1. “Old dead guys”

2.  400 BC- Democritus- first to come up with the idea that things are made of “atoms”

3.  1803- John Dalton  Proposed the atomic theory

4.  1869- Dmitri Mendeleev  Arranged elements into 7 groups with similar properties… 1 st version of periodic table.

5.  Discovered electrons and isotopes

6.  Famous experiment determined the charge of an electron… which is??

7.  Established that the nucleus of an atom was very dense and positively charged while electrons were outside the nucleus

8.  Made a model of the atom where electrons were in different orbitals

9.  Discovery of the neutron

10.  First of all… Elements are substances that cannot be broken down into simpler parts  Elements are made of atoms...Carbon is made of carbon atoms etc.  How small is an atom???  We can break down an atom but it loses its properties when we do…

11.  Three types of particles  Electrons  Protons  Neutrons

12.  Very tiny  Mass is basically zero (m=0)  Negative charge (-1)  Located flying around the nucleus

13.  Very large compared to electrons (mass =1)  Positive charge (+1)  Located in the nucleus of an atom

14.  Large like protons (mass=1)  Neutral charge or no charge  Located in the nucleus

15.  If this were the size of hydrogen nucleus, the electron would be spinning about a quarter mile away….  In a neutral atom, protons always equal electrons  Hydrogen has… 1 proton… 1 electron  Helium has… 2 protons… 2 electrons

16.  Atomic number = number of protons in nucleus  Atomic Mass= how many protons AND neurtons  How many protons in H?  How many neutron in H  How many electrons?

17.  How many P? N? E?

19.  Hydrogen:  Helium:

20.  Boron  Neon (noble gas)

21.  Magnesium