1. Valence and Core Electrons
Life on the Edge
Valence and Core Electrons

2. Atoms
The Atom is the smallest particle of a substance that can exist by itself or be combined with other atoms to form a molecule.
Atoms of course are three dimensional and actually take up space in three dimensions

3. Atomic Models
Atomic Models are used to understand atoms in a much more simplified way
Represented in 2D and not to scale.
Easier to draw

4. Electron Shells
Are the levels around the nucleus where electrons can be found
These are energy levels
These levels are represented on models by spheres or circles

5. General Patterns of Electrons
Based on your handout, what do lithium, sodium, and potassium all have in common
Each has two electrons in the first shell
One electron in the outermost shell

6. General Patterns of Electrons
If you know what group an element is in, what can you predict about its electron arrangement?
The number of electrons in the outer most shell

7. General Patterns of Electrons
What does the period an element is in tell you about its electrons?
The number of electron shells

8. General Patterns of Electrons
How can you determine the arrangement of an element’s electron from the position in the periodic table
The number of shells is the same as the period number
The number of electrons in the outermost shell is the same as the group number
The inner shells have 2 electrons in the first shell
8 electrons in the second shell,
8 electrons in the third shell for elements before the transition elements and 18 electrons in the third shell for elements after the transition elements

9. Key Points
The atomic number of an element is the same as the total number of electrons
As you go from one element to the next in the periodic table, the number of electrons increase by one.
The number of electrons corresponds to the atomic number

10. Key Points
The period (row) number of the element is the same as the number of electron shells
As you go down the periodic table, from one period to the next, the number of electron shells increase by one.
In the first period, the atoms have electrons in only one shell
In the second period, the atoms have electrons in two shells
In the fourth period, the atoms have electrons in four shells

11. Key Points
For main-group elements, (non-transitional), the group number of the elements is the same as the number of electrons in the outermost shell
Example:
All Group 4A elements have 4 electrons in their outermost shell
All Group 8A elements have 8 electrons in their outermost shell

12. Valence Shell
The valence shell is the outermost shell in an atom

13. Valence Electron
The valence electron is the electron located in the outermost electron shell of an atom
Valence
electron

14. Core Electrons
The core electrons are all the other electrons in an atom that are not on the valence shell
Valence electron

15. Do Valence and Core Electron Sheet

16. Valence and Core Electron sheet
What patterns do you see in the number of valence electrons in the table?
Valence electron same as group number
Increase by one in the period, 1-8

17. Valence and Core Electron sheet
How do the numbers of core electrons vary across the second row?
They all remain at 2

18. Valence and Core Electron sheet
Explain why there is a change in the number of core electrons across the fourth row
There are ten transitional element between Ca and Ga, so ten more electrons get filled in

19. Key Question
Why do elements in the same group in the periodic table have similar properties?
Electrons occupy distinct areas around the nucleus called electron shells. The arrangement of electrons in these shells are highly predictable
For main group elements, elements in the same group have the same number of valence electrons
The number of valence electrons increase across a period
The number of shells and the number of core electrons increase as you go down a group