Classification of Substances / Atomic Structure

Classification of Substances / Atomic Structure

1. All substances are made up of atoms

2. Elements are substances made up of only one type of atom

3. Molecules are made up of two atoms chemically combined

   • Hydrogen gas has chemical formula H2
     • hydrogen atoms not stable on their own
       • pair up into molecules
     • Oxygen
       • O2
     • Nitrogen
       • N2
     • Chlorine
       • Cl2

4. Compounds are made of two or more elements chemically combined

   • formed when atoms/molecules react with each other in order to become more stable

5. Mixtures contain two or more different substances mingled together but not chemically combined

   • easily separated
   • air
     • mixture if gases
   • sea water
     • water and salts
   • alloys
     • mixture of metals

6. The properties of a compound differ from those of the elements from which it is made

7. Atomic Structure

   • The Atom
     • The atom is the smallest part of an element ehich can take part in a chemical reaction
     • sub-atomic particles
       • protons
         • +1 charge
         • in the nucleus
       • neutrons
         • 0 charge
         • in the nucleus
       • electrons
         • -1 charge
         • orbiting the nucleus
   • Atomic Numbers and Mass Number
     • Atomic number is the number of protons (or electrons) in an atom of an electron
     • Number of protons = Number of electrons
     • Mass number is the number of protons and neutrons in an atom of an element
     • arrangement of electrons is called electronic configuration
   • The Bohr Structure
     • Electrons represented in dots
     • The first shell holds two electrons and the rest hold up to eight
   • Isotopes
     • Isotopes are atoms of the same element which have the same atomic number but different mass numbers
       • same number of protons, different number of neutrons