2. Objectives Identify three subatomic particles
Understand how subatomic particle was discovered
Compare the properties of the subatomic particles
Distinguish between atomic number and mass number
Calculate the number of protons, electrons and neutrons in an atom

3. Subatomic Particles Subatomic particles
- 3 important to chemistry: protons, neutrons, electrons

4. Protons
Part of the nucleus
Have positive (+) charge

5. Protons Definition - a positively charge subatomic
particle that is found in the nucleus of an atom
About Protons
- proton is nearly 2000 times more massive than the electron, but equal in charge and opposite in sign to the electron
- number of protons in the nucleus is electrically balanced by an equal number of electrons
ex. oxygen atom: contains 8 electrons and protons: neutral atom, no net charge

6. Electrons
Orbit around the nucleus
Have negative (-) charge

7. Electron
Definition
- a negatively charged subatomic particle that is found in the space outside the nucleus
- name comes from the Greek word for amber
- Amber: material discovered by early Greeks that was found to exhibit the effects of electrical charging
ex. Ben Franklin: Key/Kite
- lead others to experiment with electric currents through gases in sealed tubes

8. Neutrons
Part of the nucleus
Have neutral charge

9. Neutrons
Definition
- is a neutral subatomic particle that is found in the nucleus of the atom
- mass almost exactly equal to that of the proton

10. Comparing Subatomic Particles

11. Atomic Number Definition - number of protons in the atom
ex. Oxygen 8p + 8n = 16
- elements are classified by this number
- continues up to 119
- unique to a given element
- all atoms are electrically neutral, meaning the number of electrons must equal the number of protons
this arrangement of elements by their atomic numbers makes up the periodic table
Usually located at the upper left hand corner

12. # protons in an atom = # electrons
Atomic Number
Atoms are composed of identical protons, neutrons, and electrons
How then are atoms of one element different from another element?
Elements are different because they contain different numbers of PROTONS
The “atomic number” of an element is the number of protons in the nucleus
# protons in an atom = # electrons

13. Atomic Number
Atomic number (Z) of an element is the number of protons in the nucleus of each atom of that element.
Element
# of protons
Atomic # (Z)
Carbon 6
Phosphorus 15
Gold 79

16. Complete Symbols
Contain the symbol of the element, the mass number and the atomic number.
Mass
number X
Superscript →
Atomic
number
Subscript →

17. Br Symbols 80 35 Find each of these: number of protons
number of neutrons
number of electrons
Atomic number
Mass Number 80 Br 35

18. Symbols
If an element has an atomic number of 34 and a mass number of 78, what is the:
number of protons
number of neutrons
number of electrons
complete symbol

19. Symbols
If an element has 91 protons and 140 neutrons what is the
Atomic number
Mass number
number of electrons
complete symbol

20. Symbols
If an element has 78 electrons and 117 neutrons what is the
Atomic number
Mass number
number of protons
complete symbol

22. Mass Number
- although a given type of atom will usually contain a certain number of neutrons in the nucleus, a small percentage will not
ex. most hydrogen atoms contain no neutrons
- a small percentage contain one neutron and a smaller percentage two neutrons
What do we call atoms with a different number of neutrons?
- isotopes

23. Mass Number Definition
- the total number of protons and neutrons in the nucleus of an atom
Tells us how much one atom weighs in atomic mass units.
-mass number – atomic number = neutrons
ex. N: mass number of 14
atomic number of 7
7neutrons

25. How to Calculate the Mass Number
Mass number is the number of protons and neutrons in the nucleus of an isotope:
Mass # = p+ + n0

26. Mass Number Cont.
usually found at the bottom of the atomic symbol, and sometimes found written at the bottom left of an atomic symbol
ex. 16O

30. Atomic Mass

31. Atomic Mass Definition - mass of an atom in atomic mass units (amu)
- atoms have very little mass
- equal to 1/12th of the mass of carbon
- often an average mass
- weighted mass
AMU or the Dalton (Da)
- equal to x kg

32. Atomic Mass How heavy is an atom of oxygen?
It depends, because there are different kinds of oxygen atoms.
We are more concerned with the average atomic mass.
This is based on the abundance (percentage) of each variety of that element in nature.
We don’t use grams for this mass because the numbers would be too small.

33. Composition of the nucleus
Atomic Masses
Atomic mass is the average of all the naturally occurring isotopes of that element.
Isotope
Symbol
Composition of the nucleus
% in nature
Carbon-12
12C
6 protons
6 neutrons
98.89%
Carbon-13
13C
7 neutrons
1.11%
Carbon-14
14C
8 neutrons
<0.01%
Carbon =

35. Frederick Soddy (1877-1956) proposed the idea of isotopes in 1912
Isotopes are atoms of the same element having different masses, due to varying numbers of neutrons.
Soddy won the Nobel Prize in Chemistry in 1921 for his work with isotopes and radioactive materials.

37. Isotopes
Atoms with the same number of protons but different numbers on neutrons
Example: Carbon
So you can change the number of neutrons and the element still maintains its identity

38. Isotopes are atoms of the same element having different masses, due to varying numbers of neutrons.
Protons
Electrons
Neutrons
Nucleus
Hydrogen–1
(protium) 1
Hydrogen-2
(deuterium)
Hydrogen-3
(tritium) 2

39. Isotopes Elements occur in nature as mixtures of isotopes.
Isotopes are atoms of the same element that differ in the number of neutrons.

43. Mass Number/Avg Atomic Weight

46. Objectives
Describe Bohr’s model of the atom and the evidence for energy levels
Explain how the electron cloud model represents the behavior and locations of electrons in atoms

47. Bohr’s Model of the Atom
- an early conceptual model of the atom
- classic planetary model in which electrons whirl around the small but dense nucleus: like planets orbiting the Sun
- developed by the Danish physicist Niels Bohr in 1911
- each electron has a certain energy that is determined by it’s path around the nucleus
- explains how atoms (lose) emit or (gain) absorb energy
resulting energy: energy level

48. Bohr’s Model: Energy Levels
Definition
- any of the possible energies an electron may have in an atom
Evidence
- measured amount of energy gained or lost
- when energy is lost we often see it as a light
ex. fireworks
this model no longer explained all observations being made by scientists and new models were created
ex. Electron cloud model

49. Atoms have neutral charge
# of Protons (+) = # of Electrons (-) = 0 charge
Example: Hydrogen
How many electrons does C have?
carbon has 6 electrons.

50. Electrons orbit in “shells”
1st shell can fit 2 electrons
2nd and 3rd shells can fit 8 electrons
1st period/row
2nd period/row
3rd period/row

51. Atoms want their shells to be full
2 electrons in first shell
8 electrons in 2nd and 3rd shells
Examples:

52. Drawing Bohr Models

53. Bohr Models Bohr models are used to predict reactivity in elements.
Reactivity refers to how likely an element is to form a compound with another element.
When looking at Bohr models, we look at its valence electrons (the electrons on the last energy level) to determine reactivity.

54. Drawing Bohr Models Draw the nucleus.
Write the number of neutrons and the number of protons in the nucleus.
Draw the first energy level.
Draw the electrons in the energy levels according to the rules below. Make sure you draw the electrons in pairs.
Keep track of how many electrons are put in each level and the number of electrons left to use.

55. Rules for Energy Levels
Level 1 (closest to the nucleus) can hold a maximum of 2e.
Level 2 can hold a max of 8e.
Level 3 can hold a max of 18e.
Level 4 can hold a max of 32e.
You must fill one level before going on to draw the next level!

56. Guided Practice
In order to draw Bohr models of these elements, you must first determine the number of protons, neutrons, and electrons. Once you have found this information, follow the directions to draw your model. 6 6 6 6 C
Carbon
12.011
Protons: _____ Neutrons: _____ Electrons: ______
How many energy shells will this have? ____
How many valence (outer) electrons does this element have? ____
Bohr Model: 2 4

57. Guided Practice 16 S
Sulfur
32.066 16 16 16
Protons: _____ Neutrons: _____ Electrons: ______
How many energy shells will this have? ____
How many valence (outer) electrons does this element have? ____
Bohr Model: 3 6

58. Guided Practice Protons: _____ Neutrons: _____ Electrons: ______3 Li
Lithium
6.941
Protons: _____ Neutrons: _____ Electrons: ______
How many energy shells will this have? ____
How many valence (outer) electrons does this element have? ____
Bohr Model: 3 4 3 2 1

59. Guided Practice 10 10 10 10 Ne
Neon
20.180
Protons: _____ Neutrons: _____ Electrons: ______
How many energy shells will this have? ____
How many valence (outer) electrons does this element have? ____
Bohr Model: 2 8

60. Guided Practice 15 16 15 15 P
Phosphorus
30.974
Protons: _____ Neutrons: _____ Electrons: ______
How many energy shells will this have? ____
How many valence (outer) electrons does this element have? ____
Bohr Model: 3 5

61. Guided Practice 11 12 11 11 Na
Sodium
22.990
Protons: _____ Neutrons: _____ Electrons: ______
How many energy shells will this have? ____
How many valence (outer) electrons does this element have? ____
Bohr Model: 3 1