1. MATTER UNIT STRUCTURE OF AN ATOM

2.  Atom : the smallest unit of matter that retains the identity of the substance

3. THE EVOLUTION OF ATOMIC STRUCTURE

4. THE NUCLEUS IS THE SMALLEST PART OF THE ATOM, BUT CONTAINS ALMOST ALL OF THE MASS OF AN ATOM. THE MAJORITY OF THE ATOM IS EMPTY SPACE.

5.  Atoms are composed of 2 regions:  Nucleus: the center of the atom that contains the mass of the atom  Electron cloud: region that surrounds the nucleus that contains most of the space in the atom Nucleus Electron Cloud

6. ATOMIC STRUCTURE The nucleus contains 2 of the 3 subatomic particles: Protons: positively charged subatomic particles Neutrons: neutrally charged subatomic particles The 3 rd subatomic particle resides outside of the nucleus in the electron cloud Electron: the subatomic particle with a negative charge and relatively no mass

7. Atomic Particles ParticleChargeMass # Locationsymbol Electron0Electron cloud e-e- Proton+11Nucleus p+p+ Neutron01Nucleus n0n0

8.  Protons and neutrons are in the tiny positively charged nucleus accounting for most of the mass of the atom  The negatively charged electrons are small and have a relatively small mass but occupy the larger volume of space outside the nucleus

9.  In an atom :  The # of protons = The # of electrons  If 20 protons are present in an atom then 20 electrons are there to balance the overall charge of the atom—atoms are neutral  The neutrons have no charge  they do not have to equal the number of protons or electrons

10. THE NUMBER OF PROTONS IDENTIFIES THE ATOM. AN ATOM WITH 6 PROTONS = CARBON AN ATOM WITH 8 PROTONS = OXYGEN AN ATOM WITH 20 PROTONS = CALCIUM

11. ATOMIC STRUCTURE the number of protons in an atom the number of protons and neutrons in an atom He 2 4 Atomic mass Atomic number # of electrons = # of protons # of neutrons = Atomic mass – # of protons

12.  Bohr Model of the atom: All of the protons and the neutrons The 1 st ring can hold up to 2 e - The 2 nd ring can hold up to 8 e - The 3 rd ring can hold up to 8 e - The 4 th ring and any after can hold up to 18 e -

13. ATOMIC STRUCTURE Electrons are arranged in Energy Levels or Shells around the nucleus of an atom. First Shella maximum of 2 electrons Second Shella maximum of 8 electrons Third Shell a maximum of 8 electrons Fourth Shell a maximum of 18 electrons

14.  Li has a mass number of 7 and an atomic number of 3  Protons = 3 (same as atomic #)  Neutrons= 7-3 = 4 (mass # - atomic #)  Ne has a mass number of 20 and an atomic number of 10  Protons = 10  Neutrons = 20 - 10= 10

15.  The electrons are equal to the number of protons  So e - = p = atomic #  Ex: He has a mass # of 4 and an atomic # of 2  p + = 2  n o = 2  e - = 2

16.  Cl has a mass # of 35 and an atomic # of 17  p + = 17,n o = 18, e - = 17  K has a mass # of 39 and an atomic # of 19  P + = 19,n o = 20e - = 19

17. Mass # = 12 atomic # = 6 p + = 6 n o = 6e - = 6 6 p and 6 n live in the nucleus

18. PRACTICE BOHR DIAGRAMS