Groups 1, 7 and 0 and their trends

Elements in each group of the periodic table share similar chemical properties and show patterns in reactivity and physical characteristics. Understanding these trends helps explain the behaviour of certain elements and their roles in everyday applications.

Group 1

Known as the alkali metals because they react with water to produce an alkaline solution (pH above 7).

• Elements: lithium (Li), sodium (Na), potassium (K), rubidium (Rb) and caesium (Cs).
• Physical properties: the group 1 metals are soft and you can cut them with a knife. Lithium, sodium and potassium are less dense than water, so they float. They have low melting points compared to other metals and these decrease as you go down the group.
• Chemical properties: alkali metals are highly reactive; they react vigorously with water. Each metal gives off a characteristic flame colour when you heat it. For example, Li, red; Na, yellow; K, lilac.
• Key trend: alkali metals become more reactive as you move down the group because their atoms get larger. This means the outermost electron is further from the nucleus and the attraction between them is weaker, so the electron is more easily lost.

Group 7

Known as the halogens because they react with metals to form salts and in Greek, halogen means salt former.

• Elements: fluorine (F), chlorine (Cl), bromine (Br), iodine (I) and astatine (At).
• Physical properties: fluorine and chlorine are gases at room temperature, bromine is a liquid and iodine and astatine are solids. The elements get darker in colour as you go down the group (at room temperature, Cl is greenish-yellow, Br is red-brown and I is dark grey).
• Chemical properties: halogens are reactive non-metals and readily form salts when they react with metals. A more reactive halogen can displace a less reactive one from a compound.
• Key trend: halogen reactivity decreases as you move down the group because their atoms get larger, meaning there’s a weaker attraction between the nucleus and incoming electrons.

Source: © Dan Bright

Source: © Dan Bright

Source: © Dan Bright

Group 1 chemical properties

Alkali metals become more reactive as you move down the group because their atoms gets bigger. Each metal gives off a characteristic flame colour

Group 7 physical properties

Halogens are different states at room temperature. The elements also get darker in colour down the group

Group 0 physical properties

The boiling points of noble gases increase down the group, because their atoms get bigger

Group 0

Known as the noble gases because they are unreactive and generally exist as unbonded atoms, giving the idea that they’re ‘unwilling to interact’ with others.

• Elements: helium (He), neon (Ne), argon (Ar), krypton (Kr), xenon (Xe) and radon (Rn).
• Physical properties: all the group 0 elements are gases. They have very low boiling points, which increase slightly down the group.
• Chemical properties: noble gases are very unreactive and unlikely to form compounds under normal conditions.
• Key trend: the boiling points of the noble gases increase down the group because their atoms get larger. Larger atoms have stronger forces of attraction between them and require more energy to overcome.

Resources written by Louise Glynn