Relative Atomic Mass Flashcards

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What is meant by the term relative atomic mass (Ar)?

Relative atomic mass is the average mass of the atoms of an element compared with one-twelfth of the mass of a carbon-12 atom.

Why does relative atomic mass usually have decimal places instead of being a whole number?

Because it is a weighted average of all the isotopes of an element, not just one type of atom.

What is the difference between mass number and relative atomic mass?

Mass number is the total number of protons and neutrons in one atom. Relative atomic mass is the average mass of all the atoms of an element, compared with carbon-12.

What is an isotope of an element?

Isotopes are atoms of the same element that have the same number of protons but different numbers of neutrons.

How do isotopes affect the relative atomic mass of an element?

Different isotopes have different masses, so the relative atomic mass is found by taking an average based on how common each isotope is.

What does the symbol Ar stand for in chemistry?

Ar stands for relative atomic mass.

What are the units of relative atomic mass (Ar)?

Relative atomic mass has no units because it is a comparison, or ratio, to the mass of a carbon-12 atom.

How can you find the relative atomic mass of an element on the periodic table?

On the periodic table, the relative atomic mass is usually the larger number for each element and often has decimal places.

How do you calculate relative atomic mass from isotopic masses and their abundances?

Multiply each isotopic mass by its abundance, add these values together, then divide by the total abundance.

Chlorine has two isotopes: Cl-35 with 75% abundance and Cl-37 with 25% abundance. What is its relative atomic mass?

Ar = (35 × 75 + 37 × 25) ÷ 100 = (2625 + 925) ÷ 100 = 3550 ÷ 100 = 35.5.

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