A Single Atom

In the last lesson we described a few ways to think about the difference between mass and weight. We also discussed the incredibly small mass of an electron when compared to the mass of a proton or neutron. And lastly, we discussed how in chemistry, we usually neglect the mass of the electron because it is so small compared to the mass of a proton or neutron.

A caveat point I should make – you may have often heard the terms mass and weight used almost interchangeably. Even though this is “technically” not accurate, sometimes it simplifies things to do so. (There are a lot of common phrases that we use to simplify things but are technically not proper English! Can you think of some?)

Here’s why –

The simplest and most effective way to measure the mass of an object is to observe how it reacts when a force is applied to it. Imagine someone throwing a golf ball at you verses a ping pong ball. They are both the same “size”, but the golf ball has a much larger “mass” than the ping pong ball. Since the golf ball has a much larger mass, it will exert a much larger force unto your body resulting in much more pain!

Now remember that weight is simply a measure of force – more superficially, a measure of force due to gravity (Instead of being thrown)! Therefore the simplest and most effective way to measure the mass on an object is to measure how much force it applies to a scale (either in your bathroom or in a laboratory) due to gravity. More simply – weigh it! If you know the weight, you can find the mass by simply dividing by the gravitational constant. But as long as you’re on planet earth the gravitational constant is the same everywhere. So as long as you’re on planet earth, the relationship between mass and weight does not change! And thus these terms are incorrectly, but practically used interchangeably.

Okay, so back to the mass of an individual subatomic particles. Through extensive experiments it has been determined that it would take roughly 1836 electrons to equal the mass of a single proton or neutron. Think about it this way – How much of your body’s weight do you imagine is due to protons and neutrons and how much of it is due to electrons?

For a 150 pound person, protons and neutrons would account for 149.94 pounds, while electrons would account for only 0.04 pounds. That’s only 0.02%. A normal bathroom scale doesn’t even measure to this degree of accuracy, so it couldn’t tell the difference between you with electrons and you without electrons (but if you didn’t have any electrons you would be dead).

Now we still run into the challenge of trying to measure the mass of a single subatomic particle. Since it was recognized that protons and neutrons accounted for almost the entire mass of an object, scientists decided to use the number of the protons and neutrons as a measurement of the mass. (At least a measurement of mass at the tiny atomic scale) This unit of mass was termed the Atomic Mass Unit, or “AMU” for short. So 1 AMU was equal to the mass of a single proton or neutron.

The AMU unit is defined as 1/12 of the mass of a carbon atom (or divide the mass of a carbon atom by 12). This is because a carbon atom has 6 protons and 6 neutrons, for a sum of 12 total protons and neutrons. So by dividing the mass of a single carbon atom by 12, you get mass of one proton or neutron (remember they are so similar in mass that they are assumed to be equal).

The AMU is still used today in most chemistry classes as a standard unit to measurement. It is also accompanied by another standard measurement for mass called the Mole, which accounts for each element differently, since each element is made from a different number of protons and neutrons. The Mole is a simple concept but is over-complicated in most chemistry courses. However, I will have save this discussion for another time since I want to get away from talking about too many minute details and get back to overarching concepts that are so incredibly intriguing to the whole of chemistry!

A Single Atom

To recap, we know that everything you can see and touch, literally every physical object around you can be made from only three particles, called subatomic particles: protons, neutrons and electrons.

These subatomic particles combine in various numbers and combinations to form every atom in the universe, and these atoms combine in various numbers and combinations to form every molecule in the universe, and ultimately every physical thing in the universe. In the last post we discussed how incredibly small these particles are and gave a few examples to help think about their size. Now we need to discuss the second of the three properties which are most important to us: Mass.

When I talk about mass, usually the first thing people ask is: this is like weight, right? The answer is – sort of. When we speak of mass we are referring to the amount of actual physical stuff (which is referred to as “matter”), within an object. Weight does not refer to the amount of matter within an object, rather weight refers to the amount of force that an object exerts downward due to gravity.

Here’s an example of what I mean.

Let’s assume you are standing on a standard bathroom scale. Since, you are a physical object and the earth’s gravity is pulling you down onto the scale, then you are exerting a force unto that scale. The number you see in front of you, your weight, is a measure of the amount of force which you are exerting on the scale due to the influence of gravity on your body.

So what happens when you gently bounce up and down? The scale starts to jump all over the place. If you bounce up for a moment, the scale will show a lower weight, and when you come back down, you exert a greater force on the scale from your downward motion pushing down onto the scale, which causes the scale read a larger weight. But has the actual amount of matter of which you are composed actually changed? No not at all!

This brings us to mass. The mass is a measure of the total quantity of matter – the total quantity of physical stuff within the thing you are trying to measure. So what gives matter its mass? The answer is protons and neutrons! Remember, every physical and tangible object (this is matter) in our universe is composed of only three subatomic particles – protons, neutrons and electrons. And at some level, these three particles are responsible for every property of matter.

But recognize that I said the mass is the due to the protons and neutrons, and I did not include the electrons. That is because the mass of an electron – much like its size (which we learned about in the last lesson) – is incredibly small compared to that of protons and neutrons. So small in fact, that we tend to disregard it completely. In the next lesson, we will talk more about the actual mass of each of these three subatomic particles in greater detail.

So to recap:

• The mass of an object is the quantity or amount of actual matter (or physical stuff) within that object.
• The only way to change the mass of an object is add or take away matter (or physical stuff) from that object.
• The weight of an object is the force that object exert downward on the earth due to both its mass and the influence of gravity on that object.
• The mass of an electron is so much smaller than the mass of a proton or neutron that the mass of the electrons is usually disregard in chemistry.

A Single Atom

Now that we have talked about a few ways in which we all interact with subatomic particles on daily basis, let’s talk a little more about the properties of these tiny little guys! If we can understand the properties of subatomic particles, and we know that subatomic particles combine to make atoms, then we can explain many properties of the atom, by using the properties of the subatomic particles. And you should be comforted by the fact that there are only a few properties that are actually important to us (unless you’re a particle physicist)!

Those properties are size, mass and charge. Let’s focus on the size for now. The size is difficult to comprehend because subatomic particles are so incredibly small that we can only explain them by using analogy.

Here’s an example.

It would take just under half a million pennies to fill an average size American house and there are around 132 million homes in the U.S. (according to the 2010 Census). This mean it would take 54 million billion pennies to fill every house in the U.S.! Let’s compare this to the number of protons you could pack into an object the size of a marble.

You would have to pack every house in the U.S. with pennies, and then repeat this over a trillion billion times (which is a number a million times greater than the amount of pennies it would take to fill every house in the U.S.), just to come close to the number of protons you could pack into an object the size of a marble! Stop and think about that for a minute; it’s hard to even grasp!

Thankfully, there is no major difference between the size of a proton and a neutron, therefore most scientists just assume they are equal in size for all practical purposes (and mass is also assumed equal which I will explain later). This simplifies things! But how about the size difference between a proton and an electron?

Well, we know that the electron is much smaller than the proton, however, there is a fascinating problem with even asking this question! The question assumes that an electron is a particle – or more sufficiently, a small “physical” object that takes up space. In reality, an electron does sometimes “behave” like a particle, but it also “behaves” like it’s not a particle. I don’t want to confuse you, but let that just be a taste to pique your curiosity for a later post about the nature of the electron. These things are crazy!

For the sake of this analogy, let us assume that an electron is currently “behaving” like a particle. In this case, the size difference between an electron and a proton is like the size difference between a small bee bee or pellet (from a bee bee or pellet gun) and a bowling ball. The proton is somewhere around two thousand times larger than the electron, just as the bowling ball is somewhere around two thousand times larger than the bee bee.

At least you can comprehend this number! And since we are left agreeable, I will end it here!

Static Electrcity

I love pulling my laundry out of the drier right after it finishes its cycle because this is when the clothes have no wrinkles! But I have begun to notice an interesting phenomenon. When I try and pull out a piece of clothing, it usually wants to stick to the rest of the clothes in the dryer, and when I force this rebellious t-shirt out of the drier, it’s resistance is accompanied by crackling sounds and sometimes tiny little sparks.

A very similar phenomena occurs when you walk around the house in the winter with fuzzy socks on, only to receive a jolting shock when you touch a door handle. Or after touching your car door after getting into and out of your car or after sliding down a slide at a playground. So what in the world is happening when your clothes stick together or when your car or house door handle give you a shock? Or when your hair sticks up after sliding down a slide or rubbing it with a balloon? Most recognize this phenomena as static electricity. But what in the world is happening here and what does it have to do with chemistry?

The key is SUBATOMIC PARTICLES! Like we discussed earlier, there are three subatomic particles – protons, neutrons and electrons – that combine in various numbers and combinations to form every atom in the universe, and these atoms combine in various numbers and combinations to form every molecule in the universe, and ultimately every physical thing in the universe – and your clothes fall into this category!

When your clothes cycles around a drier, or when your pants rub across the car seat or down a slide at the playground, some of these subatomic particles will rub off! Since they have differing charges, they transfer this charge to their final location. This is called charging, and it’s when tiny charged particles rub off from one material and are left on another. The tiny particles which usually rub off are the electrons since they are so much smaller, lighter and mobile than the protons and neutrons.

When your clothes rub against each other in the drier, these tiny electrons will transfer from one piece of clothing to another. Since electrons have a negative charge, they cause their new home (your t-shirt) to become more negatively charged, where as their old home (your pajama pants) are now more positively charge since the negatively charged electrons have left them. Since your t-shirt and pajama pants are now oppositely charged, they attract each other!

The same thing happens to your body when you walk around the house with socks on, or slide down a slide at the park. You build up these tiny charges from all that rubbing! But why does the shock happen when you touch a door handle?

Think about the material of a door handle for a second. They are usually metal. And what is the difference between metals and a plastic slide, your socks, or pajama pants? The metal is conductive which means charges will easily flow through it, whereas the other items are what’s called insulators, materials in which charge remains immobile or does not move through it.

So this charge builds up on your body from all this rubbing, and has nowhere to go. When you touch a metal door handle, the conductive metal allows these charges to flow through it – this is the same thing as allowing electricity to flow through you, and Zap – you feel the shock!

This phenomena is even worse in the winter because the air is drier, whereas humid air (water) is more conductive and will continually cause the charges to release back to their original location instead of building up.

These tiny charges are the exact same charges that make up every atom in the universe, and thus every physical thing in the universe! In the next blog I’ll discuss more about how these crazy little charged particles make up the actual atoms!

A Single Atom

Chemistry sounds like a really complicated topic, and if you were to look up the definition it may be scary. But in simple terms chemistry is simply the subject that tries to understand how the world works and functions at the very smallest scale. For example, you could observe a drop of water just by looking at it. If you divided that drop of water in half you could still observe it by simply looking at it. But what if you divided it in half again, and again, and again… say about 20 times? The tiny drop of water you’d have left would be so small you could no longer see it with just your naked eye. You would need a magnifying glass, or a microscope just to show that it even exists. Imagine you kept dividing this water droplet in half over and over again. You’d have to ask yourself the question – can I cut up this water droplet so many times that it is no longer a water droplet? The answer is yes.

At some point you will cut up that water droplet enough times that all that will be left is a single molecule of water. This single molecule of water is still water, but if you were to divide it even one more time, you would no longer have water! This is because a single molecule of water consists of only three atoms. One atom of oxygen and two atoms of hydrogen. These hydrogen and oxygen atoms alone are not water, they are atoms. Water is simply a specific combination of hydrogen and oxygen. This is the very small “scale” that I described above. This is the very small scale that chemistry is mainly concerned with studying. In the study of chemistry you will start to ask and answer questions such as: what is a hydrogen atom and how is it different from an oxygen atom within water? Why does water have two hydrogen atoms and one oxygen atom instead of two oxygen atoms and one hydrogen atom? What other atoms exist and how do they form other molecules similar to water? …and so on…