atomic structure and the periodic table

• What are atoms?

  Atoms are the smallest part of an element that can exist.
• What do chemical symbols represent?

  Chemical symbols represent an atom of an element.
• How are compounds formed?

  Compounds are formed from elements by chemical reactions.
• What do chemical reactions involve?

  Chemical reactions involve the formation of one or more new substances and often an energy change.
• What do compounds contain?

  Compounds contain two or more elements chemically combined in fixed proportions.
• How can compounds be represented?

  Compounds can be represented by formulae using the symbols of the atoms from which they were formed.
• What is the formula for hydrochloric acid?

  HCl is a compound containing 1 atom of hydrogen and 1 of chlorine per molecule.
• How can compounds be separated?

  Compounds can only be separated into elements by chemical reactions.
• What is a mixture?

  A mixture consists of two or more elements or compounds not chemically combined together.
• What happens to the chemical properties of substances in a mixture?

  The chemical properties of each substance in the mixture are unchanged.
• How can mixtures be separated?

  Mixtures can be separated by filtration, crystallisation, simple distillation, fractional distillation, and chromatography.
• What type of processes are used to separate mixtures?

  Separation of mixtures involves physical processes, so no new substances are made.
• What was the first thought about the structure of atoms?

  Atoms were thought to be tiny spheres that could not be divided.
• What model was proposed after the discovery of the electron?

  The plum pudding model was proposed, where the atom is a ball of positive charge with negative electrons embedded in it.
• What did the alpha particle scattering experiment conclude?

  The mass of an atom was concentrated at the centre (nucleus) and that the nucleus was charged.
• What was the setup of the alpha particle scattering experiment?

  A beam of alpha particles was aimed at very thin gold foil and their passage through was detected.
• What was observed during the alpha particle scattering experiment?


  Some alpha particles emerged from the foil at different angles, and some even came straight back.
• Why were some alpha particles deflected during the experiment?

  The positively charged alpha particles were being repelled and deflected by a small concentration of positive charge in the atom (nucleus).
• Who suggested that electrons orbit the nucleus at specific distances?

  Neil Bohr suggested that electrons orbit the nucleus at specific distances.
• What did later experiments reveal about the nucleus?

  Later experiments showed that the positive charge of any nucleus could be subdivided into smaller particles, each having the same amount of positive charge (protons).
• What did James Chadwick's work provide evidence for?

  James Chadwick's work provided evidence to show the existence of neutrons within the nucleus.
• What is the atomic number?

  The atomic number is the number of protons in an atom of an element.
• Do all atoms of a particular element have the same number of protons?

  Yes, all atoms of a particular element have the same number of protons.
• How do atoms of different elements differ?

  Atoms of different elements have different numbers of protons.
• What is the relative charge of a proton?

  The relative charge of a proton is +1.
• What is the relative charge of a neutron?

  The relative charge of a neutron is 0.
• What is the relative charge of an electron?

  The relative charge of an electron is -1.
• What is the overall charge of an atom?

  An atom has an overall charge of 0, so the number of protons equals the number of electrons.
• How small are atoms?

  Atoms are very small, with a radius of about 0.1 nm.
• How does the radius of a nucleus compare to that of an atom?

  The radius of a nucleus is less than 1/10,000 of that of the atom, though it holds almost all of the mass.
• What is the mass number?

  The mass number is the sum of the protons and neutrons in an atom.
• What are isotopes?

  Isotopes are atoms of the same element with different numbers of neutrons.
• How are atoms shown in the periodic table?

  Atoms are shown in the periodic table by their atomic number.
• What is relative atomic mass?

  Relative atomic mass is an average value that takes account of the abundance of the isotopes of the element.
• What is the electronic structure of an atom?

  Electrons occupy the lowest available energy levels (the shells closest to the central nucleus).
• How many electrons are in each shell for sodium?

  The electronic structure of sodium is 2, 8, 1 (2 electrons in shell 1, 8 in shell 2, and 1 in shell 3).
• What are the key differences between compounds and mixtures?

  • Compounds are chemically combined; mixtures are not.
  • Compounds have fixed proportions; mixtures do not.
  • Compounds can only be separated by chemical reactions; mixtures can be separated by physical processes.
• What are the historical models of the atom?

  1. Tiny spheres (indivisible)
  2. Plum pudding model (positive charge with embedded electrons)
  3. Nuclear model (mass concentrated in nucleus)
  4. Bohr model (electrons orbiting nucleus at specific distances)
• What are the relative masses and charges of subatomic particles?

  • Proton: Relative mass = 1, Charge = +1
  • Neutron: Relative mass = 1, Charge = 0
  • Electron: Relative mass = very small, Charge = -1
• What is the significance of isotopes in the periodic table?

  • Isotopes are atoms of the same element with different numbers of neutrons.
  • They affect the relative atomic mass of the element.
  • They are represented in the periodic table by their atomic number.