Unit 7: Elements & Compound

Unit 7: Elements & Compound

1. Atoms

   • Different kinds of atoms
     • Scientists have discovered 94 different kinds of atoms that occur naturally in the Universe. Another 24 kinds of atoms have been made in laboratories
     • A substance that is made of just one kind of atom is called an element
     • Molecules are particles made of two or more atoms joined together.
     • Each type of atom has different properties. This is why different elements have different properties
   • Who had the idea?
     • a Greek philosopher called Democritus
       • He suggested that everything was made of tiny pieces
       • He then called his tiny pieces of matter 'Atoms'
         • 'Atoms' means 'Cannot be divided'

2. Elements

   • Each element has its own chemical symbol
     • The first letter of the symbol is always upper case. The second letter, if there is one, is always lower case
   • A substance made of more than one kind of atom bonded together.
   • THere are more than 100 different elements
     • Each element has its own chemical symbol.

3. The Periodic Table

   • The elements are arranged in the Periodic Table.
     • The Periodic Table is organised in rows and columns. The rows are called periods . The columns are called groups
   • The elements are arranged in order of the mass of their atoms.
   • Metals are towards the left hand side of the table, and non-metals on the right hand side.
   • The full Periodic Table, containing all of the 118 known elements

4. Compounds

   • If the different sorts of atoms are joined tightly together, then the substance is a compound
   • The chemical term for two atoms joining tightly together is bonding
   • Once two different elements are bonded, they completely lose the properties of the individual elements. The compound has totally new properties.
   • If the compound contains a metal, then the name of the metal comes first in the name of the compound.

5. Formulae

   • Each compound has its own chemical formula.
   • The formula tells you which elements the compound contains and how many atoms of each element are combined together.
   • Some compounds also have everyday names. For example, sodium chloride is also known as common salt.

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