Atoms

• Atom


  Tiniest particle of matter
• Atom

  • Made up of protons, neutrons and electrons
  • Protons, neutrons and electrons are the subatomic particles
• Element


  A pure substance, for example oxygen (O2)
• Compound

  A material that is made up of more than one type of atom chemically bonded together, for example Carbon Dioxide (CO2)
• Mixture

  Contains two or more different types of compounds or elements that are not chemically bonded together
• If two identical elements combine, then the name doesn't change
• When two elements join, the ending is usually -ide
• When three or more elements combine and one of them is oxygen, the ending is -ate
• Atomic number

  Number of protons = number of electrons
• Mass number

  Number of protons + neutrons
• Protons have a relative charge of +1, electrons have a relative charge of -1, neutrons have no charge
• Atoms contain an equal number of protons and electrons so carry no overall charge
• Atoms of the same element have the same number of protons (and hence electrons) in their atoms
• Number of neutrons

  Mass number - atomic number
• Electronic structure

  • Electrons occupy the lowest available energy levels (the shells closest to the central nucleus)
  • Electronic structure of an atom tells you how many electrons are in each shell
  • Maximum number of electrons in first 3 shells are: 2, 8, 8
• Isotopes

  Elements that have the same number of protons but have different number of neutrons
• Relative atomic mass


  An average value that takes account of the abundance of the isotopes of the element
• Relative atomic mass is calculated using masses and abundance of each isotope
• Groups in the Periodic Table

  • Group 1
  • Group 7
  • Group 0
• Group 1 - Alkali Metals


  • Shiny (when freshly cut), soft, low density (compared to other metals), and conduct heat and electricity
  • They lose one electron to gain a full outer shell
• Alkali Metals

  • Lithium (Li)
  • Sodium (Na)
  • Potassium (K)
  • Rubidium (Rb)
  • Caesium (Cs)
  • Francium (Fr)
• The chemical reactivity of the alkali metals increases down Group 1
• Chemical Properties of Alkali Metals

  • Alkali Metal + Water → Metal Hydroxide + Hydrogen
  • Alkali Metal + Acid → Salt + Hydrogen
  • Alkali Metal + Oxygen → Metal Oxide
  • Alkali Metal + Halogen → Salt
• Group 7 - Halogens


  • Non-metals, and as elements they exist as two atoms chemically bonded together
  • They have a low density, and low melting and boiling points
  • They gain one electron to gain a full outer shell
• Halogens


  • Fluorine (F)
  • Chlorine (Cl)
  • Bromine (Br)
  • Iodine (I)
• The chemical reactivity of the halogens decreases down Group 7
• Physical properties of halogens at room temperature

  • Fluorine is a toxic yellow gas
  • Chlorine is a toxic, dense green gas
  • Bromine is a dense red-brown liquid
  • Iodine is a dark grey solid
• Group 0 - Noble Gases


  • They have low densities, and low melting and boiling points and increasing melting and boiling point
  • They have full outer electron shells and don't lose or gain electrons
• Noble Gases


  • Helium (He)
  • Neon (Ne)
  • Argon (Ar)
  • Krypton (Kr)
  • Xenon (Xe)
• JJ Thomson discovered the first known subatomic particle – the electron


  1897
• Plum Pudding Model


  The atom is considered to be a solid sphere with a positive charge, and negatively charged electrons are embedded into this solid sphere
• Ernest Rutherford discovered the existence of the nucleus in the alpha particle scattering experiment


  1909
• Nuclear model

  Atoms consist of a tiny central nucleus that is dense, indivisible and strongly positively charged, surrounded by negatively charged electrons
• Niels Bohr's calculations suggested that the Nuclear model would be unstable if electrons simply surrounded the nucleus


  1913
• Bohr's model

  • Positive nucleus remains, but the surrounding electrons orbit in electron shells that are at fixed distances from the nucleus
  • The energy of electrons is lower in the shells closer to the nucleus
• Transition elements

  • Good conductors of electricity and thermal energy
  • Hard and strong
  • High density, melting point
  • Less reactive than group 1 (alkali metals)
  • Takes a long time to react
• Compounds of transition metals

  • Copper sulfate = blue CuSO4
  • Nickel carbonate = pale green NiCO3
  • Chromium oxide = dark green Cr2O3
  • Manganese chloride = pink MnCl2
  • Iron chloride = FeCl2
  • Manganese bromine = MnBr2
• Cu + O2

  CuO2
• Cu2 + O2

  CuO
• Why are transition metals good catalysts?

  They can easily donate and accept electrons from other molecules, which makes them good catalysts