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Ch.2 - Atoms, Molecules, and Ions
Chapter 2, Problem 30c

Fill in the gaps in the following table, assuming each column represents a neutral atom.
Symbol 112Cd
Protons 38 92
Neutrons 58 49
Electrons 38 36
Mass no. 81 235
Complete the third row of the table.

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1
Identify the given information for each element in the table: protons, neutrons, electrons, and mass number.
Recall that the number of protons in an atom is equal to the atomic number, which also equals the number of electrons in a neutral atom.
For the first element, use the mass number formula: Mass Number = Protons + Neutrons. Given: Protons = 38, Neutrons = 58, calculate the mass number.
For the second element, use the mass number formula: Mass Number = Protons + Neutrons. Given: Protons = 92, Neutrons = 143 (since Mass Number = 235), verify the number of neutrons.
For the third element, use the mass number formula: Mass Number = Protons + Neutrons. Given: Protons = 36, Neutrons = 49, calculate the mass number.

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Key Concepts

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

Atomic Structure

Atomic structure refers to the composition of an atom, which includes protons, neutrons, and electrons. Protons and neutrons reside in the nucleus, while electrons orbit around the nucleus. The number of protons defines the element, while the total number of protons and neutrons gives the atomic mass. Understanding atomic structure is essential for filling in the gaps in the provided table.
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Atom Structure

Isotopes

Isotopes are variants of a particular chemical element that have the same number of protons but different numbers of neutrons. This results in different atomic masses for the isotopes of the same element. In the context of the table, recognizing the isotopes of cadmium (Cd) and their respective neutron counts is crucial for completing the missing information accurately.
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Charge Neutrality

Charge neutrality in atoms means that the number of protons (positively charged) equals the number of electrons (negatively charged), resulting in a neutral atom. If the number of electrons differs from protons, the atom becomes an ion. In the table, understanding charge neutrality helps determine the correct number of electrons for each atom based on the given protons.
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