Lesson 3: Reactions | Mr.Q

Learning Questions:

• What makes some elements react together and not others?

• How do the chemical structure of elements help us predict reactions?

Lesson 3: Chemical reactions

​Qurious.IM, 2023

​Key Terms:

• Elements/Atoms/Molecules

• Atomic Number/Atomic Mass

• (Valence) Electrons, Shell, Octet Rule

• Groups, Periods

• Ionic bond/covalent bond

R₁

R₂

Open Ended

You are an astronaut exploring Mars. You discover two mysterious compounds. Describe them in terms of their physical properties (colour, state of matter).

Open Ended

What other information would you need to find out what these mysterious compounds are?

Open Ended

What do you think these mysterious compounds are?

Why does an explosive metal react with a poisonous gas to make salt?

​+

​→

Drag and Drop

To understand why elements react, we need to know their structure.

For a neutral chlorine atom (³⁵₁₇Cl), there are

​

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​protons,

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​neutrons and

​​

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electrons.

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17

18

35.452

3p5

3s2

35

Focus on the electrons

Chlorine atom (³⁵₁₇Cl)

​Number of protons: 17

Number of electrons: 17

​Bohr diagram

Drag and Drop

Electrons like to organize in a specific way.

How many electrons are in each shell?

1^st shell: ​

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2^nd shell: ​

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3^rd shell: ​

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2

8

7

6

5

4

3

1

Octet Rule: Atoms prefer to have eight (8) electrons in each shell.

1st shell: 2 electrons

2nd shell: 8 electrons

3rd shell: 8 electrons

...

​Bohr diagrams of Na atom and Cl atoms

What might happen?

(Hint: Remember the Octet Rule)

Bohr diagram of synthesis of sodium chloride (NaCl)​

Image: Pearson Education

​Sodium atom (Na) gives an electron to chloride atom (Cl)...

​​...to become sodium ion (Na+) and chloride ion (Cl-) both with exactly 8 electrons in its outer shell.

Lewis diagram of synthesis of sodium chloride (NaCl)​

​Sodium atom (Na) gives an electron to chloride atom (Cl)...

​​...to become sodium ion (Na+) and chloride ion (Cl-) both with exactly 8 electrons in its outer shell.

A molecule's chemical structure determines its physical structure

​Na⁺

Cl^-

​2D

​3D

​1D

​2 opposite charged ions form ionic bonds

​?

​?

A molecule's chemical structure determines its physical structure

​Na⁺

Cl^-

​2D

​3D

​1D

​2 opposite charged ions form ionic bonds

Nature is beautifully organized.

Lewis Diagrams

Focus only on electrons in the outer shell (valence electrons)

Chlorine atom (³⁵₁₇Cl)

Number of electrons: 17

​Shell	​electrons in shell	Running total
1st​	​2	​2
2nd​	8​	10​
3rd​	7	17​

How many valance electrons?

Chlorine atom (³⁵₁₇Cl)

Number of electrons: 17

​Shell	​electrons in shell	Running total
1st​
2nd​
3rd​

How many valance electrons?

Chlorine atom (³⁵₁₇Cl)

Number of electrons: 17

​Shell	​electrons in shell	Running total
1st​	​2	​2
2nd​	8​	10​
3rd​	7​	17​

How many valance electrons?

Chlorine atom (³⁵₁₇Cl)

Number of electrons: 17

​Shell	​electrons in shell	Running total
1st​	​2	​2
2nd​	8​	10​
3rd​	7​	17​

How many valance electrons?

1. Identify # electrons in each atom

2. Identify # valence electrons.

3. Draw a Lewis diagram for each atom.

3 steps to predicting how/if atoms combine into a molecule

Multiple Choice

How many valence electrons are there in a neutral sodium atom (²³₁₁Na)?

• 11

• 12

• 23

• 1

Draw

Draw a Lewis diagram for a neutral sodium atom (²³₁₁Na).

Fill in the Blanks

Fill in the Blanks

Drag and Drop

How many valence electrons are there in the following neutral elements:

Lithium (₃Li): ​

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Beryllium (₄Be): ​

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Boron (₅B): ​

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Magnesium (₁₂Mg): ​

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Aluminum (₁₃Al): ​

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1

2

3

4

5

6

7

8

Groups and Periods

Draw

Draw the Lewis diagram for this reaction:

Mg_(s) + O_2(g) → MgO

​Magnesium loses 2 e^- and oxygen gains 2 e^- so that

both have complete octet in their outer shells.

Lewis diagram of the

synthesis of Magnesium Oxide

Draw

Draw a Lewis diagram for what you think is the reaction between

calcium metal (Ca_(s)) + chlorine gas (Cl_2(g)).

..

Lewis diagram of the

synthesis of Calcium Chloride (CaCl₂)

..

Lewis diagram of the

synthesis of hydrogen fluoride (HF)

..

Lewis diagram of the

synthesis of hydrogen fluoride (HF)

..

​Lewis diagram of synthesis of

Aluminum Oxide (Al₂O₃)

Open Ended

What's the name of Group 18 on the Periodic Table?

What's so special about them? (Hint: Focus on their valence electrons.)

Drag and Drop

Group 17 on the Periodic Table is called ​

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.

It is predicted that they will react well with ​

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.

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halogen gases

alkali metals

alkaline earth metals

transition metals

post-transition metals

metalloids

other nonmetals

lanthanides

actinides

Ionic Bonds and Covalent Bonds

​Part 2

Oxygen can only be found in nature in pairs,

not single oxygen atoms.

Why do you think that is?

Hint: Think about their valence electrons.

​Cloud representation

​Molecular Oxygen (O₂)

​Bonding

representation

..

Oxygen in nature

​Na⁺

Cl^-

​2D

​3D

​1D

​2 opposite charged ions form ionic bonds

Differences

​Ionic Bonds	​Covalent Bonds
​Bond between metal and nonmetal. The nonmetal attracts the electron, so it's like the metal donates its electron to it.	​Bond between two nonmetals with similar electronegativities. Atoms share electrons in their outer orbitals.
​	​
​	​
​Solid	Liquid or Gas​

​Read More: Chem.Libretexts.org

Chemical Properties

​Part 3

Reactants-----------------Product

Na_{(s)-- +--} Cl_2(g)-------→-----NaCl_(s)

​*Equation not balanced

Drag and Drop

Describe the physical properties of the products and the reactants?

Sodium (Na): ​ ​

Placeholder

, ​

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metal

Chlorine (Cl₂): ​ ​​

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gas

Sodium chloride (table salt, NaCl): ​

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​

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powder

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solid

grey

yellow

white

liquid

Multiple Choice

How are the physical properties of the reactants related to the physical properties of the products?

• The products have some properties of the reactants.

• The products have many properties of the reactants.

• The products have a mix of properties of the reactants.

• No relationship.

​Chemistry is the study of...

matter and its properties.

Chemical changes

occur when

a new substance

is formed.

Multiple Choice

Chopping a log is an example of a...

• physical change

• chemical change.

Multiple Choice

Burning a log is an example of a...

• physical change

• chemical change.

Drag and Drop

Frying an egg: ​​

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Boiling water: ​​

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Digesting food: ​​

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Nail rusting: ​

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​

Glass breaking: ​

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chemical change

physical change, not chemical

Types of Reactions

​Part 4

​Source: BYJUS

Multiple Choice

2Na_(s) + Cl_2(g) → 2NaCl

is an example of a...

• Combination/Synthesis Reaction

• Decomposition Reaction

• Combustion Reaction

• Neutralization Reaction

• Displacement Reaction

Combination (Synthesis) Reaction

2 Na_{(s)-- +--} Cl_2(g)-----→----2 NaCl

​Mg_(s) + O_2(g) → MgO

​Magnesium loses 2 e^- and oxygen gains 2 e^- so that

both have complete octet in their outer shells.

​*Equation not balanced

​Synthesis of Magnesium Oxide (MgO)

Open Ended

Can you think of an example of a decomposition reaction?

Decomposition Reaction (分解反应)

Open Ended

Can you think of an example of a combustion reaction?

Types of Reactions

​Image: BYJUS

​Ref: Chem.Libretexts.org

​Type	​General Formula	​Description
​Combination Reaction	​A + B → AB	​Two or more compounds combine to form one compound.
​Decomposition Reaction	​AB → A + B	​The opposite of a combination reaction – a complex molecule breaks down to make simpler ones.
​Precipitation Reaction	​A + Soluble salt B → Precipitate + soluble salt C	​Two solutions of soluble salts are mixed resulting in an insoluble solid (precipitate) forming.
​Neutralization Reaction	​Acid + Base → Salt + Water	​An acid and a base react with each other. Generally, the product of this reaction is salt and water.
​Combustion Reaction	​A + O2 → H2O + CO2	​Oxygen combines with a compound to form carbon dioxide and water. These reactions are exothermic, meaning they give off heat.
​Displacement Reaction	​A + BC → AC + B	​One element takes place with another element in the compound.

Types of Reactions

​Source: BYJUS

Limiting reactants

​Part 5

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