Atomic number and mass number

• What is the structure of an atom?

  An atom consists of a nucleus containing protons and neutrons, surrounded by electrons in shells.
• How can the numbers of subatomic particles in an atom be calculated?

  The numbers of subatomic particles can be calculated from its atomic number and mass number.
• What is the atomic number of an element?

  • The number of protons in the nucleus of an atom
  • Also called the proton number
• What does it mean that all atoms of a given element have the same number of protons?

  It means that atoms of different elements have different numbers of protons.
• What is the charge and relative mass of a proton?

  A proton has a positive charge and a relative mass of 1.
• What is the charge and relative mass of an electron?

  An electron has a negative charge and a negligible mass relative to protons and neutrons.
• Why do atoms have no overall electrical charge?

  Atoms have no overall electrical charge because they contain equal numbers of protons and electrons.
• What is the atomic number of sodium?

  The atomic number of sodium is 11.
• How many protons and electrons does a sodium atom contain?

  A sodium atom contains 11 protons and 11 electrons.
• What is the mass number of an atom?

  The mass number of an atom is its total number of protons and neutrons.
• Can atoms of different elements have the same mass number?

  Yes, atoms of different elements can have the same mass number.
• If the mass number of argon atoms is 40, what can be said about calcium atoms?

  Calcium atoms can also have a mass number of 40.
• How do you calculate the number of subatomic particles in an atom?

  • Number of protons = atomic number
  • Number of electrons = atomic number
  • Number of neutrons = mass number - atomic number
• Given a sodium atom with an atomic number of 11 and a mass number of 23, how many neutrons does it contain?

  It contains 12 neutrons (23 - 11 = 12).
• What are isotopes?

  • Atoms of the same element with different numbers of neutrons
  • They have the same atomic number but different mass numbers
• What is the significance of the atomic number in identifying elements?

  • It uniquely identifies an element
  • Determines the element's position in the periodic table