Atomic Structure

Atomic Structure

1. Atoms are the smallest particle of an element that have the same chemical properties of that element

2. Nuclide Notation

   • Mass Number/ Nucleon Number: The sum of the number of protons and neutrons in its atom
   • Atomic Number/Proton number: The number of protons in its atom
   • No. of protons = No. of electrons

3. Subatomic Particles

   • Nucleons ( Inside the nucleus)
     • Proton
       • Relative mass of 1
       • +1 Relative charge
     • Neutron
       • Relative mass of 1
       • No charge
   • Outside the nucleus of the atom
     • Electron
       • Negligible Mass (1/1836 of a proton)
       • -1 Relative charge
       • Controls chemical properties of an atom

4. Isotopes

   • Atoms of the same element with the same number of protons but a different number of neutrons
   • Isotopes have the same proton number but different mass number
   • Isotopes have different masses due to the different number of neutrons in their nuclei
   • Isotopes of the same element have similar chemical properties but different physical properties (e.g. boiling and melting points, densities)

5. Arrangement of electrons (For first 20 elements)

   • First shell: 2 electrons
   • Second and third shell: 8 electrons
   • Electron shells must be filled in order of increasing energy (each shell must be completely filled beforeelectrons occupy the next shell
   • Outermost electrons are known as valence electrons (they are in the valence shell)
     • The chemical properties of an element depends on the number of valence electrons