Understanding Matter Part II

Beyond the Bohr model

ELECTRON CONFIGUIRATIONSHELL DIAGRAM

Quantum Mechanical Model

As we saw earlier, the Bohr Model had several short comings

Krypton does not follow the 2, 8, 8 pattern. In order for Krypton to have enough electrons for 36 it

needs an extra 18 electrons. The model currently used to describe the atom is the

Quantum Mechanical Model of the atom This is the current theoretical framework that is used to

describe all of the information we have about atoms and how they function

Definitions

Quantum (plural ‘quanta’) A finite amount of energy

i.e. – an energy level in an atom The amount of energy required to move an electron from its

present energy level to the next higher one Electrons can only have specific energy levels and nothing

inbetween. Mechanical

Movement of parts in relation to a whole i.e. – electrons in an atom

Hence the Quantum Mechanical Model deals with the movement and location of electrons in an atom

Uncertainty Principle

We cannot know where an electron is and where it is going

Because of this, we use probability to determine where an electron is most likely to be

Using the electron probabilities, we find areas where electrons are most likely to be

These areas are called electron clouds where the probabilities of finding electrons is very high

The shapes and distance from the nucleus of these electron clouds depends on several factors

Quantum Numbers

To describe electron clouds and where electrons probably are, we use quantum numbers

There are a total of four (4) quantum Principal Quantum Number Angular Quantum Number Magnetic Quantum Number Spin Quantum Number

We will be concerned with theses 2

Principal Quantum Number

Energy level Distance away from the nucleus

As # increases, distance from the nucleus also increases

As the number increases, so does the energy of the electrons in those orbitals

Represented by integers 1,2,3,4,5,6,7 that correspond to the seven horizontal rows on the periodic tableDetermined by counting as you move down (top to

bottom) the periodic table

Angular Quantum Number

Also known as “sub-shells” Refer to the shape of the orbital There are four (4) different shapes

S, P, D, F These correspond to the s, p, d, f blocks on the

periodic table

Periodic table shows Quantum Structure

Energy increases as you go down the periods

Subshell s Subshell p

Subshell d

Subshell f

Sub-Shells

S” Sub-shell Spherical shape

Only one (1) orbital per energy level The 1 sub shell can hold 2 electrons

“P” Sub-shell Dumbbell shape Three (3) orbitals per energy level Each shell can hold 2 electrons

3 orbitals mean the p-shell can hold up to 6 electrons

Sub-Shells Continued

“D” Sub-shell Tend to have a clover-leaf shape Five (5) orbitals per energy level Each can hold a maximum of two (2) electrons Can hold a max of 10 electrons

“F” Sub-shell Shape contains 6 lobes for the most part Seven (7) orbitals per energy level Each can hold a maximum of two (2) electrons Fourteen 14 electrons total at each energy level

To Summarize

Modeling the Quantum Atom

Krypton

Potassium

Potassium

Manganese

Three principles for electrons filling Shells Aufbau Principle:

Electrons enter sub-shells of lowest energy first 1st energy level fills up before the next

Pauli Exclusion Principle: All atomic sub-shells contain a maximum of two (2) electrons.

Each MUST have a different spin Hund’s Rule:

when electrons occupy sub-shells of equal energy, ONE electron enters EACH sub-shell until all the sub-shells contain one electron with identical directions

Electrons are added to sub-shells so that a maximum number of unpaired electrons result

ELECTRON CONFIGUIRATION ORDER OF FILLING ORBITALS Orbitals are filled in increasing order of energyDifferent blocks on the periodic table (shaded in different colors in this chart) correspond to different types of orbitals.The periodic table, from left to right, shows the ‘basic’ pattern of sub-shell filling.

Cheat Note

Orbital Notation and Electron ConfigurationORDER OF FILLING ORBITALS - HUND’S RULE The lowest energy stability of atom is attained when the number of electrons with the

same spin is maximized

Lets Try

Oxygen

Oxygen

Lets Try

Aluminum

Aluminum

Lets Try

Chlorine

Chlorine

Nobel Gas notation

An even more simplified and shorthand method for representing electron configuration.

Emphasizes the outermost energy level only Instead of listing every energy level and amount of

electrons individually, it utilizes the nearest noble gas element of the energy level below as a representation of the inner energy levels

Nobel Gas Notation Example

For Example: Sulfur Electron configuration would be:

1s22s22p63s23p4 Its Noble Gas Notation would be:

[Ne] 3s23p4 …this is because we know that the electron

configuration of Ne is: 1s22s22p6, therefore there is no need to write it all out.

Nobel Gas Examples

Examples Continued

Nobel Gas Notation

Noble Gas Configurations are especially useful for elements with a large atomic number, as their complete electron configurations become tiresome & redundant to write out each time.

You Try

Complete Orbital and noble gas practice sheet.

For additional practice you could try: Write out the orbital diagram and electron configuration of all even

number elements up to 18 Write out the Nobel gas notation for each of the following elements. Ca, Br, Nd, U, Co and Au