Structure of the atom

• What is the approximate radius of an atom?

  About $1 \times 10^{-10}$ metres
• What is the modern view of an atom?

  An atom consists of a positively-charged nucleus containing protons and neutrons, with electrons orbiting outside.

  
• What are the charges and masses of protons, neutrons, and electrons?

  Proton: +1 charge, mass 1; Neutron: 0 charge, mass 1; Electron: -1 charge, mass close to 0 (1/2000).
• Which particles make up most of the mass of an atom?

  Protons and neutrons make up most of the mass of an atom.
• What defines an element in terms of atomic structure?

  The number of protons defines the element.
• How many protons does uranium have?

  Uranium has 92 protons.
• What is the mass number of an atom?

  The mass number is the total number of protons and neutrons in an atom.
• What is the atomic number of an atom?

  The atomic number is the number of protons in an atom.
• What is another name for mass number?

  Mass number can also be called 'nucleon number'.
• What is another name for atomic number?

  Atomic number can also be called 'proton number'.
• In a neutral atom, how do the number of electrons compare to protons?

  In a neutral atom, the number of electrons is always the same as the number of protons.
• What happens to the number of electrons when an atom becomes ionized?

  The number of electrons changes when an atom becomes ionized.
• What is an ion?

  An ion is an atom that has lost or gained one or more electrons.
• What information do mass number and atomic number provide about an atom?

  • Mass number: total number of protons and neutrons
  • Atomic number: number of protons
• How can an atom be represented using symbol notation?

  An atom can be represented as $^{Z}_{A}X$, where Z is the mass number, A is the atomic number, and X is the symbol.
• How is chlorine represented in atomic notation?

  Chlorine can be represented as $^{35}_{17}Cl$.

  
• What does the atomic notation $^{35}_{17}Cl$ indicate about chlorine?


  It indicates that chlorine has 35 particles in the nucleus, 17 of which are protons, and 18 neutrons.

  
• How many electrons does a neutral chlorine atom have?

  A neutral chlorine atom has 17 electrons.