1. Unit 3 Periodic Table and Valence electrons

2. Valence electrons
Valence electrons are electrons located in the outermost energy level.
They are located only in the s and p sublevels
These electrons are involved in chemical bonding.

3. Electron Configurations
An element’s electron configuration shows how many valence electrons it has.
Example:
1s22s22p63s23p64s23d104p4
Valence electrons = 6

4. Practice How many valence electrons do the following elements have?
1s22s22p63s23p64s23d104p6
1s22s22p63s23p2
1s22s2
8 valence electrons
4 Valence Electrons
2 valence electrons

5. Octet Rule
Most elements want to have 8 valence electrons (exception He)
Elements will gain or lose electrons in their valence shell in order to achieve an octet.
This process forms Ions.
Ions have the same electron configuration as their nearest noble gas.

6. Positive Ions
Elements with less than 4 valence electrons lose their outermost “s” and “p” sublevel electrons
Example
Be: 1s22s2 has 2 valence electrons
Be2+: 1s2 notice the ion has the same
configuration as He
They always form positive ions.

7. Negative Ions
Elements with more than 4 valence electrons gain electrons in their outermost “p” sublevel
Example
O: 1s22s22p4 has 6 valence electrons
O2-: 1s22s22p6 now has 8 valence
electrons just like Ne
They always form negative ions.

8. Ion Formation Summary 1+ 2+ 3+ 3- 2- 1-
Atoms gain or lose electrons to become more stable.
They achieve the same electron configuration as the Noble Gases. 1+ 2+ 3+ 3- 2- 1-

9. Noble Gas Shorthand Electron Configurations
Longhand Configuration
S 16e-
1s2
2s2
2p6
3s2
3p4
Core Electrons
Valence Electrons
Shorthand Configuration
S 16e- [Ne] 3s2 3p4

10. Noble Gas Shorthand Configuration
Core e-: Go up one row and over to the Noble Gas.
Valence e-: On the next row, fill in the # of e- in each sublevel.

11. Noble Gas Shorthand Notation
Example - Germanium
[Ar]
4s2
3d10
4p2

12. Modern Periodic Table
Elements are arranged by increasing atomic number.
Recall that atomic number gives the number of protons in the nucleus of an atom.

13. Periods Horizontal rows on the periodic table are called periods.
Elements in the same period have the same number of valence shells.
Elements in the same period share no similar chemical properties.

14. Periods

15. Groups / Families
Vertical columns on the periodic Table are called groups.
Groups are numbered 1-18
Elements in the same group have the same chemical properties because they have the same number of valence electrons.
Some groups have special names.

16. Groups/Families

17. Group 1 Metals Known as Alkali Metals
Most active metals on periodic table
React violently with water, and become more active down the group
Only have 1 valence electron (because they all end in s1)
They all form ions with a +1 charge.

18. Group 2 Metals Known as Alkaline Earth Metals
Also extremely reactive, but not as much as Alkali Metals
Contain 2 valence electrons (they end in s2)
They all form ions with a +2 charge.

19. Groups 3-12 These groups are known as Transition Metals
Not very reactive metals
Generally have 2 valence electrons
Some of their “d” orbital electrons jump around into “p” orbitals so many of these elements have more than one possible positive charge.
Form colorful ion solutions (bright vibrant colors)

20. Group 17 Known as Halogens
Extremely reactive nonmetals; reactivity increases up a group (Fluorine the most active)
Have 7 valence electrons (e- configuration ends in s2p5)
Most of these elements are toxic in their natural state
Most are also diatomic in their natural state (F2, Br2, Cl2, I2)
They all form ions with a (-1) charge.

21. Group 18 Known as Noble gases Unreactive nonmetals
All have 8 valence electrons
(e- configuration ends in s2p6), except Helium (which has 2 electrons)
They do not form ions.