Periodic Trends – Electron Affinity and Atomic Weight


Periodic table is a table of chemical elements arranged on the basis of their atomic numbers, arrangement of electrons and recurring chemical properties. The table rows are called cycles; certain columns are called classes. The periodic table lists the elements in rows called periods, in order to increase the number of atoms.

Elements having similar properties are to be found in vertical columns called groups. The rule that elements ‘ actions can be predicted from their standpoints on the table is known as periodic law. Russian Chemist Dimitri Mendeleev announced the discovery of periodic law in 1869. There are five periodic trends that are governed by electron configuration: electron affinity, electronegativity, atomic radius, ionization energy and metallic character.

Atomic Weight of an Element 

The atomic mass is the mass of an atom at rest. The relative atomic mass, also known as atomic weight or atomic weight, is the measure of the atomic masses of all the isotopes of the elements. The term “atomic weight” is slowly being phased out in favor of “relative atomic mass”. Atomic weight (also called atomic mass) is the number found above and to the right of an element’s symbol on the periodic table.

Atomic weight is the total number of protons and neutrons found in the atom. The atomic weight of an element lets us find out how many neutrons a particular element has in an atom. The atomic weights are measured on a scale of “carbon-12.” This is the standard weight-scale used to define atomic weights worldwide. It is measured in units (amu) of atomic mass.

Electron Affinity Trend

The affinity of the electron is the potential energy change of the atom when an electron is applied to a gaseous neutral atom to form a negative ion. So the more negative the affinity of the electron the more desirable the method of adding electrons is. Not all elements form stable negative ions, in which case the affinity to the electron is zero or even positive.

  • There is a tendency towards increased electron affinity going left to right across a period.
  • The overall trend across a period occurs as a result of increased nuclear attraction.
  • Moving down the group the affinity of the electron should be decreased as the electron is gradually being taken away from the atom.
  • In fact, this pattern is a very weak one because most groups don’t change the affinities significantly.

Understanding the patterns helps one to consider not only the properties of individual elements but also standard properties such as constants of the solids and gaps of the semiconductor band. It is important to keep in mind that the trends are just generalizations and exceptions do occur throughout the periodic table.