A bond angle is the angle formed by two adjacent neighboring atoms in a molecule. And we're going to say when the central element has 0 lone pairs, it possesses what we call an ideal bond angle. Now, this ideal bond angle is the optimal angle elements take in order to minimize repulsion between one another. And we're going to say when the central element has one or more lone pairs, its ideal bond angle will be decreased. So, for example, if you take a look here, we said that the bond angle is the angle by two adjacent neighboring atoms in a molecule. So you'll have a central element. It'll be connected to two surrounding elements, and you're going to say that the angle bond angle is this portion here. If we have three surrounding elements, the bond angle will be here, it would also be here, as well as here. And if we had a lone pair, the bond angle would be in here. Now again, remember, once we have a lone pair on our central element, the bond angle is going to decrease. This decrease will be represented as a blue image for a smaller bond angle. Right. So now that we know what a bond angle is and how lone pairs help to reduce our ideal bond angle values, let's click on the next video and take a deeper look in terms of the exact values with these bond angles.
Bond Angles (Simplified) - Online Tutor, Practice Problems & Exam Prep
According to the VSEPR Model, bond angles result from surrounding elements and lone pairs around the central element positioning themselves at an optimal distance.
Ideal Bond Angles
Bond Angles (Simplified) Concept 1
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Bond Angles (Simplified) Example 1
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Here we're told if the H-C-H angle within CH4 molecule is 109.5 degrees, what is the H-N-H bond angle within NH3? Right. So if we were to draw out CH4, carbon would go in the center. Remember, bonds to hydrogens are only single bonds. This would represent CH4. We have 4 bonding groups on the carbon with 0 lone pairs on the carbon. NH3, so NH3 would have our bonds to hydrogens, but remember, if we count up the total number of valence electrons, nitrogen has 5 and then we have 3 hydrogens, each one with 1 electron because they're in group 1A. So that would be 8 total valence electrons. We have 2, 4, 6 here and we'd have a lone pair on the nitrogen for our remaining electrons. Here, the bond angle is 109.5 degrees. But remember, we said that the presence of a lone pair reduces or decreases our bond angle. So we'd expect NH3 to have a bond angle that is less than 109.5 degrees. If we take a look at our options, the only one that has an angle less than 109.5 degrees is option c, 107.3 degrees.
Bond Angles (Simplified) Concept 2
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Here we can say that bond angles can further differentiate molecules that possess the same number of electron groups. So when we have 2 electron groups, that means we have only one possibility, our central element having 2 surrounding elements. In that case, we have an ideal bond angle because our central element can't have a lone pair. So for an electron group of 2, the ideal bond angle is 180 degrees. When we have 3 electron groups around the central element, we have 2 possibilities, one where the central element just has 3 bonding groups and 0 lone pairs. In this case, because there are no lone pairs on the central element, we have an ideal bond angle of 120 degrees. But remember, another possibility exists where we could have 2 bonding groups and 1 lone pair. The presence of the lone pair means that our bond angle will decrease from its ideal value. All you need to say at this point is if the ideal bond angle for 3 electron groups is 120, then when it gets decreased, it'll be less than 120. You don't have to give an exact number. You can just say less than 120. Alright. So when we have 4 electron groups, we have 3 possibilities. We have 4 bonding groups, 0 lone pairs. 0 lone pairs means we have an ideal bond angle of 109.5° degrees. But we also have 3 bonding groups and 1 lone pair. So here we just say that our bond angle now is less than 109.5°. And then we have our last possible option, 2 bonding groups, 2 lone pairs. Here, we expect the bonding angle to be again less than 109.5°. In fact, we'd say that it's even a little bit less than this one because the presence of more lone pairs helps to further reduce the bond angle. So just remember, when we have no lone pairs on the central element, we have an ideal bond angle. The inclusion of any lone pairs after this means that our bond angle will decrease from this ideal bond angle value.
Bond angles can further differentiate molecules that possess the same number of electron groups.
Bond Angles (Simplified) Example 2
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Here we need to determine the H-Sn-H bond angle for the following compound. So we have tin connected to 2 hydrogens. Tin is in group 4A, so it has 4 valence electrons. Here we have 2 hydrogens, each one has 1 valence electron since they're in group 1A. So that's a total of 6 valence electrons involved. Here, we would place tin in the center. It is connected to the 2 hydrogens. Remember, hydrogens can only make single bonds. They don't follow the octet rule; they only follow the duet rule, so you don't have to add any additional electrons to them. So at this point, we've used 4 of our electrons because each covalent bond has 2 electrons within it. That means we have 2 valence electrons remaining, which we simply place on the tin.
Now, how many electron groups does the tin have? It has one lone pair and 2 bonding groups, so 2 surrounding elements. So we have 3 electron groups. So remember, for 3 electron groups, the ideal bond angle is 120 degrees. But when we have the presence of a lone pair on the central element, the ideal bond angle decreases. So all you have to say here is that we have a bond angle that is less than 120 degrees for the following compound.
Determine the bond angle for the following compound:BeCl2.
Determine the bond angle for the thiocyanate ion, SCN–.
Determine the Cl–O–Cl bond angle for the OCl2 molecule.