Orbital Diagrams Electron Configurations Valence Electrons Bohrs Model
Orbital Diagrams, Electron Configurations, & Valence Electrons
Bohr’s Model: electrons would exist in different rings around the nucleus just like the planets are in different orbits around the sun. This is sometimes called the planetary model of the atom
Bohr’s Atom 7 orbits correspond to 7 periods on Periodic Table.
Which Orbit has the lowest energy? n = 1, the orbit closest to the nucleus.
Bohr’s model was replaced by the quantum mechanical model of the atom.
• This new model uses principle quantum levels that are similar to Bohr’s orbits, but are then divided into sublevels
The principle quantum level is a number from 1 -7, with 1 being the lowest energy and 7 being the highest in energy. The sublevels are s, p, d, and f
These numbers and letters correspond to the periods and the “blocks” on the periodic table.
• Each sublevel has a least one orbital. • Each orbital can hold 2 electrons
The s sublevel only has 1 orbital, and each orbital holds 2 electrons Which matches the 2 elements in each period of the s block Shape: Sphere
The p sublevel has 3 orbitals, and each orbital holds 2 electrons, for a total of 6 electrons – Matching the 6 elements in each period of the p block Shape: dumbbell or peanut
The d sublevel has 5 orbitals, and each orbital holds 2 electrons, for a total of 10 electrons – matching the 10 elements in each period of the d block Shape: clover/ double dumbbell
The f sublevel has 7 orbitals, and each orbital holds 2 electrons, for a total of 14 electrons – matching the 14 elements Funky / flower
We put together the principle quantum number and sublevel letter to talk about a specific orbital But not all sublevels are possible for each energy level.
Principle Quantum Level 1 2 3 4– 7 1 s 2 s 2 p 3 s 3 p 3 d 4 s 4 p 4 d 4 f Possible Sublevels s s, p, d, f 5 s 5 p 5 d 5 f 6 s 6 p 6 d (6 f) 7 s 7 p (7 d 7 f)
The arrangement of electrons in an atom is called an orbital diagram or electron configuration.
1) There are three rules that we must follow when making an orbital diagram (OD) or an electron configuration (EC):
A) The aufbau principle says electrons must fill lower energy levels before electrons can fill higher energy levels. This means 1 s is filled before 2 s, etc
B) The Pauli exclusion principle says that only two electrons can fill each orbital…and they must have opposite spins. No Yes
C) Hund’s rule says electrons must spread out in the orbitals of each sublevel (p, d, or f) before they double up. Yes No □□□ 2 p 2 p
2) If we use boxes to represent orbitals, then the following aufbau diagram shows all the possible places an electron could be:
Remember: s p d f has 1 orbital…. . holds 2 electrons has 3 …. . holds 6 electrons has 5 …. . holds 10 electrons has 7 …. . holds 14 electrons
Notice that the energy increases from bottom to top, High Energy Low Energy
and some of the orbitals do not fill in the same number order as the others.
Fill from the bottom to the top, spreading out the electrons before doubling them up
Helium He □ □ □ 3 p □ 3 s □ □ □ 2 p □ 2 s □ 1 s Completely Filled
Neon Ne □ □ □ 3 p □ 3 s □ □ □ 2 p □ 2 s □ 1 s Completely Filled
Argon Ar □ □ □ 3 p □ 3 s □ □ 2 s □ 1 s Completely Filled □ □ 2 p
3) The correct order of filling is: 1 s 2 s 2 p 3 s 3 p 4 s 3 d 4 p 5 s 4 d 5 p 6 s 4 f 5 d 6 p 7 s 5 f 6 d 7 p Notice: s block fills in period 1 p block fills in period 2 d block fills in period 3: which is 1 behind the actual period f block fills in period 4: which is 2 behind the actual period
n = period # s & p block fill at n d block fills at n – 1 f block fills at n - 2
4) Orbital Diagram: Orbitals are sometimes shown as boxes in a horizontal row Remember: s = 1 orbital p = 3 orbitals d = 5 orbitals f = 7 orbitals
5) Arrows are used to represent the electrons, so if two arrows go in the same box, one points up and the other points down.
Nitrogen N 7 electrons □ □ □ 2 p □ 2 s □ 1 s Becomes: □ □ □□□ 1 s 2 s 2 p
Cobalt (27 electrons – 27 arrows) □ □ □□□□□ 1 s 2 s 2 p 3 s 3 p 4 s 3 d
Cations and anions • * Ions: work the same way but remember that electrons are negative. +2 means you lost two electrons, -2 means you gained two electrons.
Try Bromine
Bromine (35 electrons) □ □ □□□□□ 1 s 2 s 2 p 3 s 3 p 4 s 3 d 4 p
Try Oxygen, O 2 - and Gallium on the back of your notes
Oxygen □ □ □□□□□ 1 s 2 s 2 p 3 s 3 p 4 s 3 d 4 p
Gallium □ □ □□□□□ 1 s 2 s 2 p 3 s 3 p 4 s 3 d 4 p
6) Electron Configuration: Instead of drawing boxes and arrows, the number of electrons in each sublevel is turned into a superscript and is written with the quantum number and the sublevel letter.
A) If all the orbitals are filled, the entire sequence would be: 1 s 2 2 p 6 3 s 2 3 p 6 4 s 2 3 d 10 4 p 6 2 10 6 2 14 10 6 5 s 4 d 5 p 6 s 4 f 5 d 6 p 7 s 2 5 f 14 6 d 10 7 p 6
Nitrogen N □ □ □□□ 1 s 2 s 2 p Becomes: 1 s 2 2 p 3
Cobalt □ □ □□□□□ 1 s 2 s 2 p 3 s 3 p 4 s Becomes: 1 s 2 2 p 6 3 s 2 3 p 6 4 s 2 3 d 7 3 d
Try Bromine, Oxygen, O 2 -, Ca 2+ and Gallium on the back of your notes
Bromine (35 electrons) □ □ □□□□□ 1 s 2 s 2 p 3 s 3 p 4 s 3 d Becomes: 1 s 2 2 p 6 3 s 2 3 p 6 4 s 2 3 d 10 4 p 5 4 p
Electron configurations for: Oxygen: 2 2 4 1 s 2 s 2 p O 2 - : 1 s 22 p 6 2+ Ca : 2 2 6 1 s 2 s 2 p 3 s 3 p Gallium: 2 2 6 2 10 1 1 s 2 s 2 p 3 s 3 p 4 s 3 d 4 p
7) Short cut: Noble gas configuration. Instead of writing out the entire electron configuration, we can use the previous noble gas to take the place of part of the electron configuration: must start with a noble gas
Example: 2 2 6 2 1 s 2 s 2 p 3 s Magnesium: Neon: 1 s 22 p 6 Noble Gas configuration: Magnesium: [Ne] 3 s 2
Example: Polonium: 1 s 22 p 63 s 23 p 64 s 23 d 104 p 65 s 24 d 105 p 66 s 24 f 145 d 106 p 4 Xenon: 1 s 22 p 63 s 23 p 64 s 23 d 104 p 65 s 24 d 105 p 6 Polonium: [Xe] 2 14 10 4 6 s 4 f 5 d 6 p
Try Bromine, Oxygen, O 2 -, Ca 2+ and Gallium on the back of your notes
Noble gas configurations Bromine [Ar] 4 s 2 3 d 10 4 p 5 Oxygen: [He] 2 s 22 p 4 O 2 -: [He] 2 s 22 p 6 Ca 2+ : [Ne] 3 s 23 p 6 Gallium: [Ar] 4 s 23 d 104 p 1
8) Valence Electrons: Electrons in the outer-most orbital – which is the highest energy level. Very important: electrons involved in chemical bonds – determine chemical properties of element
These electrons are called valence electrons.
Only the s and p block electrons are counted…so the number of valence electrons must be a number from 1 to 8
9) Electron Dot Diagrams (Lewis Dot Diagrams): The number of valence electrons makes a big difference in how the element will bond, so to make it easy to predict, we draw electron dot diagrams.
A) In an electron dot diagram, we use the symbol of the element and dots to represent the number of valence electrons. The number of dots matches the group number on the Periodic Table.
B) Only s and p electrons with the highest quantum number count for dot diagrams, even if there are d and f electrons
Lithium = So 2 1 1 s 2 s Li
Beryllium = So 2 2 1 s 2 s Be
Boron = So 2 2 1 1 s 2 s 2 p B
Carbon = [He] So 2 2 2 s 2 p C
Nitrogen = [He] So N 2 3 2 s 2 p
Oxygen = So 2 2 4 1 s 2 s 2 p O
Fluorine = So 2 2 5 1 s 2 s 2 p F
Neon = So 2 2 6 1 s 2 s 2 p or [Ne] Ne All noble gases have full outer shells: 8 valence electrons (except He which is full at 2, since it only has the s orbital)
Magnesium = 1 s 22 p 63 s 2 So
Magnesium = 1 s 22 p 63 s 2 So Mg Mg
Polonium: 1 s 22 p 63 s 23 p 64 s 23 d 104 p 65 s 24 d 105 p 66 s 2 4 f 145 d 106 p 4
Polonium: 1 s 22 p 63 s 23 p 64 s 23 d 104 p 65 s 24 d 105 p 66 s 2 4 f 145 d 106 p 4 So Po Po
Look at your Periodic Table Notice: the A The group number = theofnumber group. Anumber = the number valence of valence electrons (except for He) 1 A 8 A 2 A 3 A 4 A 5 A 6 A 7 A
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