OBJ 4.7-4.9 Valence Electrons & Dot Diagrams

OBJ 4.7-4.9 Valence Electrons & Dot Diagrams

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OBJ 4.7: Explain where valence electrons are located within an atom

• The electrons in the outermost energy level are most important for bonding and a chemical reactions

• These electrons are called valence electrons.

Poll

What are valence electrons?

• Electrons in the outermost energy level

• Responsible for chemical reactions and bonding

• Electrons in the inside the nucleus

• Not important in chemistry

What are valence electrons?

• Valence electrons:  the electrons located in the outermost energy level of an atom

• Responsible for the chemical reactions between elements that form molecules. 

Multiple Choice

Where are valence electrons?

• In the nucleus

• In the last energy level

• In the first energy level

• Not in an atom

Using Bohr Notation

• The last number represents the number of valence electrons

• An atom can have 1-8 Valence electrons (for now)

• Example: Nitrogen 2-5

• How many valence elctrons?

• 5!

Multiple Choice

Given sodium (Na) Bohr: 2-8-1

How many valence electrons does sodium have?

• 2

• 8

• 1

• 11

Multiple Choice

Given chlorine (Cl) Bohr: 2-8-7

How many valence electrons does chlorine have?

• 2

• 8

• 7

• 17

OBJ 4.8: Identify the number of valence electrons in a neutral atom using the periodic table

• As we know, the periodic table has patterns

• We can use these patterns and the "A" group numbers to determine how many valence electrons are in a neutral element

Open Ended

What pattern did you notice?

Recognizing Patterns

• How do we determine the number of valence electrons in a neutral atom?

• For all elements located in the “A” groups:

• The number in front of the A is equal to the number of valence electrons.

• the group “A” number = # of valence e-

Multiple Choice

Beryllium (Be) is in group 2A. How many valence electrons does it have?

• 1

• 2

• 4

• A

Multiple Choice

Krypton (Kr) is in group 8A. How many valence electrons does it have?

• 2

• 8

• 36

• 18

OBJ 4.9: Draw Lewis dot structures for atoms

• What is a Lewis Dot Structure / Electron Dot Diagram?

• a picture representation of an element and its valence electrons

• Each dot represents one valence electron

Multiple Choice

Nitrogen is in group 5A so it has 5 valence elctrons. How many dots will be needed for the Lewis Dot Structure?

• 5

• 7

• 0

• 1

Nitrogen

5 valence electrons = 5 dots

4 locations for electrons

Fill the "empty" space first, then pair up after

Multiple Choice

Sulfur is in group 6A. Which is the correct Lewis Dot Structure?

Helium: the "exception"

How many total electrons does helium have?

Open Ended

Helium has an atomic number of 2. It is located in group 8A. How many valence electrons do you think it has?

Helium

• Helium has 2 electrons. So it only has 2 valence electrons.

• Elements in group 8A have full orbitals / shells

• All other elements in group 8A are said to have an "octet" 8 electrons

• Think: 2s² + 2p⁶ = 8 electrons

• There is only one orbital in the first energy level (1s)

• Helium is called a "duet"

Poll

Goals of today. Check off the box(es) that apply.

• I can explain what/where valence electrons are

• I can use the periodic table to identify the number of valence electrons in an element

• I can draw Lewis Structures for an element

• I cannot do any of the above

Open Ended

What question(s) do you have?