Section 4.2 & 4.2 lecture for Honors & Prep Chemistry

1. Lecture 4.1 & 4.2- Atomic structure
Quiz 4 is this Friday
Chapter 3 & 4 homework is DUE Friday

2. Everything in the world is made of
less than 100 types of atoms called
elements.

3. Everything in the world is made of
less than 100 types of atoms called
elements.
They combine to make compounds
like letters of the alphabet make
words.

4. In a chemical reaction, one
substance changes to another by
reorganizing the way the atoms are
attached to each other.

5. In 1803, John Dalton proposed a
theory which accurately
described and predicted
chemical behavior.
Dalton’s four postulates are still
accepted today (with a few
modifications)

6. Dalton’s Atomic Theory- 4 postulates
All elements are composed of tiny
indivisible particles called atoms.

7. Dalton’s Atomic Theory- 4 postulates
All elements are composed of tiny
indivisible particles called atoms.
Dalton was
wrong about
the “indivisible”
part, but the
rest of this
tenet is still
fundamental to
chemistry.

8. Dalton’s Atomic Theory- 4 postulates
Atoms of the same element are identical.
The atoms of any one element are
different from those of any other element.

9. Dalton’s Atomic Theory- 4 postulates
Atoms of different elements can
physically mix together or can chemically
combine in simple whole-number ratios
to form compounds.

10. 4.1
Dalton’s Atomic Theory- 4 postulates
Chemical reactions occur when atoms
are separated, joined, or rearranged.
Atoms of one element are never changed
into atoms of another element in a
chemical reaction.

11. Atoms are composed of protons,
neutrons, and electrons.

12. Atoms are composed of protons,
neutrons, and electrons.
Protons and neutrons are found in
the tiny nucleus of the atom.

13. Atoms are composed of protons,
neutrons, and electrons.
Protons and neutrons are found in
the tiny nucleus of the atom.
Electrons are
found outside the
nucleus. The cloud
that they form is
the majority of the
atom’s size.

14. The number of protons in an
atom determines the type of
atom.
Each element has a certain number of
protons.

15. The electrons in an atom are
involved in chemical reactions.

16. Protons and neutrons have similar mass
1 amu = 1 atomic mass unit
= the mass of 1 proton or neutron

17. Protons and neutrons have similar mass
1 amu = 1 atomic mass unit
= the mass of 1 proton or neutron
Electrons have almost no mass

18. All of an atom’s mass is in the
protons and neutrons in the
relatively small nucleus.

19. All of an atom’s mass is in the
protons and neutrons in the
relatively small nucleus.
All of an atom’s size
is created by the
electron cloud
outside the nucleus.

20. Protons have a positive charge

21. Protons have a positive charge
Electrons have a negative charge

22. Protons have a positive charge
Electrons have a negative charge
Neutrons have no charge
Neutrons are neutral

23. Atoms are neutral
because they have an equal
number of protons and
electrons.

24. Subatomic Particles

25. Sizing up the Atom
Despite their small size, individual atoms
are observable with instruments such as
scanning tunneling microscopes.
Iron Atoms
Seen
Through a
Scanning
Tunneling
Microscope

26. Dearest students,
The history of the evolution of atomic theory is
always presented in order to impress upon students
the importance of building upon current theories in
order to get closer to the truth. In science, we honor
the early “incorrect” theories because they led us to
the heightened understanding that we have today. In
keeping with this philosophy, we realize that our
current understandings are just stepping stones
towards the truth.
With love,
Mrs. Smith
P.S. The following material will be very “lightly”
tested.
The next slides are for HONORS ONLY.

27. History of the atomic model
Electrons
a. In 1897, the English physicist J. J.
Thomson discovered the electron
in his cathode ray experiments.
b. Electrons are negatively charged
subatomic particles.

28. History of the atomic model
a. Thomson performed
experiments that involved
passing electric current through
gases at low pressure.
The result was a glowing beam,
or cathode ray, that traveled
from the cathode to the anode.

29. History of the atomic model
a. Cathode Ray Tube

30. History of the atomic model
a. A cathode ray is deflected by a
magnet.

31. History of the atomic model
a. A cathode ray is deflected by
electrically charged plates.

32. History of the atomic model
a. Thomson concluded that a
cathode ray is a stream of
electrons.
b. Electrons are parts of the
atoms of all elements.

33. History of the atomic model
Protons and Neutrons
a. In 1886, Eugen Goldstein observed
a cathode-ray tube and found rays
traveling in the direction opposite to
that of the cathode rays. He concluded
that they were composed of positive
particles.
b. Such positively charged subatomic
particles are called protons.

34. History of the atomic model

35. History of the atomic model
a. In 1932, the English physicist
James Chadwick confirmed the
existence of the neutron.
b. Neutrons are subatomic particles
with no charge but with a mass
nearly equal to that of a proton.

37. History of the atomic model
a. J.J. Thompson and others
supposed the atom was filled with
positively charged material and
the electrons were evenly
distributed throughout.
b. This model of the atom turned out
to be short-lived, however, due to
the work of Ernest Rutherford
(1871–1937).

38. History of the atomic model
a. Ernest Rutherford’s Portrait

39. History of the atomic model
Rutherford’s Gold-Foil Experiment
a. In 1911, Rutherford and his
coworkers at the University of
Manchester, England, directed a
narrow beam of alpha particles
at a very thin sheet of gold foil.

40. History of the atomic model
a. Rutherford’s Gold-Foil Experiment

41. History of the atomic model
a. Alpha particles scatter from the gold foil.

42. History of the atomic model
a. Alpha particles scatter from the gold foil.

43. History of the atomic model

44. History of the atomic model
The Rutherford Atomic Model
a. Rutherford concluded that the
atom is mostly empty space.
All the positive charge and almost all
of the mass are concentrated in a
small region called the nucleus.
b. The nucleus is the tiny central core of
an atom and is composed of protons
and neutrons.

45. History of the atomic model
In the nuclear atom, the protons
and neutrons are located in
the nucleus.
The electrons are distributed
around the nucleus and
occupy almost all the volume
of the atom.