Honors Chemistry 1.1 Study Guide

What did Democritus propose about matter?

Answer explanation

Democritus proposed that matter is composed of small, indivisible particles called atoms. He believed these atoms are the fundamental building blocks of all matter, differing in shape and size.

Who developed the first scientific atomic theory and what were its key points?

Answer explanation

John Dalton developed the first scientific atomic theory in the early 19th century. Its key points include that matter is made of atoms, atoms of the same element are identical, and compounds are formed from combinations of different atoms.

What are the three main subatomic particles and their charges?

• Protons: Positive charge (+1), in nucleus.

• Neutrons: Neutral charge (0), in nucleus.

• Electrons: Negative charge (–1), in electron cloud.

Answer explanation

The three main subatomic particles are protons, neutrons, and electrons. Protons have a positive charge (+1) and are found in the nucleus, neutrons are neutral (0) also in the nucleus, and electrons have a negative charge (–1) in the electron cloud.

How do you calculate the number of neutrons in an atom?

Answer explanation

To calculate the number of neutrons in an atom, subtract the atomic number (number of protons) from the atomic mass (rounded to the nearest whole number). Neutrons = Atomic Mass - Atomic Number.

What are isotopes?

Answer explanation

Isotopes are variants of a chemical element that have the same number of protons but different numbers of neutrons, resulting in different atomic masses. They exhibit similar chemical properties but may have different physical properties.

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What did J.J. Thomson discover and what model did he propose?

Answer explanation

J.J. Thomson discovered the electron and proposed the 'plum pudding model' of the atom, which depicted it as a sphere of positive charge with negatively charged electrons embedded within.

What did Rutherford’s gold foil experiment reveal about the atom?

Answer explanation

Rutherford’s gold foil experiment revealed that atoms have a small, dense nucleus at their center, surrounded by mostly empty space, which contradicted the plum pudding model and led to the nuclear model of the atom.

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What is the Bohr model of the atom?

Answer explanation

The Bohr model describes the atom as a small, positively charged nucleus surrounded by electrons in fixed orbits. It introduced quantized energy levels, explaining how electrons can only occupy certain energy states.

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What is the Quantum Mechanical Model?

Answer explanation

The Quantum Mechanical Model describes the behavior of electrons in atoms as wave functions, emphasizing probabilities rather than fixed orbits, and incorporates principles of quantum mechanics to explain atomic structure.

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How are electrons arranged in atoms?

Answer explanation

Electrons are arranged in atoms in energy levels or shells around the nucleus. These shells can hold a specific number of electrons, with the first shell holding 2, the second 8, and so on, following the Aufbau principle.

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