Developing model atom, isotopes etc

• Who proposed the idea that all matter is made up of indivisible particles called "atomos"?

  Democritus
• What did John Dalton agree with Democritus about in 1804?

  That matter is made up of atoms that cannot be broken up
• What did J.J. Thomson discover about atoms in the 1800s?

  That atoms are made up of smaller charged particles
• What was the expectation of the alpha scattering experiment based on the plum pudding model?

  That alpha particles would pass straight through the gold sheet
• What conclusion did scientists draw from the deflection of alpha particles in the gold foil experiment?

  Most of the mass of the atom is concentrated in a nucleus
• What does the nuclear model of the atom consist of?

  A positively charged nucleus surrounded by a cloud of negative electrons
• Who proposed that electrons orbit the nucleus at certain distances called energy levels?

  Niels Bohr
• What did James Chadwick prove in 1932?

  The existence of the neutron
• What is the relative charge of a proton?

  +1
• What is the relative charge of a neutron?

  0
• How does the number of protons relate to the number of electrons in an atom?

  The number of protons equals the number of electrons
• What happens to electrons when they gain energy from absorbing EM radiation?

  They move to a higher energy level, further from the nucleus
• What occurs when one or more outer electrons leave the atom?

  The atom becomes a positively charged ion
• What is the significance of new experiments in relation to atomic models?

  They may require changes to or the replacement of current models
• What are isotopes?

  Atoms with the same number of protons but different numbers of neutrons
• What is the mass number of an atom?

  The number of protons plus the number of neutrons in its nucleus
• What happens to unstable isotopes over time?

  They tend to decay into other elements and emit radiation
• What is radioactive decay?

  The process by which unstable isotopes emit radiation to become more stable
• What types of ionising radiation are emitted by radioactive substances?

  Alpha, beta, and gamma radiation
• What is ionising radiation?

  Radiation that knocks electrons off atoms, creating positive ions
• What is an alpha particle composed of?

  Two protons and two neutrons
• How far can alpha particles travel in air?

  A few centimeters
• What materials can stop alpha particles?

  A sheet of paper
• What is a beta particle?

  A fast-moving electron released by the nucleus
• How far can beta particles penetrate into materials?

  They can penetrate moderately far and have a range of a few meters in air
• What is the notation for a beta particle in nuclear equations?

  ⁰₋₁e
• What are gamma rays?

  Waves of electromagnetic radiation released by the nucleus
• How do gamma rays interact with materials?

  They penetrate far into materials without being stopped
• What can gamma rays be absorbed by?

  Thick sheets of lead or meters of concrete
• What is the atomic number of oxygen?

  8
• What is the mass number of oxygen?

  16
• How does alpha radiation work in smoke detectors?

  It uses alpha particles to create a current in a circuit
• Why are beta emitters used to test the thickness of metal sheets?

  Because they are not immediately absorbed and penetrate moderately
• What is the purpose of nuclear equations?

  To show radioactive decay using symbols
• What must balance in nuclear equations?

  The total mass and atomic numbers on both sides
• What happens to the atomic number and mass number during alpha decay?

  The atomic number decreases by 2 and the mass number decreases by 4
• How is an alpha particle represented in nuclear equations?

  As a helium nucleus: ⁴He
• What occurs during beta decay?

  A neutron turns into a proton and releases a beta particle
• What is the effect of beta decay on the mass of the nucleus?

  The mass of the nucleus does not change
• How is a beta particle represented in nuclear equations?

  As ⁰₋₁e