The Periodic Table (HL IB Chemistry)

• The Periodic Table is a list of all known elements arranged in order of increasing atomic number, from 1 to 118
• In addition, the elements are arranged so that atoms with the same number of shells are placed together, and atoms with similar electronic configurations in the outer shell are also placed together
  • This is achieved as follows:
    • The elements are arranged in rows and columns
    • Elements with one shell are placed in the first row (i.e. H and He)
    • Elements with two shells are placed in the second row (Li to Ne) and so on

• A row of elements thus arranged is called a period
  • The period number, n, is the outer energy level that is occupied by electrons
• In addition, the elements are aligned vertically (in columns) with other elements in different rows, if they share a similar outer-shell electronic configuration
  • The outer electrons are known as the valence electrons
  • A column of elements thus arranged is called a group

The Periodic Table

The Periodic Table showing the groups and periods

• Since the electronic configurations of H and He are unusual, they do not fit comfortably into any group
• They are thus allocated a group based on similarities in physical and chemical properties with other members of the group
  • He is placed in Group 0 on this basis
  • Hydrogen does not behave like any other element and so is placed in a group of its own

Diagram to show the s, p and f blocks in the Periodic Table

The blocks of the periodic table

• All elements belong to one of four main blocks: the s-block, the p-block, the d-block and the f-block
  • s-block elements contain only s electrons in the outer shell
  • p-block elements contain at least one p-electron in the outer shell
  • The d-block elements are all those with at least one d-electron and at least one s-electron but no f or p electrons in the outer shell (up to 5d)
  • The f-block elements are all those with at least one f-electron and at least one s-electron but no d or p electrons in the outer shell

• The physical and chemical properties of elements in the periodic table show clear patterns related to the position of each element in the table
  • Elements in the same group show similar properties, and properties change gradually as you go across a period

• As atomic number increases, the properties of the elements show trends which repeat themselves in each period of the periodic table

  • These trends are known as periodic trends and the study of these trends is known as periodicity