How does the reactivity of transition metals change across the period?

The reactivity of transition metals generally decreases across the period from left to right.

Transition metals are found in the middle of the periodic table, specifically in groups 3 to 12. As you move from left to right across a period, the reactivity of these metals generally decreases. This is due to the increasing number of electrons in the outer shell and the increasing nuclear charge, which makes it harder for the atom to lose electrons and thus react.

At the start of the transition metals series, we have Scandium (Sc) and Titanium (Ti). These metals are quite reactive because they have fewer electrons in their outer shell, making it easier for them to lose electrons and form positive ions. This is a key aspect of reactivity in metals.

As we move across the period, the number of electrons in the outer shell increases. For example, Iron (Fe) has more electrons in its outer shell than Scandium. This means it's harder for Iron to lose electrons and form positive ions, making it less reactive.

Simultaneously, the nuclear charge (the total charge of all the protons in the nucleus) also increases across the period. This stronger nuclear charge pulls the outer electrons closer to the nucleus, making them harder to remove and thus decreasing the metal's reactivity.

However, it's important to note that this trend is not perfectly linear. There are exceptions due to the complex electronic configurations of transition metals. For example, Copper (Cu) and Zinc (Zn) are less reactive than you might expect based on their position in the period. This is because they have full or half-full d sub-shells, which provide extra stability and make them less likely to lose electrons.

In summary, while there are exceptions, the general trend is that the reactivity of transition metals decreases as you move from left to right across the period. This is due to the increasing number of outer shell electrons and the increasing nuclear charge.