The density of elements on the periodic table shows some interesting patterns. These patterns come from a few main factors: atomic structure, atomic mass, and atomic volume. Knowing about these factors helps us understand how density changes in different groups and periods of the table.

1. Atomic Mass

• Usually, density goes up as atomic mass increases. Think about it this way:
  • Lithium (Li) has a density of about 0.53 grams per cubic centimeter (g/cm³).
  • On the other hand, lead (Pb) has a much higher density of around 11.34 g/cm³.

2. Atomic Volume

• Atomic volume also plays a big role in figuring out density. Density can be calculated using this simple formula: $\text{Density} (\rho) = \frac{\text{Mass} (m)}{\text{Volume} (V)}$
• As we look down a group on the periodic table, atomic volume gets bigger. This happens because more electron shells are added. But just because volume increases doesn’t mean mass increases at the same rate, which causes the density to change.

3. Metallic vs Non-metallic Character

• Metals, which we usually find on the left side of the periodic table, tend to have higher densities than non-metals. For example:
  • Iron (Fe) has a density of 7.87 g/cm³.
  • Sulfur (S), however, has a lower density of 2.07 g/cm³.

4. Periodic Trends

• As you move across a period from left to right, the density of elements generally increases. For instance, sodium (Na) has a density of 0.97 g/cm³, which is lower than that of iron (Fe) mentioned earlier. The way atoms are arranged also affects how closely they fit together, which is important for figuring out density.

Understanding these properties helps us expect and explain how density works in the periodic table. This knowledge is especially helpful when studying chemistry in Year 10.