the atom

• What are all substances made of?

  Atoms
• Why can't atoms be seen with a microscope?

  They are too tiny
• What are the three subatomic particles in an atom?

  Protons, neutrons, and electrons
• What charge do protons have?

  Positive charge
• What is the mass and charge of neutrons?

  Heavy and neutral
• What is the mass and charge of electrons?

  Hardly any mass and negatively charged
• Where is the nucleus located in an atom?

  In the middle of the atom
• What does the nucleus contain?

  Protons and neutrons
• Why does the nucleus have a positive charge?

  Because of the protons
• Where is most of the atom's mass concentrated?

  In the nucleus
• How does the size of the nucleus compare to the atom?

  The nucleus is tiny compared to the atom
• How do electrons move in an atom?

  They move around the nucleus in electron shells
• What charge do electrons have?

  Negatively charged
• What is the significance of the size of electron shells?

  It determines the size of the atom
• What is the atomic radius of electrons?

  About $10^{-10} \text{ m}$
• What is true about the number of protons and electrons in an atom?

  They are equal in number
• Why are atoms neutral?

  They have equal protons and electrons
• What happens to the charges of protons and electrons?

  The charges cancel each other out
• What is an ion?

  An atom that has lost or gained electrons
• How does the number of protons compare to electrons in an ion?

  They do not equal each other
• What does the nuclear symbol of an atom indicate?

  Atomic number and mass number
• What does the atomic number represent?

  Number of protons in an atom
• How does the number of electrons relate to the atomic number in a neutral atom?

  They are equal in number
• What does the mass number indicate?

  Total number of protons and neutrons
• How do you calculate the number of neutrons in an atom?

  Subtract atomic number from mass number
• What is the nuclear symbol for sodium?

  $^{23}_{11}Na$
• What are the relative masses and charges of the different parts of the atom?

  • Protons: heavy, positive charge
  • Neutrons: heavy, neutral
  • Electrons: tiny, negative charge
• How many electrons, protons, and neutrons are in an atom of gallium with atomic number 31 and mass number 70?

  • Electrons: 31
  • Protons: 31
  • Neutrons: 39 (70 - 31 = 39)