8th Grade - Chapter 4 Key Terms

  1. atom – the smallest particle of an element
  2. electron – the negatively charged particles of an atom
  3. nucleus – the tiny center region of an atom
  4. proton – the positively charged particles of an atom
  5. energy level – the specific amount of energy an electron has
  6. neutron – the electrically neutral subatomic particle of an atom
  7. atomic number – the unique number of protons in the nucleus of an atom for each element
  8. isotope – atoms with the same number of protons and different numbers of neutrons
  9. mass number – the sum of the protons and neutrons in the nucleus of an atom
  10. atomic mass – the average mass of all the isotopes of an element
  11. periodic table – a table with a regular repeating pattern that organizes all the different elements
  12. period – the horizontal rows of the periodic table
  13. group – the vertical columns of the periodic table, sometimes known as families
  14. chemical symbol –one or two letter representation of an element’s name
  15. plasma – a state of matter that consists of a gas like mixture of free electrons and nuclei
  16. nuclear fusion – a process in which two atomic nuclei combine, forming a larger nucleus and releasing huge amounts of energy
  17. metal – an element with properties such as shininess, malleability, ductility, and conductivity
  18. malleable – a material that can be hammered or rolled into flat sheets and other shapes
  19. ductile – a material that can be pulled out, or drawn, into a long wire
  20. conductivity – the ability of an object to transfer heat or electricity to another object
  21. reactivity – the ease and speed with which an element combines with other elements and compounds
  22. corrosion – the destruction of a metal through the process of rusting
  23. alkali metal – the metals listed in Group 1 of the periodic table; very reactive metals that are usually found in compounds
  24. alkaline earth metal – Group 2; reactive metals that are good electrical conductors
  25. transition metal – the elements found in Groups 3-12; most are hard and shiny and are good conductors of electricity
  26. particle accelerator – move atomic nuclei faster and faster until they have reached very high speeds
  27. nonmetal – an element that lacks most of the properties of a metal (poor conductors, dull, and brittle)
  28. diatomic molecule – a molecule that consists of two atoms
  29. halogen – Group 17 of the periodic table, “salt forming”, very reactive
  30. noble gas – Group 18 elements; they do not form compounds because they are very stable
  31. metalloid – have characteristics of both metals and nonmetals
  32. semiconductor – substances that can conduct electricity under some conditions but not under other conditions
  33. radioactive decay – the atomic nuclei of unstable isotopes release fast moving particles and energy
  34. radioactivity – the spontaneous emission of radiation by an unstable atomic nucleus
  35. alpha particle – consists of two protons and two neutrons and is positively charged
  36. beta particle – a fast moving electron given off by a nucleus during radioactive decay
  37. gamma radiation – consists of high-energy waves, similar to X-rays
  38. tracer – radioactive isotopes that can be followed through the steps of a chemical reaction or industrial processes