Atomic Structure Quiz

Dalton’s Atomic Theory

• Proposed by John Dalton in the early 19th century
• All matter is composed of atoms, which are the smallest units of an element
• Atoms of the same element are identical in mass and properties, while atoms of different elements have different properties
• Chemical reactions involve rearranging atoms in whole number ratios to form compounds
• Atoms are indivisible in chemical reactions

Key Scientists and Discoveries

• Democritus (Ancient Greek philosopher) first proposed the idea of atoms, although his theory was not based on scientific evidence.
• John Dalton (English chemist) developed the first scientific atomic theory, based on experimental observations.
• J.J. Thomson (English physicist) discovered the electron through his work on cathode rays.
• Robert Millikan (American physicist) determined the charge of the electron through his oil drop experiment.
• Ernest Rutherford (New Zealand physicist) conducted the gold foil experiment, which led to the discovery of the nucleus and the proton.
• James Chadwick (English physicist) discovered the neutron.

Atomic Structure

• Atomic Number: The number of protons in an atom's nucleus. It defines the element.
• Mass Number: The sum of protons and neutrons in an atom's nucleus.
• Atomic Mass: The average mass of all isotopes of an element, taking into account their relative abundances.
• Isotopes: Atoms of the same element that have the same number of protons (atomic number) but different numbers of neutrons. For example, Carbon-12 and Carbon-14 are isotopes of carbon.