Question

Hydrogen has only one proton, but its IE \(_{1}\) is much greater than that of lithium, which has three protons. Explain.

Short answer

Hydrogen has a higher IE because its lone electron feels a stronger pull from the nucleus, without any shielding, unlike lithium's outer electron.

Step-by-step solution

Define Ionization Energy

Ionization energy (IE) is the amount of energy required to remove an electron from an atom in its gaseous state. It reflects how strongly an atom holds onto its electrons.

Consider Atomic Structure

Hydrogen has one proton and one electron, while lithium has three protons and three electrons. However, lithium's electrons are arranged in two energy levels or shells.

Examine the Electron Configuration

Hydrogen: 1s¹, Lithium: 1s² 2s¹. Lithium has two electrons in its first shell (1s) and one in its second shell (2s).

Discuss Shielding Effect and Effective Nuclear Charge

In lithium, the two inner electrons (1s²) shield the outer electron (2s¹) from the full attraction of its three protons. This reduces the effective nuclear charge felt by the outer electron.

Compare the Ionization Energies

Hydrogen's single electron experiences the full attraction of its one proton without any shielding. Consequently, more energy is needed to remove hydrogen's electron (higher IE) compared to lithium's outer electron which is further from the nucleus and shielded by inner electrons.

Key concepts

Atomic Structure

Atoms are the fundamental units of matter, and they consist of three main subatomic particles: protons, neutrons, and electrons.
Protons are positively charged, neutrons carry no charge, and electrons are negatively charged.
These particles are arranged in a specific manner inside an atom.
The protons and neutrons are located in the nucleus at the center of the atom, while the electrons orbit the nucleus in regions called electron shells or energy levels.
For example:

• Hydrogen has one proton and one electron.
• Lithium has three protons and three electrons.

The atomic structure determines many properties of an element, including its ionization energy, which is the amount of energy needed to remove one electron from the atom.

Electron Configuration

Electron configuration refers to the arrangement of electrons in an atom's electron shells or energy levels.
Electrons fill these shells in a specific order following the principles of quantum mechanics.
Each shell can hold a certain number of electrons, and shells are filled from the innermost to the outermost.
For instance:

• Hydrogen has the configuration 1s¹, meaning it has one electron in the 1s orbital.
• Lithium has the configuration 1s² 2s¹, meaning it has two electrons in the 1s orbital and one in the 2s orbital.

This configuration affects how strongly each electron is held by the nucleus and hence influences the ionization energy.
Electrons in outer shells are generally easier to remove, so they have lower ionization energies than those in inner shells.

Effective Nuclear Charge

The effective nuclear charge (Z_eff) is the net positive charge experienced by an electron in a multi-electron atom.
It takes into account the actual positive charge of the nucleus and the shielding effect of inner-shell electrons.
Mathematically, it can be expressed as:
\[ Z_{eff} = Z - S \]where:

• Z is the atomic number (total positive charge).
• S is the shielding constant (the reduction in nuclear charge by inner electrons).

In hydrogen, there's no shielding because it only has one proton and one electron.
Thus, the effective nuclear charge felt by the electron is just the charge of the proton (Z_eff = 1).
In lithium, the two inner-shell (1s) electrons partially shield the outer-shell (2s) electron from the full three-proton charge of the nucleus.
This results in a lower effective nuclear charge for the outer electron, making it easier to remove and hence reducing its ionization energy compared to hydrogen.