1. Activity 4: Are Atoms Divisible?

3. Ancient Greece Democritus Greek philosopher
He thought atoms were uncuttable
3. Therefore: Atoms are indivisible particles
Atomos—Greek meaning ‘indivisible
B.C.

4. John Dalton—late 18th century
1. What are atoms?
2. Do Carbon atoms differ from Oxygen atoms?
Dalton’s Atomic Model:
Hard, indivisible sphere
Yes

6. HAS THIS EVER HAPPENED TO YOU?

7. Are there things inside the atom?
YES! Subatomic particles e- p+ n0

9. Discovery of electron (e-)
Credited with the discovery of the electron in 1897.
J.J. Thomson
Thomson identified a glowing beam of particles that traveled through a chamber of gas when exposed to an electrical current.
Cathode ray tube

10. positive charges and repelled by negative charges.
-This beam (cathode ray) was attracted to
positive charges and repelled by negative
charges.
-Thomson concluded the beam must be
composed of negatively charged
particles. These came to be known as
electrons.

12. Thomson’s Atomic Model
“Plum Pudding” Model
ELECTRONS
EMBEDDED WITHIN
POSITIVE CHARGE
“If the atom contains negatively charged electrons, then there must also be something positively charged to keep the entire atom electrically neutral.”
Negative electron plums are floating around in a sphere of positive pudding.

14. Discovery of the Nucleus
Ernest Rutherford

15. Rutherford’s Au foil Experiment
“+” charge
Rutherford’s experiment

16. Rutherford’s Nuclear Atom
Negative electrons surround nucleus amidst lots of empty space.
Positive
Nucleus

17. Discovery of the proton
Eugen Goldstein
In 1886, Goldstein observed rays in a cathode ray tube that traveled oppositely than the electrons previously discovered.

18. Protons Located in nucleus Determine which element
# of protons = atomic number
equal to # of electrons in a neutral atom

19. Chadwick 1. 1932 discovered the neutron
2. This subatomic particle is heavy enough to split a nucleus
3. Led the way to the creation of the atomic bomb

20. LETS HAVE SOME PRACTICE
Atomic Number (Protons) 6 C
Carbon 12
Element Symbol
Element Name
Mass Number
(Proton+Neutrons)
Mass Number
(Protons+Neutrons) C 12 6
Atomic Number
(Protons) 20

21. Mass Number
Almost all the mass of an atom comes from protons & neutrons
# Protons + # Neutrons = mass number

22. LETS HAVE SOME PRACTICE
Atomic # = # of protons
# protons = # electrons in an atom
Mass # = number of protons and neutrons
So,to get the # of neutrons we must Subtract
Atomic # from the Mass # = # Neutrons C 12 6
6 neutrons

23. Practice Determine the # of protons,neutrons, & electrons ProtonsB Mg 12 Zn
Protons
Neutrons
Electrons He B Mg 12 Zn 30 35
Protons
Neutrons
Electrons He 2 B Mg Zn
Protons
Neutrons
Electrons He B Mg Zn
Protons
Neutrons
Electrons He B 5 6 Mg Zn

24. Subatomic Particles Electron: e- Proton: p+ Neutron: n or n0
negative charge
9.11 x kg
Proton: p+
positive charge
1.67 x kg
Neutron: n or n0
no charge

25. What did Battleship teach us?
Battleship simulated Rutherford’s Gold Foil Experiment.
Rutherford
Battleship
Alpha Particles
Your missiles
Nucleus
Pattern Drawn
Atom is mostly empty space
All of the empty boxes

26. Anions= More Electrons
Atoms vs Ions
ATOMS
IONS
Protons = Electrons
Protons ≠ Electrons
Cations= More Protons
Positive Charge
Anions= More Electrons
Negative Charge

27. IONS cation (+) anion (-) Li+1 Cl-1 3 Protons 2 Electrons 17 Protons

28. Ions An ion is a particle with a positive (+) or negative (-) charge
Atoms that gain electrons have - charges
Atoms that lose electrons have + charges

29. Isotopes
Atoms of an element can have different numbers of neutrons – these are isotopes
The number of protons and electrons is always the same, but since more neutrons add more mass, the mass number can be different

30. BUT……Neutrons are Different
Isotopes
Isotope
Protons = Protons
BUT……Neutrons are Different So
Mass # is Different
Atom
Protons
Neutrons
Electrons
Mass #
Carbon-12 6 12
Carbon-13 7 13
Carbon-14 8 14

31. How Big Is An Atom?

32. Practice
The atomic number of an atom is always equal to the total number of:
a. Neutrons in the nucleus
b. Protons in the nucleus
c. Neutrons plus protons in the nucleus
d. Protons plus electrons in the atom

33. Practice An atom of 42Ca contains: a. 20 protons and 22 neutrons
b. 20 protons and 42 neutrons
c. 20 electrons and 42 neutrons
d. 20 electrons and 22 protons

34. Practice The nucleus of an Fe-56 atom contains:
a. 26 protons, 30 neutrons and 26 electrons
b. 26 protons, 26 neutrons and 30 electrons
c. 26 protons and 56 neutrons
d. 26 protons and 30 neutrons

35. Practice A 52Cr3+ ion contains:
a. 24 protons, 52 neutrons, 21 electrons
b. 24 protons, 28 neutrons, 24 electrons
c. 24 protons, 28 neutrons, 27 electrons
d. 24 protons, 28 neutrons, 21 electrons

36. Practice
What is the total number of electrons in an atom with an atomic number of 30 and a mass number of 65?
a. 30
b. 65
c. 35
d. 95