Input interpretation
![lithium fluoride | relative molecular mass](../image_source/b5bf41032464f96a26bcfcc1c52d735d.png)
lithium fluoride | relative molecular mass
Result
![Find the relative molecular mass, M_r, for lithium fluoride: M_r = sum _iN_im_i/m_u Plan: • Write the chemical formula and gather atomic masses from the periodic table. • Determine values for N_i and m_i using these items. • Finally, compute the mass. Write the chemical formula: LiF Use the chemical formula, LiF, to count the number of atoms, N_i, for each element: | N_i F (fluorine) | 1 Li (lithium) | 1 Look up the atomic mass, m_i, in unified atomic mass units, u, for each element in the periodic table. Since m_i is divided by the atomic mass constant, m_u, the result is a unitless relative atomic mass: | N_i | m_i/m_u F (fluorine) | 1 | 18.998403163 Li (lithium) | 1 | 6.94 Multiply N_i by m_i/m_u to compute the relative mass for each element. Then sum those values to compute the relative molecular mass, M_r: Answer: | | | N_i | m_i/m_u | relative mass F (fluorine) | 1 | 18.998403163 | 1 × 18.998403163 = 18.998403163 Li (lithium) | 1 | 6.94 | 1 × 6.94 = 6.94 M_r = 18.998403163 + 6.94 = 25.94](../image_source/4bc4913156a16ba0b469cefd4cce4457.png)
Find the relative molecular mass, M_r, for lithium fluoride: M_r = sum _iN_im_i/m_u Plan: • Write the chemical formula and gather atomic masses from the periodic table. • Determine values for N_i and m_i using these items. • Finally, compute the mass. Write the chemical formula: LiF Use the chemical formula, LiF, to count the number of atoms, N_i, for each element: | N_i F (fluorine) | 1 Li (lithium) | 1 Look up the atomic mass, m_i, in unified atomic mass units, u, for each element in the periodic table. Since m_i is divided by the atomic mass constant, m_u, the result is a unitless relative atomic mass: | N_i | m_i/m_u F (fluorine) | 1 | 18.998403163 Li (lithium) | 1 | 6.94 Multiply N_i by m_i/m_u to compute the relative mass for each element. Then sum those values to compute the relative molecular mass, M_r: Answer: | | | N_i | m_i/m_u | relative mass F (fluorine) | 1 | 18.998403163 | 1 × 18.998403163 = 18.998403163 Li (lithium) | 1 | 6.94 | 1 × 6.94 = 6.94 M_r = 18.998403163 + 6.94 = 25.94
Comparisons
![≈ ( 0.13 ≈ 1/7 ) × relative molecular mass of caffeine ( ≈ 194 )](../image_source/a77a2cb1090d4b924b8912ca17aab9d0.png)
≈ ( 0.13 ≈ 1/7 ) × relative molecular mass of caffeine ( ≈ 194 )
![≈ 0.44 × relative molecular mass of sodium chloride ( ≈ 58 )](../image_source/8f842c88a1f0cbfea67512c3a8d3eaf0.png)
≈ 0.44 × relative molecular mass of sodium chloride ( ≈ 58 )
![≈ 1.4 × relative molecular mass of water ( ≈ 18 )](../image_source/893ff21b623bee075c58b29586657d5d.png)
≈ 1.4 × relative molecular mass of water ( ≈ 18 )
Corresponding quantities
![Molar mass M from M = M_uM_r: | 26 g/mol (grams per mole)](../image_source/ebc6ff0a31712fcb6230fdeb2a108dba.png)
Molar mass M from M = M_uM_r: | 26 g/mol (grams per mole)
![Molecular mass m from m = M_rM_u/N_A: | 4.3×10^-23 grams | 4.3×10^-26 kg (kilograms)](../image_source/c76d3757f4b8adb464d2960a8985fdcb.png)
Molecular mass m from m = M_rM_u/N_A: | 4.3×10^-23 grams | 4.3×10^-26 kg (kilograms)