Subatomic Particles (Simplified) - Online Tutor, Practice Problems & Exam Prep

The atom consists of a nucleus containing protons and neutrons, with electrons orbiting around it. The atomic mass unit (AMU) is defined as 1/12 the mass of a carbon atom, equating to approximately 1.66 × 10^-27 kg. Neutrons are the heaviest subatomic particles (1.00866 AMU), followed by protons (1.00727 AMU), while electrons are significantly lighter (0.0055 AMU). Neutrons have no charge, protons are positively charged (+1), and electrons are negatively charged (-1). Understanding these properties is crucial for grasping atomic structure and behavior.

Subatomic Particles (Simplified) Concept 1

We've learned that the atom itself is comprised of the nucleus and, more importantly, 3 subatomic particles. The 3 subatomic particles share key differences and similarities in their masses and charges. We're introduced to a new term, AMU. AMU is shorthand for atomic mass unit, and it's used to calculate the relative mass of an atom or a subatomic particle. The definitional term of AMU is that 1 AMU equals one twelfth the mass of a carbon atom. So, this is again the official definition of an AMU, but what you need to realize here is that one AMU is equal to 1 Dalton, which is abbreviated DA. It's named after John Dalton. John Dalton represents one of the fathers of chemistry. And the more chemistry you learn, the more you'll find out that there are quite a few fathers and mothers of chemistry. They helped with important discoveries ranging from subatomic particles to their charges to some types of radiation and radioactivity. Now, what's most important here is, remember what's in the purple box, you need to commit to memory that:

1 A M U = 1.66 × 10 - 27 kg

This conversion factor will allow you to go between AMU and kilograms. You'll be able to interconvert between the two units.

Subatomic Particles (Simplified) Concept 2

So remember, we have 3 subatomic particles when it comes to the atom itself. So here we arrange them in neutron, proton, and electron in terms of order. In terms of these 3 subatomic particles, we have information on their actual masses, their relative masses, and then their relative charges. So, the neutrons, they weigh the most out of the 3 subatomic particles. Their actual mass is 1.67493×10-27kg. Protons are slightly lighter. They're 1.6762×10-27kg, so their masses are pretty close to one another. They themselves are much heavier than the electrons. The electrons are 0.00091×10-27kg. So what does this tell us? Well, we know that the nucleus is comprised of protons and neutrons, and the nucleus itself is incredibly small. But a vast majority of the mass of an atom is found within the nucleus. So it's important to understand that the nucleus is very small but very dense. A majority of the mass of the atom is found there, and it's the result of the neutrons' and protons' masses together. Now we have their actual masses, but we also have their relative masses, which you should also remember in terms of AMU. Okay?

Now it's important to understand the trends. Neutrons are the heaviest, electrons are the lightest. These exact numbers, if you're going to deal with a question having to relate them, they'll give it to you in some form within the question. So remember, you don't have to memorize the actual number. Remember, what's in purple boxes is what you need to commit to memory. So the relative mass of a neutron is 1.00866AMU. For a proton, it's slightly less in mass, so it's 1.00727AMU. And then remember electrons weigh the least, they are only 0.00055AMU. Now their charges, we know that neutrons are neutral, so their relative charge is 0. Protons are positive, their relative charge for each proton is plus one. Electrons are negative, so they're minus one. Alright? So just remember, neutrons are neutral and protons and electrons have the exact opposite signs for their charges. So here, this represents the most important information you need to know in terms of masses and relative charge for your 3 subatomic particles.

Subatomic Particles (Simplified) Example 1

So in this example question, it says, osmium, one of the densest elements on Earth, has an actual mass of 190.23 grams. According to the table above, what is its value in terms of atomic mass units? Alright. So if we take a look here, all our answers are given in Daltons. Remember, a Dalton is the same thing as an atomic mass unit. We're going to start out with this given amount, and it is our responsibility to get to the end amount. So we need to get to this end amount. Now our given amount is 190.23 grams, and we have to get to our end amount in Daltons, which is the same thing as AMU. In order to go from our given amount to our end amount, we have to utilize conversion factors. Our first conversion factor is conversion factor 1. We're first going to do a metric prefix conversion. We're going to change grams to kilograms. We want to get rid of grams, so grams go here on the bottom, kilograms go on top. Remember, the coefficient of 1 goes on the side with the metric prefix, meaning 1 kilo is \(10^3\). Now that grams are on opposite levels, they cancel out, and we'll have kilograms at the end. We had to change to kilograms because now we're going to say for conversion factor 2, our metric prefix above says that \(1.66 \times 10^{-27}\) kilograms is equal to 1 AMU. And remember, an AMU and a Dalton are the same thing. So now our kilogram numbers cancel out and we'll get our answer here as Daltons. So what's going to be here? It's \( \frac{190.23}{10^3} \div 1.66 \times 10^{-27} \). Remember, if something is written in scientific notation, to avoid any errors within your calculator, you should put it in parentheses. If you do this correctly, what you'll get initially well, what you'll get at the end is \(1.15 \times 10^{26}\) Daltons or AMU. Remember, they're interchangeable with one another. So if we look at our choices here, which one matches up with that value? That would be option a. So here, we're talking about conversion of grams to AMU or Daltons. This is called dimensional analysis. We start out with our given amount. We have to get to our end amount, and to get there, we utilize conversion factors. Here we had to employ a metric prefix conversion with conversion factor 1, and then use the conversion factor listed above, for conversion factor 2. That takes us from kilograms to Daltons or AMU. So if you're a little bit rusty in terms of this, make sure you take a look at our videos on dimensional analysis because this is the basic setup for any dimensional analysis type of question.

According to the table above, how many electrons are needed to have a combined mass of 1.0465 x 10^-25 kg?

• A. 2.1028 x 10¹³
• B. 1.1500 x 10⁵
• C. 8.8192 x 10²⁵
• D. 3.2235 x 10²²

How many atoms are contained in 0.230 g of sodium, Na? The mass of one sodium atom is 23.99 amu.

• A. 7.197 x 10¹¹
• B. 4.182 x 10³
• C. 5.775 x 10²¹
• D. 9.181 x 10⁴¹

Here’s what students ask on this topic:

What are the three subatomic particles and their charges?

The three subatomic particles are protons, neutrons, and electrons. Protons have a positive charge (+1), neutrons have no charge (0), and electrons have a negative charge (-1). Understanding these charges is crucial for grasping atomic structure and behavior, as they influence how atoms interact with each other.

What is an atomic mass unit (AMU) and how is it defined?

An atomic mass unit (AMU) is a unit of mass used to express atomic and molecular weights. It is defined as 1/12 the mass of a carbon-12 atom, which is approximately 1.66 × 10^-27 kg. This unit helps in comparing the masses of different atoms and subatomic particles.

How do the masses of protons, neutrons, and electrons compare?

Neutrons are the heaviest subatomic particles with a mass of 1.00866 AMU. Protons are slightly lighter with a mass of 1.00727 AMU. Electrons are significantly lighter, with a mass of only 0.0055 AMU. This means that the nucleus, which contains protons and neutrons, holds most of the atom's mass.

Why is the nucleus of an atom very dense?

The nucleus of an atom is very dense because it contains protons and neutrons, which are much heavier than electrons. Despite the nucleus being incredibly small, it holds the majority of the atom's mass due to the combined weight of protons and neutrons.

What is the significance of John Dalton in chemistry?

John Dalton is considered one of the fathers of chemistry. He made significant contributions to the understanding of atomic theory, including the concept of atomic mass units (AMU). The unit Dalton (Da) is named in his honor, and it is equivalent to 1 AMU.