C2a Topic 1- Atomic Structure and the Periodic Table

C2a Topic 1- Atomic Structure and the Periodic Table

1. Atoms-

   • Protons- Heavy, positively charged
   • Neutrons- Heavy, neutral (no charge)
   • Electrons- Tiny, negatively charged
   • Nucleus- Middle, Contains protons and neutrons, positive charge, almost all mass concentrated into nucleus

2. Electron Shells

   • Electrons always occupy shells
   • Electronic configuration follows rule: 2,8,8
   • In most atoms, outer shell is not full so atoms want to react

3. Elements

   • Each element has a different number of protons
   • Each element has an atomic number and mass number
     • Atomic Number: Number of protons (so also electrons)
     • Mass number: Total number of protons and neutrons
       • Mass number is usually roughly double atomic number

4. Isotopes and RAM

   • Isotopes: Different atomic forms of the same element, which have the same number of protons but different numbers of neutrons
     • Popular example: Carbon-12 and Carbon-14
   • To work out relative atomic mass: 1) Multiply mass of each isotope by its relative abundance 2) Add those together 3) Divide by the sum of the relative abundance (however if given as a percentage, divide by 100)

5. History of the Periodic Table:

   • Mendeleev
     • Arranged known elements according to their properties and compound properties to make a 'Table of Elements'
     • Placed elements with similar chemical properties in the same vertical groups- but had to leave gaps for it to work
     • Table predicted new elements:
       • Gaps predicted the properties of undiscovered elements
       • New elements found have fit into the gaps of Mendeleev's table
       • Refined to produce the Periodic Table
   • 1880's- Scientists did not know about the structure of atoms but could work out their RAM. When elements were put in order of their RAM, scientists began to notice periodic patterns in the properties of elements

6. Periodic table

   • Metals- left side of periodic table Non-metals- right side of periodic table
   • Periods- Rows
     • Elements arranged in order of increasing atomic number along each row
     • Period number= number of electron shells
     • Properties of elements change as you go along a period
   • Groups- Columns
     • Elements in the same group have similar properties because they have the same number of electrons in their outer shell
     • Group number= number of electrons in outer shell
     • Properties of elements often gradually change (as atomic number increases)

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