Potassium, K, is more reactive than sodium, Na. Calcium, Ca, is less reactive than sodium. The comparative reactivity of these metals is often noted as: K > Na > Ca. Explain the reactivity differences of K, Na, Ca.
K is more reactive than Na because the outside electron is further away from the nucleus; thus it is easier to pull the electron away. Ca is less reactive than K because there is more positive charge holding the outside electron. Said another way, the ionization potential is lowest for K and highest for Ca with Na between.
The reactivity differences among potassium (K), sodium (Na), and calcium (Ca) can be explained by analyzing their electronic configurations and the trends in the periodic table.
1. Electronic Configuration:
Potassium has an electronic configuration of [Ar] 4s1, sodium has [Ne] 3s1, and calcium has [Ar] 4s2. The number of valence electrons determines the reactivity of an element. Valence electrons are the electrons present in the outermost energy level of an atom. In this case, potassium has one valence electron, sodium has one as well, and calcium has two.
2. Trends in Reactivity:
Reactivity generally increases as you move down a group (column) in the periodic table. This is known as the group trend. Therefore, potassium being underneath sodium in the same group implies that potassium is more reactive than sodium.
Reactivity also tends to increase from left to right across a period (row) in the periodic table. This is known as the period trend. However, calcium being the next element after sodium in the same period is less reactive than sodium. This appears to contradict the trend, so we need to consider additional factors.
3. Atomic Size:
As you move across a period, the atomic size generally decreases. This is due to the increasing positive charge in the nucleus, which attracts the electrons more strongly, resulting in a smaller atomic radius. In this case, sodium is smaller than potassium, and calcium is smaller than both sodium and potassium.
The smaller atomic size of calcium compared to sodium affects its reactivity. Calcium's valence electrons are closer to the nucleus, leading to stronger electrostatic attractions between the nucleus and the electrons. Consequently, it becomes more difficult for calcium to lose its valence electrons and react with other elements. This accounts for the lower reactivity of calcium compared to sodium.
In summary, potassium is the most reactive among K, Na, and Ca due to its single valence electron that is relatively far from the nucleus. Sodium is less reactive than potassium because its valence electron is closer to the nucleus, making it slightly more difficult to remove. Calcium, having a smaller atomic size and two valence electrons, is less reactive than both potassium and sodium.