1. Do Now Group Period Element Name Symbol P (+) N (0) E (-) 2 4 17 5 136

2. Structure of an atom:
Nucleus:
Protons +
Neutrons 0
Electrons -

3. Electrons Some electrons are closer to the nucleus than others.
The closer to the nucleus the greater the attraction, therefore the harder to remove.

4. Electron Energy Stairwell
Nucleus is the ground floor.
Electrons closest to the nucleus are the first floor, they are held most tightly.
The next sphere is the second floor and so on.
The first level is also the smallest it can hold 2 electrons.
Second floor is larger and can hold 8 electrons
Third floor can hold 18 electrons
Fourth floor can hold 32 electrons

5. Bohr Diagram
The Bohr model, introduced by Niels Bohr in 1913, depicts the atom as a small, positively charged nucleus surrounded by electrons that travel in circular orbits around the nucleus—similar in structure to the solar system, but with electrostatic forces providing attraction, rather than gravity
(Wikipedia)

7. Hydrogen 1H1 1 Atomic Mass = 1 - Atomic # = 1 # neutrons = 0
Atomic # = # protons = 1 1
# protons = 1
# neutrons = 0
NOTE: There are no
neutrons in a
Hydrogen atom!
# electrons = # protons = 1

8. Helium 4He2 2 Atomic Mass = 4 - Atomic # = 2 # neutrons = 2
Atomic # = # protons = 2 2
# protons = 2
# neutrons = 2
NOTE: The first level
of Helium is full!
# electrons = # protons = 2

9. Lithium 7Li3 2 1 Atomic Mass = 7 - Atomic # = 3 # neutrons = 4
Atomic # = # protons = 3 2 1
# protons = 3
# neutrons = 4
NOTE: The first energy
level is full, so the
3rd electron goes to the
next energy level!
# electrons = # protons = 3

10. Beryllium 9Be4 2 Atomic Mass = 9 - Atomic # = 4 # neutrons = 5
Atomic # = # protons = 4 2
# protons = 4
# neutrons = 5
NOTE: There are 2 electrons
on the outer energy level!
# electrons = # protons = 4

11. Boron 11B5 2 3 Atomic Mass = 11 - Atomic # = 5 # neutrons = 6
Atomic # = # protons = 5 2 3
# protons = 5
# neutrons = 6
NOTE: There are
3 electrons on the
outer energy level!
# electrons = # protons = 5

12. Magnesium 24Mg12 2 8 Atomic Mass = 24 - Atomic # = 12 # neutrons = 12
Atomic # = # protons = 12 2 8
# protons = 12
# neutrons =12
NOTE: The outer
level has 2 electrons!
# electrons = # protons = 12

13. Aluminum 27Al13 2 8 3 Atomic Mass = 27 - Atomic # = 13 # neutrons = 14
Atomic # = # protons = 13 2 8 3
# protons = 13
# neutrons =14
NOTE: There are
3 electrons in the
outer energy level!
# electrons = # protons = 13

14. Silicon 28Si14 2 8 4 Atomic Mass = 28 - Atomic # = 14 # neutrons = 14
Atomic # = # protons = 14 2 8 4
# protons = 14
# neutrons =14
NOTE: There are
4 electrons in the
outer energy level!
# electrons = # protons = 14

15. Phosphorous 31P15 2 8 5 Atomic Mass = 31 - Atomic # = 15
# neutrons = 16
Atomic # = # protons = 15 2 8 5
# protons = 15
# neutrons =16
NOTE: There are
5 electrons in the
outer energy level!
# electrons = # protons = 15

16. Sulfur 32S16 2 8 6 Atomic Mass = 32 - Atomic # = 16 # neutrons = 16
Atomic # = # protons = 16 2 8 6
# protons = 16
# neutrons =16
NOTE: There are
6 electrons in the
outer energy level!
# electrons = # protons = 16

17. Chlorine 35Cl17 2 8 7 Atomic Mass = 35 - Atomic # = 17 # neutrons = 18
Atomic # = # protons = 17 2 8 7
# protons = 17
# neutrons =18
NOTE: There is room for only
one more electron in the
outer energy level!
# electrons = # protons = 17

18. Argon 40Ar18 2 8 Atomic Mass = 40 - Atomic # = 18 # neutrons = 22
Atomic # = # protons = 18 2 8
# protons = 18
# neutrons = 22
NOTE: All three energy
levels are full!
# electrons = # protons = 18

19. Chemical Activity
Since the electrons on the inner shells are buried they cannot leave the atom.
Which would be the only electrons that can detach from the atom?
The one in the last layer!
They are also the most loosely attached to the nucleus because they are so far away.

20. Valence Electrons: The electrons in the outer most energy level
To determine the valence electron number look at the periodic table.
Group #
# Valence electrons 1 2
3-12
Usually 2 13 3 14 4 15 5 16 6 17 7 18
8* (He 2)

21. … or look at the box on the periodic table12
Electron
Configuration
Valence electrons are the last number 6
2 - 4

22. Lewis Dot Diagrams
Dot diagrams are used to show the number of valence electrons.
Carbon = 4 valence electrons C
Practice: Write the electron dot diagrams for the following elements.
 Magnesium Oxygen
Nitrogen Cesium
Tin Argon
Aluminum Helium

23. DO NOW What is a compound?
When two elements combine to make something new.
How do compounds form?
Electrons are transferred from one element to another.

24. DO NOW What are valence electrons?
The electrons in the outermost energy level
Is the last energy level always full? No
What is the difference between a Bohr model and a Lewis dot diagram?
A Bohr model shows all the electrons, protons and neutrons, a Lewis dot diagram only shows valence electrons

25. Chemical Bonding
All chemical reactions involve the movement of valence electrons forming or breaking chemical bonds to form a Compound.
Compound: Molecule made of two or more elements.

26. Magic Number
The Magic Number= 8 valence electrons- atoms bond to get a full valence shell.
The last shell wants to be full to be stable!
How can chlorine get another
Electron to become stable?

27. What happens if valence electrons are transferred?
Electrons are exchanged between objects, giving them a charge. + _

28. IONS
Ion- electrically charged atom formed when electrons move during reactions
+ ion- formed when electrons are lost
– ion- formed when electrons are gained

29. Ionic Bonds
Ionic Bonds- forms between a metal and a nonmetal. Electrons are moved from one atom to the other.

30. + positive Metals Metals have 1,2 or 3 valence electrons.
Will they give or get electrons?
GIVE!
It’s easier to give away a few than to get a lot.
If metals give away electrons will they become positive or negative?
+ positive

31. - negative Non Metals Nonmetals have 5 or more electrons.
Will they give away or take electrons?
TAKE
It’s easier for them to take a few than to give away a lot.
Will they become positive or negative?
- negative

32. Let’s make compounds!!
Potassium + Flourine

33. Magnesium + Iodine

34. Sodium + Oxygen

35. Sodium + Chlorine

36. Aluminum + Chlorine

37. DO NOW: Aluminum + Oxygen
Draw the dot diagrams, move the electrons and write the final compound.

38. Oxidation Number
- The charge that the ion gets when it either loses or gains electrons is called the oxidation number.
The sum of the oxidation numbers for the atoms in a compound must be zero
In order for a compound to exist, it must be electrically neutral

39. DO NOW What does oxidation number refer to?
The charge that the ion gets when electrons are transferred from one atom to another.
This also tells you the combining ability of the atom.

40. DO NOW What charge do metals get when forming an ionic bond?
What charge do nonmetal gets when forming an ionic bond?
What is the oxidation number of Calcium?
What is the oxidation number of Bromine?
What would the compound be between Calcium and Bromine?

41. NaCl
Sodium loses one electron so it has an oxidation number of 1+
Na 1+
Chlorine gains one electron so it has an oxidation number of 1-
Cl 1-
This works because 1(1+) + 1(1-) = 0
The sum of the oxidation numbers for the atoms in a compound is zero

42. Criss-Cross Method Shortcut
The ‘criss-cross’ method is a simple way of determining a formula
The oxidation number of one element becomes the subscript of the other
Na +1 O -2

43. ‘Criss - Cross’ Method
The formula for the compound composed of potassium and Sulphur
The formula for the compound composed of calcium and bromine

44. Steps to follow Step 1- write element symbols with the metal first
Step 2- write the oxidation numbers next to the elements
Metals = valence electron number (with a (+) sign)
Nonmetals = (valence electron #) – 8
Step 3- criss-cross numbers without signs
Step 4- don’t write 1’s for final compound

45. ‘Criss-Cross’ Method Practice
Using Oxidation Numbers, write formulas for the compounds formed from the following elements
Sodium & Bromine
Potassium & Iodine
Calcium & Fluorine
Hydrogen & Sulfur
Magnesium & Fluorine
Lithium & Sulfur
Remember to check that the sum of the oxidation
numbers is equal to zero!

46. NaBr

47. KI

48. CaF2

49. H2S

50. MgF2

51. Li2S

52. Sum It Up
The oxidation # of the metal becomes the subscript of the nonmetal.
The oxidation # of the nonmetal becomes the subscript of the metal.
Remember to drop the charge when you make it the subscript.

53. Naming Compounds Binary Compounds are composed of two elements
Binary Compounds are named beginning with the element with the positive oxidation number (The Metal)
The name of the second element will end in an -ide
NaCl : Sodium Chloride
CaS : Calcium Sulfide
FeO : Iron Oxide

54. Name the Compound 1. Potassium + Nitrogen 2. Magnesium + Arsenic
3. Gallium + Phosphorous
4. Indium + Iodine
5. Barium + Fluorine
6. Aluminum + Oxygen

55. Counting Atoms in a Compound
Subscripts- small number next to an element
Example: Al₂ O₃
1 compound: Al₂O₃
2 elements: Al and O
5 atoms : 2 aluminum and 3 oxygen atoms

56. Compounds with parentheses
Multiply the number outside the parentheses by all of the subscripts inside
Example:
Ga₂ (SO₄)₃
Ga = 2 , S = 1x3 = 3 , O = 4x3 = 12

57. Find the number of atoms for each element in the following compounds:
AgNO3
Al(ClO3)3
(NH4)2SO3

58. DO NOW
What is the difference between a physical change and a chemical change?

59. Physical Change
A change in a material that does not create new substances.
Examples:
Melting, and other phase changes
Cutting
Shaving
Squashing

60. Chemical Change Creates new substances. Examples: Burning anything
(new substance=ash, energy, heat)
2 chemicals reacting.