Understanding Atomic Number and Mass Number: A Simple Guide for Chemistry Beginners

-

 


Have you ever looked at the periodic table and wondered what those numbers really mean? If you’re a student studying chemistry or just curious about atoms, understanding the atomic number and mass number is key to unlocking the secrets of elements. In this post, I’ll guide you step-by-step on how to identify the atomic number, calculate the mass number, and find out how many neutrons are in an atom — using real examples from elements like lithium, beryllium, and sodium.

What Is the Atomic Number?

Let’s start with the basics: the atomic number. The atomic number of an element tells you the number of protons in the nucleus of its atoms. Protons are positively charged particles that, along with neutrons, make up the nucleus of an atom. The atomic number is usually the smaller number displayed on the periodic table square for each element.

For example, magnesium has an atomic number of 12, which means every magnesium atom contains 12 protons in its nucleus. Boron, on the other hand, has an atomic number of 5 — so it has 5 protons. Knowing the atomic number is crucial because it defines the element itself. No two different elements have the same number of protons.

What Is the Mass Number?

Now, what about the mass number? This number represents the total number of protons and neutrons in the nucleus. Neutrons are neutral particles — they don’t carry a charge but contribute to the atom’s mass.

On the periodic table, the mass number is usually the larger number shown near the element symbol. However, sometimes you may not see it directly on the table and will need to calculate it yourself based on information given.

For example, lithium (symbol Li) has a mass number of 7 and an atomic number of 3. This means it has 3 protons and 4 neutrons (because 7 - 3 = 4).

How to Calculate the Number of Neutrons

Calculating neutrons is simple once you know the atomic number and mass number. The formula is:

Number of neutrons = Mass number – Atomic number

Let’s use beryllium (Be) as an example. Beryllium has an atomic number of 4 and a mass number of 9. So:

Number of neutrons = 9 – 4 = 5 neutrons

Easy, right?

Electrons in a Neutral Atom

In a neutral atom, the number of electrons equals the number of protons. Electrons are negatively charged particles that orbit the nucleus. So, if you have an atom of beryllium, which has 4 protons, it will also have 4 electrons to balance out the positive charge of the protons.

More Examples to Practice

Let’s look at silicon (Si). The periodic table shows a mass number of 28 and an atomic number of 14 for silicon. Using our formula:

Number of neutrons = 28 – 14 = 14 neutrons

Silicon has 14 protons and 14 neutrons.

Here’s a little challenge for you: which element has 12 neutrons in its atom? Take a moment to think about it.

If you guessed sodium (Na), you’re correct! Sodium has an atomic number of 11 and a mass number of 23, so:

Number of neutrons = 23 – 11 = 12 neutrons

Quick Recap

  • Atomic Number = Number of protons in the nucleus (smaller number on periodic table)

  • Mass Number = Number of protons + neutrons (larger number)

  • Number of Neutrons = Mass number – Atomic number

  • Number of Electrons = Number of protons (in a neutral atom)

Why Is This Important?

Understanding these numbers helps you make sense of the atomic structure, isotopes, and chemical behavior of elements. It’s foundational knowledge that you’ll need for chemistry exams and beyond.

Final Thoughts

I hope this breakdown helps clear up any confusion you had about atomic and mass numbers. Don’t hesitate to pause the video or read over these notes as many times as you need. The more you practice, the easier it will become to identify these numbers and calculate neutrons quickly.

If you want to get organized for your chemistry exams, I’ve created a free exam planner that you can download and/or you can go have a look at the video 

Good luck with your studies, and if you have any questions or want to request another chemistry topic, leave a comment or reach out on my YouTube channel. Happy learning!

Comments

Post a Comment

Popular posts from this blog

How to Create Custom Flashcards in Canva: A Beginner's Guide + Using Creative Fabrica for Resellable Designs

-
Image
  As a beginner in the world of educational design, creating teaching materials like flashcards can seem daunting. However, with the right tools, it becomes a fun and simple process. In this post, I’ll walk you through how to design custom flashcards using Canva and how to incorporate Creative Fabrica elements for even more creativity. Plus, I’ll show you how to ensure that your designs are ready for resale if you want to take your flashcards to the next level! Why Canva for Flashcards? Canva is an excellent platform for designing various teaching materials because of its user-friendly interface and vast library of templates and elements. Even if you have no prior experience with graphic design, Canva makes it easy to create professional-looking materials. This is perfect for educators, especially if you want to personalize your flashcards to match your lesson plans. Step 1: Choose a Template Start by selecting a flashcard template that suits your style. There are plenty of free o...
Read more

Not Everyone’s Cup of Tea—And That’s Okay ☕💚

-
Image
 One of the most valuable lessons I’ve learned in my teaching journey is this: ✨ You’re not everyone’s cup of tea—and that’s perfectly fine. Some people need your cup of matcha, and they’ll love you for it. ✨ When I first started teaching, I was full of enthusiasm but still figuring things out. Like most new teachers, I made mistakes, faced criticism, and battled self-doubt. It’s easy to let negative feedback linger, especially when you’re still building confidence. I used to overanalyze every comment, wondering if I was really cut out for this profession. But one experience changed my perspective. Back in my brick-and-mortar classroom, I had a student who was hardworking but struggled to believe in herself. When I transitioned to online teaching, she reached out and asked if I could tutor her in science. I said yes. Over time, her confidence grew, her marks improved, and recently, she qualified for a biomedical science degree —a dream she once thought was out of reach. Even m...
Read more

How I use these flashcards to Gamify my Classroom: Making Learning Fun and Effective

-
Image
  Gamify Your Classroom with Flash Cards: Making Learning Fun and Effective As educators, we all know how challenging it can be to keep students engaged, especially when they don’t quite grasp the material or lack foundational knowledge. At times, traditional lessons can feel monotonous, and that’s when creativity comes in. In this blog post, I’m going to share how I used a simple tool—flashcards—to create an environment where learning is not only effective but also fun and interactive. The Challenge: Keeping Students Engaged I’ve noticed that students often lose interest in lessons when they struggle with the material. This is particularly true when foundational knowledge is missing. At my previous school, the students used to enjoy playing games like Monopoly and 30 Seconds, which made learning more interactive. Unfortunately, when a new principal came, we were no longer allowed to play those games in class. But this didn’t stop me. I still wanted my students to have fun whil...
Read more