Tetrahedral electronic geometry

The Lewis formula for the molecule (type AB4) predicts 4 electron groups around the central Sn atom and a tetrahedral electronic geometry. Since there are no lone pairs on Sn, the molecular geometry is also tetrahedral (Section 8-7). 

This molecule (type AB3U) has a tetrahedral electronic geometry and a pyramidal molecular geometry. Cl (EN = 3.0) is more electronegative than As (EN = 2.1). The polar As-Cl bond dipoles oppose the effect of the lone pair. The molecule is only slightly polar (Section 8-8). 

This molecule (type AB4) has a tetrahedral electronic geometry and tetrahedral molecular geometry. The C-F bonds are polar, but since the molecule is symmetrical, the bond dipoles cancel to give a nonpolar molecule (Section 8-7). 

This molecule (type AB2U2) has a tetrahedral electronic geometry and an angular molecular geometry. Oxygen (EN = 3.5) is less electronegative than F (EN = 4.0). The O-F bond dipole opposes the effect of the two lone pairs of electrons and so, OF2 is polar (Section 8-9). 

BF3 and CF4 are nonpolar molecules. CF4, NF3, OF2 and HF have tetrahedral electronic geometries, but have different molecular geometries since they have 0, 1,2, and 3 lone pairs of electrons around the center atom, respectively. 

The Lewis dot formula predicts 4 regions of high electron density around the central N atom, a tetrahedral electronic geometry and a pyramidal molecular geometry. The N atom has sp3 hybridization (Sections 8-8 and 28-14). The three-dimensional structure is shown below. 

TETRAHEDRAL ELECTRONIC GEOMETRY AB4 SPECIES (NO LONE PAIRS OF ELECTRONS ON A)... 

Tetrahedral Electronic Geometry AB Species (No Lone Pairs of Electrons on A)... 

VSEPR theory predicts that four valence shell electron pairs are directed toward the corners of a regular tetrahedron. That shape gives the maximum separation for four electron pairs around one atom. Thus, VSEPR theory predicts tetrahedral electronic geometry for an AB molecule that has no unshared electrons on A. There are no lone pairs of electrons on the central atom, so another atom is at each corner of the tetrahedron. VSEPR theory predicts a tetrahedral molecular geometry for each of these molecules. 

Because F, Cl, Br, and I are all in the same group of the periodic table, we know that their compounds would be similar. We expect that the detailed descriptions we have seen for CF would also apply to CCI4, CBr, and CI4, and we do not need to go through the entire reasoning for each one. Thus, we can say that each of the CX4 molecules (X = F, Cl, Br, or I) also has tetrahedral electronic geometry, tetrahedral molecular geometry, sp hybridization on the carbon atom, zero dipole moment, and so on. 

Each C atom in C2Hg has four regions of high electron density. The VSEPR theory tells us that each C atom has tetrahedral electronic geometry the resulting atomic arrangement around each C atom has one C and three H atoms at the corners of this tetrahedral arrangement. The VB interpretation is that each C atom is sp hybridized. The C—C bond is formed by overlap of a half-filled sp hybrid orbital of one C atom with a half-filled sp hybrid orbital of the other C atom. Each C—H bond is formed by the overlap of a half-filled sp hybrid orbital on C with the half-filled Ir orbital of an H atom. 

We have seen that CH, CF, NH3, and NF3 all have tetrahedral electronic geometry. But CH4 and CF (AB ) have tetrahedral molecular geometry, whereas NH3 and NF3 (AB3U) have trigonal pyramidal molecular geometry. 

Because this trigonal pyramidal molecular geometry is a fragment of tetrahedral electronic geometry, we expect that the H—N—H angle would be close to the tetrahedral value, 109.5°. In CH4 (a tetrahedral AB4 molecule), all H—C—H bond angles are observed to be this ideal value, 109.5°. In NH3, however, the H—N—H bond angles are observed to be less than this, 107.3°. How can we explain this deviation ... 

With the same kind of reasoning, VSEPR theory predicts that sulfite ion, 803 , has tetrahedral electronic geometry. One of these tetrahedral locations is occupied by the sulfur lone pair, and oxygen atoms are at the other three locations. The molecular geometry of this ion is trigonal pyramidal, the same as for other AB3U species. 

AB3U molecules and ions, each having four regions of high electron density around the central atom, usmlly have tetrahedral electronic geometry, trigonal pyramidal molecular geometry, and sp hybridization on the central atom. 

If the Lewis formula shows two lone pairs In trigonal planar or tetrahedral electronic geometry, we can place the lone pairs in any two positions and the bonded atoms in the other position(s). In trigonal bipyramidal electronic geometry, place the two lone pairs in two equatorial positions (120° apart) where they are least crowded, and put the bonded atoms in the other positions. In octahedral electronic geometry, place the two lone pairs in two positions across (180°) from each other, and put the bonded atoms in the other positions. 

The sulfite ion is pyramidal and has tetrahedral electronic geometry as predicted hy the VSEPR theory. 

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