Valence Electrons

Valence Electrons

Middle School

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Learning Objectives

• Define valence electrons and their role in chemical reactivity.

• Use the periodic table to determine the number of valence electrons.

• Draw electron dot diagrams for various elements.

• Explain how valence electrons determine an element's chemical properties.

• Describe why noble gases are stable and unreactive.

Key Vocabulary

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Valence Electrons

The electrons in an atom's outer shell that are involved in chemical bonding and reactions.

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Electron Dot Diagram

A model of an atom showing the chemical symbol and dots for its valence electrons.

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Periodic Table Group

A column in the periodic table where elements have the same number of valence electrons.

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Noble Gases

Group 18 elements that are very stable because they have a full outer energy level.

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Semiconductors

Elements that can conduct electricity under certain conditions, but not as well as metals.

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Understanding Valence Electrons

• Valence electrons are found in the outermost shell of an atom.

• They determine how an atom reacts and forms chemical bonds with others.

• An atom is most stable with a full outer shell of 8 electrons.

• Atoms gain, lose, or share electrons to become stable like noble gases.

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Multiple Choice

What is the primary reason atoms react to gain, lose, or share valence electrons?

• To increase the total number of electrons in the atom.

• To move their electrons closer to the nucleus.

• To become less like the noble gases.

• To achieve the most stable arrangement of 8 electrons in their outer shell.

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Electron Dot Diagrams

• An electron dot diagram is a simple model showing valence electrons.

• It shows the chemical symbol with dots for each valence electron.

• The dots are placed on four sides, with a maximum of eight dots.

• For example, Lithium (Li) has one dot and Carbon (C) has four.

Multiple Choice

An element is shown with its chemical symbol and has four dots drawn around it. What do these four dots represent?

• The number of electron shells in the atom.

• The number of protons in the nucleus.

• The total number of electrons in the atom.

• The element's four valence electrons.

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Valence Electrons & The Periodic Table

• The periodic table shows patterns in the number of valence electrons.

• Elements in the same column have the same number of valence electrons.

• This gives these elements very similar chemical properties and behaviors.

• Moving across a row increases the number of an element's valence electrons.

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Multiple Choice

Why do elements in the same group of the periodic table have similar chemical properties?

• Because they have the same number of electron shells.

• Because they have the same number of valence electrons.

• Because they are in the same row of the periodic table.

• Because they have the same number of protons.

How Valence Electrons Affect Reactivity

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Group 1: Loses Electrons

• ​These elements have only one valence electron.

• ​​They are very reactive and eager to lose one electron.

• ​Losing an electron makes these atoms become much more stable.

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Group 17: Gains Electrons

• ​These elements have seven valence electrons in their outer shell.

• ​​They are also very reactive and want to gain one electron.

• ​Gaining an electron makes these atoms become much more stable.

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Group 18: Stable

• ​These elements have a full outer shell of 8 electrons.

• ​​This makes the elements in this group very stable.

• ​They are unreactive and do not form chemical bonds easily.

Multiple Choice

Why are elements in Group 18 (noble gases) known for being stable and unreactive?

• They want to gain one more electron to be stable.

• They are eager to lose one valence electron.

• They have the fewest valence electrons.

• They already have a full outer shell of 8 valence electrons.

Valence Electrons and Electrical Conductivity

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Metals

• ​Metal atoms, like copper, easily give up their valence electrons.

• ​​These electrons can move freely, creating a flow of electric current.

• ​This is the reason why metals are good electrical conductors.

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Nonmetals

• ​Atoms of nonmetals hold on tightly to their valence electrons.

• ​​Since electrons cannot move freely, a current cannot flow easily.

• ​This makes nonmetals very poor conductors of electricity.

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Metalloids

• ​These elements are also known as semiconductors, like silicon.

• ​​They can conduct some electricity, but not as well as metals.

• ​Their conductivity can often increase as the temperature rises.

Multiple Choice

Why are metals effective at conducting electricity?

• Their valence electrons can move freely and carry a current.

• They hold onto their valence electrons very tightly.

• They are semiconductors that need high temperatures.

• They have a full outer shell of electrons.

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Common Misconceptions about Valence Electrons

Misconception	Correction
All electrons are involved in bonding.	Only the outermost valence electrons are involved in bonding.
More valence electrons means an atom is more reactive.	Atoms with 1 or 7 valence electrons are the most reactive.
Atoms in the same row have similar properties.	Elements in the same column have similar properties.
Atoms only gain electrons to form bonds.	Atoms can lose, gain, or share electrons to become stable.

Multiple Choice

An element has 2 valence electrons. How would you describe its reactivity and what does it tend to do in a chemical reaction?

• It is unreactive because its shell is full.

• It is reactive and tends to lose 1 electron.

• It is reactive and tends to lose 2 electrons.

• It is reactive and tends to gain 6 electrons.

Multiple Choice

Based on its position in Group 17 of the periodic table, what properties would you expect an element like Fluorine (F) to have?

• It is a reactive metal that tends to lose seven electrons.

• It is a stable, unreactive gas that does not form bonds.

• It is a metalloid that can conduct electricity.

• It is a highly reactive nonmetal that tends to gain one electron.

Multiple Choice

Calcium (Ca) is in Group 2 and is known to react with Oxygen (O) from Group 16. What is the most likely outcome of this reaction?

• Calcium will gain two electrons from Oxygen, forming a stable bond.

• Both atoms will share their electrons equally to become stable.

• Oxygen will lose six electrons, and Calcium will gain them.

• Calcium will lose two electrons, and Oxygen will gain two electrons, forming a stable compound.

Multiple Choice

Imagine a newly discovered element is placed in Group 15 of the periodic table. What can you predict about its valence electrons and behavior?

• It has 5 valence electrons and will likely gain 3 electrons to become stable.

• It is a metal that will lose 1 electron to react.

• It has 15 valence electrons and is an unreactive noble gas.

• It has 5 valence electrons and will likely lose them to become stable.

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Summary

• Valence electrons are the outermost electrons that control how an atom reacts.

• Atoms are most stable when they have a full outer shell of 8 valence electrons.

• An element's group on the periodic table shows its number of valence electrons.

• Atoms lose, gain, or share valence electrons to become stable.

Poll

On a scale of 1-4, how confident are you with determining an element's reactivity based on its valence electrons?

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• 2

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• 4