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Questions and Answers
What did Democritus believe all matter was made of?
What did Democritus believe all matter was made of?
Atoms
Democritus proved his theories about atoms with experiments.
Democritus proved his theories about atoms with experiments.
False
Dalton believed that atoms could be divided into smaller substances.
Dalton believed that atoms could be divided into smaller substances.
False
Dalton's model of the atom is considered the most accurate representation of the atom.
Dalton's model of the atom is considered the most accurate representation of the atom.
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What did J.J. Thomson discover that contradicted Dalton's theory?
What did J.J. Thomson discover that contradicted Dalton's theory?
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Thomson's atomic model is often referred to as the ______ model.
Thomson's atomic model is often referred to as the ______ model.
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What did Rutherford's experiment with gold foil reveal about the atom?
What did Rutherford's experiment with gold foil reveal about the atom?
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According to Bohr's model, electrons travel in a random, unpredictable path around the nucleus.
According to Bohr's model, electrons travel in a random, unpredictable path around the nucleus.
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What replaced Bohr's model of fixed electron orbits?
What replaced Bohr's model of fixed electron orbits?
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Which of the following is NOT a subatomic particle?
Which of the following is NOT a subatomic particle?
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The atomic number of an element is determined by the number of neutrons in the nucleus.
The atomic number of an element is determined by the number of neutrons in the nucleus.
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What is the simplest atom called, which consists of one proton and one electron?
What is the simplest atom called, which consists of one proton and one electron?
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Isotopes of an element have the same number of protons but different numbers of electrons.
Isotopes of an element have the same number of protons but different numbers of electrons.
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What is the term for unstable isotopes that decay over time, emitting particles and energy?
What is the term for unstable isotopes that decay over time, emitting particles and energy?
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The weak force is primarily responsible for the stability of atoms.
The weak force is primarily responsible for the stability of atoms.
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The ______ model is considered the most current and accurate representation of the atom.
The ______ model is considered the most current and accurate representation of the atom.
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Study Notes
Atomic Theory Timeline
- Democritus (440 BCE) proposed that matter is composed of indivisible particles called atoms.
- John Dalton (1803) developed a theory that:
- All matter is composed of atoms
- Atoms of the same element are identical and different from atoms of other elements
- Atoms combine in whole number ratios to form compounds
- Atoms rearrange in chemical reactions
- J.J. Thomson (1897) discovered electrons, proposing a "plum pudding" model where electrons are embedded in a positively charged sphere.
- Ernest Rutherford (1909) performed the gold foil experiment, showing that atoms have a small, dense, positively charged nucleus with electrons orbiting around it. Most of an atom is empty space.
- Niels Bohr (1913) refined the model by proposing that electrons orbit the nucleus in specific energy levels.
- Erwin Schrödinger & Werner Heisenberg (1926): Developed the modern model—modern atomic theory. Electrons do not have fixed paths but exist in regions of probability called electron clouds.
Atomic Structure
- Atoms consist of a nucleus containing protons (positive charge) and neutrons (no charge).
- Electrons (negative charge) orbit the nucleus.
- Atomic number = number of protons.
- Mass number = number of protons + neutrons.
Isotopes
- Isotopes are atoms of the same element with different numbers of neutrons, thus different mass numbers.
- Some isotopes are stable, while others are radioactive.
- Radioactive isotopes decay over time releasing particles and energy.
Forces Within Atoms
- Gravitational force: very small force.
- Electromagnetic force: strong attraction between protons and electrons. Keeps electrons in motion around the nucleus.
- Strong force: binds protons & neutrons together in the nucleus, overcoming the electromagnetic repulsion that would cause protons to repel each other.
- Weak force: involved in radioactive decay, allows neutrons to change into protons & electrons.
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Description
Explore the significant milestones in the development of atomic theory, from Democritus' early ideas to the modern models proposed by Schrödinger and Heisenberg. This quiz covers key experiments and theories that shaped our understanding of atomic structure and behavior.
