Physical Science 4-3: Chemical Formulas & Equations

Chemical Formulas and Equations

Multiple Choice

Why do bonds form?

• To fill the valence shell of electrons for the elements involved
• to release energy stored in the bonds
• because whenever you mix two chemicals, there will be a reaction
• because of attraction

Dropdown

​

Select answer

Molecules are found in nature as pairs of two atoms of the same type covalently bonded together.

Multiple Choice

A substance that has a high melting point, conducts electricity when dissolved in water, and has a crystalline structure probably has what type of bond?

• Ionic
• Metallic
• Covalent
• Crystalline

Multiple Choice

Bonds formed by sharing electrons between atoms are

• ionic

• metallic

• covalent

• dipole-dipole

​Lesson Objectives

• Read and write Chemical Formulas

• Describe what a chemical equation is

• Be able to balance a chemical equation

​What is a chemical formula?

• Scientists use the elemental symbols to write out a formula of a compound or molecule

  • Gives us a short-hand way to know what is in

• Chemical Formula: A combination of chemical symbols and numbers to represent a substance

  • Uses subscript numbers to identify the amounts of each element

    • If no number, there is only 1 of that element

Writing a Chemical formula sample Problem 1

• A water molecule is made up of two Hydrogen atoms and one Oxygen atom. Write the formula

  • Step 1: Identify the elemental symbols of the elements involved

    • Hydrogen= H

    • Oxygen = O

  • Step 2: Determine how many of each element there are and add a subscript for that number

Writing a Chemical Formula Sample Problem 2

• A Carbon Dioxide molecule is made up of One Carbon atom and two Oxygen atoms. Write the formula

  • Step 1: Identify the elemental symbols of the elements involved

Multiple Choice

What is the elemental symbol for Carbon?

• C
• Ca

• Co

• Cb

Multiple Choice

What is the Elemental Symbol for Oxygen?

• O

• Ox

• Og

• OO

Writing a Chemical Formula Sample Problem 2

• A Carbon Dioxide molecule is made up of One Carbon atom and two Oxygen atoms. Write the formula

  • Step 1: Identify the elemental symbols of the elements involved

    • Carbon = C

    • Oxygen = O

  • Step 2: Determine how many of each element there are and add a subscript for that number

    • Don't write any number ones

Writing a Chemical Formula Sample Problem 3

• A nitrogen molecule is made up of two Nitrogen atoms. Write the formula

  • Step 1: Identify the elemental symbols of the elements involved

Multiple Choice

What is the Chemical Symbol for Nitrogen?

• N

• Ni

• Ng

• No

Writing a Chemical Formula Sample Problem 3

• A nitrogen molecule is made up of two Nitrogen atoms. Write the formula

  • Step 1: Identify the elemental symbols of the elements involved

  • Step 2: Determine how many of each element there are and add a subscript for that number

​Formulas for Covalent Compounds

• Most of the time, a Covalent Compound tells you how many of each element there are using numerical prefixes

  • For the first element, we drop the Mono-Prefix

Multiple Choice

What is the formula for dinitrogen monoxide?

• N₂O

• NO₂

• NO

• N₃O

Multiple Choice

What is the Formula for Sulfur Hexafluoride?

• SF

• S₆F

• SF₆

• S₆F₆

Multiple Choice

What is the name of the compound CF₄?

• Carbon tetrafluoride
• Carbon monoxide
• Carbon dioxide
• Carbon disulfide

Multiple Choice

What is the name of the compound SeCl₂?

• selenium monochloride
• selenium tetrachloride
• selenium trichloride
• selenium dichloride

Formulas for Ionic Compounds

• All Ionic Compounds are formed by a metal and a nonmetal

• The Formula is the combination of the two element symbols, with the metal first and the nonmetal second

• An Ionic Compound has to be neutral, so the total charge has to equal 0

Writing Ionic Compounds Sample Problem 1

• Write the Formula for the compound Sodium Oxide

  • Step 1: Identify the ions and their charges for the two elements

    • Sodium = +1 Charge

    • Oxide= -2 Charge

  • Step 2: Figure out how many of each element you need to make the final charge Neutral

    • You need two Sodium ions to cancel out the -2 Charge on the Oxide

  • Final Formula: Na₂O

Writing Ionic Compounds Sample Problem 2

• Write the Formula for the compound Aluminum Bromide

  • Step 1: Identify the ions and their charges for the two elements

Multiple Choice

What is the Charge on an aluminum ion?

• -3
• +1
• +2
• +3

Multiple Choice

What is the charge on a bromide ion?

• 0
• -1
• +1
• -2

Writing Ionic Compounds Sample Problem 2

• Write the Formula for the compound Aluminum Bromide

  • Step 1: Identify the ions and their charges for the two elements

  • Step 2: Figure out how many of each element you need to make the final charge Neutral

Multiple Choice

If Aluminum has a +3 charge and Bromide a -1 Charge, How many bromides do you need to make a neutral aluminum bromide molecule?

• 1
• 2
• 4
• 3

Writing Ionic Compounds Sample Problem 3

• Write the Formula for the compound Rubidium Chloride

  • Step 1: Identify the ions and their charges for the two elements

Multiple Choice

What is the Charge on a Rubidium ion?

• +2
• +1
• 0
• -1

Multiple Choice

What is the charge of chloride ion?

• -1
• -2
• +1
• 0

Multiple Choice

If a rubidium ion has a charge of +1 and Chloride has a charge of -1, how many chlorides do you need to make a neutral compound

• 2
• 3
• 4
• 1

Multiple Choice

What is the formula for Rubidium Chloride?

• RbCl
• RbCl2
• RbCl3
• Rb2Cl

Chemical Reactions

• Chemical Reaction: The process by which one or more substances change to produce one or more different substances

  • Two or more substances are combined or broken apart to make new substances

• The Law of Conservation of Mass: Matter can not be created or destroyed, only moved into new forms

  • You have to have the same number of atoms at the beginning and end of a reaction

​Using formulas to write chemical equations

• Chemical Equation: a representation of a chemical reaction that uses symbols to show the relationship in a reaction

  • Tells you what compounds you have and how many of each you need

• You can multiply the number of molecules of an individual compound you have by adding a coefficient in front of the chemical formula

  • Multiplies every atom in the formula

Fill in the Blanks

If you have 2 H₂O in an equation, how many Hydrogen do you have?

Fill in the Blanks

If you have 2 H₂O in an equation, how many Oxygen do you have?

Fill in the Blanks

If you have 3 MgCl₂ in an equation, how many chlorine do you have?

Parts of a Chemical Equation

• Reactants: the materials you start out with in a reaction

• Products: The materials you end up with in a reaction

• We use a → to show that a reaction is taking place

  • Points from reactants to products

How to Balance a Chemical Equation

• Step 1: Start by counting all the atoms on the reactant side and the product side

• Step 2: Add coefficients to balance the atoms to make the number of each type of atom equal

  • Repeat as needed

Balancing Equations Sample Problem 1

• Sodium (Na) and Chlorine (Cl₂) combine to form Sodium Chloride (NaCl). Write this as a balanced equation

  • Step 1: Count out how many of each atom exist on both sides of the equation

Balancing Equations Sample Problem 1

• Sodium (Na) and Chlorine (Cl₂) combine to form Sodium Chloride (NaCl). Write this as a balanced equation.

  • Step 1: Count out how many of each atom exist on both sides of the equation

  • Step 2: Choose an element that is not even and add a coefficient in front of an element to try and make it the same on both sides of the equation

Drag and Drop

What Number can we put in the blank to balance out the chlorine in the following equation: ​Na + Cl2 --> ​

Placeholder

NaCl

Drag these tiles and drop them in the correct blank above

2

1

3

5

Balancing Equations Sample Problem 1

• Sodium (Na) and Chlorine (Cl₂) combine to form Sodium Chloride (NaCl). Write this as a balanced equation.

  • Step 1: Count out how many of each atom exist on both sides of the equation

  • Step 2: Choose an element that is not even and add a coefficient in front of an element to try and make it the same on both sides of the equation

  • Step 3: Recount your atoms and adjust as necessary

Drag and Drop

Balance the sodium in the equation: ​

Placeholder

Na + Cl2 --> 2 NaCl

Drag these tiles and drop them in the correct blank above

2

1

3

4

Balancing Equations Sample Problem 1

• Sodium (Na) and Chlorine (Cl₂) combine to form Sodium Chloride (NaCl). Write this as a balanced equation.

  • Step 1: Count out how many of each atom exist on both sides of the equation

  • Step 2: Choose an element that is not even and add a coefficient in front of an element to try and make it the same on both sides of the equation

  • Step 3: Recount your atoms and adjust as necessary

Balancing Equations Sample Problem 2

• Balance the Equation ____ P₄ + ____Cl₂ → ____PCl₃

  • Step 1: Count out how many of each atom exist on both sides of the equation

  • Step 2: Choose an element that is not even and add a coefficient in front of an element to try and make it the same on both sides of the equation

  • Step 3: Recount your atoms and adjust as necessary

• ____ P₄ + ____Cl₂ → ____PCl₃

Balancing Equations Sample Problem 3

• Balance the Equation ____ Na + ____H₂ O→ ____NaOH + ____ H₂

  • Step 1: Count out how many of each atom exist on both sides of the equation

  • Step 2: Choose an element that is not even and add a coefficient in front of an element to try and make it the same on both sides of the equation

  • Step 3: Recount your atoms and adjust as necessary

• ____ Na + ____H₂ O→ ____NaOH + ____ H₂

Multiple Choice

Name the part of the equation that is shown in red:

_2_H₂ + _1_O₂ -> _2_H₂O

• Coefficient
• Product
• Yield
• Subscript

Multiple Choice

Name the part of the equation that is shown in red:

H₂ + O₂ -> H₂O

• Coefficient
• Product
• Reactant
• Subscript

Multiple Choice

  Name the part of the equation that is shown in red:

H₂ + O₂ -> H₂O

• Coefficient
• Product
• Reactant
• Subscript

Multiple Choice

Which number should go in the blank?
____ H₂ + O₂ -> 2 H₂O

• 1
• 2
• 3
• 0

Multiple Choice

Is this balanced?
Al + O2 → 2Al₂O₃

• Yes
• No