The Atomic Theory & Atomic Numbers

Front: Democritus

Back: A Greek philosopher who believed all matter is made of tiny, indivisible particles called atomos (atoms).

Front: Aristotle

Back: A Greek philosopher who believed matter is continuous and made of earth, water, air, and fire.

Front: Atomos

Back: The Greek word meaning indivisible; the earliest idea of the atom.

Front: John Dalton

Back: Developed the Billiard Ball Model. He said atoms are solid, indivisible spheres that make up all matter.

Front: Billiard Ball Model

Back: Dalton's model that describes atoms as solid, indivisible spheres.

Front: Dalton's Atomic Theory

Back: Matter is made of atoms, atoms of the same element are identical, atoms combine in fixed ratios, and atoms are not created or destroyed in reactions.

Front: Limitation of Dalton's Model

Back: Atoms are not actually indivisible because they contain smaller particles.

Front: J.J. Thomson

Back: Discovered the electron and proposed the Plum Pudding Model.

Front: Electron

Back: A negatively charged subatomic particle that moves around the nucleus.

Front: Plum Pudding Model

Back: Thomson's model where electrons are embedded in a positively charged sphere.

Front: Cathode Ray Tube Experiment

Back: Thomson's experiment that proved electrons exist.

Front: Limitation of the Plum Pudding Model

Back: It could not explain Rutherford's gold foil experiment.

Front: Ernest Rutherford

Back: Discovered the nucleus using the Gold Foil Experiment.

Front: Gold Foil Experiment

Back: Rutherford fired alpha particles at gold foil and discovered that atoms are mostly empty space with a dense nucleus.

Front: Nuclear Model

Back: Rutherford's model showing a tiny, positively charged nucleus surrounded by electrons.

Front: Limitation of Rutherford's Model

Back: It could not explain why electrons don't fall into the nucleus.

Front: Henry Moseley

Back: Discovered that an element's identity depends on its atomic number (number of protons).

Front: Atomic Number

Back: The number of protons in an atom. It determines the element's identity.

Front: X-ray Spectroscopy

Back: The method Moseley used to determine atomic numbers.

Front: Moseley's Contribution

Back: Reorganized the periodic table based on atomic number instead of atomic mass.

Front: Niels Bohr

Back: Proposed that electrons move in fixed energy levels around the nucleus.

Front: Bohr Model (Planetary Model)

Back: Electrons orbit the nucleus in fixed energy levels.

Front: Energy Levels

Back: Fixed paths where electrons can exist around the nucleus.

Front: Limitation of Bohr's Model

Back: It works well only for hydrogen, not atoms with many electrons.

Front: Atom

Back: The smallest unit of an element that still has the properties of that element.

Front: Proton

Back: A positively charged particle found in the nucleus.

Front: Neutron

Back: A particle with no charge found in the nucleus.

Front: Electron

Back: A negatively charged particle that moves around the nucleus.

Front: Nucleus

Back: The dense center of an atom containing protons and neutrons.

Front: Matter

Back: Anything that has mass and occupies space.

Front: Element

Back: A pure substance made of only one type of atom.

Front: Compound

Back: A substance formed when two or more elements combine in fixed ratios.

Front: Empty Space in an Atom

Back: Most of an atom is empty space surrounding the nucleus.

Front: Positive Charge

Back: The charge carried by protons.

Front: Negative Charge

Back: The charge carried by electrons.

Front: What happens when you add a proton?

Back: The atomic number increases, creating a different element.

Front: What happens when you remove a proton?

Back: The atomic number decreases, creating a different element.

Front: Carbon + 1 Proton

Back: Carbon (6) becomes Nitrogen (7).

Front: Magnesium − 1 Proton

Back: Magnesium (12) becomes Sodium (11).

Front: Which scientist first suggested atoms exist?

Back: Democritus

Front: Which scientist believed in the four elements?

Back: Aristotle

Front: Who developed the first evidence-based atomic theory?

Back: John Dalton

Front: Who discovered the electron?

Back: J.J. Thomson

Front: Who discovered the nucleus?

Back: Ernest Rutherford

Front: Who discovered atomic number?

Back: Henry Moseley

Front: Who proposed electrons move in energy levels?

Back: Niels Bohr

Front: What determines an element's identity?

Back: The number of protons (atomic number).

Front: Which subatomic particle determines the element?

Back: Protons

Front: Which subatomic particle has no charge?

Back: Neutrons

Front: Which subatomic particle is negatively charged?

Back: Electrons