of orbital

the element’s electrons are in… especially

their valence electrons.

Orbitals and the Periodic Table

Orbitals grouped in s, p, d, and f orbitals (sharp, proximal, diffuse, and fundamental)

s orbitals p orbitalsd orbitals

f orbitals

Why only 8 valence e-?

If you look at the 4th EL you will see that

there are 18 elements in the period. BUT

there are only 8 valence electrons.

WHY? Because the elements in groups 3 –

12 are in the lower, 3rd EL. Therefore there

are only 8 electrons on the highest energy

level…EL 4.

Valence & Core Electrons

Valence electrons are the electrons in the highest energy level (those farthest from the nucleus).

Core electrons are all other electrons that are not found on the highest energy level.

Valence electrons are the only electrons that take part in reactions.

Thus the # valence electrons will determine the properties of the element.

Every Group has a distinct # of valence electrons.

Lewis Dot Notation

This is a way to show the number

of electrons in the highest energy

levels without having to draw the

full Bohr Model of the atom

To Make a Lewis Dot…

Write the element symbol from the Periodic

Table.

Determine the # of Valence Electrons by

looking at the group #.

Show the electrons with “X” around the

symbol in the 12, 3, 6 & 9 positions.

P

Valence Electrons by Groups

Group 1 1 e-

Group 2 2 e-

Group 3-12 2 e- (refer to s/p/d/f blocks)

Group 13 3 e-

Group 14 4 e-

Group 15 5 e-

Group 16 6 e-

Group 17 7 e-

Group 18 8 e-