Introduction to Chemistry

Introduction to Chemistry

1. Protons

   • Positively charged
   • Number of protons resemble the atomic number on Periodic table e.g Carbon (6)
   • Found in the nucleus

2. Neutrons

   • Neutral, Have no charge, found in nucleus
   • Affects the mass of the atom

3. Electrons

   • Negatively Charged
   • Number of electrons resemble the atomic number on periodic table e.g Carbon (6)
   • Found outside the nucleus

4. Isotopes

   • Atoms of the same element
   • Same atomic number (same amount of protons)
   • Different mass numbers (different amount of neutrons)
     • A = Mass number
       • Z = Atomic Number
       • Mass Number = Protons + Neutrons
         • E.g Carbon has 6 protons, 7 neutrons = Carbon 13
   • Example Bromine has atoms with a mass of 79 and 81
   • Isotopes can be written as 79, 35 Br
   • Can also be written as 79 Br/ 81 Br
   • Chemical Properties of isotopes of the same element are identical
     • All isotopes of an element have the same electronic structure
   • Chemical properties depend on electrons

5. Electronic Configuration

   • Electrons have a 2,8,8 config
   • E.g chlorine atomic no. 17, 1st shell 2, 2nd shell 8, 3rd shell 7
   • Atoms can achieve a full outer shell of electrons by losing/gaining electrons
   • Noble Gas config (full outer shell)
   • Na + (lost one electron)
   • Cl- (gained electron)
   • 1st ionisation energy decreases down the group
     • Outer electrons from the positive charge in the nucleus
       • Outer electrons are more shielded from the nucleus by other electrons making them easier to remove
         • these factors outweigh the increased nuclear charge
   • 1st Ionisation energy increases across the period (generally)
     • Same energy level and same distance from the nucleus is similar
       • Shielding is similar
       • Nuclear charge increases making the outer electrons more tightly held and therefore more difficult to remove

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