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Ch.2 - Atoms & Elements
Chapter 2, Problem 45a

On a dry day, your body can accumulate static charge from walking across a carpet or from brushing your hair. If your body develops a charge of -15 µC (microcoulombs), how many excess electrons has it acquired?

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Key Concepts

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

Charge and Coulombs

Charge is a fundamental property of matter that causes it to experience a force in an electromagnetic field. The unit of charge is the coulomb (C), where 1 coulomb is equivalent to the charge of approximately 6.242 x 10^18 electrons. In this context, microcoulombs (µC) are used, where 1 µC equals 10^-6 coulombs.
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Electrons and Their Charge

Electrons are subatomic particles with a negative charge of approximately -1.602 x 10^-19 coulombs. When an object accumulates a negative charge, it indicates an excess of electrons. The total number of excess electrons can be calculated by dividing the total charge by the charge of a single electron.
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Calculating Excess Electrons

To find the number of excess electrons acquired by an object with a known charge, the formula used is: Number of electrons = Total charge (in coulombs) / Charge of one electron. For example, if the body has a charge of -15 µC, this value must be converted to coulombs and then divided by the charge of an electron to determine the total number of excess electrons.
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Related Practice
Textbook Question

Which statements are inconsistent with Rutherford's nuclear theory as it was originally stated? Why? a. Since electrons are smaller than protons, and since a hydrogen atom contains only one proton and one electron, it must follow that the volume of a hydrogen atom is mostly due to the proton. b. A nitrogen atom has 7 protons in its nucleus and 7 electrons outside of its nucleus. c. A phosphorus atom has 15 protons in its nucleus and 150 electrons outside of its nucleus. d. The majority of the mass of a fluorine atom is due to its 9 electrons.

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Textbook Question

A chemist in an imaginary universe, where electrons have a different charge than they do in our universe, performs the Millikan oil drop experiment to measure the electron's charge. The charges of several drops are recorded here. What is the charge of the electron in this imaginary universe?

Drop # Charge

A –6.9×10–19 C

B –9.2×10–19 C

C –11.5×10–19 C

D –4.6×10–19 C

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Textbook Question

Imagine a unit of charge called the zorg. A chemist performs the oil drop experiment and measures the charge of each drop in zorgs. Based on the results shown here, what is the charge of the electron in zorgs (z)? How many electrons are in each drop?

Drop # Charge

A –4.8×10–9 z

B –9.6×10–9 z

C –6.4×10–9 z

D –12.8×10–9 z

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Textbook Question

On a dry day, your body can accumulate static charge from walking across a carpet or from brushing your hair. If your body develops a charge of -15 µC (microcoulombs), what is their collective mass?

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Textbook Question

How many electrons are necessary to produce a charge of -1.0 C? What is the mass of this many electrons?

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Textbook Question

Which statements about subatomic particles are true? a. If an atom has an equal number of protons and electrons, it will be charge-neutral. b. Electrons are attracted to protons. c. Electrons are much lighter than neutrons. d. Protons have twice the mass of neutrons.

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