Values of van der Waals radii (rv) and covalent radii (rcov) for the elements from Z=5 to 9 are:

Values of van der Waals radii (rv) and covalent radii (rcov)...

Key Concepts

Periodic Table Regions

This concept involves understanding the organization of elements in the periodic table. Specifically, it pertains to identifying which blocks or parts of the periodic table a set of elements reside in. For elements with atomic numbers in a given range, one typically considers their period and block (s, p, d, or f) which are determined by their electron configurations.

Covalent and van der Waals Radii

This concept distinguishes between two measures of atomic size. The covalent radius is typically defined as half the distance between two bonded atoms, reflecting the size of an atom when it's engaged in a covalent bond. In contrast, the van der Waals radius represents the effective size of an atom when it is not bonded, corresponding to the distance of closest approach between non-bonded atoms, and is generally larger due to the full extent of the electron cloud.

Atomic Size Trends and Effective Nuclear Charge

This key concept addresses how atomic radii change across the periodic table. It involves understanding that trends in atomic size are influenced by factors such as effective nuclear charge and electron-electron repulsion. As one moves across a period, increasing nuclear charge typically pulls electrons closer, affecting both covalent and van der Waals radii, while differences in measurement definitions lead to consistent relationships between the two.

Experimental Determination Methods of Atomic Radii

This concept covers the experimental approaches used to estimate atomic radii. Techniques such as X-ray crystallography, electron diffraction, and spectroscopy are employed to measure distances between atoms in bonded or non-bonded states. These methods provide the data needed to derive both covalent and van der Waals radii by analyzing the spatial distribution of electron density and interatomic distances.

Transcript

00:02 Okay, so this question is just simply asking for basically checking your understanding of what are the trends across a period in the table.

00:18 So from z equals 5 to 9, and actually let me write this out, 6, 7, 8, 9.

00:31 That's going to be z is the nuclear charge, the positive charge, or yeah, the positive charge of a nucleus.

00:42 So for five, that's five protons.

00:46 And so if you look at a periodic table, that's boron.

00:50 And then they each go up by one.

00:52 So that's carbon, nitrogen, oxygen, and fluorine.

00:57 Okay? and so you can see these are all in the second row, and they're on the right side, so that's the p block.

01:10 So they're in the 2p area of the periodic table.

01:18 Okay? so next it asks about vanderwalls versus covalent radii.

01:31 So if you have a sphere or a circle, if you have a sphere, it has a certain radius and that's what we would call the vandal walls radius.

01:44 But if you have a molecule, it's going to look a little something like this, there's this overlap right here.

01:55 So that's going to decrease from the radius.

01:59 The distance between these two centers isn't going to be equal to the radius exactly.

02:09 So the covalent radius splits this in the middle and the covalent radius radius is always going to be less than the vanderwals radius because the because you have this overlap zone that you're basically dividing by 2.

02:29 So that's really all that is.

02:32 Now the trend across the period is that the size decreases each time you go to the next number or the next element.

02:48 And so why is that? to rationalize this, you need to sort of think about what's going on in the 2p shell, or really in any shell, past the 1s.

03:03 So you have your nucleus, and you have your 1s shell, or orbital.

03:14 And then outside of that, you have the 2s.

03:20 And then outside of that, you have the 2s.

03:22 And then outside of that, you have the 2p.

03:30 This isn't what it looks like, but i will just go ahead and make it a sphere.

03:36 So you have your 1s, 2s, and 2p.

03:44 That's just going to be their general radius from the nucleus.

03:50 So electrons in the 1s, you're going to have 2, are going to feel the electric charge of the nucleus entirely.

04:02 But if you put an electron here in the 2s, they will actually feel less charge than they otherwise would because of these electrons in the 1s sort of interfering with the 2s electrons.

04:25 And so the same goes for the 2p.

04:29 So if you have your 2p shell and you have boron here, just one electron.

04:37 The z for boron is 5.

04:44 So that means this one electron has a charge of negative 1, and this has a charge of negative 5.

04:52 Or of positive 5, sorry...

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