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This video. Were going to focus on the atom its structure. What itss made up of and things like that so lets begin lets focus carbon.
If you look at the periodic table carbon has an atomic number of six. It has six protons and six electrons. The protons and the neutrons are found at the center.
Or the nucleus of the atom surrounded a nucleus you have different energy levels in the first energy level carbon has two electrons thats the greatest number of electrons. You can have in the first show in a second shell or second energy level carbon has four electrons. So as you can see the electrons are outside of the nucleus.
They are orbiting a nucleus electrons carrying negative charges protons. They have positive charges neutrons are neutral. So carbon has a total of six electrons.
The two electrons on the inside are known as core electrons and the electrons in the last or the outermost energy level are known as the valence electrons. So carbon has four valence electrons. If you look where carbon is located on a periodic table.
Its found in group 4a. Which is the same as group 14 elements in group 4a typically have four valence electrons. Alkali metals.
Which are found in group 1a. Contain one valence electron alkali earth metals group 2a. Contains two valence electrons.
The halogens will join group 7a contains seven valence electrons. So you can find a number of valence electrons based on which group the element is located in consider this symbol h e h. E stands for helium in the periodic table youre going to see something that looks like this theres a number on top and theres a number on the bottom the smaller of these two numbers represents the atomic number and the larger of these two numbers is the average atomic mass.
Which you can also use it as the mass number the number of protons is equal to the atomic number. Its always like that so because helium has an atomic number. Two it has two protons.
The number of neutrons is equal to the mass number minus. The atomic number and the number of electrons is equal to the atomic number minus the charge. So an atom which is electrically neutral.
Which doesnt have a charge atoms have equal number of protons and electrons. But ions they differ in their number of electrons and protons ions. Have unequal amounts of protons and electrons now an isotope of helium can be written this way.
Sometimes you might see it like this the top number represents. The mass number the mass number is usually the larger of the two the atomic number is the smaller one so if you see it this way just know that the mass number is on top. But if its written on a periodic table the top number is usually the atomic number whichever.
One is lower is the atomic number. The higher one is the mass number so dont get confused about that helium which we said has two protons. It also has two neutrons and as a neutral atom has two electrons so if we draw the atomic structure of helium.
It has two protons which im going to represent it with a positive charge and two neutrons the neutrons are neutral. But protons have a positive charge and surrounding the helium nucleus. You have two electrons now opposite charges opposite charges.
They feel a force of attraction that pulls them together and like charges. They repel so these two charges. They feel a force that pushes them away from each.
Other known as the electric force so now what about the two protons within the nucleus of an atom. They feel an electric force that pulls them apart. But yet they remain intact.
Therefore. There must be another force that keeps them attack. The force that holds the nucleus together is known as the strong nuclear force and so thats why the protons.
They dont repel each other now a common question that you might seem in chemistry. Is you need to be able to determine the number of protons neutrons and electrons inside an atom or an ion. So lets say.
If you have the aluminum atom. Which has a mass of 27 and the atomic number of 3 and also the aluminum ion which has a charge of plus 3 go ahead and determine the number of protons and neutrons and electrons in these two particles. So the atomic number is the number of protons.
So both the atom and the ion has 13 protons. The number of protons identifies the element. Now what about the number of neutrons.
The neutron number is the difference between the mass number and the atomic number so 27 minus. 13. Is 14.
So both the atom and the ion. They have the same number of neutrons now what about the electrons. The electrons is the atomic number minus the charge.
So this is going to be 13 minus zero. So therefore an aluminum atom has 13 electrons. An aluminum ion.
Its going to be 13 minus. 3. Which is 10.
So the aluminum plus. 3. Cation.
Contains 10. Electrons. Positively charged ions are known as cations negatively charged ions unknown as anions now.
If you add the 13 protons and the 13 electrons you get a net charge of zero. So atoms are neutral. But for the ion.
If you add the 13 protons with the 10 electrons. Which has a negative charge. 13 plus negative.
10. Is positive. 3.
Which is the net charge of the ion try these two phosphorous. 31. And also the phosphide ion.
Calculate the number of protons neutrons and electrons. So. The atomic number is 15.
Therefore both of these have 15 protons to find the neutron number is going to be 31 minus. 15. Which is 16.
So both of the atom. Any ion has 16 neutrons. But theyre going to differ in the number of electrons.
The electron number. We said was the atomic number minus a charge so 15 minus 0. Is 15.
So therefore the phosphorous atom. Contains.
15 electrons now the phosphide ion is going to be 15 minus negative. 3. Whenever you have two negative numbers or two negative signs next to each other the negatives.
They will cancel and turn into a positive number. So its really 15 plus. 3.
Therefore an ion with a negative charge has more electrons than protons. So we have 15 protons. Which has a charge of 15 and 18 electrons.
Which has a net charge of negative 18 15. Minus. 18.
Gives you a net charge of negative thing. So whenever you have a positively charged ion. It tells you that that ion has more protons than electrons.
If you have a negatively charged ion. And that ion has more electrons than protons now lets focus on carbon. What are isotopes lets consider the carbon 12 isotope and the carbon 13 isotope isotopes are composed of the same element so carbon twelve or carbon 13 these are isotopes of each other.
But chemically. They behave the same way their chemical reactivity is exactly the same. However then nuclear properties are different.
Because the nucleus of carbon. 13. Is different than that of carbon 12.
Both of these atoms contain. 6. Protons and the number of protons.
Or the atomic number identifies the element. So any substance. With 6 protons is going to behave.
As a carbon atom. Now the number of neutrons is a difference between a mass. Number and the atomic number.
So carbon. 12. Has six neutrons.
But carbon. 13. Have seven neutrons because 13 minus.
6. Is 7. Now as an atom they both contain.
6 electrons so now lets analyze carbon 12. And carbon. 13.
Which are isotopes of each other so as you can see isotopes are composed of the same element in this case. Carbon. Now because theyre made up of the same element.
They have the same atomic number in this case. 6. And they also have the same number of protons so thats the similarities between isotopes isotopes differ in two things they differ in the mass number and in the number of neutrons.
So make sure you remember. These facts. So isotopes have the same number of protons.
Same atomic number and is composed of the same element isotopes differ in the neutron number and in the mass number now if we check out the symbol for carbon now if you look at the periodic. Table youll see a six above it and below it. 1201 this number is not.
Exactly. 12 why is that why is it 1201. In that 12 this number is really called the average atomic mass.
Why is it called the average atomic mass and not simply the atomic mass. Keep in mind carbon has multiple isotopes. The predominant isotope is carbon 12.
But you also have carbon 13 and a very very tiny amount of carbon 14. But mostly carbon 12 and carbon 13 approximately 99 of carbon atoms. In a sample is carbon.
12. And the other 1 is carbon. 13.
The amount of carbon 14. Is insignificant. So were not going to worry about it here so what this means is that if you have a hundred carbon atoms 99 of those carbon atoms is going to be carbon 12 which means they have six protons six neutrons now out of those 100 atoms at least one out of those 100 carbon atoms is going to be carbon 13 where it has 6 protons 7 neutrons it turns out that this mass number is an a weighted average of these two isotopes and the way to calculate a weighted average in this particular instance you need to multiply the mass by the respective percentage and add it up the other finest sum.
So. The average atomic mass is going to be the mass of carbon. 12.
Times its percentage in the form of a. Decimal. 99 is 099.
As a decimal you simply take a 99 and divide. It by 100 or you can move the decimal two units to the. Left so its going to be 12 times.
099. Plus. 13.
Times one. Percent which is point. Zero one twelve times.
099. Is about 11 point 88 and 13 times point zero. One is point.
13. When you add these two numbers youre going to get the average atomic mass of twelve point zero one so thats how you can calculate the average atomic mass of an element you have to take the weighted average of all the isotopes that are found in nature and make sure you multiply it by the relative force and abundance try this example boron has two principal isotopes b10 and b11 approximately eighty eighty one percent is b 11 and 19 percent is b10. Useless information calculate the average atomic mass of an atom of one so the average its going to be the mass of the b10.
Isotope which is 10 multiplied by the percentage as a decimal 19 percent is point 19. And i still be. 11 has a mass of 11 and a relative percent abundance of.
08. 1 as a decimal. So 10.
Times. Point 19 thats about. 19 and 11 times.
And thats eight point nine. One. So.
If you add these two numbers youre going to get the average atomic mass of an atom of boron. Which is ten point eight. One now sometimes you may have to work this problem backwards.
Sometimes you may want to calculate the relative percent. Abundance of each isotope. Consider chlorine chlorine has two main isotopes chlorine.
35. And chlorine 37. If you look at the periodic table the average atomic mass of chlorine is thirty five point four five now knowing that do we have more of the cl 35 isotope or the cl 37 nice which one is more predominant in nature because the average is closer to 35 than this 37.
And that tells us that chlorine. 35 is more abundant in nature than chlorine 37. So how can we calculate and be percentage for each.
Now. If you remember the example of carbon 99. Was carbon 12 1.
Was carbon. 13 but. These two numbers have to add up to 100.
99. Percent is 099. One percent is point zero.
One so. Lets say. If point.
99. Was. X.
That. Means. That 1.
Minus. X is. Point.
Zero. 1. 1.
Minus. 099. Is point zero 1.
So to find the percentage. We need to use x and 1 minus x to solving so let me illustrate. Lets say.
If we want to find the relative percent for cl. 35. Its going to be 35 times.
X. For the other isotope. Its simply.
1 minus x. So we just got to solve for x. So we have 35 x.
Here. Were going to distribute the 37 37. Times.
1. Is 37. And 37 times.
Negative. X. Is negative 37.
X. So. At this point.
Lets combine like terms. 35. X.
Minus. 37. X.
Is negative. 2 x. So.
What should we do next. At this point. We need to get x by itself.
So we got to move the 37 to the other side. So lets subtract both sides by 37. So these two will cancel on the right side.
We have negative 2 x. On the left side 35 point four five minus 37. Is negative one point five five.
Im not sure what just happened there so now lets divide both sides by negative 2 so negative 1 point 5 5 divided by negative 2 is equal to x so x is. 0775. Keep.
In mind x. Was associated with cl. Thirty five point.
Seven seven five is seventy seven point five percent keep in mind to go back from a decimal to a percent you need to multiply by 100 or move. The decimal point two units to the right now one minus point seven seven five is 02. To five which is twenty two point five percent.
So thats the relative percent of chlorine 37. So if we have a thousand chlorine atoms in this sample. How many of those atoms would be chlorine 35.
And how many is chlorine 37. So out of a thousand atoms seven hundred and seven fifty i mean 775 excuse me would represent chlorine 35. The other two twenty five would represent cl.
Thirty. Seven so out of a thousand atoms. Seven hundred seventy five of those atoms is the chlorine 35 eyes to the other two hundred twenty five is the chlorine.
37 isotope so that is it for this video. Thats all i got hopefully you found this video to be educational. So thanks for watching and have a great day .
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