Additional Science - Chemistry_2

Additional Science - Chemistry_2

1. Atomic structure and the periodic table

   • Atoms and the periodic table
     • Dmitri Mendeleev
       • published the periodic table
         • Elements are arranged in order of increasing atomic number in rows called periods. Elements with similar properties are placed in the same vertical columns called groups
       • arranged the elements known at the time in order of relative atomic mass
         • Dmitri also used gaps in his table to make predictions about the properties of undiscovered elements
     • Alkali metals (group 1) Halogens (group 7) Noble gases (group 0) Transition metals Metals and non-metals
       • • Calculating the relative atomic mass - chlorine consists of two isotopes, 75% chlorine-35 and 25% chlorine-37. The average mass = [ (75 x 35) + (25 x 37) ] / 100 = 35. So the relative atomic mass of chlorine = 35.
     • The atomic number (also called the proton number) is the number of protons in an atom.
       • The mass number (also called the nucleon number) is the total number of protons and neutrons in an atom.
     • Proton: charge = +1 mass = 1 Neutron: charge = 0 mass = 1
       • Electron: charge: -1 mass: 0.0005 (almost zero)
     • Most elements exist in a number of different forms or varieties called isotopes. Isotopes have the same number of protons but different numbers of neutrons, which gives them a different total mass.

2. Atomic structure and the Periodic Table

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