Question

The first ionisation energy of sodium is \(500 \mathrm{KJ} \mathrm{mol} !\) This denotes the energy (1) Given out when 1 mole of sodium atoms dissolve in water to form sodium ions (2) Required to remove one electrons to infinity from one atom of sodium (3) Required to raise the electrons in one mole of gascous sodium atoms to a higher energy level (4) Required to change one mole of gascous sodium atoms into gascous ions \(\left(\mathrm{Na}^{\prime}\right)\)

Short answer

Option (4) is correct.

Step-by-step solution

- Understand the Problem

The problem involves the concept of ionisation energy, specifically the first ionisation energy of sodium.

- Define First Ionisation Energy

The first ionisation energy is defined as the energy required to remove one electron from each atom in one mole of gaseous atoms, forming one mole of gaseous ions.

- Analyze the Options

Read through each given option carefully and determine which one accurately describes the process of first ionisation energy.

- Match Definition to Options

Option (1): This talks about energy given out when sodium dissolves in water, which is unrelated to ionisation energy.Option (2): This describes removing one electron to infinity from one atom, which is similar but not precisely correct as it's about one mole of atoms.Option (3): This talks about raising electrons to a higher energy level, not removing them to form ions.Option (4): This describes the energy required to change one mole of gaseous sodium atoms into gaseous ions, which aligns with the definition.

- Select the Correct Answer

Based on the analysis, option (4) is the only one that accurately reflects the process described by the first ionisation energy.

Key concepts

Ionization Energy

The ionization energy is a fundamental concept in chemistry that describes the energy needed to remove an electron from an atom. This energy is often measured in kilojoules per mole (kJ/mol). It is crucial in understanding the reactivity and chemical properties of elements. For the first ionization energy, it is specifically about removing the first electron from a neutral atom.
The first ionization energy is always positive because energy must be supplied to overcome the electrostatic attraction between the negatively charged electron and the positively charged nucleus.
In simpler terms, higher ionization energy means an atom holds onto its electrons more tightly, making it harder to remove one.

Energy Levels in Atoms

Atoms have electrons arranged in various energy levels, or shells, around the nucleus. These energy levels represent the different amounts of energy that the electrons have. The first energy level is closest to the nucleus and has the lowest energy.
Electrons in higher energy levels are farther from the nucleus and have more energy. When ionizing an atom, like sodium, we are specifically concerned with the electron in the outermost energy level. Removing an electron from a higher energy level generally requires less energy compared to those closer to the nucleus.
Energy levels are crucial for understanding why different elements have different ionization energies.

Gaseous Atoms

To measure the ionization energy, we deal with gaseous atoms. This state means the atoms are free from intermolecular forces found in liquids and solids, allowing us to consider only the intrinsic properties of the atoms themselves.
For sodium, being in the gaseous state ensures that we are measuring the energy needed to remove an electron without interference from other atoms or molecules. The gaseous state provides a standardized way to measure and compare ionization energies across different elements.
This condition is essential for accurate measurement and comparison of ionization energies.

Sodium Ionization

In the case of sodium, the first ionization energy is about 500 kJ/mol. This value specifies the energy required to remove one electron from each sodium atom in one mole of gaseous sodium atoms to form gaseous sodium ions \text{(Na\(^+\)\text)}.
Sodium has a single electron in its outermost energy level. Removing this electron involves breaking the electrostatic attraction with the positively charged nucleus.
Once the electron is removed, the atom becomes a positively charged ion, specifically a Na\(^+\) ion. This process is key in many chemical reactions, such as forming sodium compounds and participating in ionic bonding.