The International School of Panama

General Chemistry Notes: Chapter 5 – Part II

Electron Configuration

Before we go on, answer questions 13 to 17 on page 134

The electron configuration is the arrangement of the elements in an atom.

The ground state electron configuration is the most stable, lowest-energy arrangement of the electrons in atoms of each element.

The aufbau principle states that electrons occupy the lowest energy orbital available.

http://www.iun.edu/~cpanhd/C101webnotes/modern-atomic-theory/aufbau-principle.html

Remember the following points:

· As the principal energy level increases the energy increases too.

Example: 3p orbitals have higher energy than 2p orbitals.

· The same types of orbitals in the same level of energy have the same energy.

Example: all 2p orbitals have the same energy.

· Different types of orbitals in the same energy level have different energy and are known as sublevels

Example: 2p orbitals have higher energy than 2s orbitals

· The sequence of energy sublevels within a principal energy level is s, p, d, and f

· Some sublevels of a principal level can overlap with sublevels of another principal level.

Example: 3d orbitals are more energetic than 4s orbitals.

Remember also the amount of orbitals and of each type per level:

Subshell Type	Number of Orbitals	Maximum Number of Electrons
s	1	2
p	3	6
d	5	10
f	7	14

The Pauli exclusion principle states that a maximum of 2e- may occupy a single atomic orbital but only if they have opposite spins.

The periodic table is divided into s, p, d and f blocks-

http://library.tedankara.k12.tr/chemistry/vol3/Ground-state%20electron%20configurations/z58.htm

The s block starts by level 1 of energy

The p block starts by level 2 of energy

The d block starts by level 3 of energy

The f block starts by level 4 of energy

Writing the electron configuration

Notation:

First method- using only the periodic table

1. Find the element in the PT

1. Start filling the orbitals, starting by 1s (Hydrogen position) following the order of increasing atomic number until the position of the element you are doing. The periodic table tells you the level, block and amount of electrons as you move following the order of increasing atomic number. The table also tells you the level and block of the last electron in the given atom.

Element Electron Configuration

H (Z = 1): 1s¹

The coefficient is the level of energy

The letter s is the type of orbital

The superscript is the amount of electrons in the orbital. (Remember that the maximum number of electrons per orbital is two)

Element Electron Configuration Element Electron Configuration

He (Z = 2): 1s²

Li (Z = 3): 1s² 2s¹

Be (Z = 4): 1s² 2s²

B (Z = 5): 1s² 2s² 2p¹

C (Z = 6): 1s² 2s² 2p²

N (Z = 7): 1s² 2s² 2p³

O (Z = 8): 1s² 2s² 2p⁴

F (Z = 9): 1s² 2s² 2p⁵

Ne (Z = 10): 1s² 2s² 2p⁶

Mg (Z = 12): 1s² 2s² 2p⁶3s²

P (Z = 15): 1s² 2s² 2p⁶3s²3p³

Cl (Z = 17): 1s² 2s² 2p⁶3s²3p⁵

Ar (Z = 18): 1s² 2s² 2p⁶3s²3p⁶

V (Z = 23): 1s² 2s² 2p⁶3s²3p⁶4s²3d³

Ge (Z = 7): 1s² 2s² 2p⁶3s²3p⁶4s²3d¹⁰4p²

Kr (Z = 7): 1s² 2s² 2p⁶3s²3p⁶4s²3d¹⁰4p⁶

1. First get the atomic number Z. The atomic number tells you the number of electrons in the atom.

2. Use the following diagram to fill the orbitals in the correct order and finish when you completed the number of e- for the given element.

Write the electrón configuration of the elements Zinc and Silver, using the afbau diagram...

Another way of representing the electrons in an atom is the use of orbital diagrams. The orbital diagrams are boxes in which an arrow up represents one electron in the box, with an specific spin, and two arrows, one up and one down, represents two electrons in the orbital with opposite spins.

When you start filling equivalent orbitals in the same level apply the Hund’s rule.

Hund’s rule states that single electrons with the same spin may occupy each equal-energy orbital before additional electrons with opposite spins can occupy the same orbital. In other words: If two or more energetically equivalent orbitals are available (same level, same sublevel), then electrons should be spread out before they are paired up.

The electron configuration can also be written in short form by putting, between brackets, the noble gas before the given element and continue the electron configuration from there.

Valence electrons: are the electrons in the atom’s outermost s p orbitals (associated with the atoms highest principal energy level).

Electron dot structure: Consists of the element’s symbol which represents the nucleus of the atom and the inner electrons, surrounded by dots representing the atom’s valence electrons.

Electron Configuration

Subshell Type