1. 3.2 Introduction to the Atom The Nucleus

2. Atomic History The term atom coined by the Ancient Greeks.
Greeks had no evidence for the atom. It was more of a philosophical idea.
John Dalton – early 1800s – witnessed elements reacting in “set ratios.” Assumed there must be smaller parts combining in specific ways.
“Atoms are indivisible!”

3. Atomic History
JJ Thompson – 1897 – showed cathode rays had mass but very low amounts. Showed these particles were negatively charged and he believed them to be evenly spaced throughout the atom. Nobel Prize – 1906
Ernest Rutherford – 1909 – bombarded gold foil with alpha (positive) particles to see if they would pass straight through. Some particles were deflected leading to the idea that their was a tiny positive nucleus in the atom.

4. History of the Atom
Niels Bohr – 1913 – proposed that electrons orbited the atom in fixed positions
Many others were involved in the development of atomic theory: Shrodinger, de Broglie, Heisenberg, Chadwick, Einstein, Max Planck

6. Earth’s Matter Everything in the universe is composed of matter.
Matter: anything that has volume and mass.
Mass: the quantity of matter an object has.

7. Elements and Atoms
Elements are pure substances that cannot be broken down into simpler forms of matter.
All matter is composed of elements.
Each element is made up of tiny particles called atoms.
Atom: the smallest part of an element that has all the properties of that element.

8. Atomic Structure: The Nucleus
The central core of the atom.
Consists of two kinds of particles:
Protons: have a positive electrical charge.
Neutrons: have a neutral charge.
Both have almost exactly equal masses of 1 amu (atomic mass unit).
Most of the mass in an atom is held in the nucleus.

9. Atomic Structure: The Nucleus

10. How do we know how many protons?
BY USING THE PERIODIC TABLE!!!!!
Atomic Number:
Number of protons in an atom; usually appears directly above the chemical symbol.

11. How do we know how many neutrons?
BY USING THE PERIODIC TABLE!
Atomic Mass (Weight):
Average masses of all the isotopes
Mass (Weight) Number:
Number of protons plus neutrons in an atom; usually appears directly below the chemical symbol.

12. Atomic Structure How many protons? How many neutrons? What atom is this? What is the Mass Number?

13. Atom Equations
Atomic Number = # of Protons Mass Number = # of Protons + # of Neutrons # of Neutrons = Mass Number - # of Protons # of Protons = Mass Number - # of Neutrons

14. Example
Copper – 65
How many protons?
How many neutrons?

15. Isotopes
Isotopes:
Have the same atomic # but different mass numbers because of a different number of neutrons.