1. Electron Arrangements
Electron Arrangements – Lewis Dot Structures
Electron Arrangements
Lewis Dot Structures

2. Electron Arrangements
Learning Objectives
Express the arrangement of electrons in atoms using Lewis valence electron dot structures
After this lesson you will be able to express the arrangement of electrons in atoms using Lewis valence electron dot structures.

3. Octet Rule
Chemistry is almost all about stability. Compounds, reactions, almost everything will behave in ways that enhance stability.
Atoms are most stable when the outer shell (valence shell) is full or empty.
Empty means the shell beneath it is full.
In all cases, there are up to 8 electrons in the valence (outer) shell.
You can tell how many valence electrons there are based on which group the element is in

4. Lewis Dot Structures
Valence electron – an electron in an atom’s highest occupied energy level
Outermost electrons of the electron cloud
Establish chemical characteristics of elements
Only electrons shown in Lewis electron dot structures
Symbolized as dots
Valence electrons are the electrons found in the highest occupied energy level (or shell).
They are the outermost electrons of the electron cloud.
Valence electrons are important because they establish the chemical characteristics of elements.
They are the only electrons represented in Lewis electron dot structures, where they are symbolized as dots.

5. Lewis Dot Structures
Number of valence electrons is the same as the group number for representative elements (notice transition metals are not included).
The number of valence electrons is the same as the group number of representative elements (or group A elements). For example, group 7A contains elements with seven valence electrons.

6. Lewis Dot Structures
Helium is an exception because its highest occupied energy level can only hold two electrons
The exception to this pattern in the representative elements is helium. Though it is in group 8A, it only has two valence electrons because its valence shell (or highest occupied energy level) can only hold two electrons. Notice that this figure contains only representative elements. Transition metals are not representative elements and do not always have the same number of valence electrons as their group number.

7. Lewis Dot Structures Number of valence electrons determines behavior
Elements in the same group have similar chemical properties
The number of valence electrons an element has plays a major role in the behavior of the element. Notice how elements in the same group (column) of the periodic table have the same number of valence electrons.
This helps explain why elements in the same group have similar chemical properties.

8. Drawing an Electron Dot Structure
Step 1
Step 2
Identify the symbol for the element and its number of valence electrons using the periodic table.
Place the corresponding number of electron dots around the symbol. Imagine that the symbol has four sides: top, right, bottom, and left. Begin by assigning one dot per side, moving clockwise around the symbol. Then, if there are still more dots to assign, start adding a second dot to each side until all of the valence electrons have been accounted for.
Here are the steps for drawing an electron dot structure for an atom.
Step 1: Identify the symbol for the element and its number of valence electrons using the periodic table.
The element’s symbol will be the central part of the electron dot structure, while the number of valence electrons will dictate how many dots surround the symbol.
Step 2: Place the corresponding number of electron dots around the symbol. Imagine that the symbol has four sides: top, right, bottom, and left. Begin by assigning one dot per side, moving clockwise around the symbol. Then, if there are still more dots to assign, start adding a second dot to each side until all of the valence electrons have been accounted for.
The four sides represent the four orbitals in the outermost energy level of an atom of a representative element. These electrons are all negatively charged, so they repel each other and will not pair up until there is one electron in each orbital. Dot structures should never have more than two dots on any side.

9. Drawing an Electron Dot Structure
Ex) Draw the electron dot structure for phosphorus.
Step 1
Step 2
Does the result make sense?
Identify the symbol for the element and its number of valence electrons using the periodic table.
The symbol for phosphorus is P. Phosphorus is in group 5A so it has 5 valence electrons.
Place the corresponding number of electron dots around the symbol. Imagine that the symbol has four sides: top, right, bottom, and left. Begin by assigning one dot per side, moving clockwise around the symbol. Then, if there are still more dots to assign, start adding a second dot to each side until all of the valence electrons have been accounted for.
Draw the electron dot structure for phosphorus.
First, identify the symbol for the element and its number of valence electrons using the periodic table.
The symbol for phosphorus is P. phosphorus is in group 5A so it has 5 valence electrons.
Next, place the corresponding number of electron dots around the symbol. Imagine that the symbol has four sides: top, right, bottom, and left. Begin by assigning one dot per side, moving clockwise around the symbol. Then, if there are still more dots to assign, start adding a second dot to each side until all of the valence electrons have been accounted for.
The electron dot structure of phosphorus is shown.
Finally, check to make sure the result makes sense.
The result makes sense because phosphorus has five valence electrons. The first four dots are assigned singly to each side and the fifth dot is assigned to a side of the symbol that already has a dot.
Yes.

10. Practice H, As, Cl C, S, Mg Ne, Fr, Ge N, I, Te Sb, Sr, Sn
Each student in a group needs to do 1 of the following sets and then we will white board answers.
H, As, Cl
C, S, Mg
Ne, Fr, Ge
N, I, Te
Sb, Sr, Sn

11. Electron Arrangements
Learning Objectives
Express the arrangement of electrons in atoms using Lewis valence electron dot structures
You should now be able to express the arrangement of electrons in atoms using Lewis valence electron dot structures.