Atomic Structure and Electron Configuration

Atomic Structure and Electron Configuration

Atomic Structure

  • Every atom is made up of three types of particles: protons, neutrons, and electrons.
  • Protons and neutrons make up the centre or nucleus of the atom, while electrons orbit this nucleus.
  • Protons carry a positive charge, neutrons have no charge, and electrons carry a negative charge.
  • The atomic number (or proton number) of an atom defines the type of atom (or element) it is. It is the number of protons in an atom.
  • The mass number of an atom is the total number of its protons and neutrons.
  • As atoms have equal numbers of protons and electrons, they are neutral overall.

Electronic Configuration

  • An electron’s energy level also called a shell, is the path or orbit followed by electrons around an atom’s nucleus.
  • The first shell can hold up to 2 electrons, the second can hold up to 8, and the third can hold up to 8.
  • Electrons always occupy the lowest available energy level first. This is often referred to as the ‘energy level filling rule’.
  • The electronic configuration of an atom represents the distribution of electrons in the atom’s energy levels. For example, flow of electrons in hydrogen is 1, in helium is 2, in lithium is 2,1 and in oxygen is 2,6.
  • The Arrangement of electrons into their shells or energy levels in an atom is called Electron Configuration.
  • The outer-most energy level of an atom is known as its valence shell and the electrons in this shell are called valence electrons- they are of utmost importance as they determine the chemical behaviour of the atom.
  • The electron configuration or the number of electrons in the outer most shell results in attempts to achieve stable electron configuration like that of Noble Gases which leads to interactions with other atoms, forming Chemical Bonds.

Isotopes

  • Isotopes are atoms that have the same number of protons (and so are the same element) but different numbers of neutrons.
  • Because they have different numbers of neutrons, isotopes have different mass numbers.
  • The chemical properties of isotopes are the same, but their physical properties are different.
  • Some isotopes are radioactive, meaning they decay over time and emit radiation.