Chemistry: Atoms, Elements and Compounds

Chemistry: Atoms, Elements and Compounds

1. Atom

   • all substances are made up of matter
   • the fundamental unit of matter is an atom
   • the atom is made up of a central nucleas containing protons (positively charged) and neutrons (negatively charged)
   • The electrons revolve around the nucleas in different imaginary paths called orbits or shells

2. Element

   • substance made up of atoms of one kind
   • There are 82 naturally occurring elements and 31 artificially made elements. (Periodic Table)

3. Atomic Number

   • number of protons in the nucleas of an atom

4. Atomic Weight

   • number of times an atom of that element is heavier than an atom of hydrogen

5. Mass Number

   • sum of the number of protons and neutrons in the nucleas of an atom

6. Molecule

   • formed when atoms of the same or different elements combine
   • smallest particle of a substance that can normally exist independently

7. Compound

   • formed when atoms or molecules of different elements combine