Atomic Structure and the Periodic Table

Understanding Atomic Structure

Atoms are the fundamental building blocks of all matter. They are composed of three main subatomic particles:

• Protons: Positively charged particles located in the nucleus
• Neutrons: Neutral particles also found in the nucleus
• Electrons: Negatively charged particles orbiting the nucleus

The number of protons in an atom determines its element, while the number of neutrons creates different isotopes of that element.

Atomic Models

Throughout history, various models have been proposed to explain the structure of atoms:

• Dalton's Atomic Theory: Proposed that atoms are indivisible and indestructible
• Thomson's Plum Pudding Model: Atoms are positively charged with negative electrons embedded in them
• Rutherford's Nuclear Model: Atoms have a dense, positively charged nucleus with electrons orbiting around it
• Bohr's Planetary Model: Electrons orbit the nucleus in distinct energy levels

The Periodic Table

The periodic table arranges elements in order of increasing atomic number, reflecting their atomic structure. Key features include:

• Groups (Vertical Columns): Elements in the same group share similar properties due to having the same number of outer electrons (valence electrons)
• Periods (Horizontal Rows): Elements in the same period have the same number of electron shells
• Metals and Non-Metals: Metals are generally found on the left side of the periodic table, while non-metals are on the right side. Their properties differ due to their varying ability to lose or gain electrons.

Worked Example

Problem: Identify the element with 8 protons, 8 neutrons, and 8 electrons.

Solution:

• The number of protons (8) determines the element: Oxygen (O)
• The number of neutrons (8) and protons (8) gives the mass number (16)
• Since the number of electrons equals the number of protons, the atom is electrically neutral
• Therefore, the element described is Oxygen-16 (¹⁶O), a stable isotope of oxygen.