1. Atoms, Molecules, isotopes, and Ions

2. John Dalton proposed the first table of atomic masses
Dalton is best known for proposing Atomic Theory

3. Dalton’s Atomic Theory
Elements are made up of tiny particles called atoms.
Atoms are indivisible and indestructible
Atoms of a given element are identical
Atoms of different elements differ in some fundamental way(s)

4. Dalton’s Atomic Theory
Compounds form when atoms of different elements combine with each other.
A given compound always has the same relative number and types of elements.

5. Dalton’s Atomic Theory
Chemical reactions occur when atoms change how they are bound to each other.
Individual atoms are not changed, just rearranged

6. Radioactivity Becquerel, Marie and Pierre Curie: ~1896
Suggested that matter was composed of smaller particles than atoms.
Only person to have 2 Nobel prizes in two different disciplines.
Total B.A.

7. Plum Pudding Model of the Atom
In the early 1900’s the plum pudding model of the atom:
Electrons (tiny and negatively charged) were pictured to be dispersed in a ‘cloud’ of positive charge.

8. Rutherford and the Nuclear Atom
In 1911 Ernest Rutherford’s lab showed the “plum pudding” model to be incorrect.
Gold foil experiment

9. Rutherford’s Atom First to propose a nuclear atom.
An atom has a dense positive center containing all of positive charge and most of the mass of the atom – the nucleus
Electrons occupy a volume that is huge as compared to the size of the nucleus.

10. A New Model of the Atom Expected based on Plum pudding model
Rutherford’s model
Based on ”his” results

11. Modern Atomic Structure
~1932 James Chadwick proposed the existence of a third subatomic particle, the neutron.
No one cares about me…

12. Subatomic Particles Subatomic Particle Charge Mass, amu
Location in atom
Purpose
Electron
(e-)
Proton (p+)
Neutron (n)

13. Subatomic Particles and the Elements
Each element has a unique number of protons.
Number of protons defines the element.
Atomic # = # protons
6 protons has Carbon and Carbon has 6 protons C 6

14. Terms
Mass number = sum of the # of protons and the # neutrons in the nucleus of an atom

15. Terms Isotopes = atoms of a given element that differ in mass number
Example: Carbon-14, Carbon-15, Nitrogen-12

16. Isotopes
Writing atomic symbols like this is called isotope notation. 11
Mass # B
Symbol for element 5
Atomic #

17. FAQ - Isotopes
What are the protons, neutrons, and electrons of each of the elements at the bottom? C Po
(209)

18. Determining total mass from %
You find a sample of nitrogen made up of two isotopes. Nitrogen-14 which has a mass of and Nitrogen-15 which has a mass of The nitrogen-14 is 99.63% abundant and the nitrogen-15 is 0.37% abundant. Determine the average atomic weight of the sample.

19. IONS!!!!
Ions are atom which have gained or lost electrons.

20. 10N5!!!!
Hg4+
Mg2+
O-2 Ag

22. Summarize what you learned
What were the important experiments which helped uncover the nature of the atom?
What is the difference between atomic mass and atomic number?
Summarize in your own words.