Helium is easier to ionize compared to other elements because it has a low ionization energy. The ionization energy is the amount of energy required to remove an electron from an atom or ion in its ground state. In the case of helium, it has the lowest ionization energy among all the elements.
There are a few reasons for this:
Electron-electron repulsion: In helium, both electrons are confined to a small space around the nucleus. Since electrons have negative charges, they repel each other. This repulsion makes it easier to remove one of the electrons because the remaining electron experiences less shielding from the other electron, reducing its attraction to the nucleus.
Effective nuclear charge: The effective nuclear charge experienced by the electrons in helium is relatively high. The effective nuclear charge is the net positive charge felt by an electron, taking into account the shielding effect of other electrons. In helium, with its two protons, the effective nuclear charge experienced by each electron is relatively strong, making it easier to remove an electron.
Regarding the energy levels in helium, it is true that helium has fewer energy levels compared to other atoms despite having two protons and two neutrons in its nucleus. This is because the energy levels in atoms are determined by both the number of protons and the number of electrons.
In helium, the two electrons occupy the lowest available energy level, known as the 1s orbital. The 1s orbital can accommodate a maximum of two electrons. Once the 1s orbital is filled, there are no more available energy levels at lower energies for additional electrons to occupy.
Other elements with more protons and electrons have additional energy levels and orbitals available for electrons to occupy. These additional energy levels result from the increasing number of protons and the electron configurations that follow. Each additional electron in these atoms can occupy higher energy levels and orbitals.
In summary, helium is easier to ionize due to its low ionization energy, which arises from factors such as electron-electron repulsion and the effective nuclear charge. The presence of only two electrons in helium limits the number of energy levels available, as both electrons occupy the lowest energy level, resulting in fewer energy levels compared to other atoms.