4.3 Electron Structure

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 1stlevel 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!

Electron Proton Neutron Hydrogen-1 Helium-4 Lithium-6 Pictures of the Bohr Models 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 3 CLOSED Floor 2 CLOSED Floor 2 CLOSED Floor 1 CLOSED f Tower Seven rooms per floor Floor 1 CLOSED d Tower Five rooms per floor Floor 1 CLOSED p Tower Three rooms per floor s Tower One room 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.

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.

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.

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

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

Assign 26 guests to the Electron Hotel Floor 3 CLOSED Floor 2 CLOSED Floor 2 CLOSED Floor 1 CLOSED f Tower Seven rooms per floor Floor 1 CLOSED d Tower Five rooms per floor Floor 1 CLOSED p Tower Three rooms per floor s Tower One room 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.

Translations

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)

4f 5d 4d 3d 5p 6p 2p 3p 4p Energy and Subshells 6s 5s 4s 3s Subshells are filled from the lowest energy level to increasing energy levels. 2s Energy Does this look familiar? Electron Hotel! 1s

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 • Aufbau Principle (rule 1 in the hotel) • Pauli Exclusion Principle (rule 2 in the hotel) • 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 • # electrons = # protons = atomic number! • For an ion it only requires a little math • Charge = # protons − # electrons, so • # electrons = # protons – charge • Watch out for negative charges!!!!!

Orbital Notation • Determine the number of electrons • Draw all the boxes for a subshell when you add the first electron in that subshell (we name only subshells). • The name of a subshell is the principal energy level and the subshell. • Example an electron in an orbital of the p subshell in the 3rd principal energy level would be in the “3p” • subshells are individually drawn starting from the left and moving to the right. • How many orbitals (drawn as boxes)? • s subshell has one, p has 3, d has 5, f has 7 • Follow AufbauPrinciple, Pauli Exclusion Principle and Hund’s Rule to fill in the electrons.

Example – Draw the orbital notation for chlorine • Determine the number of electrons. • Since there is no charge indicated, the atom must be neutral. • # electrons = # protons = Atomic Number • Atomic number is 17, so… there are 17 electrons to fill. • Draw all boxes for a subshell when you add the first electron to that subshell • 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: • Memorize it • Use a mnemonic device • 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 • Determine the number of electrons. • Since there is no charge indicated, the atom must be neutral. • # electrons = # protons = Atomic Number • Atomic number is 11, so… there are 11 electrons to fill. • Draw all boxes for a subshell when you add the first electron to that subshell • 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 • Determine the number of electrons. • Since there is no charge indicated, the atom must be neutral. • # electrons = # protons = Atomic Number • Atomic number is 25, so… there are 25 electrons to fill. • Draw all boxes for a subshell when you add the first electron to that subshell • Follow Aufbau Principle, Pauli Exclusion Principle and Hund’s Rule to fill in the electrons. 1s 2s 2p 3p 3s 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) • Determine the number of electrons in the atom. • Follow the Aufbau Principle for filling the subhells in order. • The name of each subshell is written in order • ex 1s • Only the subshells that have electrons in them are written • 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 orbitalsand 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

Write the electron configuration for chlorine • Determine the number of electrons in the atom. 17 • Follow the Aufbau Principle for filling the subhells in order. • The name of each subshell is written in order • The number of electrons is written as a superscript after the name of the subshell 1s22s22p63s2 1s22s22p63s23p 1s22s22p63s23p5 1s 1s2 1s22s 1s22s2 1s22s22p 1s22s22p6 1s22s22p63s

Write the electron configuration for aluminum • Determine the number of electrons in the atom. 13 • Follow the Aufbau Principle for filling the subhells in order. • The name of each subshell is written in order • The number of electrons is written as a superscript after the name of the subshell 1s22s22p63s23p1

Write the electron configuration for zinc • Determine the number of electrons in the atom. 30 • Follow the Aufbau Principle for filling the subhells in order. • The name of each subshell is written in order • The number of electrons is written as a superscript after the name of the subshell 1s22s22p63s23p64s23d10

Write the electron configuration for cesium • Determine the number of electrons in the atom. 55 • Follow the Aufbau Principle for filling the subhells in order. • The name of each subshell is written in order • The number of electrons is written as a superscript after the name of the subshell 1s22s22p63s23p64s23d104p65s24d105p66s1

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 Configuration • Determine the number of electrons in the atom • 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) • Use the Aufbau Principle to fill in the remaining electrons

Write the noble gas configuration for chlorine • Determine the number of electrons in the atom 17 • Determine the noble gas to use • Use the noble gas in the previous period • Use the Aufbau Principle to fill in the remaining electrons • Don’t forget – we’ve already accounted for all the electrons before 3s [Ne]3s [Ne]3s2 [Ne]3s23p [Ne]3s23p5 [Ne]

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 • Determine the number of electrons in the atom 19 • Determine the noble gas to use • Use the noble gas in the previous period • 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 • Determine the number of electrons in the atom 33 • Determine the noble gas to use • Use the noble gas in the previous period • 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 • Determine the number of electrons in the atom 51 • Determine the noble gas to use • Use the noble gas in the previous period • 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 • Determine the number of electrons in the atom 83 • Determine the noble gas to use • Use the noble gas in the previous period • 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

4.3 Electron Structure