4.3 Electron Structure

Bohr Model Revisited-convenient way to show electrons in energy levels

• It consists of the nucleus with protons & neutrons and electrons in concentric orbits (circles) outside the nucleus

• The circle closest to the nucleus contains the lowest energy electrons

• The 1st level can hold a max. of 2 electrons, the 2nd level can hold a max. of 8 electrons, the 3rd can hold a maximum of 18, and the 4th level a maximum of 32.

• BE CAREFUL: At first, only 8 electrons enter the 3rd block, then 2 in the 4th and then any other remaining will enter back into the 3rd energy level. (This will be explained later.)

Bohr Model Revisited-convenient way to show electrons in energy levels

• If electrons want to move to a higher energy level, they have to GAIN energy!

• If electrons want to move to a lower energy level, they have to LOSE energy!

Pictures of the Bohr Models

Electron

Proton

Neutron

Hydrogen-1 Helium-4Lithium-6

1 p 0 n 1 e 2 p 2 n 2 e 3 p 4 n 3 e

Examples

• Draw Bohr model diagrams for the following elements.

Nitrogen= __e- Magnesium=__e- Iron=__e-

Electron Hotel

Floor 1 CLOSED

Floor 1 CLOSED

Floor 2 CLOSEDFloor 1 CLOSED

Floor 2 CLOSED

Floor 3 CLOSED

s TowerOne room per floor

p TowerThree rooms per

floor

d TowerFive rooms per floor

f TowerSeven rooms per floor

Electron Hotel

• The hotel is also built on a hill. As you can see, the first floor of f Tower is higher than the first floor of d Tower, which is higher than the first floor of p Tower, etc.

• It is also important to note that the hill is so steep, the 3rd floor of d Tower is actually between the 2nd floor of s Tower and the 2nd floor of d Tower. The f tower has a similar structure

• Please note that the lower floors of some towers are closed, so they cannot be filled (actually they were never even built ).

Electron Hotel

• There are some physical restrictions of the rooms. – Each room has two single beds, a top bunk (represented

by an up arrow) and a bottom bunk (represented by a down arrow).

• The Electron Hotel is managed by three basic rules. As the guests come in they are placed in rooms based only on these rules, so as the hotel fills, it always follows the same pattern.

• Watch the following animation silently and see if you can figure out the three rules.

Electron Hotel

Floor 1 CLOSED

Floor 1 CLOSED

Floor 2 CLOSEDFloor 1 CLOSED

Floor 2 CLOSED

Floor 3 CLOSED

s TowerOne room per floor

p TowerThree rooms per

floor

d TowerFive rooms per floor

f TowerSeven rooms per floor

Rule 1

• People MUST be placed in rooms on the lowest floor available – note again that the lowest floor built for the p

Tower is floor 2, the lowest for d Tower is floor 3 and the lowest for f Tower is floor 4

– Also remember that floor 3 for the d Tower is actually higher up than floor 4 for the s Tower but lower than floor 4 for the p Tower.

Electron Hotel

Floor 1 CLOSED

Floor 1 CLOSED

Floor 2 CLOSEDFloor 1 CLOSED

Floor 2 CLOSED

Floor 3 CLOSED

s TowerOne room per floor

p TowerThree rooms per

floor

d TowerFive rooms per floor

f TowerSeven rooms per floor

Rule 2

• A room may have a maximum of two people in it, and when two people are in the same room, they are ALWAYS in separate bunks, one in the top bunk, one in the bottom bunk.– The employees also will fill the top bunk before

filling the bottom bunk.

Electron Hotel

Floor 1 CLOSED

Floor 1 CLOSED

Floor 2 CLOSEDFloor 1 CLOSED

Floor 2 CLOSED

Floor 3 CLOSED

s TowerOne room per floor

p TowerThree rooms per

floor

d TowerFive rooms per floor

f TowerSeven rooms per floor

Rule 3

• When a tower has more than one room per level, you must put one person in each room before putting two people in any of the rooms on that floor

Electron Hotel

Floor 1 CLOSED

Floor 1 CLOSED

Floor 2 CLOSEDFloor 1 CLOSED

Floor 2 CLOSED

Floor 3 CLOSED

s TowerOne room per floor

p TowerThree rooms per

floor

d TowerFive rooms per floor

f TowerSeven rooms per floor

The rules

1. Fill all rooms on the lowest available floor before putting anyone in a room on a higher level floor.

2. Each room can have a maximum of two people, and when two people are in the same room, one must be in the top bunk, the other in the bottom bunk.

3. When a floor has more than one room, each room must have one person in it before putting a second person in any of them.

Electron Hotel

Floor 1 CLOSED

Floor 1 CLOSED

Floor 2 CLOSEDFloor 1 CLOSED

Floor 2 CLOSED

Floor 3 CLOSED

s TowerOne room per floor

p TowerThree rooms per

floor

d TowerFive rooms per floor

f TowerSeven rooms per floor

Assign 26 guests to the Electron Hotel

Floor 1 CLOSED

Floor 1 CLOSED

Floor 2 CLOSEDFloor 1 CLOSED

Floor 2 CLOSED

Floor 3 CLOSED

s TowerOne room per floor

p TowerThree rooms per

floor

d TowerFive rooms per floor

f TowerSeven rooms per floor

Atoms are NOT hotels

• Electrons, of course, are really in the electron cloud of an atom, not in a hotel, but the rules we learned still apply.

• The rules are based on energy and stability, not on some arbitrary rules some hotel manager came up with.

TranslationsHotel •The electron cloud

•Where all electrons in an atom are located

Floor •Principal energy level•How far an electron is from the nucleus and how much energy it has – designated 1, 2, 3, etc

Tower •subshell•Some energy levels have more than one subshell – the higher the principal energy level, the more subshells it can have

Room •Orbital•The higher the energy of the subshell (within the same principal energy level) the more orbitals it has, and the more complex the orbital shapes are

Bunk •Spin•The spin is the angular momentum of the electron. If two electrons occupy the same orbital, they must have opposite angular momentum.

Details• An electron cloud describes the area where the electrons

of an atom are likely to be. It includes all subshells and orbitals

• A subshell is a set of orbitals with equal energy

• An orbital is an area of high probability of the location of the electron

• There is always some uncertainty

Electron Configurations

• What is an electron configuration?– It shows the position and grouping of electrons in an atom– The position and grouping of electrons in an atom

determine when and how it can glow.– Chemical properties of elements are closely related to the

arrangement of their electrons• Several ways to write electron configurations– Orbital notation (shows the most detail)– Full electron configuration (standard notation)– Noble gas configuration (a shorthand of the standard)

Energy and Subshells

1s

2s

3s

4s

5s

2p

3p

4p

5p

3d

4d

6s

6p5d 4f

Ener

gy

Subshells are filled from the lowest energy level to increasing energy levels.

Does this look familiar? Electron Hotel!

Subshells!

• As noted before, the higher the principal energy level the more subshells it can have.

• Level 1 only has 1 subshell: s• Level 2 can have 2 subshells: s and p• Level 3 can have 3 subshells: s, p and d• Level 4 can have 4 subshells: s, p, d and f• Level 5 can have 5 subshells: s, p, d, f and “g”– No element that has been discovered to occur naturally, and

no element that has been made in a laboratory has a g subshell in the ground state

Rules Review and Translation

1. Aufbau Principle (rule 1 in the hotel)2. Pauli Exclusion Principle (rule 2 in the hotel)3. Hund’s Rule (rule 3 in the hotel)

Rule 1/Aufbau Principle

• Electrons fill subshells so that the total energy of the atom is minimum.

• What does this mean?– This means you fill the lowest energy subshells

first, and that a subshell must be completely full before beginning to fill any higher energy subshells.

• The word aufbau comes from a German word that means “building up”. You “build up” the electrons from low energy to higher.

Rule 2/Pauli Exclusion Principle

• Two electrons that occupy the same orbital must have opposite spins.

• What does this mean?– As you fill the electrons, whenever one orbital has

two electrons, there must be one with positive spin (up arrow) and one with negative spin (down arrow).

• We always fill the up arrow first, and the down arrow second

Rule 3/Hund’s Rule• Place electrons in unoccupied orbitals of the

same energy before placing a second electron in an already occupied orbital.

• What does this mean?– Fill all positive spin electrons (up arrows) in a subshell

before putting any negative spin electrons (down arrows)• and remember you can’t have two “positive spins” in the

same orbital

• As a convention, we always fill the orbitals from left to right (within the same subshell).

Number of electrons

• No matter what type of electron configuration you are showing, you must first determine the number of electrons in the atom

• This is very simple for a neutral atom o # electrons = # protons = atomic number!

• For an ion it only requires a little matho Charge = # protons − # electrons, so o # electrons = # protons – charge

Watch out for negative charges!!!!!

Orbital Notation1. Determine the number of electrons2. Draw all the boxes for a subshell when you add the first

electron in that subshell (we name only subshells).a. The name of a subshell is the principal energy level and the

subshell.b. Example an electron in an orbital of the p subshell in the 3rd

principal energy level would be in the “3p”c. subshells are individually drawn starting from the left and

moving to the right.d. How many orbitals (drawn as boxes)?

• s subshell has one, p has 3, d has 5, f has 7

3. Follow Aufbau Principle, Pauli Exclusion Principle and Hund’s Rule to fill in the electrons.

Example – Draw the orbital notation for chlorine

1. Determine the number of electrons.a. Since there is no charge indicated, the atom must be

neutral.b. # electrons = # protons = Atomic Numberc. Atomic number is 17, so… there are 17 electrons to fill.

2. Draw all boxes for a subshell when you add the first electron to that subshell

3. Follow Aufbau Principle, Pauli Exclusion Principle and Hund’s Rule to fill in the electrons.

1s 2s 2p 3s 3p

What is the order for subshells?

• You won’t have that energy and subshells chart on your test, so how did I know the order to draw and fill the subshells without looking back at that chart?

• There are three possible ways, listed here in order of increasing preference:

1. Memorize it

2. Use a mnemonic device

3. Use the periodic table• We’ll cover these later. • For right now, just use the chart in your notes.

Example – Draw the orbital notation for sodium

1. Determine the number of electrons.a. Since there is no charge indicated, the atom must be

neutral.b. # electrons = # protons = Atomic Numberc. Atomic number is 11, so… there are 11 electrons to fill.

2. Draw all boxes for a subshell when you add the first electron to that subshell

3. Follow Aufbau Principle, Pauli Exclusion Principle and Hund’s Rule to fill in the electrons.

1s 2s 2p 3s

Example – Draw the orbital notation for manganese

1. Determine the number of electrons.a. Since there is no charge indicated, the atom must be

neutral.b. # electrons = # protons = Atomic Numberc. Atomic number is 25, so… there are 25 electrons to fill.

2. Draw all boxes for a subshell when you add the first electron to that subshell

3. Follow Aufbau Principle, Pauli Exclusion Principle and Hund’s Rule to fill in the electrons.

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

Full Electron Configuration (Standard Notation)

• Often just called “electron configuration,” • A much shorter way to show the arrangement of

electrons in an atom compared to orbital notation.• Keeps the most important parts that determine

the atom’s chemical properties, including how it will interact with light (and glow!).

• Of the three rules, only the Aufbau Principle will apply to this notation.

• Sometimes called spectroscopic notation.

Full Electron Configuration (Standard Notation)

1. Determine the number of electrons in the atom.2. Follow the Aufbau Principle for filling the subhells in

order.3. The name of each subshell is written in order• ex 1s• Only the subshells that have electrons in them are

written4. The number of electrons is written as a superscript

after the name of the subshell• Ex 1s2

Full Electron Configuration (Standard Notation)

• How many electrons can each subshell hold?• Remember orbital notation? – The s subshell has 1 orbital, p has 3 orbitals, d has 5 orbitals and f has

7 orbitals• Remember each orbital can hold two electrons (one positive

spin, one negative spin)?• So the maximum electrons it can hold depends on the type of

subshell

– s can hold 2– p can hold 6– d can hold 10– f can hold 14

1s22s22p63s21s22s22p63s23p1s22s22p63s23p5

Write the electron configuration for chlorine

1. Determine the number of electrons in the atom.

172. Follow the Aufbau Principle for filling the

subhells in order.3. The name of each subshell is written in order4. The number of electrons is written as a

superscript after the name of the subshell1s1s21s22s1s22s21s22s22p1s22s22p61s22s22p63s

Write the electron configuration for aluminum

1. Determine the number of electrons in the atom. 132. Follow the Aufbau Principle for filling the

subhells in order.3. The name of each subshell is written in order4. The number of electrons is written as a

superscript after the name of the subshell1s22s22p63s23p1

Write the electron configuration for zinc

1. Determine the number of electrons in the atom. 302. Follow the Aufbau Principle for filling the

subhells in order.3. The name of each subshell is written in order4. The number of electrons is written as a

superscript after the name of the subshell1s22s22p63s23p64s23d10

Write the electron configuration for cesium

1. Determine the number of electrons in the atom. 552. Follow the Aufbau Principle for filling the

subhells in order.3. The name of each subshell is written in order4. The number of electrons is written as a

superscript after the name of the subshell1s22s22p63s23p64s23d104p65s24d105p66s1

Noble Gas Configuration

• Also called shorthand configuration• Since we follow the same pattern every time, all

electron configurations look just like a noble gas plus a few extra electrons – Exceptions: hydrogen and helium

• Cannot be used for elements in the 1st period (the two exceptions above)

• Generally not used for elements in the 2nd period (it can be used, but it doesn’t really save any writing, so it usually isn’t)

Noble Gas Configuration

• Why use noble gases?• Noble gases are stable – they have a full

valence (outermost) shell of electrons (usually 8)

• Noble gases are at the far right of the periodic table, so they are easy to find.

Noble Gas Configuration1. Determine the number of electrons in the atom2. Determine the noble gas to use

Use the noble gas in the previous period Example – chlorine is in period 3. Neon is the noble gas in

period 2 – use Neon Warning: you can’t use a noble gas if it has the same

number of electrons you are filling in either, so for argon you must use neon (which is the noble gas in the previous period)

3. Use the Aufbau Principle to fill in the remaining electrons

Write the noble gas configuration for chlorine

1. Determine the number of electrons in the atom17

2. Determine the noble gas to use Use the noble gas in the previous period

3. Use the Aufbau Principle to fill in the remaining electrons Don’t forget – we’ve already accounted for all the

electrons before 3s

[Ne][Ne]3s[Ne]3s2[Ne]3s23p[Ne]3s23p5

Using the periodic table

• The noble gas is written in square brackets• The next subshell is always an s subshell• The principal energy level (the number in front

of the s) is always the period number that the element is in.– Chlorine is in the 3rd period, so after [Ne] we wrote

3s

Write the noble gas configuration for potassium

1. Determine the number of electrons in the atom19

2. Determine the noble gas to use Use the noble gas in the previous period

3. Use the Aufbau Principle to fill in the remaining electrons Don’t forget – we’ve start with the s subshell with

the principal energy level equal to the period number for potassium

[Ar]4s1

Write the noble gas configuration for arsenic

1. Determine the number of electrons in the atom33

2. Determine the noble gas to use Use the noble gas in the previous period

3. Use the Aufbau Principle to fill in the remaining electrons Don’t forget – we’ve start with the s subshell with

the principal energy level equal to the period number for arsenic

[Ar]4s23d104p3

Write the noble gas configuration for antimony

1. Determine the number of electrons in the atom51

2. Determine the noble gas to use Use the noble gas in the previous period

3. Use the Aufbau Principle to fill in the remaining electrons Don’t forget – we’ve start with the s subshell with

the principal energy level equal to the period number for antimony

[Kr]5s24d105p3

Write the noble gas configuration for bismuth

1. Determine the number of electrons in the atom83

2. Determine the noble gas to use Use the noble gas in the previous period

3. Use the Aufbau Principle to fill in the remaining electrons Don’t forget – we’ve start with the s subshell with

the principal energy level equal to the period number for antimony

[Xe]6s24f145d106p3

Periodic Table and Electron Configurations

• How does the periodic table relate to electron configurations?

• The periodic table has its “funny shape” because it is arranged based on electron configurations.

• There are 4 distinct areas on the periodic table– 2 groups on the far left– 6 groups on the far right– 10 groups in the middle (the transition metals!)– 14 groups moved to the bottom (the inner transition

metals)

Periodic Table and Electron Configurations

• What is the highest energy subshell that has electrons for each of the alkali metals?– Write the noble gas configuration for each

• Lithium [He] 2s1

• Sodium [Ne] 3s1

• Potassium [Ar] 4s1

• Rubidium [Kr] 5s1

• Cesium [Xe] 6s1

• Francium [Rn] 7s1

• They all have one electron in an s subshell• For group 2 they all have 2 electrons in an s subshell• Groups 1 and 2 are called the “s block” on the periodic table• Any s subshell can hold a maximum of 2 electrons… the “s block” is

two groups wide!

Periodic Table and Electron Configurations

• Look back at the noble gas configuration examples you did for arsenic, antimony and bismuth– They all have 3 electrons in a p subshell– How many electrons do you think nitrogen has in the 2p subshell?– How many electrons do you think phosphorous has in the 3p

subshell?• Groups 13 through 18 are known as the “p block” since the

subshell with the highest energy is a p subshell for each of those elements– Exception: helium

• Any p subshell can hold a maximum of 6 electrons… the “p block” is six groups wide!

Periodic Table and Electron Configurations

• The transition metals consist of 10 groups…• Which subshell has a maximum of 10 electrons?• The 10 groups of the transition metals, groups 2

through 12 are known as the d block• The inner transition metals are 14 across• An f subshell can hold up to 14 electrons• The inner transition metals are known as the

f block

Electron configurations and the periodic tables block

p blockd block

f block

Don’t forget helium!!!

What is the order for subshells?

• Now lets figure out how to remember the proper order to fill the subshells in an atom

• There are three possible ways, listed here in order of increasing preference:

1. Memorize it

2. Use a mnemonic device

3. Use the periodic table• We’ll cover these in reverse order, starting with

Use the periodic table.

Electron configurations and the periodic tableWhat is the order for subshells?

• No matter which method you use to remember the order of the subshells, there are some important facts:– Remember that the lowest energy p subshell is 2p (1p

doesn’t exist)– The lowest d subshell is 3d– The lowest f subshell is 4f

• So we can label our periodic tables to help us with electron configurations (method 3 – Use the periodic table)

Electron configurations and the periodic tables block

p blockd block

f block

Don’t forget helium!!!

1s

2s

3s

4s

5s

6s

7s

2p

3p

4p

5p

6p

3d

4d

5d

6d

4f

5f

1s1s

Electron configurations and the periodic tableWhat is the order for subshells?

• If you label your periodic table this way, you can simply follow the periodic table to figure out what order to fill sublevels for the Aufbau Principle.

• Start with hydrogen and keep adding sublevels until you run out of electrons!

What is the order for subshells?

• Method 2 – use a mnemonic device.• The problem with this, is that you still have to

remember how to make the mnemonic device, as well as how to use it.

• I don’t like this very much, but its better than Method 1 “memorize it”

Mnemonic Device

1s2s 2p3s 3p 3d4s 4p 4d 4f5s 5p 5d 5f6s 6p 6d

• Construct a grid – it helps if your boxes are perfectly square

• In the first column, start with 1s and end with 6s

• In the second column, start with 2p (remember 1p doesn’t exist!) and end with 6p.– Be sure that 2p is in the same

ROW as 2s• 3d to 6d goes in the 3rd column• 4f and 5f go in the last column

Mnemonic Device

1s2s 2p3s 3p 3d4s 4p 4d 4f5s 5p 5d 5f6s 6p 6d

• Now draw diagonal arrows starting in the upper right corner of the top box in the first column

• Continue drawing arrows for each box across the top row… extend the arrows through to the far left of the grid

• Now move down the right column until you run out of boxes

• To help you remember what order to follow the arrows you may want to number them (in the order that we drew them)

1 2 3 4

5

6

7

8

Mnemonic Device

1s2s 2p3s 3p 3d4s 4p 4d 4f5s 5p 5d 5f6s 6p 6d

• To correctly order the subshells, simply follow the arrows.

• And so on

1 2 3 4

5

6

7

8

1s 2s 2p 3s 3p 4s 3d 4p 5s