Atoms and Nuclei — Definition
Definition
Imagine zooming into any object around you – a piece of metal, a drop of water, even your own body. If you keep zooming in, you'll eventually reach tiny, invisible particles called atoms. For a long time, people thought atoms were the smallest, indivisible units of matter, hence the name 'atomos' meaning 'uncuttable' in Greek.
However, modern physics has revealed that atoms themselves have an intricate internal structure. At the very heart of every atom lies a tiny, incredibly dense core called the nucleus. This nucleus is positively charged and contains two types of particles: protons, which carry a positive charge, and neutrons, which have no charge at all.
Together, protons and neutrons are called nucleons. The number of protons in the nucleus determines the element an atom belongs to – for example, all hydrogen atoms have one proton, all helium atoms have two, and so on.
This number is known as the atomic number (Z). The total number of protons and neutrons in the nucleus is called the mass number (A). Surrounding this central nucleus, like planets orbiting a star, are much lighter, negatively charged particles called electrons.
These electrons occupy specific energy levels or 'shells' around the nucleus. The attractive force between the positively charged nucleus and the negatively charged electrons holds the atom together. In a neutral atom, the number of electrons is equal to the number of protons, balancing the charges.
The study of how these electrons are arranged and how they interact with the nucleus and with each other is what we call atomic physics. When we delve deeper into the nucleus itself – its composition, stability, the powerful forces holding it together, and how it can transform (like in radioactivity or nuclear reactions) – that's the domain of nuclear physics.
Both atomic and nuclear physics are fundamental to understanding the universe at its most basic level, explaining everything from the light emitted by stars to the energy released in nuclear power plants.