What occurs when an atom loses one or more electrons during the process of ion formation?

Introduction / Context:
Ion formation is a basic concept in atomic structure and chemical bonding. When atoms gain or lose electrons, they form ions with different sizes and charges compared to the original neutral atom. This question specifically asks what happens when an atom loses electrons, including the effect on its radius and its resulting charge.

Given Data / Assumptions:
- A neutral atom has equal numbers of protons and electrons.
- Losing electrons means that the number of positive charges in the nucleus exceeds the number of negative charges in the electron cloud.
- Atomic radius is influenced by electron electron repulsion and attraction between electrons and the nucleus.

Concept / Approach:
When an atom loses electrons, it forms a cation, a positively charged ion. The loss of electrons reduces electron electron repulsion and often reduces the total number of occupied energy levels, especially in metals where an outer shell may become empty. The remaining electrons are pulled closer to the nucleus due to the stronger effective nuclear attraction, leading to a smaller ionic radius compared to the neutral atom. Therefore, the radius decreases and the ion becomes positively charged.

Step-by-Step Solution:
Step 1: Start with a neutral atom where the number of protons equals the number of electrons. Step 2: When the atom loses one or more electrons, it now has more protons than electrons. Step 3: This imbalance gives the species a net positive charge, so it becomes a cation. Step 4: With fewer electrons, electron electron repulsion decreases and the attractive force from the nucleus becomes more effective on the remaining electrons. Step 5: As a result, the electron cloud contracts and the ionic radius becomes smaller than the original atomic radius.

Verification / Alternative check:
Compare the sizes of sodium atom and sodium ion. Neutral sodium has one electron in its third shell. When it loses that electron to form Na+, the outermost occupied shell becomes the second shell, which is closer to the nucleus. Measured ionic radii confirm that Na+ is significantly smaller than neutral Na. Similar comparisons for magnesium and aluminium show the same pattern. These examples confirm that losing electrons produces a smaller, positively charged ion.

Why Other Options Are Wrong:
- The radius increases and the atom becomes a negative ion: This describes what happens when an atom gains electrons to form an anion, not when it loses electrons.
- The radius decreases and the atom becomes a negative ion: Negative ions form by gaining electrons, not losing them, so this is inconsistent.
- The radius increases and the atom becomes a positive ion: Losing electrons does not increase radius; it generally shrinks because of reduced repulsion and stronger effective nuclear attraction.
- The radius and charge do not change: Losing electrons always changes the charge and typically changes the size of the species, so this is incorrect.

Common Pitfalls:
Many learners remember that anions are larger than their parent atoms but forget that cations are smaller. Others may incorrectly assume that removing particles always reduces size without considering charge and electron distribution. Keeping two separate rules in mind helps: losing electrons produces a smaller cation, gaining electrons produces a larger anion.

Final Answer:
When an atom loses electrons, The radius of the atom decreases and the atom becomes a positive ion.