How many protons and neutrons are in the nucleus of each of...

How many protons and neutrons are in the nucleus of each of the following atoms? In a neutral atom of each element, how many electrons are present?
a. $^{79} \mathrm{Br}$
d. $^{133} \mathrm{Cs}$
b. $^{81} \mathrm{Br}$
e. $^{3} \mathrm{H}$
c. $^{239} \mathrm{Pu}$
f. $^{56} \mathrm{Fe}$

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Key Concepts

Atomic Number

The atomic number of an element is the number of protons in the nucleus and uniquely identifies the element. It also determines the number of electrons in a neutral atom since the number of electrons equals the number of protons when there is no net charge.

Mass Number

The mass number is the sum of the number of protons and neutrons in an atom’s nucleus. It represents the approximate total mass of an atom in atomic mass units and is typically used in isotopic notation.

Isotopes

Isotopes are different forms of the same element that have the same number of protons but different numbers of neutrons. They are identified by their mass numbers, and understanding them aids in determining the nuclear composition of an atom.

Transcript

00:02 Chapter 1, problem 43, asks to determine how many protons, neutrons, and electrons are present in each of these different molecules.

00:12 So, let's start with 79 br.

00:17 This 79 tells us the number of protons and neutrons that we have inside of the atom.

00:25 So, to find out the number of protons, we'll need to look for the atomic number on our paper.

00:32 Periodic table.

00:34 The atomic number tells us the number of protons every single atom of this element has.

00:41 In the case of br, the atomic number is 35, so that's how many protons we have.

00:50 To find the number of neutrons, we'll use the mass number 79 minus the number of protons.

00:57 So 79 minus 35 gives us 44.

01:03 Finally, for the number of electrons.

01:06 We're told that this is a neutral atom.

01:09 Therefore, there should be no net charge.

01:13 Therefore, the number of electrons should equal the number of protons.

01:18 Remember that protons are positively charged, and net neutrons have no charge, and electrons are negatively charged.

01:27 Therefore, for a net charge of zero, or a neutral atom, protons and electrons should be equal.

01:36 Next, let's move on to 133 -cs.

01:39 Cs has an atomic number of 55, which is its number of protons.

01:47 133 minus 55 gives us 78 as our number of neutrons...

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