Chemistry Unit 1

Chemistry Unit 1

1. Atoms, elements & compounds

   • Mixtures can be separated into simpler substances
   • A compound can be broken down into simpler compounds or elements
   • Elements are substances that can't be broken down by chemical reactions into simpler substances

2. Inside the atom

   • Sub-atomic particles have both a charge and a mass
   • Mass number = no of protons + no of neutrons
   • Since an atom has equal no of protons and electrons, the charges cancel out
   • Neutrons have no charge/are neutral
   • Electronic configuration of atom gives no of electrons & arrangement of shells
     • Electrons can be shown as dots or crosses
       • Each shell can hold limited no of electrons
         • 1st shell can hold up to 2 electrons
           • 2nd shell can hold up to 8 electrons
             • 3rd shell can hold up to 18 electrons but fills up with only 8 before 4th shell is started

3. Element patterns

   • The periodic table lists all of the known elements by increasing proton no. Horizontal rows are periods and vertical columns are groups
     • Group no tells how many outer electrons the atom has
       • No of outer electrons in atom determines how an element reacts
   • Noble gases (group 0) are unreactive as they have full outer electron shells

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