Period 3 Elements

Across the period, the metallic character of the Period 3 elements decreases. This is evident as sodium, magnesium and aluminium, the first three elements in period 3, are all classified as metals. We observed that they display highly metallic characteristics, as they are all solid, malleable and lustrous. On the other hand sulfur, which is further along the period in group 16, is too a solid although it is quite brittle and in powdered form. It is a dull, pale yellow and does not possess the shiny lustrous exterior that one would expect from a metallic element. It is regarded as a non-metal.

The reason for this trend is because the atoms further along the period are more likely to gain electrons to fill their valence shell rather than lose them. This is because across the period the first ionisation energy increases, as the higher core charge results in significant attraction between the nucleus and outer electrons, making it more difficult to remove them. As metals gain their reactivity by losing their electrons, the increased first ionisation energy across the period does not allow for this, and so metals are located at the start of the period where the first ionisation energy is lower. In addition, the higher electronegativity towards the end of the period corresponds with the non-metals, due to their increased ability to attract and gain electrons to complete their outer shell.

As you move across the period, the Period 3 elements' reactivities with water decreases. This is evident because the first element in period 3, sodium, reacts very violently with water; igniting vigorously to form a pink flame, whereas sulfur, which is located further along the period, merely demonstrated no visible reaction at all. This is due to the increased core charge across the period, which results in increased first ionisation energy. This makes it more difficult for the elements further along the period to lose their electrons, therefore accounting for the minimal reactivity that we observed.

As you move across the period, the Period 3 elements' reactivities with acid also decreases. This was apparent as magnesium's reaction with hydrochloric acid was fairly vigorous, with significant heat produced as well as bubbling and frothing. In addition to this, hydrogen gas was detected in the reaction, whereas sulfur, which is situated further along the Periodic Table, displayed no visible reaction at all and