Describe the molecular geometry of: (b) AsH 3

All right. Hi everyone. So for this question, let's go ahead and draw the structure or a structure of ph three and describe its molecular geometry. So Ph three is also referred to as phosphine. Now there are two ways of going about this question starting off with simply going from scratch from the very beginning, right. So in this method, you take your molecular formula which is ph three and you find the number of valence electrons that each atom is going to contribute to the Lewis structure starting off with phosphorus. Now phosphorus, if you recall is in group five a of the periodic table, which means that it has five valence electrons in Haugen on the other hand, has one valence electron. However, there are three atoms of hydrogen present in this molecule. So I will multiply the one valence electron by three to find that there are three more valence electrons that the hydrogen atoms are contributing. So when I add together my five valent electrons from phosphorus and the three from my hydrogen atoms, I get that there are a total of eight valence electrons to distribute in my Lewis structure. So now in my actual Lewis structure recall that hydrogen is only capable of making one covalent bond. Therefore, phosphorus is going to be in the center. And I'm going to draw three different bonds from phosphorus to each hydrogen atom. Now, three covalent bonds multiplied by two electrons. Each gives me a total of six electrons that I have spent so far or that I have used. So now the remaining two electrons that I have left are going to go on phosphorus as an extra loan pair of electrons. And so here is the lowest structure of phosphate. Now, the other method that's arguably faster would be to recognize that there are similarities between the structures of phosphine and the structure of ammonia or NH three, right. And the reason for this is because both nitrogen and phosphorus belong in the same group of the periodic table and therefore have the same bond preference, meaning both phosphorus and nitrogen prefer to have three covalent bonds and one lone pair of electrons. So by recognizing the similarity, you can also find the lowest structure of phosphine by taking the structure of ammonia and simply replacing the nitrogen in the center with phosphorus. However, either way will lead you to the same answer, right. So now with regard to the geometry, when it comes to the geometry, we have one lone pair of electrons as well as three covalent bonds to other atoms, which gives us a total of four electron domains. Now, when we have four electron domains. One of them being a lone pair of electrons recall that that corresponds to trigonal petal geometry. And there you have it. So here is the Lewis structure of phosphine found in two different ways with a geometry described as trigonal parameter. And with that being said, thank you so very much for watching. And I hope you found this helpful.

Ch.22 - The Main Group Elements

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McMurry 8th Edition

Ch.22 - The Main Group Elements

Problem 62b

Chapter 22, Problem 62b

Describe the molecular geometry of:
(b) AsH₃

Verified step by step guidance

Determine the number of valence electrons for AsH_3. Arsenic (As) has 5 valence electrons, and each hydrogen (H) has 1 valence electron.

Count the total number of valence electrons: 5 from As and 3 from H, giving a total of 8 valence electrons.

Draw the Lewis structure for AsH_3. Place As in the center and arrange the three H atoms around it, using single bonds to connect them.

Identify the electron pair geometry. AsH_3 has 3 bonding pairs and 1 lone pair, which corresponds to a tetrahedral electron pair geometry.

Determine the molecular geometry. With 3 bonding pairs and 1 lone pair, the molecular geometry of AsH_3 is trigonal pyramidal.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

VSEPR Theory

Valence Shell Electron Pair Repulsion (VSEPR) Theory is a model used to predict the geometry of individual molecules based on the repulsion between electron pairs in the valence shell of the central atom. According to this theory, electron pairs will arrange themselves as far apart as possible to minimize repulsion, leading to specific molecular shapes.

Trigonal Pyramidal Geometry

Trigonal pyramidal geometry occurs when a central atom is bonded to three other atoms and has one lone pair of electrons. This arrangement results in a pyramid-like shape with the central atom at the apex and the three bonded atoms at the base, which is characteristic of molecules like AsH3.

Hybridization

Hybridization is the concept of mixing atomic orbitals to form new hybrid orbitals that can accommodate bonding. In the case of AsH3, the arsenic atom undergoes sp3 hybridization, which involves the mixing of one s orbital and three p orbitals, resulting in four equivalent sp3 hybrid orbitals that facilitate the formation of bonds with hydrogen atoms.