Planetary Electrons and Orbital Shells

  • Heavy atoms are usually unstable and decompose by form stable atoms. The atom that undergoes decomposition by emitting energy is called a radioactive atom.
  • Matter made up of only one type of atom is called an element, but if it is made up of two or more different atoms, then it is called a compound.
  • In the atom, the electron orbits around the nucleus – which is made up of protons and neutrons (except for the hydrogen atom). This orbiting electron is called an orbital or planetary electron.
Negatively-charged electrons orbiting the nucleus made up of positively-charged protons and neutrons (red circles) that have no charge
  • Each atom has orbital shell(s) depending on the number of electrons, and the further the electron is from the nucleus, the less strongly it is bound to the nucleus. This means that the electron in the outermost orbital shell is least strongly bound to the nucleus as compared to the electron in the innermost orbital shell.
  • The orbital shell that surrounds the nucleus can hold 2 electrons, and it is called the innermost shell.
  • The shell surrounding the innermost shell can hold a maximum of 8 electrons, and the next outer shell can hold 18 electrons.
  • The electron that is tightly bound to the nucleus is called the valence or bound electron, while the loosely bound electron in the outermost orbit that can move away from the nucleus is called the free electron. To move this free electron, there is need for an energy input to overcome the resistance of the nucleus to allow for this electron to exit its orbital shell. This energy is best described as the electron-moving force.

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