2. Atoms and the Periodic Table
Atomic Mass (Conceptual)
The atomic mass of an element can be found on the Periodic Table.
Determining Atomic Mass
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Atomic Mass (Conceptual) Concept 1
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atomic masses of elements can be found by simply looking at the periodic table. So let's start off by looking at the symbol of H, which represents hydrogen. And if you take a look at hydrogen as well as the other elements on the periodic table, you'll see these whole numbers. These whole numbers represent our atomic number. They are the number of protons. When we say atomic mass. Though the atomic mass is the number that is seldom a whole number, this is our atomic mass. So you can find the atomic mass of any element on the periodic table. Just by simply looking it up. Now we're gonna say the atomic mass itself is an average of all its isotopes that use the units of grams per mole am you or dalton's. And we're going to say remember that one a.m. U. Equals 1.66 times 10 to the negative kg. So just remember these atomic masses that you see on the periodic table. They are usually not whole numbers. You'd have to get way down below here to these heavy elements down here. So you see whole numbers for atomic masses. And remember they are the average of all the isotopes for that given element
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example
Atomic Mass (Conceptual) Example 1
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So here for this example question it says which of the following represents an element from the first column with the greatest atomic mass. Alright, so our first column, if we look at this periodic table, our first column is this with all of these different elements. And remember the number in red? Which is not a whole number. Normally that represents the atomic mass of any of these given elements. Now here, if we take a look we have barium, be a again later we'll learn about how the names are attached to the element symbol B A is not in the first column here, it's in the second column. So this cannot be a choice then we're gonna say next that we have A L A. L. Stands for aluminum, Aluminum is over here in the third column. All the way over here. In this 13th column actually. So this is out next we have C S Gcse um here it is right here. It's in the first column it's pretty low down there. It's 1 32.91 for its atomic mass. Remember that could be in grams per mole atomic mass units. Or dalton's so far, it looks like it's the highest one. The only one higher than that would be F R. Notice that in the bottom rows here, most of them are whole numbers, these are super large mass elements that are pretty unstable. They typically don't have numerous isotopes as a result they have no decimal places. So next so so far C looks like it's our best choice if we look at D. We have Ally, which is up here, not hiring mass, not greater atomic mass. And then we have N. A. Which is right here. So it looks like C is our best choice. It has the greatest mass atomic mass from column one from the choices provided. So just remember we have our element symbols, We have our atomic masses, which normally are not whole numbers, and then we actually have whole numbers. Those represent our atomic numbers.
On the Periodic Table, the atomic mass is represented by the number with decimal places.
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Problem
ProblemWhich of the following choices has the greatest atomic mass?
A
Element A (0.283 kg)
B
Element B (3.20 x 1024 amu)
C
Element C (0.350 kg)
D
Element D (4.14 x 1026 Da)
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Atomic Mass (Conceptual) Concept 2
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when dealing with isotopes, we can talk about the most abundant isotope, recall the atomic mass of an element is an average mass of all its isotopes. And we're going to say that the most abundant isotope for an element is the one with a mass number closest to the atomic mass of the element. Remember your mass number gives you the number of protons and neutrons together forgiven isotope. So if we take a look here, we have our element, there are atomic mass that isotope symbols and then we talk about their most abundant isotope. So for hydrogen, its atomic mass according to the periodic table is 1.008 am you and its isotope symbols are hydrogen. When it has a mass number of two, it's called deuterium and when it has a nice, when it has a mass number of three, it's called trillium. All right now, remember we said that the most abundant isotope is the one that has a mass number closest to the atomic mass. The atomic mass is one. Here are our mass numbers 1 2 and three. The one closest to the Atomic Mass is Hydrogen one. Its atomic its mass numbers one and its closest to the atomic mass of 1.008. Let's go to the next door, boron Born has two forms boron 10 and born 11. The atomic mass of boron is 10.81 A. M. You Looking at more on 10 and Boron 11. Which one has a mass number closest to this atomic mass? The answer would be boron 11 because 11 is closer to 1081 than tennis. And then finally we have sulfur. Sulfur has an atomic mass of 32.6 A. M. You when you look on the periodic table. All right now, some version of my show 0.7 But then remember, it's okay, you can either be 32.6 or 30 06 or 32. depending on which periodic table you're looking at. But that doesn't matter. Here is my atomic mass. Which mass number is closest to that? 32.06. And we see that the answer is sulfur. 32, 32 is closer to 32.06 than either 33, or 36. All right, so, just remember the most abundant isotope. To figure it out. Look at what the atomic mass of the element is on the periodic table. Look at the different mass numbers for all the isotopes, the one that has a mass number closest to that atomic mass is the most abundant isotope.
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example
Atomic Mass (Conceptual) Example 2
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oxygen consists of three isotopes, oxygen 16 17 and 18. If the atomic mass for oxygen on the periodic table is 15.999 a. M. U, which isotope is the most abundant. Remember we look at the atomic mass, which you can find on the periodic table for the element, and then you look to see which mass number is closest to it. The one closest to it represents the most abundant isotope, oxygen 16 would have to be the answer because it's number 16 is closest to the atomic mass of 15. am you.
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Problem
ProblemVanadium consists of two isotopes, 5023V and 5123V. If the atomic mass for copper on the periodic table is 50.942 amu, are there more atoms of 5023V and 5123V in a sample of vanadium?
A
B
C
They are equal.
D
Cannot be determined.
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Problem
ProblemPotassium consists of three isotopes, 3919K, 4019K, and 4119K. Based on its atomic mass, which isotope of potassium is the most abundant?
A
B
C
D
None of the following