In each of the following sets, which atom or ion has the smallest radius? a. H, He b. Cl, In, Se

In each of the following sets, which atom or ion has the...

Key Concepts

Atomic Radius

The atomic radius is a measure of the size of an atom, often defined as the distance from the nucleus to the outer edge of the electron cloud. This concept is central to understanding how atoms compare in size based on their number of electrons, nuclear charge, and electron configuration.

Periodic Trends in Atomic Size

Periodic trends describe how atomic properties vary across the periodic table. As you move from left to right across a period, atomic radii generally decrease due to increasing effective nuclear charge, while moving down a group the radii increase because of the addition of electron shells.

Effective Nuclear Charge

This term refers to the net positive charge experienced by electrons in an atom after accounting for the shielding effects of inner electrons. A higher effective nuclear charge pulls the electrons closer to the nucleus, resulting in a smaller atomic or ionic radius.

Isoelectronic Series

An isoelectronic series consists of atoms or ions that have the same number of electrons but different nuclear charges. Within such a series, a species with a higher nuclear charge will typically have a smaller radius because its electrons are drawn closer to the nucleus.

Ionic Radii

Ionic radii involve the comparison of sizes among ions, which can differ considerably from their neutral atoms. Cations (positively charged ions) are generally smaller than their neutral atoms due to a loss of electrons and reduced electron-electron repulsion, while anions (negatively charged ions) are larger due to increased repulsion among more electrons.

Relativistic Effects in Heavy Elements

For very heavy elements, relativistic effects become significant. These effects, stemming from the high velocities of inner electrons, can alter the distribution of electron density and thus affect the atomic radius, making the size trends of superheavy elements more complex than those predicted solely by classical periodic trends.

Transcript

00:01 Okay, so to quickly draw the sketch again of the overall trends on the periodic table, for atomic radius increases right to the left, increases as you go down.

00:20 So overall, the diagonal trend looks like that.

00:23 So keeping that in mind, if we are trying to distinguish the largest radius between, i'm sorry, the smallest radius between hydrogen and helium, let's check out our periodic table.

00:33 Hydrogen's here, helium's here, same row, different columns, helium's in the top right corner.

00:38 Which means it's going to be the smallest.

00:44 That's because even though it has both more protons and electrons, it has a greater effective nuclear charge.

00:56 Looking between cl, ln, and s .e.

01:06 So we've got selenium, indium, and chlorine.

01:12 So they sort of make a diagonal like here you can see.

01:16 So looking back at this diagonal, we've got the smallest here and the largest here.

01:24 So therefore the smallest is going to be the one in the upper right most diagonal, which is chlorine.

01:36 Now we are given element numbers.

01:40 So 116 on the periodic table is down here.

01:43 This row we can see ends in 118.

01:46 So that means row 119 and row 120.

01:49 I'm sorry, element 119 and 120 are both going to be kicked off this row onto the next row, which means they would be an in greater and level than 7, which automatically increases the size.

02:00 Quite a bit...

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