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How does Coulomb's law explain the relative sizes of neutral atoms and ions?
Coulomb’s Law describes the force between charged particles and states that the force of attraction between the nucleus (positively charged) and electrons (negatively charged) depends on the distance between them and the charge of the particles.
The size of an atom depends on the balance between the nuclear charge and the electronic repulsion within the atom.
Larger nuclear charge (more protons) leads to a stronger attraction and a smaller radius for the atom or ion.
How does Coulomb’s law explain the size of neutral atoms?
In neutral atoms, the number of electrons is equal to the number of protons, and the electrons are attracted by the positive charge of the nucleus.
The atomic radius is determined by the distance between the outermost electrons and the nucleus.
Across a Period: As Z* (effective nuclear charge) increases, the attractive force between the nucleus and electrons becomes stronger, pulling electrons closer, decreasing atomic radius.
Down a Group: Electrons are added to higher energy levels, farther from the nucleus, and the increase in electron shielding reduces the effective attraction, increasing atomic radius.
How does Coulomb’s law explain the size of cations?
Cations are positively charged ions formed by the loss of electrons.
When an atom loses an electron, there is less electron-electron repulsion, and the remaining electrons are drawn more closely to the nucleus.
As a result, the ionic radius of a cation is smaller than the atomic radius of the neutral atom.
Example: Na → Na⁺ (Na⁺ has a smaller radius because it loses one electron and has less shielding).
How does Coulomb’s law explain the size of anions?
Anions are negatively charged ions formed by gaining electrons.
When an atom gains an electron, the increased electron-electron repulsion causes the electrons to spread out, increasing the distance between them.
As a result, the ionic radius of an anion is larger than the atomic radius of the neutral atom.
Example: Cl → Cl⁻ (Cl⁻ has a larger radius because it gains one electron, increasing electron-electron repulsion).
