Rev Pisgah High School M. Jones Electron Energy Diagrams Electron Configuration and Valence Electrons Electrons and their Arrangements

The Bohr Model The Bohr Model went through a number of changes as it evolved into the modern Quantum Mechanical model of the atom. But the basic idea that electrons can exist in only certain allowed energy levels stayed the same.

Electrons and energy levels From quantum theory we get a simple expression that gives the maximum number of electrons in each energy level. 2n 2 = maximum number of electrons in the n th energy level.

n = the principal quantum number n12345 n n The expression 2n 2 gives the maximum number of electrons at each energy level. What is familiar about these numbers?

And why is the periodic table … …the shape that it is?

It has to do with 2n n2n How many elements are in the first row? Each element is the location of one more electron.  2 

n2n How many elements are in the second row?  8 

n2n How many elements are in the third row? 2266 Where are the other 10?  10 

n2n How many elements are in the fourth row? 2266 Where are the other 14?  10   14  32 – 18 = ???

Electrons Exist in Discrete Energy Levels

Energy Levels and Sublevels energy Consider the first four Bohr orbits. Each of these major energy levels can be subdivided into energy sublevels.

Energy Levels and Sublevels energy What’s going on here? The energy levels overlap

Energy Levels and Sublevels energy The sublevels are designated by the letters s, p, d and f.

The s, p, d, f notation… … originally came from the words that spectroscopists used to describe the lines in spectra. s = sharp p = principal d = diffuse f = fundamental

Energy Levels and Sublevels energy We will label the sublevels as we increase in energy. 4p 3d 4f 1s 2p 2s 3s 4s 4d 3p

Energy Levels and Sublevels energy Notice that we get to the 4s sublevel before the 3d sublevel 4p 3d 4f 1s 2p 2s 3s 4s 4d 3p

Energy Levels and Sublevels energy Where do you think the 5s sublevel will go? 5s There are still other cases of overlap. More later. 4p 4f 1s 2p 2s 3s 4s 4d 3p 3d

Energy Levels and Sublevels energy How many electrons are in an s-sublevel? 4p 3d 4f 1s 2p 2s 3s 4s 4d 3p 2 Both the electrons in the first energy level must be in the s- sublevel

There are 8 electrons in the second energy level. Energy Levels and Sublevels energy How many electrons are in a p-sublevel? = 6 4p 4f 1s 2p 2s 3s 4s 4d 3p 3d

Energy Levels and Sublevels energy How many electrons are in a d-sublevel? 2 8 electrons are in the s and p = p 4f 1s 2p 2s 3s 4s 4d 3p 3d 18 electrons for n=3

Energy Levels and Sublevels energy Figure out how many electrons are in the f-sublevel? 2 Max of 32 e - in the 4 th energy level = p 4f 1s 2p 2s 3s 4s 4d 3p 3d

Energy Levels and Sublevels energy The number of electrons in each sublevel: s2 p6 d10 f14 4p 4f 1s 2p 2s 3s 4s 4d 3p 3d

Now. Why is the periodic table the shape it is? It’s the sublevels!

The periodic table is subdivided … … into four regions. s d p f

Just by looking at the location of an element in the periodic table, one can determine which orbitals, in which energy level, are being filled.

Where is the last electron for nitrogen? The last electrons go into the 2p sublevel s d p f N

Where is the last electron for barium? s d p f Ba The last electrons go into the 6s sublevel

Where is the last electron for iron? s d p f Fe The last electrons go into the 3d sublevel

Orbitals and Energy Diagrams

Quantum Numbers 1.Each electron in an atom has a set of four (4) quantum numbers. 2.The quantum numbers are like an address: name, street, city, state. 3.Pauli exclusion principle: no two electrons in the same atom can have the same set of quantum numbers.

Quantum Numbers AddressQuntm. #Sym.What it tells StatePrincipal nMajor energy level CityAzmuthal LSublevel StreetMagnetic M L Orbital NameSpin M S Which e - in orbital We will deal primarily with the Principal Quantum Number

What is an orbital? An orbital is a region in space occupied by at most, two electrons. An orbital is defined as the probability density for a pair of electrons.

What is an orbital? An orbital is a region in space occupied by at most, two electrons. An orbital is defined as the probability density for a pair of electrons. “Orbital” is a very unfortunate choice of words. It suggests an orbit, like planets orbiting the sun. That simply isn’t the case. The word “orbital” has nothing to do with electrons going around in circles like the planets orbiting the sun.

What is an orbital? An orbital is a region in space occupied by at most, two electrons. An orbital is defined as the probability density for a pair of electrons.

What is an orbital? An orbital is a region in space occupied by at most, two electrons. It is a three dimensional representation of the probability of finding a pair of electrons.

This probability density is a three dimensional shape. The shapes of the orbitals are based on a calculation of the probability of finding an electron at a certain distance from the nucleus.

In the case of an s-orbital… … the shape is a sphere, … with the nucleus at the center.

In the case of a p-orbital… … the shape is a “dumb-bell”

There are three p-orbitals. y x z The orbitals are arranged at right angles to each other. They accommodate 6 electrons two per orbital.

One p-orbital x

Two p-orbitals x

Three p-orbitals z x

How do we represent an orbital? An orbital is a region in space occupied by at most, two electrons The line represents an orbital Use arrows to represent electrons of opposite spins

We will use this notation to represent the electrons in an atom. It’s not what an atom actually looks like, it’s only a representation of the electrons.

This is a radio

This is a schematic diagram of the radio

The radio looks different from the schematic diagram of the radio. The schematic diagram of the radio shows all of the parts and how they are connected, but it isn’t the radio.

Radio Schematic diagram

We can’t actually see an atom or its electrons. But we can represent the electrons with a schematic diagram. The schematic diagram of the electrons in an atom is called an electron energy diagram.

1s 2s 2p 3s 4s 5s 6s 3p 4p 5p 3d 4d 5d 4f Electron Energy Diagram This is an example of an Energy Diagram for Xe

Electron Energy Diagram The Electron Energy Diagram shows the arrangement of electrons in orbitals. The orbitals are arranged by increasing energy. The order in the energy diagram comes from the periodic table.

Follow Z from left to right, top to bottom s d p f Energy Levels in the Periodic Table

1s 2s 2p 3s 4s 5s 6s 7s 3p 4p 5p 6p 3d 4d 5d 4f Electron Energy Diagram Copy the energy diagram into your notebook.

The ground state is where the electrons are in their lowest possible energy sublevels. We will add electrons, one at a time, into their ground-state orbitals.

1s 2s 2p 3s 4s 5s 6s 7s 3p 4p 5p 6p 3d 4d 5d 4f Energy levels and orbitals in the Energy Diagram

1s 2s 2p 3s 4s 5s 6s 7s 3p 4p 5p 6p 3d 4d 5d 4f H

1s 2s 2p 3s 4s 5s 6s 7s 3p 4p 5p 6p 3d 4d 5d 4f He

1s 2s 2p 3s 4s 5s 6s 7s 3p 4p 5p 6p 3d 4d 5d 4f Li

1s 2s 2p 3s 4s 5s 6s 7s 3p 4p 5p 6p 3d 4d 5d 4f Be

1s 2s 2p 3s 4s 5s 6s 7s 3p 4p 5p 6p 3d 4d 5d 4f B See Hund’s Rule

1s 2s 2p 3s 4s 5s 6s 7s 3p 4p 5p 6p 3d 4d 5d 4f C See Hund’s Rule

1s 2s 2p 3s 4s 5s 6s 7s 3p 4p 5p 6p 3d 4d 5d 4f N See Hund’s Rule

1s 2s 2p 3s 4s 5s 6s 7s 3p 4p 5p 6p 3d 4d 5d 4f O See Hund’s Rule

1s 2s 2p 3s 4s 5s 6s 7s 3p 4p 5p 6p 3d 4d 5d 4f F See Hund’s Rule

1s 2s 2p 3s 4s 5s 6s 7s 3p 4p 5p 6p 3d 4d 5d 4f Ne

1s 2s 2p 3s 4s 5s 6s 7s 3p 4p 5p 6p 3d 4d 5d 4f Na

1s 2s 2p 3s 4s 5s 6s 7s 3p 4p 5p 6p 3d 4d 5d 4f Mg

1s 2s 2p 3s 4s 5s 6s 7s 3p 4p 5p 6p 3d 4d 5d 4f Al See Hund’s Rule

1s 2s 2p 3s 4s 5s 6s 7s 3p 4p 5p 6p 3d 4d 5d 4f Si See Hund’s Rule

1s 2s 2p 3s 4s 5s 6s 7s 3p 4p 5p 6p 3d 4d 5d 4f P See Hund’s Rule

1s 2s 2p 3s 4s 5s 6s 7s 3p 4p 5p 6p 3d 4d 5d 4f S See Hund’s Rule

1s 2s 2p 3s 4s 5s 6s 7s 3p 4p 5p 6p 3d 4d 5d 4f Cl See Hund’s Rule

1s 2s 2p 3s 4s 5s 6s 7s 3p 4p 5p 6p 3d 4d 5d 4f Ar

1s 2s 2p 3s 4s 5s 6s 7s 3p 4p 5p 6p 3d 4d 5d 4f K

1s 2s 2p 3s 4s 5s 6s 7s 3p 4p 5p 6p 3d 4d 5d 4f Ca

1s 2s 2p 3s 4s 5s 6s 7s 3p 4p 5p 6p 3d 4d 5d 4f Sc

1s 2s 2p 3s 4s 5s 6s 7s 3p 4p 5p 6p 3d 4d 5d 4f Ti

1s 2s 2p 3s 4s 5s 6s 7s 3p 4p 5p 6p 3d 4d 5d 4f V

1s 2s 2p 3s 4s 5s 6s 7s 3p 4p 5p 6p 3d 4d 5d 4f Cr

1s 2s 2p 3s 4s 5s 6s 7s 3p 4p 5p 6p 3d 4d 5d 4f Cr Click to see exceptions

1s 2s 2p 3s 4s 5s 6s 7s 3p 4p 5p 6p 3d 4d 5d 4f Mn

1s 2s 2p 3s 4s 5s 6s 7s 3p 4p 5p 6p 3d 4d 5d 4f Fe

1s 2s 2p 3s 4s 5s 6s 7s 3p 4p 5p 6p 3d 4d 5d 4f Co

1s 2s 2p 3s 4s 5s 6s 7s 3p 4p 5p 6p 3d 4d 5d 4f Ni

1s 2s 2p 3s 4s 5s 6s 7s 3p 4p 5p 6p 3d 4d 5d 4f Cu

1s 2s 2p 3s 4s 5s 6s 7s 3p 4p 5p 6p 3d 4d 5d 4f Cu Click to see exceptions

1s 2s 2p 3s 4s 5s 6s 7s 3p 4p 5p 6p 3d 4d 5d 4f Zn

1s 2s 2p 3s 4s 5s 6s 7s 3p 4p 5p 6p 3d 4d 5d 4f Ga

1s 2s 2p 3s 4s 5s 6s 7s 3p 4p 5p 6p 3d 4d 5d 4f Ge

1s 2s 2p 3s 4s 5s 6s 7s 3p 4p 5p 6p 3d 4d 5d 4f As

1s 2s 2p 3s 4s 5s 6s 7s 3p 4p 5p 6p 3d 4d 5d 4f Se

1s 2s 2p 3s 4s 5s 6s 7s 3p 4p 5p 6p 3d 4d 5d 4f Br

1s 2s 2p 3s 4s 5s 6s 7s 3p 4p 5p 6p 3d 4d 5d 4f Kr

1s 2s 2p 3s 4s 5s 6s 7s 3p 4p 5p 6p 3d 4d 5d 4f Rb

1s 2s 2p 3s 4s 5s 6s 7s 3p 4p 5p 6p 3d 4d 5d 4f Sr

1s 2s 2p 3s 4s 5s 6s 7s 3p 4p 5p 6p 3d 4d 5d 4f Y

1s 2s 2p 3s 4s 5s 6s 7s 3p 4p 5p 6p 3d 4d 5d 4f Zr

1s 2s 2p 3s 4s 5s 6s 7s 3p 4p 5p 6p 3d 4d 5d 4f Nb

1s 2s 2p 3s 4s 5s 6s 7s 3p 4p 5p 6p 3d 4d 5d 4f Mo

1s 2s 2p 3s 4s 5s 6s 7s 3p 4p 5p 6p 3d 4d 5d 4f Tc

1s 2s 2p 3s 4s 5s 6s 7s 3p 4p 5p 6p 3d 4d 5d 4f Ru

1s 2s 2p 3s 4s 5s 6s 7s 3p 4p 5p 6p 3d 4d 5d 4f Rh

1s 2s 2p 3s 4s 5s 6s 7s 3p 4p 5p 6p 3d 4d 5d 4f Pd

1s 2s 2p 3s 4s 5s 6s 7s 3p 4p 5p 6p 3d 4d 5d 4f Ag

1s 2s 2p 3s 4s 5s 6s 7s 3p 4p 5p 6p 3d 4d 5d 4f Cd

1s 2s 2p 3s 4s 5s 6s 7s 3p 4p 5p 6p 3d 4d 5d 4f Sb

1s 2s 2p 3s 4s 5s 6s 7s 3p 4p 5p 6p 3d 4d 5d 4f Xe

1s 2s 2p 3s 4s 5s 6s 7s 3p 4p 5p 6p 3d 4d 5d 4f Cs

1s 2s 2p 3s 4s 5s 6s 7s 3p 4p 5p 6p 3d 4d 5d 4f Ba

1s 2s 2p 3s 4s 5s 6s 7s 3p 4p 5p 6p 3d 4d 5d 4f La

1s 2s 2p 3s 4s 5s 6s 7s 3p 4p 5p 6p 3d 4d 5d 4f Hg

1s 2s 2p 3s 4s 5s 6s 7s 3p 4p 5p 6p 3d 4d 5d 4f Bi

1s 2s 2p 3s 4s 5s 6s 7s 3p 4p 5p 6p 3d 4d 5d 4f Rn

1s 2s 2p 3s 4s 5s 6s 7s 3p 4p 5p 6p 3d 4d 5d 4f Fr

1s 2s 2p 3s 2p 3p 3d 4s 3d 4p s d p f

s d p f

But! These energy diagrams are long and tedious. Isn’t there something easier?

Look at the following electron configuration for phosphorous and see if you can figure out how it was done.

Electron Configuration for Phosphorous 1s 2 2s 2 2p 6 3s 2 3p 3 1s 2s 2p 3s 4s 3p See the connection?

We can make it even easier! 1s 2 2s 2 2p 6 3s 2 3p 3 Look at the electron configuration for phosphorous

We can make it even easier! 1s 2 2s 2 2p 6 3s 2 3p 3 Look at just this part: It’s the electron configuration for the inert gas neon (Ne).

We can make it even easier! 1s 2 2s 2 2p 6 3s 2 3p 3 Replace this … …with this. [Ne]

We can make it even easier! 1s 2 2s 2 2p 6 3s 2 3p 3 [Ne] This is called the “inert gas core”… …and can be replaced with the symbol of the inert gas…

We can make it even easier! 3s 2 3p 3 [Ne] …to give the simplest version of the electron configuration … Why can we use the inert gas core?

Here’s the reason why. We call the inert gases “inert” because they don’t react with other chemicals. Well, almost. There are a few compounds of krypton and xenon, but not many. There is a reason why they don’t react.

Here’s the reason why. The electron arrangements of the inert gases are so stable that no chemical reaction would make them more stable. Reactions occur so that the products are lower in energy and hence, more stable than the reactants.

Here’s the reason why. In the electron configuration, those electrons are represented with the symbol for the inert gas. The electrons in the inert gas core will rarely, if ever, take part in any chemical reaction.

Write the electron configuration for the following elements (use the inert gas core) 1. C 2. Al 3. Sr 4. Sn 5. Bi [He] 2s 2 2p 2 [Ne] 3s 2 3p 1 [Kr] 5s 2 [Kr] 5s 2, 4d 10, 5p 2 [Xe] 6s 2, 4f 14, 5d 10, 6p 3

Valence Electrons

Which are the representative elements? Valence electrons for the representative elements are the electrons with the highest principal quantum number. Valence electrons are those electrons that are involved in chemical reactions.

The representative elements… … are those in columns that have an “A” with the Roman numeral. IA IIA IVA IIIA VA VIA VIIA VIIIA

How many valence electrons? How many valence electrons are in an atom of arsenic (As)? Start with the electron configuration [Ar] 4s 2, 3d 10, 4p 3 5 valence electrons What is the highest principal quantum number? The highest principal quantum number is 4.

Find the valence electrons [He] 2s 2 2p 2 [Ne] 3s 2 3p 1 [Kr] 5s 2 [Kr] 5s 2, 4d 10, 5p 2 [Xe] 6s 2, 4f 14, 5d 10, 6p 3 1. C 2. Al 3. Sr 4. Sn 5. Bi

Find the valence electrons [He] 2s 2 2p 2 1. C 2. Al 3. Sr 4. Sn 5. Bi 4 valence electrons

Find the valence electrons [Ne] 3s 2 3p 1 1. C 2. Al 3. Sr 4. Sn 5. Bi 3 valence electrons

Find the valence electrons [Kr] 5s 2 1. C 2. Al 3. Sr 4. Sn 5. Bi 2 valence electrons

Find the valence electrons [Kr] 5s 2, 4d 10, 5p 2 1. C 2. Al 3. Sr 4. Sn 5. Bi 4 valence electrons

Find the valence electrons [Xe] 6s 2, 4f 14, 5d 10, 6p 3 1. C 2. Al 3. Sr 4. Sn 5. Bi 5 valence electrons

How many valence electrons? 5 valence electrons But, it’s even easier than that! What group (column) is arsenic in? VA The Roman numeral tells the number of valence electrons. (Except VIIIB) Arsenic has 5 valence electrons! [Ar] 4s 2, 3d 10, 4p 3 Go back to arsenic.

Determine the number of valence electrons in the following elements: 1. Mg 2. S 3. Sb 4. V 5. Ag

Lewis Dot Diagrams

The Lewis dot diagram represents the valence electrons. Following are the dot diagrams for the elements in the second period. See if you can figure out how they were done.

LiBeB C N Ne O F

The number of dots is the number of valence electrons! First, write the symbol for the element. Then imagine a box around the element. Start at one side and go around the box, putting one electron at a time, up to a maximum of eight dots (electrons). E

Draw the Lewis Dot Diagram for the following elements: 1. Al 2. Se 3. Ti 4. Br 5. Pb

Draw the Lewis Dot Diagram for the following element: 1. Al 2. Se 3. Ti 4. Br 5. Pb Al

Draw the Lewis Dot Diagram for the following element: 1. Al 2. Se 3. Ti 4. Br 5. Pb Se

Draw the Lewis Dot Diagram for the following element: 1. Al 2. Se 3. Ti 4. Br 5. Pb Ti

Draw the Lewis Dot Diagram for the following element: 1. Al 2. Se 3. Ti 4. Br 5. Pb Br

Draw the Lewis Dot Diagram for the following element: 1. Al 2. Se 3. Ti 4. Br 5. Pb Pb

This concludes the presentation on energy diagrams, electron configuration, and valence electrons. Click here to return to Part One

Hund’s Rule “Orbitals of equal energy are each occupied by one electron before any one orbital is occupied by a second electron, and all electrons in the singly occupied orbitals will have the same spin.” Return

Exceptions There are several exceptions to the order in which electrons are added to the orbitals. Primarily: chromium (Cr) and copper (Cu) Reasons for the exceptions 

Since the 4s and the 3d sublevels are so close in energy, one electron can move from the s-sublevel to the d-sublevel to make the d-sublevel either half- filled or completely filled, and hence more stable. Exceptions

There are electron arrangements which are more stable: 1.Inert gas arrangement (filled p) 2.A completely filled d-sublevel 3.A half-filled d-sublevel Exceptions

Chromium has one 4-s electron and five 3-d electrons. Copper has one 4-s electron and ten electrons in the 3-d sublevel. Exceptions Click to return

Exceptions There are several exceptions to the order in which electrons are added to the orbitals. Primarily: chromium (Cr) and copper (Cu) Reasons for the exceptions 

Exceptions Since the 4s and the 3d sublevels are so close in energy, one electron can move from the s-sublevel to the d-sublevel to make the d-sublevel either half- filled or completely filled, and hence more stable.

There are electron arrangements which are more stable: 1.Inert gas arrangement (filled p) 2.A completely filled d-sublevel 3.A half-filled d-sublevel Exceptions

Chromium has one 4-s electron and five 3-d electrons. Copper has one 4-s electron and ten electrons in the 3-d sublevel. Exceptions Click to return