Ordnungszahl und Massenzahl

Introduction to Atomic and Mass Numbers00:00:12

Every element in the periodic table has its own box containing two numbers: the atomic number (Ordnungszahl) and the mass number (Massen-Zahl). This video will explain the meaning of these numbers.

Understanding the Atomic Number (Ordnungszahl)00:00:31

The atomic number, symbolized as Z, indicates the number of protons in an atom of an element. This number is unique and constant for all atoms of a specific element. For example, hydrogen has an atomic number of 1 (one proton), and oxygen has an atomic number of 8 (eight protons).

Understanding the Mass Number (Massen-Zahl)00:01:09

The mass number, symbolized as A, represents the total number of protons and neutrons in an atom. Protons and neutrons each have a relative mass of one, while electrons are so small that their mass is not considered in the mass number. If you know the mass number and the atomic number, you can calculate the number of neutrons.

Calculating Neutrons: Formula and Example (Oxygen)00:01:40

The mass number equals the atomic number plus the number of neutrons (A = Z + neutrons), or simply protons plus neutrons. To find the number of neutrons, you subtract the number of protons from the mass number (neutrons = A - Z). For example, oxygen has a mass number of 16 and 8 protons. Therefore, it has 16 - 8 = 8 neutrons.

Calculating Neutrons: Example (Lithium)00:02:45

Another example is lithium, which has a mass number of 7 and 3 protons. Using the formula (neutrons = mass number - protons), we find that lithium has 7 - 3 = 4 neutrons.

Summary of Definitions00:03:13

In summary, the atomic number is the count of protons in an atom, and the mass number is the total count of protons and neutrons in an atom.