1. 4.1 Defining the Atom 4.2 Atomic Structure

2. ATOM: Defined
The smallest particle of an element that retains its identity in a chemical reaction.
A copper coin contains 2.4 X 1022 atoms.
100,000,000 copper atoms lined up would make a line only 1cm long.
Point is…atoms are VERY small.

3. FAMOUS DEAD PEOPLE Democritus (4.1) John Dalton (4.1)
J.J. Thomson (4.2)
Robert A. Millikan (4.2)
Eugen Goldstein (4.2)
James Chadwick (4.2)
Ernest Rutherford (4.2)

4. Democritus’s Atomic Theory
Greek philosopher: 370 B.C.
Atoms are indivisible and indestructible
Problem: did not explain chemical behavior, lacked experimental support, not based on scientific method.

5. Dalton’s Atomic Theory
Used experiments to make Democritus’s idea into a scientific theory.
4 Parts (picture on pg. 102)

6. Dalton’s Atomic Theory
All elements are composed of tiny indivisible particles called atoms.
Atoms of the same element are identical.
Atoms of different elements can physically mix together or can chemically combine in simple whole-number ratios to form compounds.
Chemical reactions occur when atoms are separated, joined, or rearranged. Atoms of one element are never changed into atoms of another element as a result of a chemical reaction.

8. Subatomic Particles Electrons (-) Protons (+) Neutrons (neutral)
**Pg. 106**

9. J.J. Thomson Discovered the electron (negatively charged)
Cathode-Ray Tube
Plum Pudding Atomic Model

10. Robert A. Millikan
Calculated the mass and amount of charge carried by an electron.
Electron carried one unit of negative charge and has 1/1840 the mass of a hydrogen atom.

11. Eugen Goldstein Discovered protons
Mass is 1840 times that of an electron (relative mass = 1)

12. James Chadwick Discovered the neutron
Mass is same as proton (relative mass = 1)

13. Ernest Rutherford Gold-Foil Experiment
The nucleus is tiny and composed of protons and neutrons

14. TODAY Protons and neutrons are located in the nucleus.
Electrons are distributed around the nucleus and occupy almost all of the volume of an atom.

16. Atomic Number and Mass Number

17. Atomic Number
Elements are different because they contain different numbers of protons.
ATOMIC #: number of protons in the nucleus of the element.
Found on the P.T.

18. Example
How many protons are in the nucleus of a lithium atom if its atomic number is 3?
Answer: 3

19. Atomic Number Continued…
Atoms are electrically neutral so the number of electrons (negative) must equal the number of protons (positive).

20. Example
If there are three protons in the nucleus of a lithium atom, how many electrons surround it?
Answer: 3

21. Mass Number
Definition: the total number of protons and neutrons in an atom.

22. Example
If an oxygen atom has 8 protons and 8 neutrons, what is its mass number?
Answer: 16

23. Mass Number Continued…
Example: If the mass number of an element is 19 and there are 9 protons, how many neutrons does it contain?
Answer: 10
Number of neutrons = mass number – atomic number

24. Shorthand Notation Also can be written as: name of element – mass #
EX: Carbon - 12

25. NOTE: atomic number does NOT equal average atomic mass.

26. Isotopes
Definition: Atoms with the same number of protons but different numbers of neutrons.

27. Example
Two stable isotopes of carbon are carbon – 12 and carbon – 13. Write the symbols of each using the proper subscripts and superscripts.

28. Atomic Mass Weights of atoms are measured in atomic mass units
This unit is a reference to the isotope C-12
One amu = 1/12 of the mass of a C-12 atom.
Therefore, one proton or neutron has the weight of 1 amu.

29. Atomic Mass Most elements have more than one isotope.
Each isotope has a fixed mass and natural percent abundance.
The atomic mass is a weighted average mass.

30. Atomic Mass Calculation
Multiply the mass of each isotope by its natural abundance, expressed as a decimal, and then add the products.

31. Example
There are two stable isotopes of carbon. Carbon-12 (mass = amu) has a natural abundance of 98.89% and Carbon-13 (mass = amu) has a natural abundance of 1.11%. Determine the atomic mass.
Answer: amu

32. Example 2
Isotopes of chlorine are chlorine-35 ( amu) and chlorine-37 ( amu). Chlorine-35 accounts for 75% of the naturally occurring chlorine atoms while chlorine-37 accounts for 25%. What is the average atomic mass?
Answer: amu

33. Periodic Table Basics
Horizontal row is called a period.
Vertical row is called a group or family.