Answer:
An atom is the smallest unit of ordinary matter that forms a chemical element. Every solid, liquid, gas, and plasma is composed of neutral or ionized atoms. Atoms are extremely small, typically around 100 picometers across. They are so small that accurately predicting their behavior using classical physics—as if they were tennis balls, for example—is not possible due to quantum effects.
Atom
Helium atom ground state
An illustration of the helium atom, depicting the nucleus (pink) and the electron cloud distribution (black). The nucleus (upper right) in helium-4 is in reality spherically symmetric and closely resembles the electron cloud, although for more complicated nuclei this is not always the case. The black bar is one angstrom (10−10 m or 100 pm).
Classification
Smallest recognized division of a chemical element
Properties
Mass range
1.67×10−27 to 4.52×10−25 kg
Electric charge
zero (neutral), or ion charge
Diameter range
62 pm (He) to 520 pm (Cs) (data page)
Components
Electrons and a compact nucleus of protons and neutrons
Explanation:
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