Trends – Density Within a group, density increases from top to bottom in a group. While both mass and volume (due to an increase in atomic radius) are increasing as one moves down a group, the rate of increase for mass outpaces the increase in volume. In this instance, density peaks in the middle of the period.

Density is the mass of a substance per unit volume. It is a measure of how much matter is packed into a particular space. With each group in the periodic table, density increases as you read down the column. With each period, however, the elements at the right and left edges of the row are the least dense.

Hence density increases down a group as size increase down the group. First group elements are generally the largest. Larger the size larger is the density because there is large increase in mass with considerable increases in volume. Hence density increases down a group as size increase down the group.

As you go down a group in the periodic table, density increases. This is because, as you go down, atomic radius increases, and volume increases, so it will be more dense.

The group 7 elements exist as diatomic molecules . The bond between the atoms in a molecule is very strong, but the forces of attraction between molecules are weak. This explains why group 7 elements have low boiling points.

Intermolecular forces (IMFs) can be used to predict relative boiling points. The stronger the IMFs, the lower the vapor pressure of the substance and the higher the boiling point. Therefore, we can compare the relative strengths of the IMFs of the compounds to predict their relative boiling points.

Elements in group seven have a number of similar properties, most importantly they have low melting and boiling points. Each element has five electrons in the outer p shell. For each element down the group, we add an extra shell. The result is that each successive element has a larger atomic radii than the one before.