Atomic Structure & Periodic Table: Essential Chemistry Concepts

Atomic Structure Fundamentals

What Are Electrons?

Electrons are negatively charged particles found in all atoms and charged particles.

Thomson's Atomic Model

According to Thomson, the atom was a mass of positive charge with embedded electrons. The negatively charged electrons were distributed within this positive charge to ensure the atom was neutral.

Rutherford's Atomic Model

In Rutherford's model, the atom is formed by a very small nucleus and an electron cloud (cortex). In the nucleus, all its positive charge and almost all its mass are concentrated. In the electron cloud, electrons orbit the nucleus.

Bohr's Atomic Model

The Danish scientist Niels Bohr conducted a series of studies and concluded that electrons orbit the nucleus in specific, quantized circular orbits.

Modern Atomic Model: Orbitals

An atomic orbital is a region of space where there is a high probability of finding an electron.

Key Chemical Definitions

What Are Isotopes?

Isotopes are atoms of the same element that have the same number of protons but a different number of neutrons.

Understanding Ions: Cations & Anions

Ions are atoms that have gained or lost electrons. When an atom loses electrons, it acquires a positive charge and becomes a positive ion (cation). When an atom gains electrons, it acquires a negative charge and becomes a negative ion (anion).

Defining Chemical Elements

Elements are substances formed by only one type of atom.

What Are Chemical Compounds?

Compounds are substances formed by the chemical grouping of two or more different elements.

Molecules & Molecular Substances

A molecule is a grouping of atoms that may belong to the same element or different elements. It is the smallest unit of a substance that retains its chemical properties. A molecular substance is composed of these molecules.

The Periodic Table of Elements

Dmitri Mendeleev & The Periodic Table

Dmitri Mendeleev published the first periodic table. He arranged elements by their atomic mass and grouped them by similar properties. This became known as the periodic table of elements.

Group 1: Alkali Metals (s¹ Configuration)

• Hydrogen (H)
• Lithium (Li)
• Sodium (Na)
• Potassium (K)
• Rubidium (Rb)
• Cesium (Cs)
• Francium (Fr)

Group 2: Alkaline Earth Metals (s² Configuration)

• Beryllium (Be)
• Magnesium (Mg)
• Calcium (Ca)
• Strontium (Sr)
• Barium (Ba)
• Radium (Ra)

Group 13: Boron Group (p¹ Configuration)

• Boron (B)
• Aluminum (Al)
• Gallium (Ga)
• Indium (In)
• Thallium (Tl)

Group 14: Carbon Group (p² Configuration)

• Carbon (C)
• Silicon (Si)
• Germanium (Ge)
• Tin (Sn)
• Lead (Pb)

Group 15: Nitrogen Group (p³ Configuration)

• Nitrogen (N)
• Phosphorus (P)
• Arsenic (As)
• Antimony (Sb)
• Bismuth (Bi)

Group 16: Chalcogens (p⁴ Configuration)

• Oxygen (O)
• Sulfur (S)
• Selenium (Se)
• Tellurium (Te)
• Polonium (Po)

Group 17: Halogens (p⁵ Configuration)

• Fluorine (F)
• Chlorine (Cl)
• Bromine (Br)
• Iodine (I)
• Astatine (At)

Group 18: Noble Gases (p⁶ Configuration)

• Helium (He)
• Neon (Ne)
• Argon (Ar)
• Krypton (Kr)
• Xenon (Xe)
• Radon (Rn)