1. Valence Electrons

2. Valence Electron
An electron in an outer shell of an atom that can participate in forming chemical bonds with other atoms.

3. Valence Electron
In a single covalent bond both atoms contribute one valence electron to form a shared pair.
For main group elements, only the outermost electrons are valence electrons.
In transition metals, some inner-shell electrons are also valence electrons.

4. Valence Electron
Valence electrons are important in determining how the atom reacts chemically with other atoms.
Atoms with one or two valence electrons more than a closed shell are highly reactive because the extra electrons are easily removed to form positive ions.
Atoms with one or two valence electrons fewer than a closed shell are also highly reactive because of a tendency either to gain the missing electrons and form negative ions, or to share electrons and form covalent bonds.

5. Valence Electron
Valence electrons have the ability, like electrons in inner shells, to absorb or release energy in the form of photons.
Photon-a quantum of electromagnetic radiation, usually considered as an elementary particle that is its own antiparticle and that has zero rest mass and charge and a spin of one.
This gain or loss of energy can trigger an electron to move (jump) to another shell or even break free from the atom and its valence shell.
When an electron absorbs energy in the form of one or more photons, then it moves to a more outer shell depending on the amount of energy gained.
When an electron loses energy (photons), then it moves to a more inner shell.

6. “Blocks” of the Periodic Table
S, D, P, and F

7. Blocks
Because of the importance of the outermost electron shell, the different regions of the periodic table are sometimes referred to as periodic table blocks, name because of the subshell in which the last electron resides.

9. S-Block Consists of the first two groups:
Alkali Metals
Alkaline Earth Metals
Hydrogen and Helium
Very easily lost to form positive ions.
Helium configuration is chemically exceedingly stable and thus helium has no known stable compounds
All extremely powerful reducing agents, so much so that they never occur naturally in the free state.
Metallic forms of these elements can only be extracted by electrolysis of a molten salt, since water is much more easily reduced to hydrogen than the ions of these metals .

10. S-Block
The s-block metals vary from extremely soft (all the alkali metals) to quite hard (beryllium).
With the exception of beryllium and magnesium, the metals are too reactive for any structural use except as very minor components (<2%) of alloys with lead.

11. P-Block
The p-block of the periodic table consists of the last six groups minus helium (which is located in the s-block).
Groups 13 through 18
In the elemental form of the p-block elements, the highest energy electron occupies a p-orbital.
Contains, among others, all of the semimetals.

12. D-Block The d-block contains groups 3-12.
These groups correspond to the filling of the atomic d-orbital subshell
The d-block elements are often also known as transition metals or transition elements.
In the s- and p- blocks of the periodic table, similar properties across the periods are generally not observed: the most important similarities tend to be vertical, down groups. However the d-block is notable in that horizontal similarities across the periods do become important.

13. F-Block
The f-block, usually offset below the rest of the periodic table, comprises the lanthanides and actinides.
Consists of those elements whose atoms or ions have valence electrons in f-orbitals.
Elements of the series in which the electrons are in 4f orbitals belong to the lanthanide series.
Elements of the series in which the electrons are in 5f orbitals belong to the actinide series.