Question

In The valence electron of a sodium atom does not sense the full \(+11\) of the sodium nucleus. Why not?

Short answer

The valence electron of sodium only senses an effective nuclear charge of +1 due to electron shielding from inner electrons.

Step-by-step solution

Understanding Atomic Structure

A sodium atom consists of 11 protons in the nucleus and 11 electrons that surround the nucleus in various orbitals. The electrons are arranged in shells around the nucleus, with each shell having different energy levels.

Concept of Electron Shielding

Electron shielding, also known as the screening effect, occurs when inner shell electrons partially block the attraction between the nucleus and the outer shell electrons. This is due to the repulsion between negatively charged electrons.

Valence Electron of Sodium

The valence electron of a sodium atom is located in the outermost electron shell. In sodium (atomic number 11), there are 2 electrons in the first shell, 8 in the second shell, and 1 in the third shell, which is the valence electron.

Calculating Effective Nuclear Charge

The effective nuclear charge ( Z_{ ext{eff}} ) felt by the valence electron is calculated by subtracting the shielding effect of other electrons from the total nuclear charge. The shielding electrons (10 inner electrons) reduce the effective impact of the nuclear charge. Thus, Z_{ ext{eff}} = 11 - 10 = 1.

Explanation of Reduced Nuclear Attraction

Because of electron shielding, the valence electron of the sodium atom only effectively feels a nuclear charge of +1, rather than the full +11 from the nucleus. This is due to the presence of inner electrons that block the valence electron's view of the full nuclear charge.

Key concepts

Valence Electron

Understanding the concept of a valence electron is crucial in chemistry, particularly when studying atomic behavior and reactivity. A valence electron is an electron located in the outermost shell of an atom.
These electrons are vital because they are involved in forming chemical bonds with other atoms.
For a sodium atom, which has an atomic number of 11, the valence electron resides in the third shell.
The configuration is as follows:

• First shell: 2 electrons
• Second shell: 8 electrons
• Third shell: 1 electron

Hence, the single electron in the third shell is the valence electron. Its position makes it central to reactions where sodium atoms donate this electron to achieve a stable configuration.

Effective Nuclear Charge

The effective nuclear charge, often represented as \( Z_{\text{eff}} \), is a measure of the actual nuclear force felt by an electron from the nucleus.
This differs from the total charge because other electrons between the nucleus and the electron of interest shield some of this attraction.
For sodium, with its 11 protons, you might think the nucleus exerts a charge of +11 on its electrons.

• However, only the lone valence electron in the third shell truly feels this effect reduced to +1.
• This decrease results from the inner coupled 10 electrons that reduce the charge effectively.

This reduced charge influences how easily the valence electron can be lost in reactions, affecting sodium's chemical properties.

Atomic Structure

The atomic structure of an atom forms the basis for understanding chemical behavior and the nature of different elements.
Each atom consists of a nucleus at its center, containing protons and neutrons, with electrons orbiting this nucleus in shells or energy levels.
The arrangement and number of these subatomic particles define the element.

• In sodium, the nucleus has 11 protons, giving it an atomic number of 11.
• The electrons are arranged in three main shells, dictating interactions with other atoms.

The structure explains why sodium commonly forms ions by losing its valence electron, seeking a stable electronic arrangement.

Sodium Atom

The sodium atom, known by its chemical symbol Na, is a fundamental element in many chemical processes.
It belongs to the alkali metals in Group 1 of the periodic table, characterized by a single electron in their outermost shell.
The simplicity of its electron configuration makes sodium highly reactive, particularly with non-metals like chlorine to form stable compounds such as sodium chloride (table salt).

• The high reactivity is due to sodium's tendency to give away the lone valence electron easily.
• This action results in a stable ionic bond, critical for forming a vast array of compounds.

Understanding sodium's properties and its atomic structure reveals why it is so commonly found in nature and widely used in industry.