What Are the First 20 Elements? - Free Printable

- The atomic number of an element is equal to the number of protons in its nucleus.
- For example, Hydrogen (H) has an atomic number of 1, meaning it has 1 proton.
- Helium (He) has an atomic number of 2, meaning it has 2 protons.
- This pattern continues: Lithium (Li) has 3 protons, Beryllium (Be) has 4 protons, and so on up to Calcium (Ca), which has 20 protons.
- The atomic mass is the weighted average mass of all naturally occurring isotopes of the element, measured in atomic mass units (amu).
- Atomic mass is not a whole number because it accounts for the different masses and abundances of isotopes.
- For instance, Carbon (C) has an atomic mass of 12.0107 amu, reflecting the presence of isotopes like Carbon-12 and Carbon-13.
- The elements are arranged in order of increasing atomic number, which corresponds to the number of protons.
- This arrangement reflects the periodic law, where elements with similar properties recur at regular intervals.
- The table shows the first 20 elements, from Hydrogen (atomic number 1) to Calcium (atomic number 20).