Question

Compare the elements Na, Mg, O, and 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) Ionization energy order: Na < Mg < P < O.

Step-by-step solution

Understanding Atomic Radius

The atomic radius is the distance from the nucleus of an atom to the outer shell of electrons. In general, the atomic radius decreases across a period (from left to right) in the periodic table due to the increase in effective nuclear charge which pulls the electrons closer to the nucleus.

Identifying the Largest Atomic Radius

In the periodic table, Na (Sodium), Mg (Magnesium), O (Oxygen), and P (Phosphorus) all belong to the same period (Period 3). According to the trend, the atomic radius decreases across the period, making Na, which is furthest left, the element with the largest atomic radius. Therefore, Na has the largest atomic radius.

Understanding Electron Attachment Enthalpy

Electron attachment enthalpy, particularly negative values, indicates an atom's tendency to gain an electron, forming a negative ion. The more negative the value, the more energy released, and thus the higher the tendency.

Determining Most Negative Electron Attachment Enthalpy

Oxygen (O), with its high electronegativity, has a strong tendency to gain an electron. Therefore, it has the most negative electron attachment enthalpy among the given elements because it's more electronegative than the others.

Understanding Ionization Energy

Ionization energy is the energy required to remove an electron from an atom in the gaseous state. This energy increases across a period because atoms hold onto their electrons more tightly as effective nuclear charge increases.

Ordering Elements by Ionization Energy

To order by increasing ionization energy using the periodic trend, note that it increases across a period. Therefore, the order from lowest to highest ionization energy is: Na < Mg < P < O. Each subsequent element holds its electrons more tightly than the last.

Key concepts

Understanding Atomic Radius

The atomic radius refers to the size of an atom, specifically the distance from the nucleus to the outermost electron shell. This measurement is critical to understanding how elements react and bond. Generally, as you move from left to right across a period on the periodic table, the atomic radius decreases. This trend occurs because protons are added to the nucleus, increasing the nuclear charge. With a higher nuclear charge, the nucleus more effectively pulls electrons inward, reducing the atomic radius. If we consider elements like Na, Mg, O, and P, all located in Period 3, we notice this trend: Sodium (Na) is on the far left, consequently having the largest atomic radius, while Oxygen (O) on the right has a much smaller atomic radius due to its higher effective nuclear charge.

• Atomic radius decreases from left to right across a period.
• Sodium (Na) has the largest atomic radius among these elements.

Ionization Energy Trends

Ionization energy is the amount of energy required to remove an electron from an atom in its gaseous state. As one moves across a period from left to right, ionization energy generally increases. This is because atoms more on the right of a period, like Oxygen or Phosphorus, have higher effective nuclear charges and smaller atomic radii, which means they hold their electrons more tightly. Consequently, it requires more energy to remove an electron from these atoms compared to those like Sodium and Magnesium, which are on the left and have larger radii and weaker nuclear attractions for their outer electrons.

• Ionization energy increases across a period due to stronger nuclear attraction.
• Order from lowest to highest: Na < Mg < P < O.

Examining Electron Attachment Enthalpy

Electron attachment enthalpy reflects the energy change when an electron is added to a neutral atom, forming a negatively charged ion. A more negative electron attachment enthalpy indicates a greater tendency for an atom to gain an additional electron, releasing more energy in the process. This often correlates with an element's electronegativity. Oxygen, renowned for its high electronegativity, will likely have a more negative electron attachment enthalpy compared to the other elements like Sodium, Magnesium, or Phosphorus. This high electronegativity of oxygen is indicative of its strong attraction for electrons, allowing it to release significant energy on gaining an extra electron.

• More negative values suggest stronger tendencies to gain electrons.
• Oxygen (O) has the most negative electron attachment enthalpy due to high electronegativity.