<Tr> <Td> Diameter range: </Td> <Td> 62 pm (He) to 520 pm (Cs) (data page) </Td> </Tr> <Tr> <Td> Components: </Td> <Td> Electrons and a compact nucleus of protons and neutrons </Td> </Tr> <P> An atom is 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 extremely small; typical sizes are around 100 picometers (a ten - billionth of a meter, in the short scale). </P> <P> Atoms are small enough that attempting to predict their behavior using classical physics--as if they were billiard balls, for example--gives noticeably incorrect predictions due to quantum effects . Through the development of physics, atomic models have incorporated quantum principles to better explain and predict this behavior . </P>

What is the meaning of atom in science
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