Unraveling the Atom: From Ancient Ideas to Modern Structure

Since antiquity, attempts were made to understand matter by dividing it into its tiny parts. The Greeks called these tiny, allegedly invisible parts of matter 'atoms'.

Dalton's Atomic Theory

In 1808, John Dalton took the ideas of the Greeks and further developed them into a comprehensive theory. Key definitions and postulates from his theory include:

• Matter consists of indivisible particles called atoms.
• An element is a substance composed of identical atoms.
• A compound is a substance formed by atoms of two or more different elements combined in fixed ratios.

It is important to note that Dalton believed atoms were indivisible, a concept later disproven by the discovery of subatomic particles.

The Electrical Nature of Matter

Experiments can easily demonstrate how certain materials, when rubbed, exhibit phenomena of attraction and repulsion. These phenomena are explained by the electrical charges of matter, which can be either positive or negative. Objects that have acquired a charge of the same type repel each other, while objects with different types of charges attract. Despite these interactions, most material is electrically neutral overall.

Electrons and Protons

In early 20th-century studies, particles within atoms were identified. Electrons were found to be responsible for the negative charge. Subsequently, protons, carrying a positive charge, were also discovered. The balance or imbalance of these charges determines the overall electrical charge of an atom or ion.

Atomic Models and Structure

Various atomic models were proposed over time, each attempting to explain the distribution of particles within the atom. Ernest Rutherford, based on his groundbreaking experiments, arrived at significant conclusions, proposing his nuclear atom model:

Rutherford's Nuclear Model

1. The atom has a central core, called the nucleus, where virtually all of its positive charge and mass are concentrated.
2. The positively charged protons in the nucleus are balanced by the negative charge of electrons located outside the nucleus.
3. The nucleus contains protons equal in number to the electrons, making the atom electrically neutral.
4. Electrons revolve around the nucleus at high speed and are separated from it by a great distance, occupying mostly empty space.

Discovery of Neutrons

A problem with Rutherford's model was that the combined mass of protons and electrons did not account for the total mass of the atom. Therefore, it was assumed that other particles without an electric charge existed. These particles were later discovered and named neutrons.

Modern Atomic Structure

Consequently, the structure of the atom was refined to its current understanding:

1. A central zone, the nucleus, contains a positive charge (protons) and the majority of the atom's mass (protons + neutrons). The variable number of neutrons can lead to different isotopes of an element, affecting its atomic mass.
2. An external area, often described as an electron cloud, where electrons orbit the nucleus. The number of electrons is equal to the number of protons, ensuring the whole atom remains electrically neutral.