Elements and Compounds

Elements and Compounds

1. Elements are pure substances made up of only one type of atom.

2. Compounds are pure substances made up of two or more different types of elements

3. VALENCE SHELL: The valence shell is the outermost shell of an atom. The electrons that are located in this shell are called valence electrons, and sue responsible for the chemical properties of substances

4. All the noble gases unless He, have a electronic configuration in the last shell: 26. It means they have the last shell, valence shell, complete. Its because they are very stable and they don't need to react with other atoms

   • ISOLATED:noble gases due to the stability of its valence shell that its complete.They are gases at room temperature, they don't react to other compounds and they don't conduce electricity
   • MOLECULES:most non-metalic elements are made up in nature of groups of two atoms of the same elements. They are gases at room temperature except Bi2 and I2, they have low boiling and melting point and they don't conduct the electricity
   • CRYSTALS: all metals are made up in nature of crystals and some non-metals such as Carbon
     • Metal crystals: with metalic bond = all the free elctrons circulate freely thoughout the metal
     • Covalent crystals: with covalent bond= Diamond: atoms form a network Graphite: atoms form layers