Ch.2 - Atoms, Molecules & Ions

McMurry8th EditionChemistryISBN: 9781292336145Not the one you use?Change textbook

McMurry 8th Edition

Ch.2 - Atoms, Molecules & Ions

Problem 97

Chapter 2, Problem 97

What is the difference between an element's atomic number and its atomic weight?

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The atomic number of an element is the number of protons found in the nucleus of an atom of that element. It is a whole number and is unique to each element, serving as an identifier on the periodic table.

The atomic weight (also known as atomic mass) of an element is the average mass of atoms of an element, measured in atomic mass units (amu). It takes into account the relative abundances of all the naturally occurring isotopes of that element.

The atomic number determines the chemical properties of the element because it defines the element's electron configuration, which dictates how it will interact with other atoms.

The atomic weight is important for calculations in chemistry involving mass, such as when determining the mass of reactants and products in a chemical reaction.

In summary, while the atomic number is fundamental to the identity and chemical behavior of an element, the atomic weight is crucial for practical measurements and calculations in chemistry.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Atomic Number

The atomic number of an element is defined as the number of protons found in the nucleus of an atom. It uniquely identifies an element and determines its position in the periodic table. For example, hydrogen has an atomic number of 1, indicating it has one proton. The atomic number also influences the element's chemical properties and behavior.

Atomic Weight

Atomic weight, often referred to as atomic mass, is the weighted average mass of an element's isotopes, measured in atomic mass units (amu). It takes into account the relative abundance of each isotope in nature. For instance, carbon has an atomic weight of approximately 12.01 amu, reflecting the presence of both carbon-12 and carbon-13 isotopes. Unlike atomic number, atomic weight is not a whole number due to the presence of isotopes.

Isotopes

Isotopes are variants of a particular chemical element that have the same number of protons but different numbers of neutrons, resulting in different atomic masses. For example, carbon-12 and carbon-14 are isotopes of carbon, with 6 protons but differing neutron counts. The existence of isotopes is crucial for understanding atomic weight, as the average is calculated based on the relative abundances of these isotopes in nature.

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Isotopes

Related Practice

Textbook Question

Write symbols for the following isotopes:(a) Z = 58 and A = 140 (b) Z = 27 and A = 60

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Textbook Question

A period at the end of sentence written with a graphite pen-cil has a diameter of 1 mm. How many carbon atoms would it take to line up across the period if a single carbon atom has a diameter of 150 pm?

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Textbook Question

What is the difference between an atom's atomic number and its mass number?

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Textbook Question

The subscript giving the atomic number of an atom is often left off when writing an isotope symbol. For example, 6 often written simply as 13C. Why is this allowed?

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Textbook Question

A period at the end of sentence written with a graphite pencil has a diameter of 1 mm. If the period represented the nucleus, approximately how large is the diameter of the entire atom in units of m?

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