Periodic Table of the Elements: Structure and Use in GOB Chemistry

Periodic Table of the Elements

Introduction to the Periodic Table

The periodic table is a systematic arrangement of all known chemical elements, organized by increasing atomic number. It is a foundational tool in chemistry, including General, Organic, and Biological (GOB) Chemistry, for understanding element properties, trends, and relationships.

• Element Symbol: A one- or two-letter abbreviation representing each element (e.g., H for hydrogen, Na for sodium).

• Atomic Number (Z): The number of protons in the nucleus of an atom, unique to each element.

• Atomic Mass: The weighted average mass of an element's naturally occurring isotopes, expressed in atomic mass units (amu).

• Element Name: The full name of the element (e.g., Carbon, Oxygen).

• Electronegativity: A measure of an atom's ability to attract electrons in a chemical bond (not always shown on all tables).

Organization of the Periodic Table

• Groups (Columns): Vertical columns numbered 1-18 (or labeled with A/B notation). Elements in the same group have similar chemical properties.

• Periods (Rows): Horizontal rows numbered 1-7. Elements in the same period have the same number of electron shells.

• Main Group Elements: Groups 1A-8A (1, 2, 13-18) are called representative elements.

• Transition Metals: Groups 3B-2B (3-12) are transition elements, often forming colored compounds and variable oxidation states.

• Inner Transition Metals: The lanthanides and actinides, shown separately at the bottom.

Key Features and Trends

• Metals, Nonmetals, and Metalloids:

  • Metals: Located on the left and center; good conductors, malleable, ductile.

  • Nonmetals: Located on the right; poor conductors, brittle in solid form.

  • Metalloids: Elements with properties intermediate between metals and nonmetals (e.g., Si, B).

• Periodic Trends:

  • Atomic Radius: Decreases across a period, increases down a group.

  • Ionization Energy: Increases across a period, decreases down a group.

  • Electronegativity: Increases across a period, decreases down a group.

Reading an Element Box

Each element box typically contains:

• Atomic Number (top): Number of protons.

• Element Symbol (center): Abbreviation.

• Element Name (below symbol): Full name.

• Atomic Mass (bottom): Average mass.

For example, the element box for Nickel (Ni) would show:

• Atomic number: 28

• Symbol: Ni

• Name: Nickel

• Atomic mass: 58.69

Example: Calculating the Number of Subatomic Particles

• Protons: Equal to the atomic number.

• Neutrons: Atomic mass (rounded to nearest whole number) minus atomic number.

• Electrons: Equal to protons in a neutral atom.

Example: For Carbon (C), atomic number = 6, atomic mass ≈ 12.

• Protons = 6

• Neutrons = 12 - 6 = 6

• Electrons = 6 (neutral atom)

Table: Classification of Elements

Type	Location	Examples	Properties
Metals	Left and center	Na, Fe, Cu	Conductive, malleable, shiny
Nonmetals	Right	O, N, Cl	Poor conductors, brittle
Metalloids	Stair-step line	B, Si, As	Intermediate properties

Formulas and Equations

• Atomic Number: $Z = \text{number of protons}$

• Mass Number: $A = \text{number of protons} + \text{number of neutrons}$

• Number of Neutrons: $\text{Neutrons} = A - Z$

Applications in GOB Chemistry

• Understanding the periodic table is essential for predicting element reactivity, bonding, and chemical behavior in biological and environmental systems.

• Periodic trends help explain why certain elements are found in biological molecules (e.g., C, H, O, N in proteins and nucleic acids).