Summary of the structure of the Periodic Table

1. Summary of the structure of the Periodic Table

1a. The basic structure of the Periodic Table

See the notes 1. to 4. in the full Periodic Table at the end of this page.

• The idea of the Periodic Table is to arrange the elements in a way that enables chemists to understand patterns in the properties of elements, but some reminders first.
• An ATOM is the smallest particle of a substance which can have its own characteristic properties, BUT atoms are built up of even more fundamental sub-atomic particles - the electron, proton and neutron and the structure of an atom ultimately determines its properties.
• An ELEMENT is a pure substance made up of only one type of atom, 92 of the elements in the Periodic Table (part of which is shown above) naturally occur, from hydrogen H (element 1) to uranium U (element 92).
• Note that each element has symbol which is a single capital letter like H or U or a capital letter + small letter e.g. cobalt Co, chlorine Cl or sodium Na.
• The majority of elements are readily divided into two types with common characteristic physical and chemical properties.
  • Most elements on the left are METALS and their typical properties are described in section 2a. e.g. elements 3 to 4 (lithium to beryllium), elements 11 to 13 (sodium to aluminium), elements 19 to 31 (potassium to gallium), elements 37 to 50 (rubidium to tin).
  • The elements on the right are NON-METALS and their typical properties are described in section 2b. e.g. elements 1 to 2 (hydrogen to helium), elements 5 to 10 (boron to neon), elements 15 to 18 (phosphorus to argon), elements 35 to 36 (bromine to krypton).
  • BUT a few elements are referred to as SEMI-METALS which have mixed metal/non-metal character and not so easy to classify, see section 2c. They occur in a diagonal band (down and L to R) e.g. silicon (₁₄Si), germanium (₃₂Ge), arsenic (₃₃As) and tellurium (₅₂Te).
• The elements are laid out in order of Atomic (proton) Number* (*see atomic structure page).
  • Originally they were laid out in order of 'relative atomic mass' (the old term was 'atomic weight').
  • This is not correct for some elements now that we know their detailed atomic structure (detailed GCSE notes) in terms of protons, neutrons and electrons, and of course, their chemical and physical properties.
  • For example: Argon (at. no. 18, electrons 2,8,8) has a relative atomic mass of 40. Potassium (at. no. 19, electrons 2,8,8,1) has a relative atomic mass of 39. Argon, in terms of its physical, chemical and electronic properties is clearly a Noble Gas in Group 8 (0). Likewise, potassium is clearly an Alkali Metal in Group 1.
• Many of the similarities and differences in the properties of elements can be explained by the electronic structure of the atoms (electron configuration = electron arrangement in shells or energy levels, so watch out the varying phrases used!).
• The idea of the Periodic Table is to arrange the elements in a way that enables chemists to understand patterns in the properties of elements.
• The main structural features of the periodic table are ...
  • to produce columns of similar elements called Groups.
    • They are usually similar chemically and physically BUT there are often important trends in physical properties and chemical reactivity up/down a group.
  • The resulting complete horizontal rows are called Periods and usually consist of a range of elements of different character.
    • There are important trends from left to right across a period e.g. the most important overall change is from metallic ==> non-metallic element character.
    • Certain 'horizontal blocks' of elements within a period, which have specific chemical features in common, may be known as a particular block or series e.g. from ₂₁Sc to ₃₀Zn are called the 1st Transition Metal Series within period 4.