For transition elements, describe and explain the observed trends in atomic radius as you move:

step 1 So this video is going to take a look at the trends in atomic radius. So before we can really lo

For transition elements, describe and explain the observed...

Key Concepts

Atomic Radius

Atomic radius is the distance from an atom's nucleus to the outermost electrons. In general, factors such as the number of electron shells and the effective nuclear charge influence the size of this radius. For transition elements, the atomic radius is influenced by the filling of the d orbitals, which behave differently compared to the s or p orbitals in terms of shielding and contraction.

Effective Nuclear Charge

Effective nuclear charge refers to the net positive charge experienced by electrons in an atom. As the number of protons increases across a period, this increased charge pulls the electron cloud closer to the nucleus, leading to a reduction in atomic radius. In transition metals, even as electrons are added to the d orbitals, the increased nuclear charge is not fully offset by the added electron-electron repulsion, resulting in a contraction of the radius across the period.

Electron Shielding

Electron shielding is the effect by which inner electrons reduce the full attractive force of the nucleus on the outer electrons. Although the addition of electrons in the d orbitals during transitions adds some repulsion, these electrons do not completely shield the outer electrons from the increasing nuclear charge. Consequently, the atomic radius decreases across a period despite the incremental increase in electron count.

Trends Across a Period and Down a Group

Across a period, particularly in transition metals, the increasing effective nuclear charge overcomes the additional electron repulsion, resulting in a gradual decrease in atomic radius. Conversely, as you move down a group, additional electron shells are added which increases the atomic radius despite any changes in nuclear charge. This has the combined effect of contracting atomic size across the period and expanding it down the group for transition elements.

Transcript

00:01 So this video is going to take a look at the trends in atomic radius.

00:05 So before we can really look at the trends of atomic radius, we first need to define what atomic radius is.

00:12 So atomic radius is basically the distance between the center of the nucleus.

00:17 So in the schematic, it would be center of the nucleus to the peripheral valence electrons.

00:23 So it's the distance from the nucleus to the outer electrons.

00:28 That's what is known as atomic radius.

00:29 So that we have that squared away, what are the trends that we see? so as you go down a column in the periodic table, as you go down a group, you will notice atomic radius increases.

00:45 Likewise, as you go across a period on the periodic table, atomic radius decreases, right? so it goes to show that elements in this region of the periodic table are the largest, and elements kind of in this region in the periodic table are the smallest.

01:03 So sort of rationalize why we see this.

01:05 Why is it that these trends exist? because it's not enough to just know them.

01:08 You have to know why they occur.

01:10 So let's start with the easier one.

01:11 Let's try to understand why as you go down a group, the atomic radius increases.

01:18 Well, as you go down a group, you're increasing energy levels.

01:21 So up here, you may only have one energy level.

01:23 But as you go down the group, you're going to be adding more and more energy levels around the atom...