To find the atomic mass of lithium, you generally look at the periodic table, but if you need to calculate the mass of one atom, you'd use a conversion factor involving Avogadro's number. The video explains this process.
Understanding Atomic Mass and Molar Mass
Atomic mass is the mass of a single atom of an element, while molar mass is the mass of one mole of that element.
- Atomic Mass: Usually expressed in atomic mass units (amu), it is the weighted average of the masses of all the isotopes of an element.
- Molar Mass: Expressed in grams per mole (g/mol). The molar mass of an element is numerically equal to its atomic mass in amu, but has the units g/mol.
Steps to Find the Mass of One Atom of Lithium
According to the video, finding the mass of one atom of lithium involves the following steps:
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Identify the Molar Mass: Look up lithium's molar mass on the periodic table. The molar mass of lithium is approximately 6.94 g/mol.
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Use Avogadro's Number: Avogadro's number is a conversion factor representing the number of atoms, molecules, or formula units in one mole, which is about 6.022 x 1023 entities per mole.
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Set up a Conversion Factor: To find the mass of a single lithium atom, set up a conversion factor using the molar mass and Avogadro's number as described in the video:
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You know that 1 mole of lithium (6.94 g) contains 6.022 x 1023 atoms of lithium.
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To find the mass of one atom, divide the molar mass by Avogadro's number: (6.94 g/mol) / (6.022 x 1023 atoms/mol).
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Calculation: (6.94 g/mol) / (6.022 x 1023 atoms/mol) ≈ 1.15 x 10-23 g/atom.
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Calculate the mass of one atom of lithium: Perform the division. The result is the mass of a single lithium atom in grams.
Example:
- Molar mass of Li: 6.94 g/mol
- Avogadro's Number: 6.022 x 1023 atoms/mol
- Calculation: (6.94 g/mol) / (6.022 x 1023 atoms/mol) = 1.152 x 10-23 g/atom
- Result: The mass of one lithium atom is approximately 1.152 x 10-23 grams.
Summarized Table:
| Property | Value | Unit |
|---|---|---|
| Molar Mass of Li | 6.94 | g/mol |
| Avogadro's Number | 6.022 x 1023 | atoms/mol |
| Mass of one Li atom | 1.152 x 10-23 | g/atom |
Importance of Using the Correct Units
It is important to ensure that your calculations have the correct units, especially during conversions like the above example. Using moles and Avogadro's number allows us to switch from mass per mole to mass per atom, which is very important for understanding chemical concepts.
Conclusion
The atomic mass of lithium, as found on the periodic table, is 6.94 amu (or g/mol). By using Avogadro's number, the mass of one atom of lithium is approximately 1.152 x 10-23 grams.
