Atoms- Smallest Unit of Matter  - Online Tutor, Practice Problems & Exam Prep

Atoms, the smallest units of matter, consist of protons, neutrons, and electrons. The atomic number, representing the total protons, defines each element, while the mass number combines protons and neutrons. Electrons occupy energy shells, with the outermost shell, or valence shell, containing valence electrons that determine reactivity. The octet rule states that atoms are more stable when their valence shells are full, influencing chemical bonding. Key elements in life, known as CHNOPS (carbon, hydrogen, nitrogen, oxygen, phosphorus, sulfur), form the basis of biological structures and functions.

Atoms- Smallest Unit of Matter

In this video, we're going to begin our lesson on atoms, which are the smallest unit of matter. Now, the term matter is used by scientists to refer to anything that takes up space and has mass. This includes all living organisms like me and you, but also nonliving things too, like rocks, oceans, and the device that you're watching this video through. Pretty much anything that takes up space and has mass will be matter. So, matter is really, really, really broad, and it's going to be at the top here of our lesson for that reason. It includes living and nonliving things. Now, all matter, regardless of if it's living or nonliving, is going to be made up of at least one chemical element, and that's exactly what we're saying right here. It's going to be made up of at least one chemical element.

Now, the term chemical element is defined as a pure substance that's made up of only one type of atom. Over here in our image, you can see that all matter is made up of at least one chemical element, and chemical elements are made up of atoms. And so the atom can therefore be defined as the smallest unit of an element. Now, because atoms make up elements and chemical elements make up matter, we can also define the atom as the smallest unit of matter, and that's exactly what we're saying right here and up above in our title. Now once again, atoms are going to make up both living and nonliving matter.

Let's take a look down below at our example image to get a better idea of some of these concepts. Notice on the far left over here, we're showing you an image of a diamond and a honeybee in this plant. Now, the diamond and the honeybee, because they both take up space and have mass, are both considered types of matter. Now, the diamond, of course, is going to be nonliving matter, whereas the honeybee and the plant are going to be living matter. Now, if we zoom into the diamond here, which you can see is the diamond structure that we're showing you over here, which is made up of all of these "C" symbols that we see here. These "C" symbols represent a type of element, and so it's made up of just one type of element, which is the element carbon, abbreviated with just a "C." Now, if we zoom into one of these chemical element symbols, one of these "C" symbols, what you'll see is that it's made up of a carbon atom. And so here on the far right, we're showing you a representation of a carbon atom.

In our next video, we're going to talk more about the structures and properties of atoms. But for now, you should notice that nonliving matter like diamonds is going to be made up of at least one chemical element, and the smallest part of a chemical element is going to be the atom itself. Now similarly, down below with the honeybee and the plant, when we zoom into one of its chemical structures, you can see that it's going to have a sugar like, for example, glucose, which is a sugar that can be found in these living organisms. And what you'll notice is that this glucose structure over here actually has multiple types of elements. In fact, it has 3 types of elements: it has the same carbon element as the diamond, but then it also has the element oxygen and the element hydrogen, and you can see those throughout this glucose structure here. Now if we zoom into just one of the chemical elements of hydrogen here, what you'll see is that the smallest unit of this element is a hydrogen atom. And so this is the representation of a hydrogen atom, and once again we'll talk more about the components of the atom and the properties of the atom moving forward in our course. But for now, this here concludes our introduction to how atoms are the smallest unit of matter. And once again, the biggest takeaway is that all matter is going to be made up of chemical elements and the smallest unit of a chemical element is the atom.

So I'll see you guys in our next video.

Atomic Structure

In this video, we're going to talk about atomic structure or the structure of atoms. Now, atoms are made up of 3 subatomic particles, each with their own characteristic charge, mass, and location within the atom. Notice over here, we have this table that gives you information about the 3 subatomic particles that make up an atom. And so, those 3 subatomic particles are protons, neutrons, and electrons. When it comes to the electric charge of a proton, it's actually going to be plus 1, so it has a positive charge. You can think of the 'p' here as positively charged. When it comes to the electric charge of the neutron, the neutron is going to be, as its name implies, neutral, meaning that it has a neutral electric charge of 0. When it comes to the electron and its electric charge, it's going to have a negative one electric charge. The way that you can think about it is 'electron' kinda sounds like getting electrocuted, and getting electrocuted is definitely not something positive; it's something negative, and that's how you can remember that it's going to have a negative one charge.

When it comes to the mass of subatomic particles, these particles are so incredibly small that it doesn't really make sense to measure their mass in pounds or ounces or kilograms or even grams. They are so small that scientists have come up with a new unit to measure their mass, and that unit is called the atomic mass unit (AMU). Protons and neutrons both have an atomic mass unit of 1. However, electrons are going to be different. Electrons have a mass that is so incredibly small that it's practically negligible, meaning that we can pretty much ignore its mass and just round it off to say that it is a 0 AMU.

In terms of the location of these subatomic particles within the atom, the proton is found within the nucleus of the atom. The neutron is also found within the nucleus of the atom. However, the electrons are going to be different. Instead of being found within the nucleus, the electrons are going to be found orbiting the nucleus or revolving around the nucleus, as illustrated in our image over here, where you can see the image of a carbon atom. Notice that the nucleus is indicated with a purplish background. Notice that within the nucleus, we have these positively charged protons, and we also have these neutral, gray circles that represent the neutrons, both found packed within the nucleus of the atom, just like what we see here. However, notice that the electrons, which are these little blue circles, are not found within the nucleus. Instead, the electrons are going to be found orbiting the nucleus in these electron shells that we see here.

We'll talk more about these electron shells as we move forward in our course. But for now, what you guys should know are the subatomic particles, our protons, neutrons, and electrons, you should know their characteristic electric charge, their characteristic atomic mass unit, and the location of each subatomic particle. And so, this here concludes our introduction to atomic structure and as we move forward, we'll be able to get some practice. So, I'll see you all in our next video.

Atoms- Smallest Unit of Matter Example 1

Alright. So here we have an example problem that wants us to fill in the sentence here using one of these 5 potential answer options down below. It says that negatively charged particles of atoms with almost no mass are called either electrons, protons, neutrons, ions, or polymers. Now, so far at this point in our course, we have not yet introduced ions or polymers. However, later in our course, we definitely will talk about these two terms, but because we have not yet introduced these two terms, we should have been able to figure out that these 2 are not going to be the correct answer for this problem. So now we're between either electrons, protons, or neutrons, which are the 3 subatomic particles of a typical atom. Recall that the 'p' in protons can remind us that this subatomic particle is positively charged. So you can think the 'p' in protons is for the 'p' in positively charged. And so because protons are positively charged, they are not going to be negatively charged, and so we can eliminate answer option b. And also recall that neutrons are as their name implies neutral, and neutral means that it has a net charge of 0 and so it will not be negatively charged, it will have a charge of 0. So once again, we can eliminate neutrons. And of course, this only leaves the electrons, which is the correct answer for this example problem, and so electrons are negatively charged and recall that electrons kinda sounds like getting electrocuted and getting electrocuted is something negative. And so that can remind us that electrons are negatively charged. And also, electrons have almost no mass, and so we can pretty much say that their mass is about equal to 0. And so, we can go ahead and indicate that 'a' here is the correct answer to this example problem, and that concludes this example. So I'll see you guys in our next video.

A proton ___________:

a) Has one positive charge.

b) Has one AMU.

c) Is found in the nucleus of the atom.

d) Only a and b are true.

e) a, b, and c are true.

• A. Has one positive charge.
• B. Has one AMU.
• C. Is found in the nucleus of the atom.
• D. Only a and b are true.
• E. a, b, and c are true.

Elements of Life

In this video, we're going to talk about the elements of life. And what's interesting to note is that of all the known elements that exist in the universe, only a small subset of those elements is found in living organisms. Now the periodic table of elements, which I'm sure you guys have probably heard of before in your previous courses, is a table that arranges all of the known elements that exist based on their chemical properties. And so if you take a look down below at our image, what you'll notice is we're showing you a periodic table of elements showing you all of the known elements that exist. Now once again, living things do not utilize all of these elements. Instead, they only utilize a small subset of them. In fact, about 97% of the mass of most living organisms, which is the vast majority of the mass, is made up of just six elements which are carbon, hydrogen, nitrogen, oxygen, phosphorus, and sulfur. And if you take the chemical symbols for each of these elements, it spells the word CHNOPS. And so if you can remember CHNOPS, then you'll be able to remember these six elements that make up the vast majority of most living organisms. And so because these six elements make up the vast majority of most living organisms, they're referred to as bulk elements, which we're showing you down below here in the periodic table. So notice that the bulk elements are highlighted in blue. And so you can see the positions of these six elements that make up the vast majority of life. And so these are once again going to be hydrogen, carbon, nitrogen, oxygen, phosphorus, and sulfur. And so if you arrange them in the right way it'll spell out that word CHNOPS. Now what you'll also notice is that we've got these other elements that are highlighted in this yellowish color and these are referred to as the trace elements. And as the name implies with trace elements, these are required for life. However, they're only required in trace amounts or in very, very small amounts. And so if you take a look down below, notice once again that the trace elements that are required for life, however, they're required in very very small amounts, they are highlighted in yellow throughout our table here. And so you don't need to memorize all of these trace elements. Don't worry about doing that. Instead, what you should be aware is that there are some trace elements that are required in small amounts, and you should be familiar with the bulk elements which again you can remember just by remembering CHNOPS. And so this here concludes our lesson on the elements that are required for life and we'll get some practice as we move along through our course and so I'll see you all in our next video.

Atomic Properties

Alright. So here in this video, we're going to talk about some atomic properties. Each atom of an element has unique properties, and we're going to discuss three specific properties that you all should be familiar with. Now the very first property that you all should be familiar with is the atomic number. The atomic number is defined quite simply; it's a straightforward idea. All it is is the total number of protons in the nucleus of an atom. So all you need to do to get the atomic number is count up the total number of protons, and that's it. The atomic number or the total number of protons defines each element. If we change the total number of protons in the nucleus of an atom, then we change the element it falls under. However, changing other subatomic particles like neutrons or electrons does not change the element. Thus, only changing the number of protons or the atomic number will change the element, and that's why the atomic number defines each element. So let's take a look at our example below to clear some of this up.

Here we're examining the atomic properties of a carbon atom, specifically this carbon atom shown here. To determine the atomic number, which is once again just the number of protons in the nucleus, all we need to do is count up the total number of protons in this nucleus here. What we'll see is that there are a total of 6 protons in the nucleus, which means the atomic number of this atom is 6. The protons are shown here in red, and by counting the red circles, we find there are six of them, which is why the atomic number is 6. If we were to add a seventh proton, then we would be changing the element, and it would no longer be carbon but rather nitrogen. Adding another neutron or another electron, which revolves around the nucleus, would still leave it as a carbon atom. Therefore, the number of protons in the nucleus defines the element.

Moving on, the next property is the mass number, which is also straightforward. It's the mass of the nucleus of a single atom. To determine the mass number, we consider the subatomic particles inside the nucleus, which include both protons and neutrons. The mass number is therefore the total number of protons and neutrons found in the nucleus. For example, if we know the number of protons and count the neutrons in the nucleus, what you'll find is that there are also six neutrons. To get the mass number, all we do is add up the two: 6 protons plus 6 neutrons give us a mass number of 12.

The last property we'll discuss is the atomic mass, sometimes called the atomic weight. The atomic mass is remarkably similar to the mass number; however, the key difference is that the atomic mass is an average total mass of all the atoms of an element, whereas the mass number is the mass of just one atom. If you look at a periodic table, you might notice a number like 12.011 for carbon. This number represents the atomic mass, which is the average total mass of all carbon atoms, thus the .011 indicating a decimal value. The atomic mass is very close to the mass number but differs because it is an average. This idea will become clearer when we discuss isotopes later in the course. The atomic number, shown as 6 for carbon, indicates the total number of protons, and the chemical symbol for carbon is 'C'.

This concludes our introduction to these atomic properties of atomic number, mass number, and atomic mass or weight. We'll be able to get some practice applying these concepts as we move forward in our course. I'll see you all in our next video.

Atoms- Smallest Unit of Matter Example 2

Alright. So here we have an example problem that wants us to complete the sentence here using one of these 5 potential answer options down below. And it says that the atomic number of an element is equal to the number of neutrons only, neutrons plus electrons, protons plus electrons, protons only, or protons plus neutrons. Now, of course, we know from our last lesson video that the atomic number is going to be exactly equal to the number of protons only that are found in the nucleus. And so this here is our atomic number, and it is the correct answer to this example problem. Now, of course, protons plus neutrons might sound familiar, but that's because this is referring to the mass number or the mass of the nucleus of an atom. But it's not the same thing as the atomic number, so that's why it's not correct. The protons plus electrons are going to dictate the net charge of the atom because remember protons are positively charged and electrons are negatively charged. And so the balance of protons and electrons, which are oppositely charged, is going to dictate the overall net charge of the atom. But once again, option b here is not going to be the atomic number. And then neutrons only and neutrons plus electrons, they once again are not going to be the atomic number. So that concludes this example problem, and I'll see you in our next video.

The average oxygen atom has a mass number of 16 and an atomic number of 8. This means that the number of neutrons in this oxygen atom is:

a) 24.

b) 8.

c) 16.

d) 4.

e) 2.

• A. 24.
• B. 8.
• C. 16.
• D. 4.
• E. 2.

Electron Orbitals & Energy Shells

In this video, we're going to continue to talk about atoms by focusing on their electron orbitals and energy shells. Now, electron orbitals are really defined as three-dimensional regions around the nucleus of an atom where electrons can be found. Although electron orbitals are three-dimensional regions, they can still be envisioned in two dimensions as energy shells. In our course, we're mainly going to focus on the energy shell aspect. You'll learn more about the three-dimensional shapes of electron orbitals in a chemistry class. So let's take a look down below at our example image here of the carbon atom on the far left to get a better understanding of these ideas of energy shells.

What you'll notice is that the chemical symbol in the middle represents the nucleus of this carbon atom, but then revolving around the nucleus of the carbon atom, what we have are these black circles, two of them for that matter, that represent energy shells. Again, energy shells are just the two-dimensional representation of the electron orbitals, which are really three-dimensional regions. The energy shells will contain electrons, and these little blue circles that you see here are the electrons that are revolving or orbiting around the nucleus of the atom in these energy shells. Any typical atom could have multiple energy shells as you can see from our image down below.

In the carbon atom here, notice that it has two energy shells. It has one that is closer to the nucleus and then a second energy shell that is further away from the nucleus. The energy shells closer to the nucleus of the atom are actually going to be lower in energy than the energy shells that are more distant from the nucleus. This means that the distant shells that are further away from the nucleus are going to be higher in energy and this is why these distant shells are the ones that are more reactive. These are the shells that scientists tend to focus most of their attention on when they're looking at chemical bonds, which we'll talk about more later in a different video. Notice once again that the energy shell that is furthest away from the nucleus is going to be the one that is highest in energy and the one that is more reactive and the one that tends to form chemical bonds.

This leads us to the idea of valence electrons because valence electrons are defined as the electrons that are found in the outermost energy shell, the valence shell, for carbon would be the one that is furthest away from the nucleus. Electrons that are found within the valence shell, like these four that we see here are termed valence electrons. These are the ones that are higher in energy and more reactive. The other electrons that are closer to the nucleus are not as high in energy and they're not nearly as reactive, so they're not going to be the ones to form chemical bonds with other atoms.

If you look down below the atom, you'll find a different way to represent these atoms. The chemical symbol is shown here, and to the top left of the chemical symbol, we can show the mass number, which from our previous lesson videos is just the total number of protons and neutrons. To the bottom left of the chemical element, we can show the atomic number, which is the total number of protons in the nucleus. You can see that the carbon atom here has six protons in its nucleus which aren't being shown; they're just being symbolized here with the letter C, but it also has six electrons that are negatively charged and balance out the positively charged protons. This means that the carbon atom being shown here is going to have a neutral net charge. In fact, all of the atoms that we're showing you here are going to have a neutral net charge as shown.

In terms of the first energy shell, it is always going to hold a maximum of two electrons. The second energy shell is going to hold a maximum of eight electrons. And then each of the shells beyond that is all going to hold a varying number of characteristic electrons. For our purposes in this biology course, you only need to know that the first shell holds up to two electrons and the second shell holds up to eight electrons. If we take a look down below at the carbon atom once again, notice that the first energy shell here is holding a maximum of two electrons and any additional electrons need to be in a different energy shell.

If we move on to the hydrogen atom here, you will see that its atomic number is 1, meaning it has one proton, and its mass number up here is also 1, meaning it only has one proton and no neutrons. Because all of the atoms shown here are neutral, the number of protons is going to balance out exactly with the number of electrons for all of the ones shown here. If it has one proton, that means it also has one electron and because it only has one electron, it only needs one energy shell, and this is a way to represent the hydrogen atom.

Now moving on to the nitrogen atom, nitrogen atoms have seven protons in their nucleus and when we count up the number of electrons, you'll see that there are also seven electrons to balance out the positively charged protons. The first energy shell gets filled with two electrons and then all of the other electrons need to make their way into the second shell, which holds up to a maximum of eight electrons. If we move on to the oxygen atom, it has a characteristic atomic number of 8. Its mass number is 16, meaning it modelAndView.has eight neutrons in its nucleus. But once again, you can count up the total number of electrons. It's going to add up to the total number of protons if it's a neutral oxygen atom, which once again these are all neutral atoms. What you'll see once again is that the first two electrons are going to go into the first energy shell and then all other electrons are going to move to the second shell, which can hold up to a maximum of eight electrons. Here it holds six electrons, so it's fine.

However, once we go to the phosphorus atom over here, notice that its atomic number is 15, meaning it has 15 protons in its nucleus. Its mass number is 31, meaning it has 16 neutrons in its nucleus. But once again, because these are neutral atoms, the number of protons is going to equal the number of electrons. So when you count up all of the electrons here, you'll count that there are 15 of them. Once again, the first energy shell is filled with two electrons.<|vq_8086|> So then it goes on to the second shell, and the second shell is filled with eight electrons. That means that all of the other electrons need to move into the third shell here. The sulfur atom over here is a similar example. It is going to have an atomic number of 16, a mass number of 32, which means that it has 16 neutrons in its nucleus. The number of electrons that you see revolving around the nucleus is going to match the number of protons if it's a neutral atom. Once again, the first shell gets filled with two electrons, the second shell gets filled with eight electrons, and all of the other electrons are going to need to move into the third shell here for this sulfur.

This here really concludes our lesson on electron orbitals and energy shells, and we'll be able to get some practice applying these concepts moving forward in our next few videos. So I'll see you in our next one.

How many valence electrons does an atom with five total electrons have?

a) 5.

b) 7.

c) 3.

d) 2.

e) 1.

• A. 5.
• B. 7.
• C. 3.
• D. 2.
• E. 1.

Which of the following is true about electron energy shells?

a) They represent regions around the nucleus in which the electrons orbit.

b) The shells closest to the nucleus contain electrons with higher energy.

c) They contain electrons of the same energy.

d) a and b only.

e) a and c only.

• A. They represent regions around the nucleus in which the electrons orbit.
• B. The shells closest to the nucleus contain electrons with higher energy.
• C. They contain electrons of the same energy.
• D. a and b only.
• E. a and c only.

Octet Rule

In this video, we're going to introduce the octet rule. Now, the octet rule is really just a rule of thumb that says that atoms are more stable and less reactive when their valence shells are fully occupied. Recall from our last lesson video that the first energy shell will hold up to a maximum of just 2 electrons, but the second energy shell will hold up to a maximum of 8 electrons, and really, this 8-electron maximum is where this octet is coming from with the octet rule. Most of the simple atoms that we'll be talking about in our biology course are going to apply to this octet rule. But really, the main takeaway here of the octet rule is that atoms are going to be less reactive when their outer valence shells are fully occupied.

So let's take a look at our image down below to get a better idea of this octet rule. Notice that here in the middle what we have is an electron; these little blue circles that you see throughout our image represent electrons. This represents some electron that wants to react. What you will see is that on the left we have an atom and on the right, we have another atom, and so what you'll notice is that the dinner table here, with the Thanksgiving turkey, represents the nucleus of these atoms, and then, revolving around the nucleus what we have are the electrons. We're specifically focusing on the second energy shell here, which we know holds up to a maximum of 8 electrons. Notice that the electrons that have an open slot in their energy shells are going to be more likely to react. You can see that this atom over here, because it does have an open slot that's available, says "yes, there is a spot for you here," and so it will react with other electrons from other atoms. However, this atom over here notice has a full octet of electrons and because it is full it says "nope, we're full," and they do not react with other electrons from other atoms. The idea once again is that atoms are going to be less reactive when their valence shells are full. Like this one has a full octet in its second shell, so it's going to be much less reactive and it will not react with other electrons that want to react. That's the main takeaway here of the octet rule, and we'll be able to get a little bit of practice in our next few videos. So I'll see you guys there.

Atoms- Smallest Unit of Matter Example 3

Alright. So here we have an example problem that says according to the octet rule, electron distribution in each shell of a neutral Nitrogen atom with an atomic number of 7 is which one of these 4 potential answer options down below, where the first number of each answer option suggests the total number of electrons in the first energy shell, and the second number of each answer option represents the total number of electrons in the second energy shell. And so really what we need to do is draw ourselves a little sketch of a neutral nitrogen atom, which once again has an atomic number of 7. So let's go ahead and say that this green circle here represents the nucleus of our nitrogen atom, which once again we know has an atomic number of 7, so we know that it has 7 positively charged protons in its nucleus. But then, it tells us that the nitrogen atom is neutral, which means that it's going to have an overall net charge of 0, which means that the positively charged protons are going to be balanced out perfectly with the number of negatively charged electrons. So, if there are 7 positively charged protons, there must be 7 negatively charged electrons in order to make this nitrogen atom neutral. So we have to draw a total of 7 electrons. So, considering that we can go ahead and draw our first energy shell, and we know that the first energy shell holds a maximum of 2 electrons. So, we can go ahead and fill this first energy shell here with 2 electrons as we see here, and then the other electrons need to go into the next shell. So, we can go ahead and draw our second energy shell, and, of course, we can put the remaining electrons here. So we know that there must be a total of 7 electrons. We've already got 2, so we got to put 5 more in the second shell. So we can go ahead and put 1, 2, 3, 4, and 5 electrons in this outer shell. So once again, there's a total of 7 electrons here that balance out the 7 protons, which makes this nitrogen atom neutral. And so now all we need to do is take a look at the answer options. And once again, we can see that the first energy shell here has a total of 2 electrons, not one electron as option a and option d indicate. So we can go ahead and eliminate answer option a and answer option d just based on that. However, when we look at answer option b and answer option c, notice that they both suggest the first energy shell has 2 electrons, which once again is correct. We can see the first energy shell does have 2 electrons. So then we need to look at the second number, which is really how these two answers differ, and you can see that the second energy shell, when you count them up, there's a total of 5 electrons not 4 electrons. So we can go ahead and eliminate answer option b here. We can eliminate answer option b and go ahead and indicate that his answers option c here that is the correct answer for this example problem. And the reason for that is once again the 2₁ here indicates the number of electrons in the first energy shell, which you can see there's one here and the other is right here. And then the second number of 5₁ indicates the number of electrons in the second energy shell. And, once again, there are 5 when you count those up. And so c here is the correct answer to this example, and I'll see you guys in our next practice video.

A neon atom (Ne) is unreactive for which of the following reasons?

a) It has 7 valence electrons.

b) It has 8 valence electrons.

c) Its valence shell is full of electrons. 

d) It has 20 valence electrons.

e) b and c only.

• A. It has 7 valence electrons.
• B. It has 8 valence electrons.
• C. Its valence shell is full of electrons.
• D. It has 20 valence electrons.
• E. b and c only.

How many electrons does an Oxygen atom need to fulfill the octet rule by filling its valence shell?

a) 8.

b) 4.

c) 1.

d) 2.

e) 6.

• A. 8.
• B. 4.
• C. 1.
• D. 2.
• E. 6.

Here’s what students ask on this topic:

What are the three subatomic particles that make up an atom?

An atom is composed of three subatomic particles: protons, neutrons, and electrons. Protons have a positive charge (+1) and are located in the nucleus of the atom. Neutrons are neutral (0 charge) and also reside in the nucleus. Electrons have a negative charge (-1) and orbit the nucleus in energy shells. The mass of protons and neutrons is approximately 1 atomic mass unit (AMU) each, while the mass of electrons is negligible, often considered as 0 AMU. Understanding these particles is crucial for grasping atomic structure and behavior.

What is the atomic number and why is it important?

The atomic number of an element is the total number of protons in the nucleus of an atom. It is crucial because it defines the element itself. For example, carbon has an atomic number of 6, meaning it has 6 protons. Changing the number of protons changes the element; for instance, adding a proton to carbon would make it nitrogen. The atomic number also determines the element's position in the periodic table and its chemical properties.

What is the octet rule and how does it influence chemical bonding?

The octet rule is a principle stating that atoms are more stable and less reactive when their valence shells are fully occupied with electrons. For most atoms, this means having 8 electrons in their outermost shell. Atoms will often gain, lose, or share electrons to achieve a full valence shell, leading to the formation of chemical bonds. For example, in a water molecule (H₂O), oxygen shares electrons with hydrogen atoms to fill its valence shell, resulting in a stable molecule.

What are the key elements in living organisms and why are they important?

The key elements in living organisms are carbon (C), hydrogen (H), nitrogen (N), oxygen (O), phosphorus (P), and sulfur (S), collectively known as CHNOPS. These elements are crucial because they form the building blocks of biological molecules. For instance, carbon is the backbone of organic molecules, hydrogen and oxygen are components of water, nitrogen is essential for amino acids and nucleic acids, phosphorus is a part of DNA and ATP, and sulfur is found in some amino acids and vitamins. Together, they make up about 97% of the mass of most living organisms.

How do energy shells and electron orbitals relate to an atom's reactivity?

Energy shells and electron orbitals determine an atom's reactivity by dictating the arrangement of electrons around the nucleus. Electrons occupy energy shells, with the outermost shell known as the valence shell. Atoms with incomplete valence shells are more reactive because they tend to gain, lose, or share electrons to achieve a full shell, following the octet rule. For example, sodium (Na) has one electron in its outer shell and readily loses it to achieve a stable configuration, making it highly reactive.