Periodic table

• Element


  A substance that cannot be split into simpler substances by chemical means
• Greek philosophers had the idea that the universe was made up of four basic substances or elements: earth, air, water and fire
• Robert Boyle

  • He gave the first accurate definition of an element as a simple substance that cannot be broken into anything simpler
• Copper

  An example of an element that cannot be split into simpler substances by chemical means
• Water

  Not an element because it can be split into hydrogen and oxygen
• Humphry Davy


  • He discovered many elements by passing electricity through their compounds, including potassium, sodium, calcium, barium, strontium and magnesium
• Dobereiner's Triads

  Groups of three elements with similar chemical properties where the atomic weight of the middle element is approximately the average of the other two
• Newlands' Octaves

  Arrangements of elements in which the first and the eighth element, counting from a particular element, have similar properties
• Newlands' Law of Octaves worked for only about the first sixteen elements and after that some of the elements were forced into the wrong groups
• Mendeleev's Periodic Law

  When elements are arranged in order of increasing atomic weight (relative atomic mass), the properties of the elements recur periodically
• Mendeleev's Periodic Table

  • He left gaps in the table for undiscovered elements and predicted the properties of these elements
  • He reversed the order of some elements to put them in groups with similar properties
• Mendeleev arranged the elements in order of atomic weight, but realised properties were more important so he reversed the order to put elements with similar properties together
• Atomic number

  The number of protons in the nucleus of an atom
• Modern Periodic Law

  When elements are arranged in order of increasing atomic number, the properties of the elements recur periodically
• Differences between Mendeleev's Periodic Table and the modern Periodic Table

  • Elements arranged in order of increasing atomic weight vs atomic number
  • Only 60 elements vs over 100 elements
  • Contains gaps vs no gaps
  • Transition elements not in separate block vs in separate block
• Mass number

  The sum of the number of protons and neutrons in the nucleus of an atom
• Isotopes

  Atoms of the same element (same atomic number) with different mass numbers due to different numbers of neutrons
• Relative atomic mass

  The average mass of an atom of an element, measured relative to the mass of the carbon-12 isotope
• Relative atomic mass

  The average of the mass numbers of the isotopes of the element, as they occur naturally, taking their abundances into account and expressed on a scale in which the atoms of the carbon-12 isotope have a mass of exactly 12 units
• Mass spectrometer

  • Used to separate and identify isotopes, measure their relative abundances and measure the relative atomic mass of an element
• Operation of mass spectrometer

  1. Vaporisation

  2. Ionisation

  3. Acceleration

  4. Separation in a magnetic field

  5. Detection
• Principle of mass spectrometry: is that charge particles moving in a magnetic field are deflected to different extents according to their masses and are thus separated according to these masses
• Uses of mass spectrometer

  • Identify presence of isotopes
  • Measure relative abundances of isotopes
  • Measure relative atomic masses and relative molecular masses
  • Identify unknown compounds
• Bohr model of electron configuration

  Writing electron configuration in terms of main energy levels
• Electron configuration using energy sublevels

  • Each main energy level, excluding the first, consists of a number of sublevels (s, p, d, f)
  • Maximum number of electrons in an orbital is 2
  • s sublevel holds 2 electrons, p sublevel holds 6 electrons, d sublevel holds 10 electrons
• Aufbau principle

  When building up the electron configuration of an atom in its ground state, the electrons occupy the lowest available energy levels
• Individual orbital

  Can hold two electrons
• Aufbau Principle

  Electrons occupy the lowest available energy levels when building up the electronic structure of an atom
• The order in which the sublevels are filled is 1s, 2s, 2p, 3s, 3p, 3d, 4s, etc.
• The Periodic Table can be divided into s block, p block, d block and f block
• Elements in the s block have their outer electrons in an s sublevel
• Elements in the p block have their outer electrons in a p sublevel
• Elements in the d block have their outer electrons in a d sublevel
• Sublevels that are exactly half filled or completely filled have extra stability
• Flipover: This causes the electron configurations of chromium and copper to be different from what might be expected
• Ion

  An atom that has lost or gained electrons
• Hund's Rule of Maximum Multiplicity


  When two or more orbitals of equal energy are available, the electrons occupy them singly before filling them in pairs
• Pauli Exclusion Principle


  No more than two electrons may occupy an orbital and they must have opposite spin