The Periodic Table

The Periodic Table

  • The Periodic Table is a collection of all known elements, arranged in order of increasing atomic number.

  • It is organised in rows known as periods and columns or groups.

  • Elements in the same group have similar properties because they have the same number of electrons in their outer shell.

  • The Periodic Table is split into metals (on the left) and non-metals (on the right). The metals are further divided into alkali metals, alkaline earth metals, transition metals, and post-transition metals. The non-metals include halogens and noble gases.

Atomic Structure and the Periodic Table

  • The atomic number of an element denotes the number of protons in an atom of the element.

  • The atomic mass of an element is the weighted average mass of the atoms in a naturally occurring sample of the element.

Periodic Trends

  • Atomic radius decreases across a period from left to right and increases down a group.

  • Ionisation energy – the energy required to remove an electron from an atom – increases across a period from left to right and decreases down a group.

  • Electronegativity – a measure of the ability of an atom to attract a bonding pair of electrons – also increases across a period from left to right and decreases down a group.

Chemical Reactions and Analysis

  • Elements in the same group undergo similar chemical reactions. For instance, all alkali metals react vigorously with water, producing hydroxide ions.

  • Mass spectrometry, chromatography, and spectrophotometry are analytical techniques used to determine the elements and compounds present in a substance.

  • Analysis of substances can provide evidence for theories about the structure of atoms and the arrangement of elements in the Periodic Table.

Predicting Properties and Reactions

  • Predicting properties and reactions of elements becomes possible by understanding periodic trends and similarities within a group. For example, a new element discovered in Group 1 would be expected to behave like other alkali metals.

  • By synthesising new compounds and observing their properties and reactions, scientists have been able to validate and expand on this predictive capacity.