Electron Configurations and Periodic Properties: Week 3 Study Notes

Electron Configurations

Introduction to Electron Configurations

Electron configurations describe the arrangement of electrons in the orbitals of an atom. The order in which sublevels are filled follows the increasing energy levels, which can be visualized using the periodic table.

• Electron configuration is a notation that shows the placement of electrons in atomic orbitals.

• Electrons fill energy levels and sublevels in order of increasing energy: s < p < d < f.

• Abbreviated configurations use noble gas symbols to represent filled inner shells.

Periodic Table Blocks and Electron Filling Order

The periodic table is divided into blocks (s, p, d, f) that correspond to the type of atomic orbital being filled.

• s block: Groups 1A and 2A; final electrons enter s sublevel.

• p block: Groups 3A to 8A; final electrons enter p sublevel.

• d block: Transition metals; final electrons enter d sublevel.

• f block: Inner transition metals; final electrons enter f sublevel.

Orbital Diagrams

Drawing Orbital Diagrams

Orbital diagrams use boxes to represent orbitals and arrows to represent electrons. They help visualize electron arrangement and spin.

• Draw boxes for each orbital in a sublevel (e.g., one for s, three for p).

• Fill orbitals from lowest to highest energy.

• Place electrons in orbitals singly before pairing (Hund's rule).

• Paired electrons have opposite spins (represented by up and down arrows).

Example: Orbital Diagram for Carbon

Carbon (atomic number 6):

• Configuration: $1s^2 2s^2 2p^2$

• Diagram: 1s and 2s orbitals are filled (paired arrows), 2p has two unpaired electrons (single arrows in two boxes).

Electron Configurations for Periods 1 and 2

Period 1: Hydrogen and Helium

Element	Atomic Number	Orbital Diagram	Electron Configuration
H	1	1s (↑)	$1s^1$
He	2	1s (↑↓)	$1s^2$

Period 2: Lithium to Neon

Element	Atomic Number	Orbital Diagram	Electron Configuration	Abbreviated Configuration
Li	3	1s (↑↓), 2s (↑)	$1s^2 2s^1$	[He]$2s^1$
Be	4	1s (↑↓), 2s (↑↓)	$1s^2 2s^2$	[He]$2s^2$
B	5	1s (↑↓), 2s (↑↓), 2p (↑)	$1s^2 2s^2 2p^1$	[He]$2s^2 2p^1$
C	6	1s (↑↓), 2s (↑↓), 2p (↑,↑)	$1s^2 2s^2 2p^2$	[He]$2s^2 2p^2$
N	7	1s (↑↓), 2s (↑↓), 2p (↑,↑,↑)	$1s^2 2s^2 2p^3$	[He]$2s^2 2p^3$
O	8	1s (↑↓), 2s (↑↓), 2p (↑↓,↑,↑)	$1s^2 2s^2 2p^4$	[He]$2s^2 2p^4$
F	9	1s (↑↓), 2s (↑↓), 2p (↑↓,↑↓,↑)	$1s^2 2s^2 2p^5$	[He]$2s^2 2p^5$
Ne	10	1s (↑↓), 2s (↑↓), 2p (↑↓,↑↓,↑↓)	$1s^2 2s^2 2p^6$	[He]$2s^2 2p^6$

Step-by-Step Guide to Drawing Orbital Diagrams

Steps for Drawing Orbital Diagrams

1. Draw boxes to represent the occupied orbitals.

2. Place a pair of electrons with opposite spins in each filled orbital.

3. Place remaining electrons in the last occupied sublevel in separate orbitals (Hund's rule).

Example: Nitrogen (N) Orbital Diagram

• Nitrogen atomic number: 7

• Configuration: $1s^2 2s^2 2p^3$

• Diagram: 1s (↑↓), 2s (↑↓), 2p (↑,↑,↑)

Additional info: These notes cover foundational concepts in GOB Chemistry, including electron configurations, orbital diagrams, and their relationship to the periodic table. The tables and diagrams are reconstructed for clarity and completeness.