Atoms and the periodic table

• Protons and neutrons

  Particles found in the nucleus of an atom
• Atomic number


  The number of protons in the nucleus of an atom
• Mass number


  The number of protons and neutrons in the nucleus of an atom
• Nuclear symbol


  Representation of an atom that includes the atomic number and mass number
• Atom


  The smallest particle of an element that can take part in chemical reactions
• Atom


  • Neutral overall charge
  • Protons, electrons and neutrons have different properties and relative masses
• Proton


  Positively charged particle found in the nucleus
• Neutron


  Particle found in the nucleus with no charge
• Electron


  Negatively charged particle found in electron shells orbiting the nucleus
• Working out the number of neutrons in the nucleus of an atom

  Mass number - Atomic number
• Ion


  An atom with a positive or negative charge due to the loss or gain of electrons
• Compound


  A substance that contains at least two elements chemically joined together
• Element

  A substance that contains only one type of atom
• Isotopes


  Atoms of the same element that have the same number of protons but differ in the number of neutrons
• Relative Atomic Mass (RAM)


  The average mass of an atom of an element relative to 1/12 the mass of a carbon-12 atom
• Isotopes


  • X and Z
  • P and Q
• The number of protons defines the element
• Relative atomic mass is not always a whole number because it is an average mass that takes into account the relative abundance of isotopes
• Relative abundance


  The proportion or number of isotopes of an element
• Working out the relative atomic mass (RAM) of an element


  Sum of (isotope abundance x isotope mass number) / Sum of abundances of all isotopes
• The relative atomic mass of an element will lie between the highest and lowest mass of its isotopes
• Boron's relative atomic mass is 10.8 because it has two isotopes with different masses and abundances
• Calculating the relative atomic mass of chlorine

  (75% of 35Cl x 35) + (25% of 37Cl x 37) / (75% + 25%) = 35.5
• Calculating the relative atomic mass of copper

  (69% of 63Cu x 63) + (31% of 65Cu x 65) / (69% + 31%) = 63.6
• Atomic models


  • Dalton's atomic theory
  • Thomson's plum pudding model
  • Rutherford's nuclear model
  • Bohr's solar system model
• In a chemical reaction, atoms are rearranged but the law of conservation of mass still applies
• Isotopes are atoms of the same element with the same number of protons but different numbers of neutrons
• Mendeleev arranged elements in order of increasing atomic mass and left gaps for undiscovered elements, which were later filled and found to have the predicted properties
• The modern periodic table arranges elements in order of increasing atomic number, with elements in the same group having similar chemical properties
• Electron shells


  • Electrons occupy the lowest energy levels first
  • Certain shells have a maximum number of electrons allowed
• Electronic configuration


  The arrangement of electrons in the shells of an atom
• Elements in the same group have the same number of electrons in the outer shell and similar chemical properties
• Atoms in the same period have the same number of electron shells but different numbers of electrons in the outer shell
• Relative formula mass (RFM)


  The sum of the relative atomic masses of the atoms in a chemical formula
• Calculating the percentage composition by mass of an element in a compound

  Mass of element / Total mass of compound x 100