Answer:
An atom is the smallest unit of matter that retains the chemical properties of an element. Atoms are composed of a central nucleus, which contains protons and neutrons, surrounded by a cloud of negatively charged electrons.
The idea of the atom has been around for centuries, but it was not until the late 19th and early 20th centuries that scientists began to understand its structure. Some of the scientists involved in the discovery of the atom include:
John Dalton (1766-1844) - Dalton proposed the atomic theory, which stated that all matter is composed of small, indivisible particles called atoms.
J.J. Thomson (1856-1940) - Thomson discovered the electron and proposed the "plum pudding" model of the atom, in which electrons are embedded in a positively charged sphere.
Ernest Rutherford (1871-1937) - Rutherford conducted the gold foil experiment, which led to the discovery of the nucleus and the proposal of the nuclear model of the atom.
Niels Bohr (1885-1962) - Bohr proposed the planetary model of the atom, in which electrons orbit the nucleus in discrete energy levels.
The particles that atoms are composed of are protons, neutrons, and electrons. Protons have a positive charge and are located in the nucleus, while neutrons have no charge and are also located in the nucleus. Electrons have a negative charge and orbit the nucleus in shells or energy levels.
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