Atom
Atom and Atomic Theory
The term atom refers to the smallest constituent unit of ordinary matter that has the properties of a chemical element. Every solid, liquid, gas, and plasma is composed of neutral or ionized atoms. Atoms are incredibly small, typically around 100 picometers (a ten-billionth of a meter) across. They are composed of a dense core called the atomic nucleus surrounded by a space populated by orbiting electrons.
Atomic Structure
The atomic structure is primarily made up of three particles: protons, neutrons, and electrons. The nucleus, at the center of the atom, is composed of protons and neutrons and accounts for most of the atom's mass. Surrounding the nucleus is a cloud of electrons, which are negatively charged particles. The number of protons in the nucleus, known as the atomic number, defines the element. For example, a hydrogen atom has one proton, while helium has two.
Nucleus
The concept of the atomic nucleus was discovered by Ernest Rutherford in 1911. This dense region within the atom contains protons and neutrons, which are collectively known as nucleons. The number of protons equates to the atomic number, which uniquely identifies a chemical element, while the sum of the protons and neutrons gives the mass number.
Electrons
Electrons are subatomic particles that orbit the nucleus in various orbits or shells. The arrangement of these electrons around the nucleus, known as the electronic configuration, is crucial because it determines the chemical properties and reactivity of the atom. The interaction of electrons between different atoms plays a key role in forming chemical bonds, the basis of chemistry.
Atomic Theory
Atomic theory is the scientific theory of the nature of matter, which states that matter is composed of discrete units called atoms. The origins of atomic theory trace back to ancient philosophers like Democritus, but it was not until the early 19th century that John Dalton formulated a coherent scientific theory of atoms.
Historical Development
- Dalton's Atomic Theory: Around 1805, Dalton proposed that each element is composed of indivisible and indestructible atoms, unique to each element in mass and properties.
- Thomson's Model: The discovery of the electron led J.J. Thomson to propose the plum pudding model, which suggested that atoms consist of electrons within a "soup" of positive charge.
- Rutherford's Model: Rutherford proposed that the atom has a small, dense nucleus with electrons orbiting around it.
- Bohr Model: Niels Bohr introduced the Bohr model in 1913, which incorporated quantum theory to describe electron orbits as discrete energy levels.
- Quantum Mechanical Model: The current model of the atom is based on quantum mechanics, which considers the probability distribution of electrons rather than defined paths, as explained by the Schrödinger equation.
Modern Atomic Theory
Modern atomic theory comprises various sophisticated models to explain atomic and subatomic phenomena. The quantum mechanical model uses mathematical functions to determine the likelihood of finding an electron in a particular location around the nucleus. The development of quantum chemistry has furthered the understanding of atomic interactions, fostering the advancement of materials science, pharmacology, and other fields.