VESPR theory and covalence
A molecule with square planar geometry but with six electron regions has ______ lone pairs.
A molecule with square planar geometry but with six electron regions has two lone pairs. Square planar molecular structure accounts for four bonding pairs. If there are six total electron dense regions, and four are taken up by those bonding pairs, then the remaining two will be lone pairs. These lone pairs will occupy the positions that are opposite from one another in order to accommodate the greater repulsion, giving rise to the square planar geometry.
N2 + 3H2 → 2NH3 Bond Bond Energy (kJ/mol)
-97 ΔH = [bond energy (N≡N)] + 3 [bond energy (H₋H)] + 6 [bond energy (N₋H)] ΔH = [941] + 3 [436] + 6 [-391] = -97 KJ. Before solving this problem, be sure to draw out the structures of N2, H2 and NH3. Doing this, you should find that this reaction involves the dissociation of a N≡N bond and three H−H bonds (one in each H2 molecule), as well as the formation of six N−H bonds (three in each molecule of NH3). The enthalpy of the reaction is given by the following: ΔHΔHΔHΔH=∑Dbonds broken−∑Dbonds formed=[(N≡N)+3(H−H)]−6(N−H)=941 kJ+(3×436 kJ)−(6×391 kJ)=−97 kJ Notice that the number of bonds (used as a coefficient) is an exact value, so it does not constrain the number of significant figures.
How many lone pairs must an atom possess to have trigonal pyramidal molecular structure?
1 If an atom has four electron domains and precisely one of them is a lone pair, it will have trigonal pyramidal molecular structure.
A molecule with linear geometry but five electron regions has ______ lone pairs.
3 A molecule with linear geometry but five electron regions has three lone pairs. Linear geometry accounts for two bonding pairs. If there are five total electron dense regions and two are taken up by bonding pairs, then the remaining three must be by lone pairs.
How many molecular geometries are possible for a compound that has a central atom with five regions of electron density (trigonal bipyramidal electron pair geometry)?
4 The molecular geometry of a compound with trigonal bipyramidal electron pair geometry is dependent on the number of lone pairs on the central atom. If all five regions of electron density are bonding pairs, then the molecular geometry is the same as the electron pair geometry, trigonal bipyramidal. If there is only one lone pair and four bonding pairs, the compound will have a see-saw molecular geometry. If there are two lone pairs and three bonding pairs, the compound will have a t-shaped molecular geometry. If there are three lone pairs and two bonding pairs, the compound will have a linear molecular geometry. Therefore, 4 different molecular geometries are possible for a compound with a central atom that has five regions of electron density.
Which of the following is a step in predicting electron pair geometry and molecular structure using VSEPR theory? count the number of regions of electron density around the central atom write the Lewis structure of the molecule use the number of lone pairs to determine the molecular structure identify the electron-pair geometry based on the number of regions of electron density
All VSEPR theory can be used to determine both the electron pair geometry and the molecular structure. First, we write the Lewis structure of the molecule, and then count the number of electron dense regions around the central atom. Single bonds, double bonds, triple bonds, and lone pairs each count as one electron dense region. After determining the electron dense regions, the electron pair geometry can be determined based on the number of regions. Finally, we can use the number of lone pairs to determine the molecular structure by focusing on minimizing repulsions.
Which molecule has the same electron-pair geometry and molecular structure? SO2 H2O NH3 CO2
CO2 Carbon dioxide has linear geometry and structure, whereas the others have at least one lone pair on the central atom, which changes the molecular structure The electron-pair geometries will be the same as the molecular structures when there are no lone electron pairs around the central atom, but they will be different when there are lone pairs present on the central atom. Sulphur dioxide, SO2 Sulphur has 6 electrons in its outer level, and the oxygens between them contribute another 4 (1 for each bond). That gives 10 electrons in total - 5pairs. 4pairsare needed for the bonds, leaving 1lone pair. Each double bond uses 2 bondpairsand can be thought of as a single unit. Water has four electron pairs and the coordination geometry of oxygen is based upon a tetrahedral arrangement of electron pairs. Since there are only two bonded groups, there are two lone pairs. Since the lone pairs are not 'seen', the shape of water is bent. Ammonia also has four electron pairs and the coordination geometry of nitrogen is based upon a tetrahedral arrangement of electron pairs. There are just three bonded groups, therefore there is one lone pair. However since the lone pairs are 'invisible', the shape of ammonia is pyramidal. The geometry of ammonia, NH3.
which of the following has bonds with the greatest bond-polarity. HCl NO2 NH3 H2O
H2O Calculating the difference between the electronegativities for each element of each molecules, we find that H and O have the greatest difference, so H2O has bonds with the greatest polarity.
which of the following is the least polar. CO HCl ICl NaCl
ICl The least polar bonds are formed between elements with the smallest difference in their electonegativities. In this case, ICl, has the smallest difference of 0.5.
Which molecule will have the strongest bond? F2 Cl2 O2 N2
N2 A nitrogen molecule has a triple bond, while the rest have double or single bonds.
Which pair of molecules has the same electron-pair geometry? NH3 and BH3 H2O and CO2 CH4 and SF4 SF6 and XeF4
SF6 and XeF4 Though the structures are different, both have octahedral geometry.
Predict the molecular structure of NH4+
Tetrahedral We can see that NH4+ contains four bonds from the nitrogen atom to the four hydrogen atoms, and no lone pairs. We thus expect the four regions of high electron density to arrange themselves so that they point to the corners of a tetrahedron, with the central nitrogen atom in the middle (see the chart provided in the question). Therefore, the molecular structure of NH4+ is tetrahedral.
Which spatial orientation will involve more than one bond angle value?
Trigonal bipyramidal geometry will exhibit both 120∘ and 90∘ bond angles.
What counts as an electron domain? a single bond a double bond a lone pair all of the above
all of the above Any kind of bond as well as a lone pair all count as one electron domain.
According to VSEPR theory, electrons in the valence shell of a central atom form __________.
both lone pairs and bonding pairs of electrons According to VSEPR theory, electrons around a central atom are "electron dense regions." These regions can either be in the form of lone pairs (nonbonding) or in the form of bonding pairs (bonded atoms).
Lewis structures are limited because they do not display the __________.
correct bond angles in the molecule Lewis structures DO show connectivity and the presence of different bonds and lone pairs, but they do not accurately show the shape of the molecule in three dimensions. Hence, the bond angles will be incorrect.
The number of electron domains surrounding an atom will determine the:
electron-pair geometry or Steric Number Each number of electron domains will correspond with a specific electron-pair geometry.
VSEPR theory considers which of the following? nuclear-electron attractions nuclear-nuclear repulsions electron-pair repulsions all of the above
electron-pair repulsions1 VSEPR theory considers electron-pair repulsions in that it predicts molecular structure based on electron pairs minimizing their repulsions from each other in order to achieve the most stable structure.
Electronegativity is measured in:
electronegativity is dimensionless There are no units on electronegativity, it is an arbitrary relative scale designed by Linus Pauling.
Lone pairs present in trigonal bipyramidal electron-pair geometry always occupy which position?
equatorial positions In a trigonal bipyramidal electron-pair geometry, lone pairs always occupy equatorial positions because these more spacious positions can more easily accommodate the larger lone pairs. Theoretically, we can come up with three possible arrangements for the three bonds and two lone pairs for the ClF3 molecule
The VSEPR model assumes that electron pairs in the valence shell of a central atom will adopt an arrangement that __________ repulsions by __________ the distance.
minimizes repulsion between these electron pairs by maximizing the distance The VSEPR model assumes that electron pairs in the valence shell of a central atom will adopt an arrangement that minimizes repulsions by maximizing the distance between electron pairs because this will allow for the most stable geometry. This assumption allows us to predict molecular structure and bond angles.
which of the following describes Cl2.
nonpolar covalent1 Using the figure, we can determine that Cl2 is nonpolar and covalent (0 electronegative difference).
In a polar covalent bond, the more electronegative atom will bear a:
partial negative charge The more electronegative atom will be partially negative.
What will be the molecular structure of the ammonium ion (NH+4)?
tetrahedral Nitrogen will have four electron domains, all of which are bonds, so both the geometry and structure will be tetrahedral.
What is the electron pair geometry of SnCl−3?
tetrahedral SnCl−3 has four electron regions with one resulting from a nonbonding pair. The electron pair geometry is tetrahedral (4), and the molecular structure is trigonal pyramidal.
Identify the electron pair geometry of ClF3.
trigonal bipyramidal ClF3 has five electron domains (three bonds and two lone pairs) so the electron pair geometry is trigonal bipyramidal (5). These are arranged in a trigonal bipyramidal shape with a 175° F(axial)-Cl-F(axial) bond angle. The two lone pairs take equatorial positions because they demand more space than the bonds.
What will be the electron-pair geometry of XeF2?
trigonal bipyramidal With five domains, two being bonds and three being lone pairs, the electron-pair geometry must be trigonal bipyramidal.
What is the electron pair geometry of SF4?
trigonal bipyramidal* SF4 has five electron domains with one resulting from a nonbonding pair. The electron pair geometry is trigonal bipyramidal (5), and the molecular structure is seesaw because the the nonbonding pair will occupy a equatorial position.
H2 (g) + C2H4 (g) → C2H6 (g) Bonds to break (endothermic): one H-H bond @ 436 kJ/mol four C-H bonds @ 413 kJ/mol one C=C bond @ 614 kJ/mol
−124 kJ The enthalpy of the reaction is given by HH= Sum of bonds broken− Sum of bonds formed=[(H-H)+4(C-H)+(C=C)]−[6(C-H)+ (C-C)]=[436+4(413)+614]−[6(413)+348]=−124 kJ Notice that the number of bonds (used as a coefficient) is an exact value, so it does not constrain the number of significant figures.
