yego.me
💡 Stop wasting time. Read Youtube instead of watch. Download Chrome Extension

Elements and atomic number | Atoms, isotopes, and ions | High school chemistry | Khan Academy


3m read
·Nov 10, 2024

We know that everything in the universe is composed of atoms, but not all atoms are the same. There are many different types of atoms called elements, each with a unique set of physical and chemical properties. Many elements are probably familiar to you; oxygen and carbon, for example, are elements, and so is gold. Others may be less familiar, such as bismuth, xenon, and osmium.

A particular element is identified by the number of protons in its atoms, and the number of protons in the nucleus of an atom is its atomic number, represented by the symbol Z. For example, helium has an atomic number of two; that means that every helium atom has two protons. Here's another example: iron. Its atomic number is 26, so every iron atom has 26 protons.

An element's atomic number can also tell us the number of electrons in a neutral atom of an element. Remember, equal and opposite charges cancel each other out, so to be neutral, an atom must have an equal number of protons, which have a charge of one plus, and electrons, which have a charge of one minus. This means that our helium atom must have two electrons, and our iron atom must have 26 electrons.

All of the known elements are organized according to their atomic numbers in the periodic table. The periodic table lists the elements in order of increasing atomic number as you go from left to right and from top to bottom. The elements are further organized into columns based on their properties. Elements in the same column tend to have similar physical and chemical properties.

Every element is represented by a chemical symbol, a unique one or two-letter abbreviation that appears below the element's atomic number on the periodic table. Many chemical symbols are based on the English name for an element; for example, the symbol for hydrogen is H, and the symbol for aluminum is Al. But some chemical symbols are based on the Latin name for the element; for example, the symbol for lead is Pb, which actually comes from its Latin name, plumbum.

Notice that whenever the chemical symbol for an element has two letters, the second letter is written in lowercase. All of this information is contained inside of each element's box on the periodic table. For example, here's the box for the element nitrogen. At the top of the box is nitrogen's atomic number, which is seven. Remember that this is equal to the number of protons in each atom of nitrogen, as well as the number of electrons.

Below that is nitrogen's chemical symbol, N, followed by its name. Often you'll also see another number listed at the bottom of an element's box, which has to do with atomic mass. We'll cover details about this in another video. What's neat about having all of this information in one place is that if we know one detail about an element, either its atomic number, chemical symbol, or name, we can often use the periodic table to find out the other details.

Let's take a look at a few examples. Say we have the element phosphorus. What is its atomic number and chemical symbol? Looking through the periodic table, we can find phosphorus and see that its atomic number is 15 and its chemical symbol is P. Let's do another example. Say we know the chemical symbol Hg. What is this element's name, and how many protons does it have?

Here is the symbol Hg on the periodic table; its name is mercury, and its atomic number is 80. So it has 80 protons. Let's review: the universe is made up of different types of atoms called elements, and these elements are organized by atomic number in the periodic table. So the next time that you stare up at the starry sky, you know that everything out there is made up of elements.

More Articles

View All
What Could Trigger a Shark Attack? | Rogue Shark
Across the Whit Sundays, hundreds of baited cameras are deployed and listening stations fixed as scientists race to understand why these previously safe waters have turned deadly. As the footage comes in, one big clue emerges: the poor visibility. What w…
Analyzing tables of exponential functions | High School Math | Khan Academy
Let’s say that we have an exponential function h of n, and since it’s an exponential function, it’s going to be the form a times r to the n, where a is our initial value and r is our common ratio. We’re going to assume that r is greater than 0. They’ve g…
Teaching Social Studies with Khanmigo
Hi, I’m Michelle, a professional learning specialist here at KH Academy and a former classroom teacher just like you. Meet K Migo, your AI-driven companion who’s revolutionizing teaching for a more engaging and efficient experience. Kigo has many exciting…
Worked example: Using the ideal gas law to calculate number of moles | AP Chemistry | Khan Academy
We’re told an athlete takes a deep breath, inhaling 1.85 liters of air at 21 degrees Celsius and 754 millimeters of mercury. How many moles of air are in the breath? How many molecules? So pause this video and see if you can figure this out on your own. …
Can Your Dreams Tell the Future?
Have you ever had a dream that came true the next day? Have you ever had a vision of the future and then watched it play out in the real world? Have you ever had a feeling that something big was going to happen, and then it does? You are not alone. One ni…
How to Build An MVP | Startup School
[Music] All right, uh today I’d like to talk to you about how to build an MVP or a minimum viable product. So if you haven’t seen this before, this is a meme that we love to talk about when trying to help founders with their MVP. It’s called the midwit me…