Simple atomic structure for home learning

Atomic number, mass number and electron arrangement. Check your learning with a 30 second 5 question quiz

Atomic Number and Mass Number.

  • The atomic number is the number of protons in the nucleus of an atom.
  • In a neutral atom the numbers of protons (+) and electrons (-) are the same.
  • The mass number is the total number of protons and neutrons in the nucleus of an atom.


But wot about the electrons?

    • Electrons are arranged in cloud like shells around the nucleus.
    • Shells closest to the nucleus fill up with electrons first.
    • The first shell is full with two electrons.The second and third shells are full with eight electrons.
    • For the first twenty elements remaining electrons go in the fourth shell.


The sodium atom



  • the atomic number is 11. There are 11 protons in the nucleus and eleven electrons in the shells around the nucleus.
  • Two electrons go in the first shell, eight in the second and the remaining electron goes in the third shell.
  • The electron configuration for sodium is Na(2,8,1). This is enough information to understand how the first 20 elements in the periodic table react with each other,
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