For chlorine, identify the group number, give the number of electrons in each occupied shell, and write its valence-shell configuration.
Ch.2 Atoms and the Periodic Table
Chapter 2, Problem 32
How do atoms of different elements differ?
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Understand that atoms of different elements are defined by the number of protons in their nucleus, which is called the atomic number. Each element has a unique atomic number.
Recognize that the number of neutrons in the nucleus can vary among atoms of the same element, leading to isotopes, but the atomic number remains constant for a given element.
Note that the number of electrons in a neutral atom equals the number of protons. However, atoms can gain or lose electrons to form ions, which affects their charge but not their identity as an element.
Consider that the arrangement of electrons in energy levels or orbitals around the nucleus differs between elements, influencing their chemical properties and reactivity.
Understand that the mass of an atom is primarily determined by the combined number of protons and neutrons in the nucleus, which varies between elements and isotopes.

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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Atomic Structure
Atoms are the basic units of matter, consisting of protons, neutrons, and electrons. The number of protons in the nucleus defines the element and is known as the atomic number. Different elements have unique atomic structures, which determine their chemical properties and behavior.
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Elemental Properties
Each element has distinct properties, such as atomic mass, electronegativity, and ionization energy, which arise from its atomic structure. These properties influence how elements interact with one another, forming compounds and participating in chemical reactions. Understanding these properties is essential for distinguishing between different elements.
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Periodic Table
The periodic table organizes elements based on their atomic number and properties, revealing trends and relationships among them. Elements are grouped into categories such as metals, nonmetals, and metalloids, which exhibit similar characteristics. This organization helps in predicting how different elements will behave in chemical reactions.
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Related Practice
Textbook Question
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Textbook Question
Use the following blank periodic table to show where the elements matching the following descriptions appear.
a. Elements with the valence-shell electron configuration ns2 np5
b. An element whose third shell contains two p electrons
c. Elements with a completely filled valence shell
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Textbook Question
Use the following orbital-filling diagram to show the electron configuration for As:
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Textbook Question
Find the mass in atomic mass units of the following:
a. 1 O atom, with a mass of 2.66 × 10-23 g
b. 1 Br atom, with a mass of 1.31 × 10-22 g
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Textbook Question
How many O atoms of mass 15.99 amu are in 15.99 g of oxygen?
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Textbook Question
Where within an atom are the three types of subatomic particles located?
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