Those spikes in density are caused by much higher number density, which is in Again, note how they scale roughly with the atomic weight. Atomic number is actually the number of protons in an atom while mass number is the number of nucleons i. e, number of protons plus the number of neutrons. Chemical behavior is the ability of an atom to combine with other atoms. In more technical terms, chemical behavior depends upon the type and number of the.
Atomic weight and atomic mass (video) | Khan Academy
I'll do it in blue. So if you draw the same analogy that we did up here, you might say, "Okay, this must be a This is still a mass. But it's not the mass of just one atom or just one molecule. It's a weighted average across many, many What do I mean by that? Well, on Earth, there are two The primary isotope of carbon is carbon Carbon, which is defined as having a mass of exactly 12 atomic mass units.
But there's also some carbon What do these numbers mean, just as a reminder? Well, carbon has six protons, and the six protons are what make it carbon. Carbon is also going to have six protons. But carbon, carbon also has six neutrons. While carbon has eight neutrons. I know what you're already thinking.
You're, like, "Well, wait. In fact, when I'm kind of just working through chemistry, that is how I think about it. But they don't weigh exactly one atomic mass unit by this definition. Remember, the electron is ever so small, it has very small mass, but it is contributing, or the electrons are contributing, something to the mass.
So, a proton or a neutron have very, very, very close They are close to one atomic mass unit.
- Atomic number, atomic mass, and isotopes
- What is the relationship between atomic mass and mass number?
Let me write this down. One proton, one proton, or one neutron, one neutron, very close to one atomic mass unit, but not exactly.
Relation Between Atomic Number and Atomic Mass
But anyway, going back to what atomic weight is, right over here, the most common isotope of carbon Remember, when we're saying "isotopes," we're saying the same element, we have the same number of protons, but we have different number of neutrons.
The most common isotope on Earth is carbon, but there's also some carbon If you were to take a weighted average, as found on the Earth, of all the carbon and all of the carbon, the weighted average of the atomic masses is the atomic weight. And the atomic weight of carbon And you'll see this on a periodic table. In fact, I have one right over here. Notice, the six protons, this is what defines it to be carbon.
But then they write Now, it's very close to 12, as opposed to being closer to 14, because most of the carbon on Earth is carbon We could write this down. This is the atomic weight. This is the atomic weight of carbon on Earth.
Atomic number, atomic mass, and isotopes (article) | Khan Academy
Typically, if people are telling you, "Hey, I'm talking about the isotope. Hopefully, this clarified it more than it confused. All right, see you in the next video. Radioactivity is actually a property of an atom.
Atomic weight and atomic mass
Radioactive atoms have unstable nuclei, and they will eventually release subatomic particles to become more stable, giving off energy—radiation—in the process. Often, elements come in both radioactive and nonradioactive versions that differ in the number of neutrons they contain. These different versions of elements are called isotopes, and small quantities of radioactive isotopes often occur in nature.
For instance, a small amount of carbon exists in the atmosphere as radioactive carbon, and the amount of carbon found in fossils allows paleontologists to determine their age. Atomic number, atomic mass, and relative atomic mass Atoms of each element contain a characteristic number of protons. In fact, the number of protons determines what atom we are looking at e. In contrast, the number of neutrons for a given element can vary.
Forms of the same atom that differ only in their number of neutrons are called isotopes. If you want to calculate how many neutrons an atom has, you can simply subtract the number of protons, or atomic number, from the mass number.
The atomic mass of a single atom is simply its total mass and is typically expressed in atomic mass units or amu. By definition, an atom of carbon with six neutrons, carbon, has an atomic mass of 12 amu. In general, though, an atom's atomic mass will be very close to its mass number, but will have some deviation in the decimal places. The relative atomic mass is an average of the atomic masses of all the different isotopes in a sample, with each isotope's contribution to the average determined by how big a fraction of the sample it makes up.
The relative atomic masses given in periodic table entries—like the one for hydrogen, below—are calculated for all the naturally occurring isotopes of each element, weighted by the abundance of those isotopes on earth. Extraterrestrial objects, like asteroids or meteors, might have very different isotope abundances. Isotopes and radioactive decay As mentioned above, isotopes are different forms of an element that have the same number of protons but different numbers of neutrons.
Many elements—such as carbon, potassium, and uranium—have multiple naturally occurring isotopes. A neutral atom of Carbon contains six protons, six neutrons, and six electrons; therefore, it has a mass number of 12 six protons plus six neutrons.