Question

Compare the elements \(\mathrm{Na}, \mathrm{Mg}, \mathrm{O},\) and \(\mathrm{P}\) (a) Which has the largest atomic radius? (b) Which has the most negative electron attachment enthalpy? (c) Place the elements in order of increasing ionization energy.

Short answer

(a) Na has the largest atomic radius. (b) O has the most negative electron attachment enthalpy. (c) Order of increasing ionization energy: Na < Mg < P < O.

Step-by-step solution

Understanding Atomic Radius

The atomic radius generally increases as you move down a group in the periodic table and decreases as you move across a period from left to right. Among Na (sodium), Mg (magnesium), O (oxygen), and P (phosphorus), Na is furthest to the left and is in the third period, similar to Mg and P, while O is in the second period. Therefore, Na will have the largest atomic radius.

Understanding Electron Attachment Enthalpy

Electron attachment enthalpy, often considered as electron affinity, becomes more negative as the tendency to gain an electron increases. Generally, across a period, the electron attachment enthalpy becomes more negative. Oxygen will have the most negative electron attachment enthalpy among Na, Mg, O, and P, as it tends to gain electrons to achieve a stable noble gas configuration.

Ordering by Ionization Energy

Ionization energy generally increases across a period from left to right and decreases down a group. Therefore, for Na, Mg, O, and P, the order of increasing ionization energy is Na < Mg < P < O. Sodium has the lowest ionization energy due to its position on the leftmost side of the period, while oxygen, being furthest to the right in the same period, has the highest.

Key concepts

Atomic Radius

The atomic radius is a fundamental concept in chemistry. It represents the size of an atom from its nucleus to the outer boundary of its electron cloud. Imagine it like the radius of a sphere where the center is the nucleus, and the surface is the outermost electrons.

When comparing elements within the same period across the periodic table, such as sodium (Na), magnesium (Mg), oxygen (O), and phosphorus (P), it's important to note that atomic radius generally decreases from left to right. This happens because more protons are added to the nucleus as you move across a period. These additional protons pull the electrons closer to the nucleus, decreasing the atomic size. However, when comparing elements in a different period, those lower (higher atomic number) in the table will have a larger atomic radius.

In our specific example, sodium (Na) is the element with the largest atomic radius among Na, Mg, O, and P. This is because sodium is located the most to the left and is in the same period as Mg and P, while oxygen is a period above. Thus, Na has fewer protons and a bigger atomic radius compared to the others.

Electron Attachment Enthalpy

Electron attachment enthalpy, often referred to as electron affinity, describes the energy change when an electron is added to an atom. It indicates how eagerly an atom wants to gain an extra electron to form a negative ion. A more negative electron attachment enthalpy suggests that an atom more readily accepts an additional electron.

Across a period in the periodic table, electron attachment enthalpy becomes increasingly negative. This is due to atoms striving to achieve a noble gas configuration, meaning they are more eager to gain electrons as they become closer to being filled. In the given elements, oxygen (O) has the most negative electron attachment enthalpy. Oxygen, being in the group of chalcogens, is just two steps away from achieving the stable electron configuration of neon, a noble gas.

Out of Na, Mg, O, and P, oxygen's drive to complete its electron shell makes its electron attachment enthalpy the most negative. This trend is a key consideration in predicting how these elements react to gain or share electrons during chemical bonding.

Ionization Energy

Ionization energy is the energy required to remove an electron from an atom, which inherently reflects how tightly the electron is held. As you move across a period from left to right, ionization energy generally increases. This increase occurs because additional protons make the nucleus more positive, attracting electrons more strongly.

Sodium (Na), magnesium (Mg), phosphorus (P), and oxygen (O) show a clear trend in ionization energies. Since Na is furthest to the left in the periodic table, it has the lowest ionization energy among them. As we move to the right, the ionization energies increase due to the stronger pull by the nucleus. Therefore, the order of increasing ionization energy is Na < Mg < P < O.

This sequence describes how much energy each element requires to remove an electron. Elements to the right, like oxygen, tend to hold onto electrons more tightly than those on the left, because they are closer to reaching a stable filled electron shell.