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Questions and Answers
Which model of the atom proposed that atoms are tiny, hard spheres without subatomic particles?
What is the role of neutrons in the stability of an atom?
What happens during a flame test when electrons return to their ground state?
Which type of radioactive decay involves the emission of a positron?
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What is the significance of half-life in radioactive substances?
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Which of the following statements about isotopes is true?
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Which type of radiation is known for having low penetrating power and can be used in smoke detectors?
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Electrons are found in which part of the atomic structure according to the Bohr model?
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How can exposure to extreme levels of radiation affect human health?
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What distinguishes isotopes of the same element from one another?
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Which model of the atom introduced the concept of electrons orbiting the nucleus at set distances?
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Which type of radiation is emitted when a helium nucleus is released from an unstable atom?
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During the flame test, what happens to electrons when they absorb energy?
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What is the purpose of radiation therapy in medicine?
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What is the effect of alpha radiation when it comes into contact with human skin?
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Which of the following terms describes the time required for half of a radioactive substance to decay?
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What historical contribution did J.J. Thompson make to atomic theory?
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Which of the following best describes gamma radiation?
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What happens to unstable isotopes during radioactive decay?
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Study Notes
Development of the Atomic Model
- Matter is everything that has mass and takes up space; it’s composed of atoms, the smallest building blocks of matter.
- Scientific theories are proposals that explain phenomena based on observations and experiments. They are revised or disproven through changing data over time.
- John Dalton's model: atoms are tiny, hard spheres that cannot be split up (no subatomic particles).
- J.J Thompson's model: electrons are distributed in a positive mass like a plum pudding (no empty space).
- Rutherford's model: most of the atom's mass is in the nucleus; electrons circle the nucleus, and the rest is empty space (no neutrons).
- Bohr's model: the nucleus contains protons and neutrons with electrons orbiting the nucleus at set distances (shells).
Subatomic Particles
- Protons are equal to electrons and given by the atomic number.
- Neutrons are calculated by subtracting the atomic number from the mass number.
Relative Atomic Mass
- The average mass of an atom, determined by different isotopes with different numbers of neutrons.
Isotopes
- Atoms of the same element with different numbers of neutrons.
- Isotopes have the same chemical properties but different atomic masses.
Flame Test
- Heating an element causes electrons in the ground state to jump to higher electron shells in their excited state, absorbing energy.
- When they return to the ground state, they release light energy. The bigger the jump, the more energy released, resulting in a deeper color on the rainbow.
- Each element has a unique flame test color.
Radioactivity
- Some isotopes are unstable because the forces between neutrons and protons are out of balance, causing them to undergo radioactive decay by ejecting subatomic particles.
- This turns the unstable isotope into a more stable one.
Types of Radioactive Decay
- Alpha decay: emission of a helium nucleus (2 protons, 2 neutrons) with a charge of 2+. It has low penetrating power and is used in smoke detectors.
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Beta decay:
- Positive beta decay: a proton converts into a neutron and emits a positron (opposite of an electron), used to treat bone cancer.
- Negative beta decay: A neutron converts into a proton and emits an electron with a charge of -1.
- Gamma decay: If alpha and beta decay occur and the atom is still unstable, gamma radiation takes place. Gamma radiation releases energy through high-speed electromagnetic waves (used in customs inspections).
Half-Life
- The time it takes for the radioactivity of a substance to halve.
Effects of Radiation
- Radiation can alter the DNA of cells, damaging or destroying them and leading to cancer. Extreme levels of radiation can cause death in days with symptoms such as diarrhea and hair loss.
- Alpha radiation: easily blocked by skin and only causes damage if ingested.
- Beta/Gamma radiation: can cause damage as it penetrates the skin.
Use of Radiation in Medicine
- Used in radiation therapy and x-ray radiation to treat cancer cells and diagnose problems in the body.
- Strontium-90 is used to treat bone cancer by emitting beta particles to kill cancer cells.
Nuclear Power
- Nuclear fission generates heat to produce electricity.
Atom Structure and Properties
- Matter is anything that has mass and takes up space.
- All matter is made up of atoms, which are the smallest building blocks of matter.
- Scientific theories explain phenomena based on observations and experiments, and are constantly revised or disproven as new data emerges.
Models of the Atom
- John Dalton: Proposed atoms as tiny, hard spheres that cannot be split. No subatomic particles were known at this time.
- J.J. Thomson: Discovered electrons, leading to the "plum pudding" model, where electrons are dispersed in a positive mass, like plums in a pudding.
- Rutherford: Discovered the nucleus, where the majority of the atom's mass is concentrated. Electrons orbit the nucleus, and the rest of the atom is mostly empty space.
- Bohr Model: Depicts the nucleus containing protons and neutrons, with electrons orbiting in specific, defined shells (energy levels).
Subatomic Particles
- The number of protons in an atom determines its atomic number, which is the same as the number of electrons.
- Neutrons are calculated by subtracting the atomic number from the mass number.
- Relative atomic mass: The average mass of an atom of an element. It's influenced by the presence of different isotopes.
- Isotopes: Atoms of the same element with the same number of protons, but differing numbers of neutrons. They exhibit similar chemical properties but have different atomic masses.
Flame Tests and Electronic Transitions
- When an element is heated, its electrons absorb energy and jump to higher energy levels (excited state).
- As electrons return to their ground state, they release energy in the form of light, creating unique colors for each element.
- The intensity and color of the emitted light depend on the energy difference between the energy levels.
Radioactivity and Radioactive Decay
- Unstable isotopes undergo radioactive decay, releasing particles and transforming into more stable isotopes. This happens when the forces between protons and neutrons are unbalanced.
- Alpha decay: Emission of an alpha particle (helium nucleus: 2 protons, 2 neutrons) with a charge of 2+. Alpha particles have low penetrating power and are used in smoke detectors.
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Beta decay:
- Positive beta decay: A proton transforms into a neutron, emitting a positron (anti-particle of an electron), used in treating bone cancer.
- Negative beta decay: A neutron transforms into a proton, emitting an electron with a charge of -1.
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Gamma decay: If an atom is still unstable after alpha or beta decay, it undergoes gamma decay, releasing energy in the form of high-energy electromagnetic radiation.
- Used in customs inspections.
Half-life and Effects of Radiation
- Half-life: Time taken for the radioactivity of a substance to reduce by half.
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Effects of radiation: Radiation can alter the DNA of cells, potentially damaging or destroying them, leading to cancer.
- High levels of radiation can cause death within days. Symptoms include diarrhea, hair loss, etc.
- Alpha radiation: Easily blocked by skin, harmful if ingested.
- Beta and Gamma radiation: More penetrating, can cause damage to internal tissues.
- Applications of Radiation in Medicine: Radiation therapy uses high-energy radiation to kill cancer cells. X-rays help diagnose illnesses. Isotopes like Strontium-90 are used to treat bone cancer by emitting beta particles.
Nuclear Power
- Nuclear fission generates heat through the splitting of atoms.
- This heat is used to produce steam, which drives turbines to generate electricity.
- Nuclear power is a carbon-free energy source, but it also poses risks related to radioactive waste and potential accidents.
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Description
Test your knowledge on the evolution of atomic models from Dalton to Bohr. This quiz covers key concepts about matter, subatomic particles, and relative atomic mass. Challenge yourself to understand the fundamental theories that shaped modern chemistry!
