Which of the following statements about the bonding atomic...

Which of the following statements about the bonding atomic radii in Figure 7.7 is incorrect? (i) For a given period, the radii of the representative elements generally decrease from left to right across period. (ii) The radii of the representative elements for the $n=3$ period are all larger than those of the corresponding elements in the $n=2$ period. (iii) For most of the representative elements, the change in radius from the $n=2$ to the $n=3$ period is greater than the change in radius from $n=3$ to $n=4$. (iv) The radii of the transition elements generally increase moving from left to right within a period. (v) The large radii of the Group 1A elements are due to their relatively small effective nuclear charges.

Key Concepts

Transition Metal Behavior

Transition metals exhibit unique trends in atomic radii that differ from the representative elements. This is largely due to the involvement of d-orbitals and the varying effects of electron shielding and effective nuclear charge in these atoms. Understanding their behavior requires an appreciation of how these factors can lead to less predictable or even anomalous trends compared to main group elements.

Effective Nuclear Charge

Effective nuclear charge is the net positive charge experienced by an electron in an atom after accounting for the shielding effect of inner electrons. This concept is crucial in explaining why atoms with similar electron configurations can have different sizes, and it influences the contraction or expansion of atomic radii as one moves across a period.

Principal Quantum Number

The principal quantum number, denoted as 'n', indicates the main energy level or shell of the electron. It plays a fundamental role in determining the size of an atom because electrons in higher energy levels (with larger n values) are found further from the nucleus, contributing to larger atomic radii.

Atomic Radii

This concept refers to the size of an atom, usually measured as the distance from the nucleus to the outer boundary of the electron cloud. When atoms form bonds, the effective size can change slightly from that measured in isolation, leading to the idea of bonding atomic radii which are important in understanding molecular structures.

Periodic Trends

Periodic trends describe how atomic properties such as size, ionization energy, and electronegativity systematically change across periods and down groups on the periodic table. In the context of atomic radii, trends typically include a decrease across a period due to increasing nuclear charge and an increase down a family as electrons occupy orbitals with higher principal quantum numbers.

Transcript

00:01 This question addresses the important periodic trend of atomic radius and how it basically is laid out and how we can utilize the periodic table to help us with this trend.

00:12 We're going to answer a series of questions determining whether they're true or false based on what we see according to this trend on the periodic table.

00:21 So the first question we're looking at right here, letter a, is the question is, do we see a bigger gap or an increase? and distance as we transition from shell 2 to 3 as compared to transitioning between shells 3 and 4.

00:39 And so you can tell from my lovely diagram here as it's laid out that what ends up happening is, if this is shell 1 in the center here, that as we add shell number 2, there's a fairly big gap that results from adding that next shell.

01:02 And that distance is fairly large between shell 1 and 2.

01:08 But notice what happens when we add shell number 3.

01:11 That gap closes and it's less distance as we add shell number 3.

01:18 And that's going to be a trend that we see with each additional shell that we add.

01:23 The gap or the energy level that's between each subsequent shell gets less and less.

01:31 There's a lower gap there.

01:32 So indeed, this is a true statement that each shell that we add, as we get farther and farther from that nucleus, there's less of a gap to cover or less of an energy difference between the shells as we continue to add or build that atom.

01:51 Number letter b asks, is it true that, especially for the representative elements, that we see a decrease in radius as you move left, to right across any row on the periodic table.

02:05 And indeed, that is true.

02:08 That is a general periodic trend for atomic radius.

02:11 I tell students think about it as moving from being a big and bulky metal, which are metals are generally going to be located on the left side of the periodic table, toward a smaller electron -hungry kind of non -metal on the right side of the periodic table.

02:28 And what ends up happening is effective nuclear charge or the ability to attract electrons toward itself, especially those outermost valence electrons, is much larger for non -metals than it is for metals.

02:43 And so that results in an overall decrease in radius or a more close contact for valence electrons toward the inner nucleus for non -metals on the right side of the periodic table than for metals on the left.

02:58 So this too is a true statement.

03:02 C asks us, is it true that as we move down the periodic table and we look at row number three where we would have shell number three corresponding to those valence electrons? is it true that in general if we compare the second row of the periodic table with the valence electrons in shell number two versus the third row of the periodic table that we're going to see a noticeably larger increase or larger radii for those species that are corresponding to the atoms that are just above them in row number two...

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