16/10: Relative atomic and molecular/formula mass

• Chemistry
• Secondary Education

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CHEMISTRY 10

                   17 & 18:

Relative Atomic Mass & Relative Molecular Mass

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CHEMISTRY 10

                   17 & 18:

Relative Atomic Mass & Relative Molecular Mass

define relative atomic mass and relative formula/molecular mass.

calculate the relative molecular/formula mass of ionic and covalent substances. 

assess my thinking and how I learn to identify growth areas and improve my learning.

Boron has two naturally occurring isotopes with the natural abundances shown in the table.

Calculate the relative atomic mass of boron.

What is the relative molecular mass 

of hydrogen gas?

1. 2
2. 1
3. 4
4. 3

Relative atomic mass

• Aᵣ is the average mass of the isotopes of an element compared to ¹⁄₁₂ of the mass of an atom of ¹²C.

Relative atomic mass

• Aᵣ is the average mass of the isotopes of an element compared to ¹⁄₁₂ of the mass of an atom of ¹²C.

Relative atomic mass

• Aᵣ is the average mass of the isotopes of an element compared to ¹⁄₁₂ of the mass of an atom of ¹²C.

1 piece of egg is like 1 particle in a carbon-12 atomic nucleus.

The tray is like the nucleus of a carbon-12 atom

Is the atom's mass the same as its ion's mass?

Is the atom's mass the same as its ion's mass?

Relative atomic mass

• Aᵣ is the average mass of the isotopes of an element compared to ¹⁄₁₂ of the mass of an atom of ¹²C.

Aᵣ (atom)  =

How do we calculate the relative atomic mass?

Sample 1:

• Lithium has two naturally occurring isotopes: ⁶Li (7% abundance) and ⁷Li (93% abundance). Calculate the relative atomic mass of lithium.

How do we calculate the relative atomic mass?

Sample 2:

• Gallium has two naturally occurring isotopes. The mass of gallium-69 is 68.93 amu, and it is 60.108% abundant. The mass of gallium-71 is 70.92 amu, and it is 39.892% abundant. Calculate the atomic mass of gallium.

Relative Molecular Mass

• Mᵣ is the sum of the relative atomic masses. Relative formula mass, Mᵣ , will be used for ionic compounds.

Relative Molecular Mass

• Mᵣ is the sum of the relative atomic masses. Relative formula mass, Mᵣ , will be used for ionic compounds.

Sample 1

• What is the relative molecular mass of one hydrogen molecule?

Sample 1

• What is the relative molecular mass of one hydrogen molecule?

Relative Molecular Mass

• Mᵣ is the sum of the relative atomic masses. Relative formula mass, Mᵣ , will be used for ionic compounds.

Sample 1

• What is the relative molecular mass of one hydrogen molecule?

Relative Molecular Mass

• Mᵣ is the sum of the relative atomic masses. Relative formula mass, Mᵣ , will be used for ionic compounds.

Sample 2

• What is the relative molecular mass of one water molecule?

Relative Molecular Mass

• Mᵣ is the sum of the relative atomic masses. Relative formula mass, Mᵣ , will be used for ionic compounds.

Sample 3

• What is the relative formula mass of one unit of sodium chloride?

Relative Molecular Mass

• Mᵣ is the sum of the relative atomic masses. Relative formula mass, Mᵣ , will be used for ionic compounds.

Sample 4

• What is the relative formula mass of one unit of ammonium sulfide?

Relative Molecular Mass

• Mᵣ is the sum of the relative atomic masses. Relative formula mass, Mᵣ , will be used for ionic compounds.

Calculate the relative molecular/formula mass of ionic and covalent substances 

I can calculate ionic and covalent substances' relative molecular/formula mass. 

Yes, I can confidently do it.

Yes, I can but need more practice.

No, I lack confidence so I need more practice or ask help from my teacher.

Practice your skill:

What is the relative formula mass of:

• calcium carbonate,
  
• potassium sulfate?

What is the relative molecular mass of:

• ammonia,
• carbon tetrachloride?

Share your thought process in calculating the relative molecular/formula mass.

Calculate the relative molecular/formula mass of ionic and covalent substances 

I can calculate ionic and covalent substances' relative molecular/formula mass. 

Yes, I can confidently do it.

Yes, I can but need more practice.

No, I lack confidence so I need more practice or ask help from my teacher.

Assess your skill:

Choose two only. Two marks in total

Calculate the Mᵣ of one of the following:

• oxygen gas (if you choose this, choose two more)
• carbon dioxide (if you choose this, choose two more except oxygen)
• magnesium oxide
• ammonium nitrate
• propanol, C₃H₇OH