Question

Order the elements in each set from the smallest to largest first ionization energy. (a) \(\mathrm{Na}, \mathrm{I}, \mathrm{P}\) (b) \(\mathrm{P}, \mathrm{Sr}, \mathrm{Mg}\) (c) \(\mathrm{Ca}, \mathrm{Cs}, \mathrm{Se}\)

Short answer

(a) Na, I, P (b) Sr, Mg, P (c) Cs, Ca, Se

Step-by-step solution

Understand Ionization Energy

Ionization energy is the amount of energy required to remove an electron from an atom in the gaseous state. Elements with higher ionization energies hold their electrons more tightly.

Recall Periodic Trends

Ionization energy generally increases across a period (from left to right) and decreases down a group (from top to bottom) in the periodic table. This is because atoms on the right side of a period have more protons, attracting electrons more strongly, while atoms further down a group have more electron shells, which decrease the attraction due to greater distance and shielding.

Analyze Part (a) - Na, I, P

Locate Na (Sodium), I (Iodine), and P (Phosphorus) on the periodic table. Na is in Group 1, Period 3; P is in Group 15, Period 3; and I is in Group 17, Period 5. According to periodic trends, P has the highest ionization energy as it is to the right of Na and I and I is above P and Na. Therefore, the order from lowest to highest ionization energy is Na, I, P.

Analyze Part (b) - P, Sr, Mg

Locate P (Phosphorus), Sr (Strontium), and Mg (Magnesium) on the periodic table. P is in Group 15, Period 3; Mg is in Group 2, Period 3; and Sr is in Group 2, Period 5. Sr, being below Mg and further to the left of P, will have the lowest ionization energy. Mg is to the left of P but in the same period, so it will have lower ionization energy than P. The order is Sr, Mg, P.

Analyze Part (c) - Ca, Cs, Se

Locate Ca (Calcium), Cs (Cesium), and Se (Selenium) on the periodic table. Ca is in Group 2, Period 4; Cs is in Group 1, Period 6; and Se is in Group 16, Period 4. Cs, being down a group and further to the left, has the lowest ionization energy. Se, being to the right and in the same period as Ca, has the highest ionization energy. The order is Cs, Ca, Se.

Key concepts

Periodic Table Trends

The periodic table organizes chemical elements in such a way that patterns and trends can be observed. These trends help predict how an element might react or what its properties might be. One major trend is the increase in ionization energy as you move across a period from left to right.
The primary reason for this trend is the increase in protons as one moves across a period. More protons mean a stronger positive charge in the nucleus, pulling electrons more tightly. Hence, more energy is needed to remove an electron.
Moreover, as you go down a group from top to bottom, the ionization energy decreases. This occurs because each subsequent element has an additional electron shell, leading to a phenomenon called electron shielding. This means the outer electrons are less tightly bound to the nucleus.
Understanding these trends is crucial for making predictions about the behavior of elements and their chemical reactions.

Ionization Energy Trends

Ionization energy is an essential concept that illustrates how tightly an atom holds its electrons. As mentioned, it represents the energy needed to remove an electron from an atom. This energy provides insight into the reactivity and chemical properties of an element.
Key Patterns:

• Ionization energy tends to increase across a period. This is because additional protons strengthen the nuclear charge, increasing the attraction for electrons.
• Conversely, ionization energy typically decreases down a group. This is primarily due to increased electron shielding and a greater distance between the nucleus and the outermost electron.

These patterns help us understand why certain elements form positive ions more readily than others. For example, alkali metals (found on the left side of the periodic table) have low ionization energies and tend to lose electrons easily, forming cations.

Chemical Elements Comparison

Comparing elements based on ionization energy allows us to rank them and better understand their chemical behavior. When comparing elements like Na, I, and P, or any other set of elements, it's crucial to reference their positions on the periodic table.
In the exercise, Example (a): Na, I, P, we place Sodium (Na) with the lowest ionization energy since it is in Group 1, quite reactive and loses electrons easily. Iodine (I) sits higher in ionization energy, but Phosphorus (P) tops the list in terms of ionization energy due to its group position and the associated increase in nuclear charge.
For Example (b): P, Sr, Mg, Strontium (Sr) has the lowest ionization energy as it's located lower in the groups. Magnesium (Mg) comes next due to its placement left of Phosphorus, which again boasts the highest ionization energy due to its rightward position.
Lastly, in Example (c): Ca, Cs, Se, Cesium (Cs) is lowest due to its position in Group 1, far down the periodic table. Calcium (Ca) holds a middle ground, whereas Selenium (Se) has the highest ionization energy for being further right within the same period as Ca.
Understanding these comparisons aids in predicting how elements will react and the types of bonds they might form.