Orbitals and the Periodic Table: Electron Arrangement and Chemical Properties

Electron Arrangement: The Quantum Model

Principal Energy Levels (Shells)

Atoms contain electrons arranged in distinct energy levels, called shells. These shells roughly correlate to the average distance of electrons from the nucleus. The principal quantum number (n) designates each shell.

• Definition: A shell is a set of electron energy levels surrounding the nucleus.

• Example: The first shell (n=1) is closest to the nucleus.

Sublevels (Subshells)

Each principal energy level is divided into one or more sublevels (or subshells), designated as s, p, d, and f. Each sublevel contains one or more orbitals.

• Definition: A subshell is a group of orbitals within a shell that share the same energy.

• Example: The second shell (n=2) contains both 2s and 2p subshells.

Orbitals

Orbitals are regions in space where there is a high probability of finding an electron. Each orbital can hold a maximum of two electrons.

• Definition: An orbital is a mathematical function describing the location and wave-like behavior of an electron in an atom.

• Example: The 1s orbital is spherical and closest to the nucleus.

Atomic Orbitals and Electron Capacity

Types of Orbitals

There are four main types of atomic orbitals: s, p, d, and f. Each type has a characteristic shape and electron capacity.

• s-orbital: Spherical, 1 per shell, holds 2 electrons.

• p-orbital: Dumbbell-shaped, 3 per shell (from n=2), holds 6 electrons.

• d-orbital: Clover-shaped, 5 per shell (from n=3), holds 10 electrons.

• f-orbital: Complex shapes, 7 per shell (from n=4), holds 14 electrons.

Maximum electrons per orbital: 2

Electron Capacity Table

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

what does this (number of orbitals) even mean???

Electron Configurations

Subshell Notation

Electron configuration describes the arrangement of electrons in an atom using subshell notation. This notation shows the number of electrons in each subshell.

• Format: $1s^2 2s^2 2p^6$

• Example: Nitrogen (N, atomic number 7): $1s^2 2s^2 2p^3$

Order of Filling Orbitals

Electrons fill orbitals in order of increasing energy, following the Aufbau principle. The order is determined by the sum of the principal quantum number and the sublevel type.

• Order-of-filling chart: s → p → d → f (with overlaps, e.g., 4s fills before 3d)

• Example: Oxygen (atomic number 8): $1s^2 2s^2 2p^4$

Valence Electrons

Definition and Importance

Valence electrons are the electrons in the outermost shell of an atom. They are crucial for chemical bonding and determine the chemical properties of elements.

• How to determine: Count electrons in the highest principal energy level.

• Example: Chlorine (atomic number 17): $1s^2 2s^2 2p^6 3s^2 3p^5$ (7 valence electrons) (when the orbitals of like the subshell are filled, then added it with the previous orbital)

Valence Electron Table (First 20 Elements)

Element	Atomic Number	Electron Configuration	Valence Electrons
Hydrogen	1	1s1	1
Helium	2	1s2	2
Lithium	3	1s22s1	1
Beryllium	4	1s22s2	2
Boron	5	1s22s22p1	3
Carbon	6	1s22s22p2	4
Nitrogen	7	1s22s22p3	5
Oxygen	8	1s22s22p4	6
Fluorine	9	1s22s22p5	7
Neon	10	1s22s22p6	8
Sodium	11	1s22s22p63s1	1
Magnesium	12	1s22s22p63s2	2
Aluminum	13	1s22s22p63s23p1	3
Silicon	14	1s22s22p63s23p2	4
Phosphorus	15	1s22s22p63s23p3	5
Sulfur	16	1s22s22p63s23p4	6
Chlorine	17	1s22s22p63s23p5	7
Argon	18	1s22s22p63s23p6	8
Potassium	19	1s22s22p63s23p64s1	1
Calcium	20	1s22s22p63s23p64s2	2

Periodic Table Organization

Groups and Periods

The periodic table is organized into groups (columns) and periods (rows). Elements in the same group have similar valence electron configurations and chemical properties.

• Group names: Alkali metals, alkaline earth metals, transition metals, halogens, noble gases, etc.

• Example: Group 1 elements (alkali metals) all have 1 valence electron.

Metals vs. Non-metals

Elements are classified as metals, non-metals, or metalloids based on their properties and position in the periodic table.

• Metals: Good conductors, malleable, shiny, mostly on the left and center of the table.

• Non-metals: Poor conductors, brittle, found on the right side of the table.

• Metalloids: Properties intermediate between metals and non-metals.

Key Concepts and Applications

Mole Conversions

The mole is a fundamental unit in chemistry for counting particles. It links grams, moles, and number of particles using molar mass and Avogadro's number.

• Molar mass: $\text{grams} \leftrightarrow \text{moles}$

• Avogadro's number: $6.022 \times 10^{23}$ particles/mol

• Equation: $\text{Number of particles} = \text{moles} \times 6.022 \times 10^{23}$

Visualizing Orbitals: The Hotel Analogy

Think of an atom as a hotel:

• The building = atom

• Each floor = electron shell

• Rooms on a floor = subshells

• Each room = orbital

• Each guest = electron

Summary and Takeaways

• Electrons exist in orbitals with specific energy levels.

• The periodic table is organized based on valence electrons.

• Understanding electron configurations is essential for predicting chemical bonding and element behavior.

Next class: Chemical bonds (Chapter 4)

Additional info: The notes also reference radioactivity, mole conversions, and periodic table groupings, which are foundational for introductory chemistry.