Define unified atomic mass unit .

A unified atomic mass unit is defined as one-twelfth of the mass of a carbon-12 atom. Its symbol is u (or Da, Dalton), and 1 u = 1.66 x 10 -27 kg.

How is the relative atomic mass ( A r ) of an element calculated from its isotopes?

Multiply each isotope's mass number by its percentage abundance , sum the results, then divide by 100. This gives the weighted average of the isotope masses.

True or False? Relative atomic mass has units of grams.

False. Relative atomic mass is a ratio (mass of one atom relative to one-twelfth of the mass of a carbon-12 atom), so the units cancel and it is dimensionless.

The relative atomic mass ( A r ) is the ratio of the average mass of atoms of an element to the .......... , defined as one-twelfth of the mass of a .......... atom.

The relative atomic mass ( A r ) is the ratio of the average mass of atoms of an element to the unified atomic mass unit , defined as one-twelfth of the mass of a carbon-12 atom.

Define relative isotopic mass .

Relative isotopic mass is the mass of one atom of a specific isotope compared to the value of the unified atomic mass unit.

What is the relative molecular mass ( M r ) of water (H 2 O)? (A r : H = 1.0, O = 16.0)

M r = (2 x 1.0) + (1 x 16.0) = 18.0 . It is calculated by summing the relative atomic masses of all atoms in one molecule.

True or False? Isotopes of an element have the same number of neutrons but different numbers of protons.

False. Isotopes have the same number of protons but different numbers of neutrons, giving them different mass numbers.

The relative .......... mass ( M r ) is used for ionic compounds. It is calculated in the same way as the relative .......... mass by summing the relative atomic masses of all atoms in the formula unit.

The relative formula mass ( M r ) is used for ionic compounds. It is calculated in the same way as the relative molecular mass by summing the relative atomic masses of all atoms in the formula unit.

Define relative molecular mass .

Relative molecular mass ( M r ) is the ratio of the weighted average mass of a molecule of a molecular compound to the unified atomic mass unit. It has no units and is found by adding the relative atomic masses of all atoms in one molecule.

A LevelChemistryCambridge (CIE)Flashcards2. Atoms, Molecules & StoichiometryRelative Masses of Atoms & Molecules

Relative Masses of Atoms & Molecules (Cambridge (CIE) A Level Chemistry): Flashcards

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FrontRelative Masses
Define unified atomic mass unit.

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Define unified atomic mass unit.
A unified atomic mass unit is defined as one-twelfth of the mass of a carbon-12 atom. Its symbol is u (or Da, Dalton), and 1 u = 1.66 x 10^-27 kg.
How is the relative atomic mass (A_r) of an element calculated from its isotopes?
Multiply each isotope's mass number by its percentage abundance, sum the results, then divide by 100. This gives the weighted average of the isotope masses.
True or False?
Relative atomic mass has units of grams.
False.
Relative atomic mass is a ratio (mass of one atom relative to one-twelfth of the mass of a carbon-12 atom), so the units cancel and it is dimensionless.
The relative atomic mass (A_r) is the ratio of the average mass of atoms of an element to the .........., defined as one-twelfth of the mass of a .......... atom.
The relative atomic mass (A_r) is the ratio of the average mass of atoms of an element to the unified atomic mass unit, defined as one-twelfth of the mass of a carbon-12 atom.
Define relative isotopic mass.
Relative isotopic mass is the mass of one atom of a specific isotope compared to the value of the unified atomic mass unit.
What is the relative molecular mass (M_r) of water (H₂O)? (A_r: H = 1.0, O = 16.0)
M_r = (2 x 1.0) + (1 x 16.0) = 18.0. It is calculated by summing the relative atomic masses of all atoms in one molecule.
True or False?
Isotopes of an element have the same number of neutrons but different numbers of protons.
False.
Isotopes have the same number of protons but different numbers of neutrons, giving them different mass numbers.
The relative .......... mass (M_r) is used for ionic compounds. It is calculated in the same way as the relative .......... mass by summing the relative atomic masses of all atoms in the formula unit.
The relative formula mass (M_r) is used for ionic compounds. It is calculated in the same way as the relative molecular mass by summing the relative atomic masses of all atoms in the formula unit.
Define relative molecular mass.
Relative molecular mass (M_r) is the ratio of the weighted average mass of a molecule of a molecular compound to the unified atomic mass unit. It has no units and is found by adding the relative atomic masses of all atoms in one molecule.

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