This document outlines key concepts about electron arrangements and the periodic table. It discusses atomic energy levels and how electrons fill these levels based on the Aufbau principle and octet rule. The periodic table is introduced as a way to arrange elements based on atomic number and properties like valence electrons. Common ion formations are explained through gaining or losing electrons to achieve stable noble gas configurations. Lewis dot structures represent valence electrons and whether they are paired or unpaired.

1. Chapter 2: Electron Arrangements and The Periodic Table
Outline:
1. Atomic Energy Levels
2. Electronic Configuration
3. The Periodic Table
4. Ions
5. Lewis Electron Dot Symbol
1. Atomic Energy Levels
 Electrons rotate around the nucleus very fast and with different energies forming
orbitals called Energy Levels/Shells.
 Stöner's Rule is used to calculate the maximum number of electrons a shell can hold.
Z= 2n2 where Z= maximum number of electrons
n= number of the shell
for shell number 1 (K) : Z= 2(1)2 = 2 e-
for shell number 2 (L): Z= 2(2)2 = 8 e-
for shell number 3 (M): Z= 2(3)2 = 18 e-
for shell number 4 (N): Z= 2(4)2 = 32 e-
etc
2. Electronic Configuration
 Definition: Is the distribution of electrons in energy levels of an atom.
As distance from nucleus increases
 the energy of es- increases

2.  Rules:
i) Electrons are filled successivley from the lowest energy level to the highest energy level.
ii) The LAST energy level in the electronic configuration should NOT occupy more than 8 electrons.
Example:
to memorize!! Terms NOTE:
Group= Valence es- = number of es- on the last shell
Period =
number of shells
Valence Shell = Last Shell
4
3
M
Example
K
L
M
N
K2 L8 M8 N1
K2 L8 M9
K2 L8 M10
K2 L8 M8 N2

3. 3. The Periodic Table
 Definition: is a tabular arrangement of the chemical elements in the increasing order of atomic number (Z)
 Properties:
 Elements to the LEFT of the stairstep line (EXCEPT Hydrogen) are metals, where as elements to the RIGHT of the stairstep line are non-metals.
 Elements on the stairstep line are metalloids/ semi-metals.
 Elements belonging to the same group/column have the same number of valence es-.
 Elements belonging to the same period/row have the same number of shells.
 Elements of group I / column 1 are called Alkali metals (EXCEPT Hydrogen).
 Elements of group II/ column 2 are called Alkaline Earth metals.
 Elements of group VII/ column 17 are called Halogens.
 Elements of group VIII/ column 18 are called Nobel Gases or Inert Gases.
 Elements belonging to the same column possesses similar chemical properties.
Period= Row
Group (in Roman) = Column (-10 for more than column 13)
Stairstep Line

4. NOTE:
4. Ions
 Definition: Atoms are electrically neutral, yet they seek to become stable as the noble gases. So, atoms could lose or gain electrons and thus changed into ions according to two rules:
NOTE: 1H, 3Li, 4Be and 5B satisfy Deut Rule, while all other atoms satisfy
Octet Rule.
Where P=Period C=Column

5.  How to know if the atom will LOSE or GAIN electrons?
 Classification of Ions:
Anions
Cations
Atoms that gained es-
Atoms that lost es-
Definition
Since p+<es-
Then negatively charged
Since p+>es-
Then positively charged
Charge
X + n es-  X n-
X  X n+ + n es-
Ionic reaction
V, VI, and VII become anions
I, II, and III become cations
Group
V : 3
VI : 2
VII : 1
I : 1
II : 2 III : 3
Valency = number of es- lost or gained
5. Lewis Electron Dot Symbol
 Definition: It's the chemical symbol of an atom surrounded by its valence electrons as dots in an anti clockwise manner.
Lose 1 electron
Lose 2 electron
Lose 3 electron
Gain 1 electron
Gain 2 electron
Gain 3 electron
STABLE

6.  Example:
NOTE:
Lewis elctron dot symbol of Helium is and not
The number of unpaired electrons in a lewis electron dot symbol is equals to the valency.
Lewis electron dot symbol
Valence electrons
Electronic configuration
Atom
2
K2L2
4Be
5
K2L5
7N
1
2
3
4
5
6
7
8
Paired es- = Lone pair Unpaired e- = Free e-