1. Subatomic Particles
In an atom Protons and neutrons are clumped together in a very small dense nucleus
The Electrons are found outside of the nucleus in the electron cloud

2. It is NOT that simple
Within the electron cloud there are different principal energy levels (more to come)

3. Principle Energy Levels
Principle Energy Levels are found at different distance from the nucleus
Lowest energy levels are closest to the nucleus
Highest energy levels are farthest from the nucleus

4. Remember the periods…
Elements in the same row of the periodic table have the same number of occupied energy levels

5. H and He, have one energy level
Li thru Ne, have two energy levels
AND so on…

6. Bohr
The Bohr model is used to show electron placements in the energy levels.

7. Steps to drawing a Bohr model
First step: Determine the number of protons, neutrons and electrons in each element.
Second step: Represent the nucleus as the chemical symbol and indicate the number of protons and neutrons.
Third step: Making larger circles around to represent # of energy level

8. Steps to drawing a Bohr model
Fourth step: Place electrons into the different energy levels (closest first) following the maximum # of electrons and the octet rule

9. Determine # of Electrons in each energy level (part 1)
The electrons in an atom will fill the lower energy levels before filling the higher energy levels
Electron Capacity = 2n2
n = the quantum #, the same as the energy level in question

10. Energy Levels First energy level- max 2 electrons
Second energy level- max 8 electrons
Third energy level- max 18 electrons
Fourth energy level- max 32 electrons

11. BUT WAIT IT IS NOT THAT EASY!

12. Octet Rule
Even though an energy level can contain more electrons, it stops adding at 8 electrons because having 8 electrons in an energy level makes it stable
This is why Noble Gases don’t react

13. Exceptions to the rule
Exception – 1st energy level will be stable at max # of 2 electrons
This only works easily for the 1st 20 elements

14. Why is this important
Because the valence electrons determine the how the atom reacts and forms bonds
What are valence electrons?

15. Valence Electrons
The electrons that occupy the highest energy level (outtermost)
Determines atoms likelihood of being involved in chemical reactions
Stable – non-reactive
Unstable - reactive
the number of valence electrons determines an element’s chemical properties

16. Look Back at Bohr Models
Moving across a period, what happened to the number of valence electrons.
Compare Bohr Model of Li and Na
What Trends do you notice?

17. Valence Electrons
elements in the same column of the Periodic Table have the same number of valence electrons and have similar chemical properties.

18. Valence Electron Patterns
~SKIP~

19. Stable Atoms
Have 8 valence electrons (2 valence electrons if only 1st energy level is present)
Non-reactive

20. UNstable atoms
Do NOT have 8 valence electrons (or 2 if only 1st energy level is present)
These atoms react with other atoms to achieve stability
HOW?

21. It’s all about electrons!
Atoms will gain, lose, or share electrons to become stable and will form chemical bonds

22. Molecules
A molecule is neutral chemically bonded group of atoms that act as a unit.
Molecules consist of two or more atoms. (not 2 or more elements)

23. Molecules Diatomic molecules consist of two of the same atom.
Ex. O2, N2, F2, Cl2, Br2, I2, H2

24. Compounds
Compounds are formed when two or more different elements combine.
All compounds are molecules but not all molecules are compounds.

25. What does that mean? Ex = H2O is a compound & molecule
Ex = Br2 is molecule NOT a compound

26. Compounds Two types -covalent (also called molecular) compounds
-ionic compounds

27. Covalent Compounds Made of two or more nonmetals.
Formed when electrons are shared between the atoms
This is a covalent bond
Smallest particle is called a molecule.

28. Covalent Compounds Properties include: Low melting and boiling points
Tendency to be soft and flexible

29. Covalent Compounds Do not conduct electricity
There are no electrons available to carry the current.
When in water, these compounds dissolve as molecules not ions.

30. Covalent Compounds
These compounds will dissolve in other covalent compounds.

31. Ionic Compounds
Form as the result of the attraction between of positive and negative ions

32. Ionic Compound Example
Na - Based on #p and #e; (11 p + 10 e- = +1) Na positive ion
Fl – Based on #p and #e; (9 p + 10 e- = -1) Fl negative ion
ionic bond results from the attraction of opposite charges.
sodium fluoride

33. Ion Review Ion – atom or groups of atoms with an overall charge.
Charge can be positive or negative.
Ions are formed when electrons are lost or gained.

34. Ions If electrons are lost, a positive ion is formed = CATION
If electrons are gained, a negative ion is formed = ANION

35. Ionic Compounds
The number of electrons gained or lost is shown along with the symbol of the element.
A + following the number indicates a positive charge.
A – indicates a negative charge.

36. Ionic Compounds Properties of ionic compounds include:
High melting and boiling points
Tendency to be hard and can be split.

37. Ionic Compounds
Most conduct electricity when dissolved in water or when molten.
The ion separate in water. This allows for the conduction of electricity.

38. Ionic Compounds
Ionic solids do not conduct electricity. (must be dissolved or molten)
The ions do not separate. As solids, ionic compounds are good insulators.
Many are soluble in water.

39. Ion Charges
The number of electrons that it has lost or gained determines an ion’s charge
Ions that GAIN electrons have a NEGATIVE charge and are called anions.
Ions that LOSE electrons have a POSITIVE Charge and are called cations.

40. Atoms losing and Atoms gaining
In our last example; the Na lost an electron – where did it go?
F gained that electron

41. We can figure out the number of electrons either being lost or gained without being told

42. Electrons are Lazy!
In order to be a stable atom the outside shell must either be completely filled with electrons or emptied (leaving the next shell filled).
To do this, you must decide if it’s easier to lose or gain electrons.

43. Column #
# Valence
Bohr Model
# Gain to be 8
# Lose to be 0
Gain or Lose ?
Charge?

44. Lithium Loses an Electron
Li  Li e-

45. Fluorine gains an electron
F + 1 e-  F-1

46. Ionic Bond = LiF

47. What if it was Mg instead of Li
Bohr Model of Each Mg and F
How many electrons does Mg need to gain or lose?
How many can F gain or lose?
What is the problem?
What is the solution?

48. Ionic Bond = MgF2

49. Review Based on number of valence electrons,
we can determine whether atoms will gain or lose electrons, and then
we can determine the number of atoms of each element needs to make all atoms involved STABLE
Provides chemical formula

50. Remember covalent is a little different
Two non-metals*****
Electrons are shared not lost and gained

51. Covalent Examples C H H is going to share its 1 electron with C;
this electron counts for both H and C
H is stable it has 2 electrons in 1st energy level
Carbon now has 5 electrons, what needs to happen? C H

52. Covalent Example (cont.)
Covalent Bonds
Compound = CH4

53. Okay… Lets make it a little easier
Only valence electrons involved in bonding
Use Lewis Dot Structures

54. Lewis Dot Diagram
show the bonding between atoms of a molecule by using the valence electrons.

55. Energy Level ‘Clouds’ hoku.as.utexas.edu/.../a309f04/lect1cos.html
phycomp.technion.ac.il/~phr76ja/lecture1.html