P4

• Who originally proposed the idea that everything is made up of tiny particles that cannot be broken down further?

  Democritus
• What is located at the center of every atom?

  The nucleus
• What are isotopes?

  Forms of an element with different numbers of neutrons
• What is the unit of measurement for activity in radioactive materials?

  Becquerels
• Around what year did Democritus propose his atomic theory?

  500 BC
• What is the charge of a proton?

  Positive (+1)
• Why is the decay process of radioactive isotopes considered random?

  Because we cannot predict when any individual isotope will decay
• Why are most isotopes unstable?

  They undergo radioactive decay to become more stable
• What is the charge of a neutron?

  Neutral (0)
• What did John Dalton suggest about atoms in the 1800s?

  Atoms are solid spheres, and different types of spheres make up different elements
• What does one becquerel represent?

  One decay per second
• What does it mean for a material to be radioactive?

  It consists of unstable isotopes that can decay
• What is the relative mass of a proton or neutron?

  1
• Who proposed the plum pudding model of the atom?

  J.J. Thompson
• What is the relationship between the number of radioactive nuclei and the activity of a sample?

  Fewer radioactive nuclei result in lower activity
• What are the four types of nuclear radiation?

  Alpha particles, beta particles, gamma rays, neutrons
• What is the charge of an electron?

  Negative (-1)
• What did J.J. Thompson's experiments show about atoms?

  Atoms contain negatively charged particles (electrons)
• What is the composition of an alpha particle?

  Two protons and two neutrons
• What are the two definitions of half-life?

  Time for nuclei to halve or activity to halve
• How much smaller is an electron compared to a proton or neutron?

  About 2000 times smaller
• What did Ernest Rutherford and his students fire at a thin sheet of gold in their experiment?

  Positively charged alpha particles
• Why are alpha particles strongly ionizing?

  They have a strong charge and large size
• What is the term for the boxes on the periodic table that represent elements?

  Nucleus symbol
• If a sample has an activity of 600 becquerels, how many decays occur each second?

  600 decays per second
• How far can alpha particles travel in air?

  A few centimeters
• What does the elemental symbol represent in a periodic table box?

  The element
• What did Rutherford's gold foil experiment reveal about the atom?

  Atoms have a compact nucleus containing all the positive charge
• Why does the rate of decay decrease over time in a radioactive sample?

  Because fewer radioactive nuclei remain to decay
• Where is the atomic number located in a periodic table box?

  Bottom left
• What can stop alpha particles?

  A single sheet of paper
• What was the flaw in Rutherford's nuclear model of the atom?

  Nothing stopped electrons from collapsing into the nucleus
• What is a beta particle?

  An electron
• If the half-life of a radioactive sample is 2 hours, how long will it take for the activity to drop from 600 to 150 becquerels?

  4 hours
• What does the atomic number represent?

  Number of protons
• How are beta particles produced?

  A neutron decays into a proton and an electron
• What did Niels Bohr propose to fix the flaw in Rutherford's model?

  Electrons orbit the nucleus in shells, preventing collapse
• What device is used to measure the activity of a radioactive sample?

  Geiger-Muller tube
• Why is the atomic number important?

  It determines the element
• What is the charge of a beta particle?

  -1