Atom

• smallest part on an element
• has the chemical properties of the element

Structure of an atom

Atomic symbol

1. Atomic number: no. of protons in the atom

   • electrically neutral: equal number of protons and electrons

2. Mass number: sum of the no. of protons and neutrons in the atom

3. Full atomic symbol

   1. Mass no: left top, > atomic no.
   2. Atomic no: left bottom
   3. Atomic symbol (Chemical symbol): right

Isotopes

• atoms of the same element with the same number of protons but different numbers of neutrons

• atoms of the same element with the same atomic number but different mass number

• similar physical properties (boiling point/ density) ← similar mass

• the same chemical properties (reactivity) ← same arrangement of electrons

Relative mass

<aside> 🗣 The “12C = 12.000” scale

• Carbon-12 isotope (12C)
  • contains 6p, 6n, 6e-
  • standard form
  • mass = 12 units </aside>

Relative atomic mass (RAM)

• weighted average mass of isotopes