1. The Structure of the AtomOr
Modern Atomic Theory

2. Dalton’s Atomic Theory
revised Democritus’s ideas based on his research
matter is made of tiny particles called atoms
atoms of the same element are identical (size, mass, chemical properties)
English school teacher
( )

3. Dalton’s Atomic Theory (continued)
atoms of one element differ from atoms of another element
atoms cannot be created, destroyed or divided
atoms combine to form compounds
atoms can combine, separate or rearrange in chemical reactions

4. Structure of the Atom
atom – the smallest particle of an element that can exist that retains the properties of the element.

5. The size of an atom a single copper penny contains:
29,000,000,000,000,000,000 atoms
in scientific notation that number is
2.9 x1019 atoms of copper
atoms can be seen with a special kind of microscope

6. Questions remained what is the shape of an atom?
are atoms made of smaller particles?
is an atom homogenous or heterogenous?

7. Subatomic particles and the atomic nucleus

8. Static Electricity
have you ever been shocked when you touched a doorknob
static electricity made scientists in the 1800s look for a relationship between matter and electric charge

9. Experiments with Electricity
how would electricity behave in the absence of matter (in a vacuum)
they connected electrodes to the ends of vacuum tubes allowing electricity to travel through the tube

10. Cathode Rays
streams of negatively charged particles could travel through the tubes
similar cathode rays were found in all types of matter

11. JJ Thompson
researched the ratio of a cathode ray particle’s mass and charge
placed electrical and magnetic fields around cathode ray tubes and measured changes in the particle’s path

12. JJ Thompson
discovered the mass of a cathode ray particle was smaller than the smallest known atom (hydrogen)
this was the electron
based on the mass, atoms must contain other particles
This was called the Cathode Ray Tube Experiment

13. Lingering Questions
How can atoms be neutral, if they contain negative particles?
Thompson proposed his plum pudding model
cookie dough
dough is positively charged sphere
chips are negatively charged particles in it

14. Ernest Rutherford studied positively charged alpha particles
shot alpha particles at gold foil (a few atoms thick) to see if the path would deflect
An alpha particle is a helium nucleus
Gold Foil Experiment

15. Rutherford’s Results
he thought the alpha particles would go straight through or deviate a little
some particles bounced almost straight back
they must have hit something BIG

16. Rutherford’s Experiments Showed
an atom is mostly empty space
there is a tiny dense region (nucleus) in the center of an atom
the nucleus contains most of the atom’s mass
positive charges are found in the nucleus
(Be sure to write these down. The results/analysis/conclusions are the most important parts of an experiment.)

17. More Rutherford Discoveries
later he concluded the atomic nucleus contains protons
the charge of a proton is equal (but opposite) to that of an electron

18. Nuclear Atomic Model

19. Atomic Particles Particle Charge Mass (kg) Location Electron -1
9.109 x 10-31
Electron cloud
Proton +1
1.673 x 10-27
Nucleus
Neutron
1.675 x 10-27

20. Subatomic Particles
Neutrons
Protons
Electrons
Nucleus
Orbitals

21. Modern View The atom is mostly empty space Two regions
Nucleus- protons and neutrons
Electron cloud- region where you might find an electron

22. How atoms differ
Chapter 4.3

23. How atoms differ There are over 110 different kinds of atoms.
What makes atoms of one element different than another?

24. Henry Moseley ( )
discovered atoms of each element have a unique positive charge
the number of protons determines the element (e.g. every atom with 6 protons is carbon)
corresponds to the number of protons
corresponds to the atomic number

25. Atomic Number
elements are listed in order of increasing atomic number in periodic table
the number of protons is the atomic number (e.g. every atom with 6 protons is carbon)
since an atom has no net charge:
Atomic # = # of protons = # of electrons

26. Isotopes
atoms of the same element always have the same number of protons
but they can have different numbers of neutrons
most elements are a mixture of isotopes
isotopes are atoms of the same element with a different number of neutrons and a different mass

27. How atoms differ
Chapter 4.3B

28. atom
the smallest piece of an element that has all the properties of that element

29. electron
small negatively charged particle found in all atoms in the electron cloud. It has a charge of -1

30. proton
subatomic particle found in an atom’s nucleus. It has a charge of +1

31. neutron
subatomic particle found in an atom’s nucleus it has no charge (it is neutral)

32. Atomic Particles Location Mass (g) Charge Particle Nucleus
1.67 x 10-24
Neutron +1
Proton
Electron cloud
9.11 x 10-28 -1
Electron
Location
Mass (g)
Charge
Particle

33. atomic number the number of protons in an atom. It identifies the atom
Remember: APE
Atomic number = # Protons = # Electrons
(since atoms are neutral)

34. mass number
number written after an elements name, representing the sum of its protons and neutrons

35. isotope
atoms of the same element with the same # of protons, but different # of neutrons

36. Mass Number the mass of an atom is called the mass number
to calculate the number of neutrons in an isotope:
mass number - atomic number = number of neutrons

37. Isotope Notation
To distinguish between two isotopes the mass number is given along with the elements name
Potassium-39
Potassium-40
Potassium-41

38. X Symbols of isotopes Mass number Atomic number
Contain the symbol of the element, the mass number and the atomic number
Mass
number X
Atomic
number

39. Messy Math
the mass of subatomic particles are so small, they are difficult to work with
scientists adopted an atomic standard
the mass of a carbon-12 atom is said to be 12 atomic mass units (amu)
protons and neutrons have an approximate mass of 1 amu

40. Why aren’t atomic masses whole numbers?
atomic mass reported on the periodic table are a weighted average of the isotopes of that element
Chlorine is a mixture of 2 isotopes
75.770% chlorine-35 (atomic mass = )
24.230% chlorine-37 (atomic mass = )
( )(34.969) + ( )(36.966) =
=  amu

41. atomic mass unit
1/12th the mass of a carbon-12 atom

42. atomic mass
weighted average mass of the isotopes of that element

43. Measuring Matter
Chapter 11.1

44. Common Counting Units eggs paper shoes pencils dozen (12)
ream (500 sheets)
shoes
pair (2)
pencils
gross (144)

45. Chemist’s Counting Units
need a counting unit for atoms and molecules
since they are extremely small
mole = counting unit to measure the amount of a substance
1 mole = the number of particles in exactly 12 grams of pure carbon-12

46. Avogadro’s Number 1 mole = 6.0221367 x 1023 particles
rounded to 6.02 x 1023 particles
particles can be
atoms (elements)
molecules
formula units

47. How much is a mole?

48. Converting from moles to particles
use conversion factors
how many roses are in 3.5 dozen?
3.5 dozen  12 roses = 42 roses
dozen

49. mole conversions how many particles are in 3.50 moles of sucrose?
3.50 moles  6.02 x 1023 particles
mole
21.1 x 1023  2.11 x 1024 particles

50. particle to mole conversions
how many moles are in 4.50 x 1024 atoms of Zn?
4.50 x 1024 atoms  mole
6.02 x 1023 atoms
7.48 moles Zn

51. mole
SI base unit to measure the amount of a substance (element or compound)

52. molar mass
mass in grams of any pure substance; for elements, the molar mass is the atomic mass

53. Avogadro’s number
the number x 1023, represents particles in a mole