1. CHAPTER 3 Atoms: The Building Blocks of Matter
CHEMISTRY

2. Foundations of Atomic Theory
History
Greek
Democritus – “atom” – could not be divided anymore
Aristotle and Plato - argued s
Natural Philosophers
Experimentation – balances – quantitative measurements
Atom
Comes from Greek
“a” – not
“tomos” – cutting
indivisible

3. Foundations of Atomic Theory
Chemical Reaction
Transformation of substances into one or more new substances
Chemical change
Law of Conservation of Mass
Mass is neither created nor destroyed in ordinary chemical reactions
Law of Definite Proportions
A chemical compound contains the same elements in exactly the same proportions by mass regardless of size of sample
Ex – H2O, CO2

4. Foundations of Atomic Theory
Law of Multiple Proportions
If two or more compounds are composed of the same 2 elements, the masses can be expressed as ratios of small whole numbers

5. Dalton’s Atomic Theory
John Dalton
English School Teacher
1803

6. Dalton’s Atomic Theory
5 Points in his theory
All matter is composed of extremely small particles called atoms
Atoms of a given element are identical in size, mass, and other properties
Atoms cannot be subdivided, created, or destroyed
Atoms of different elements combine in simple whole number ratios to form compounds
In chemical reactions, atoms are combined, separated, or rearranged

7. Dalton’s Atomic Theory

8. Modern Atomic Theory
There have been some changes since Dalton’s Theory
Important concepts of modern theory
All matter is composed of atoms
Atoms of one element differ in properties from atoms of another element

9. Structure of the Atom
Atom – smallest particle of an element that can exist alone
Two regions of an atom
Nucleus
Center of atom
Protons and neutrons
Electron “cloud”
Area surrounding nucleus
containing electrons

10. Discovery of the electron
Symbol  e-
Cathode ray tubes
Vacuum tube containing an electron gun (a source of electrons) and a fluorescent screen, with internal or external means to accelerate and deflect the electron beam, used to form images in the form of light emitted from the fluorescent screen.
Used in TV, computer monitors

11. Discovery of the electron
Charge and mass of the electron
JJ Thomson – 1897
Discovered the electron
1907 Nobel Prize in Physics
Did experiments with CRT –
Found that the charge to mass
ration was always the same

12. Discovery of the atomic nucleus
Ernest Rutherford – 1908
Gold Foil Experiment

13. Composition of the nucleus
Protons
Positive charge
Neutrons
Neutral charge

14. Forces in Nucleus Nuclear forces
Forces that hold nuclear particles together
Binds protons and neutrons into the atomic nucleus

15. Sizes of Atoms

16. Summary

17. Counting Atoms Atomic Number Symbol  Z Number of protons in nucleus
The number of protons determines identity of the element!!

18. Counting Atoms Isotopes
Atoms of the same element with varying number of neutrons
Nuclide – general term for any isotope of any element
Mass Number – total number of protons + neutrons

19. Counting Atoms The isotope of hydrogen Protium – one proton only; 1e-
Deuterium – one proton, one neutron, one electron
Tritium – one proton, two neutrons, one electron; radioactive

20. Counting Atoms Designating Isotopes Hyphen notation
Name-mass #
Uranium-235
Ex – Neon with 12 neutrons?
Nuclear Symbol Notation
MNAN Element symbol
31H
23592U
How many p,n,e- in chlorine-37?

21. Relative Atomic Mass Relative scale Atomic mass unit Standard
Way to compare
Carbon-12
All others compared to Carbon-12
Atomic mass unit
amu
Approximate mass of a proton or a neutron

22. Average Atomic Mass
Weighted average of the atomic masses for all known isotopes
Calculating average atomic mass:

23. Relating mass to the number of atoms
“Particle” – a generic term
Mole – SI unit for amount of substance, counting unit
Symbol – mol
Avogadro’s number
6.02 x 1023 – number of particles in 1mol of substance
Molar mass
Mass of 1mol of substance = atomic mass

24. Calculating Molar Mass
H2O
CO2
C6H12O6

25. Conversions Gram  Mole Mole  Gram Mole  Particle Particle  Mole
Gram  Particle
Particle  Gram

26. Conversions
Gram  Mole; Mole  Gram

27. Conversions
Mole  Particle; Particle  Mole

28. Conversions
Gram  Particle; Particle  Gram