Ionic Radius Trends, Basic Introduction, Periodic Table, Sizes of Isoelectric Ions, Chemistry

Summary

This video explains the concept of ionic radii and how ion sizes change across the periodic table. It highlights trends such as ions getting larger as you move down a group and smaller as you move right across a period. The video also explores differences between cations (positively charged ions) and anions (negatively charged ions), noting that anions are generally larger due to additional electrons. Multiple examples, including magnesium, beryllium, calcium, and bromide ions, are used to illustrate these trends and how nuclear charge and energy levels influence ionic size.

Takeaways

• 🔍 Ionic radii follow the same trend as atomic radii, increasing as you go down a group in the periodic table.
• 🔬 Positively charged ions (cations) decrease in size from left to right across a period.
• ⚖️ Cations with higher positive charges are smaller than those with lower charges (e.g., Al3+ is smaller than Mg2+).
• 🔄 Negatively charged ions (anions) are generally larger than positively charged ions.
• ⬆️ Anions increase in size as the negative charge increases (e.g., O2- is larger than F-).
• 📉 Ionic radii decrease as effective nuclear charge increases, making cations smaller.
• 📏 Beryllium (Be2+) is smaller than magnesium (Mg2+) because it is higher in the periodic table.
• 🧲 Bromide (Br-) is larger than potassium (K+), because anions are larger due to electron gain and increased electron repulsion.
• ⚛️ The sodium atom (Na) is larger than the sodium ion (Na+) because the loss of an electron reduces the number of electron shells.
• 🔋 Isoelectronic ions have the same electron configuration but vary in size based on their charges, with the most negatively charged being the largest (e.g., O2- > F- > Na+ > Mg2+).

Q & A

What trend does ionic radii follow in the periodic table?

Ionic radii increase as you move down a group and decrease as you move across a period from left to right.

Why is the potassium ion (K⁺) larger than the lithium ion (Li⁺)?

The potassium ion is larger than the lithium ion because it is lower in the periodic table. As you move down a group, the number of energy levels increases, resulting in a larger ion.

How do the sizes of cations compare to anions of the same element?

Cations (positively charged ions) are smaller than anions (negatively charged ions) of the same element. This is due to the loss of electrons in cations, which reduces electron-electron repulsion and energy levels, while anions gain electrons, increasing the electron cloud.

Why is the magnesium ion (Mg²⁺) smaller than the sodium ion (Na⁺) despite being in the same period?

Magnesium ion is smaller than the sodium ion because it has a higher positive charge (+2 vs +1), which increases the effective nuclear charge, pulling the electrons closer and reducing the ionic radius.

How does the charge of an ion affect its size?

The more positive the charge on an ion, the smaller the ion. The more negative the charge, the larger the ion. Positive charges reduce electron-electron repulsion, shrinking the ion, while negative charges increase repulsion, expanding the ion.

What is the size of the bromide ion (Br⁻) compared to the potassium ion (K⁺), and why?

The bromide ion is larger than the potassium ion. Bromide has 36 electrons, which occupy more energy levels and create more electron-electron repulsion, making it larger than the potassium ion with only 18 electrons.

Why are cations smaller than their parent atoms?

Cations are smaller than their parent atoms because they lose one or more electrons, resulting in fewer electron shells and reduced electron-electron repulsion, making the ion more compact.

Why are anions larger than their parent atoms?

Anions are larger than their parent atoms because they gain one or more electrons, increasing electron-electron repulsion and expanding the electron cloud, making the ion larger.

What is the general rule for the size of isoelectronic ions?

For isoelectronic ions (ions with the same number of electrons), the more positive the charge, the smaller the ion. Conversely, the more negative the charge, the larger the ion.

Why is chloride (Cl⁻) larger than chlorine (Cl) even though both have the same number of energy levels?

Chloride is larger than chlorine because the extra electron in chloride increases electron-electron repulsion, causing the electron cloud to expand, making the anion significantly larger than the neutral atom.