1. Atomic Theory and the Atom

2. Early Models of the Atom Democritus
Matter could be divided until the smallest particle is reached
Called these atomos
Atoms could not be divided

3. Early Models of the Atom Dalton
All elements are made of atoms that cannot be divided
Atoms of the same element have the same mass
Atoms cannot be changed into other atoms – may not be
created or destroyed
Compounds consist of atoms in a specific ratio

4. Early Models of the Atom Lavoisier
Demonstrated that burning wood caused no change in mass
Law of Conservation of Matter

5. Early Models of the Atom Thomson
Atoms contain negatively charged particles – electrons
Because atoms are neutral, he proposed a plum pudding model
Negative charges scatter throughout a ball of positive charges

6. Early Models of the Atom Rutherford
Gold foil experiments
Nucleus contains particles with a positive charge - protons

7. Early Models of the Atom Bohr
Electrons move in definite orbits around the nucleus
The Atom Song

8. Early Models of the Atom Chadwick
Noted that the mass of atoms was too large to just contain protons
The neutron – no charge

9. Modern Model of the Atom The electron cloud
Electrons may be found anywhere
in a cloud-like region
Movement is related to energy level

10. The Atomic Structure
The Atom and its sub-particles
Inside an Atom

11. Atomic Structure Proton Has a positive charge Located in the nucleus
Has a mass of 1 amu
Symbol p+ 

12. Atomic Structure Neutrons No charge Located in the nucleus
Has a mass of 1 amu
Symbol n 

13. Atomic Structure Have a negative charge
Electron
Have a negative charge
Located in a cloud outside the nucleus
Mass is 1/1836 – adds little to the atom
Symbol e-

14. Atomic Structure Protons and neutrons found in the nucleus make
up nearly all the mass of an atom
An atom’s volume is the space in which the electrons move

15. Describing Atoms Atomic Number – the number of protons
In a neutral atom, the # of protons = the # of electrons

16. Describing Atoms Mass Number – sum of the protons and neutrons
Isotopes – atoms of the same element that have a
different number of neutrons
Example … C-12, C-13, C-14
Have the same properties but different masses

17. Isotopes The number of protons for a given atom never changes.
Two atoms with different numbers of neutrons are called isotopes

18. Isotopes Have the same atomic number (number of protons)
Have different mass numbers
(number of protons + neutrons)

19. Isotopes

20. The Periodic Table Patterns in the Elements 1869 – 63 known elements
Mendeleev
- organizes the elements based on atomic mass
- further grouping based on similar properties
- able to predict the properties of three missing elements
Moseley
discovered a way to measure the positive charge
of an atom’s nucleus
- table rearranged by atomic number; a few elements shifted

21. The Periodic Table Atomic Number – the number of protons Atomic Mass
– the average of the masses of the isotopes based on the percentage of each found on
Earth

22. Q: What are the three main parts of the atom, and where are
they located?
A: The proton and neutron are located in the nucleus. The
electrons are found in the cloud surrounding the nucleus.
Q: What charge do each of the particles carry?
A: protons have a positive charge; electrons have a negative
charge;neutrons have no charge.
Q: Why do atoms have no electrical charge even though most of
their particles have charges?
A: The atom has an equal number of positive and negative charges.

23. Q: What is atomic number and how is it used to distinguish one
element from another?
A: Atomic number is the number of protons in each atom of a
specific element. Each element has a unique atomic number;
each atom of the element has the same number of protons.
Q: If the atomic number of the isotope N-15 is 7, how many protons,
neutrons, and electrons would it have?
A: Protons = Neutrons = Electrons = 7

24. Element
Atomic #
Protons
Neutrons
Electrons
Atomic Mass Al 13 27 Rb 48 85 F 9 19 K 20 Ti 22 25
Check your answers on the next slide

25. Element
Atomic #
Protons
Neutrons
Electrons
Atomic Mass Al 13 14 27 Rb 37 48 85 F 9 10 19 K 20 39 Ti 22 25 47

26. Q: The information about atoms and their structure is referred
to as a theory. Explain