The periodic table is an important tool in chemistry. It helps students learn about the properties of different elements and how they relate to each other. For Year 7 students, it's important to understand atomic numbers and atomic mass to read the periodic table well.

Atomic Number

1. What is it?: The atomic number of an element is the number of protons in its nucleus (the center of the atom).

2. Why is it important?:

   • It tells us what the element is. For example, hydrogen (H) has an atomic number of 1, while carbon (C) has an atomic number of 6.
   • The periodic table is organized by increasing atomic number.

3. Example: Look at the element Sodium (Na). Its atomic number is 11, and you can find it at the top of its box in the table.

Atomic Mass

1. What is it?: Atomic mass is the average weight of an element's isotopes, which are different versions of the same element. This is measured in atomic mass units (amu).

2. How is it calculated?:

   • You can estimate atomic mass by adding the number of protons and neutrons in the nucleus. For example, carbon has 6 protons (atomic number 6) and usually 6 neutrons. So, its atomic mass is about 12 amu.

3. Example: Chlorine (Cl) has an atomic number of 17 and an atomic mass of about 35.5 amu, which means it has different isotopes.

The Connection Between Atomic Number and Mass

• General Trend:

  • As you go from left to right on the periodic table, both the atomic number and atomic mass usually go up.
  • Elements in the same row (called periods) have different atomic numbers, but they are listed in increasing atomic mass.

• Comparison:

  • In Period 2, Lithium (Li) has an atomic number of 3 and an atomic mass of about 6.94. Neon (Ne) has an atomic number of 10 and an atomic mass of about 20.18. You can see that both atomic number and mass increase.

Conclusion

Knowing how atomic numbers and atomic mass are related is key to understanding the periodic table. Students will see that where an element is located in the table helps explain its properties. By learning these ideas, Year 7 students can have a better understanding of the basic building blocks of everything around them. They can appreciate both the simple and complex nature of elements in the world.