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# 10 Exercises on Determining Molecular Shapes (PEB and PEI) and Their Discussion

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Team Space Chemistry This time, we will provide 11 examples of How to Determine Molecular Shape (PEB and PEI) questions that we have compiled from various book publishers for students to study in preparation for daily tests and National Examinations. Because this question often appears in various

It is hoped that by studying the examples of Multiple Choice Determination of Molecular Shapes for grade 10 students can understand and understand the basic concepts.

## 1 – 11 Problems Determining Molecular Shape and Answer

1. Determine the molecular shape of:

a. BeCl2 (4Be, 17Cl)

b. CO2 (4C, 8O)

Discussions:

2. If atomic number A=5 and B=17, the hybrid orbital that occurs in molecule AB is….

A. sp

B. sp²

C. sp³

D. sp³d

E. sp³d²

Answer: A

Discussions:

3. Molecules with sp² hybrid orbitals have the shape of the orbital…

A. Linear

B. Flat triangle

C. Triangle pyramid

D. Tetrahedral

E. Octahedral

Answer: B

Discussions:

Planar triangle or trigonal planar is the shape of the sp² . molecule

4. The trigonal bipyramidal molecular shape has hybrid orbitals

A. sp

B. sp²

C. sp³

D. sp³d

E. sp³d²

Answer : D

Discussions:

The correct one is: sp³d

Why is that?

Example: the trigonal bipyramid is PCl5

To prove it, first configure it with the aufbau principle of the central element, namely P, which only consists of 1. P atomic number 15

P : 1s², 2s², 2p6, 3s², 3p³

Take the last part starting from s

Mean -> 3s² and 3p³

5. The molecular shape of NH3 (7N and 1H) is…

A. Flat triangle

BV shape

C. Tetrahedral

D. Triangle pyramid

E. Triangle bipyramid

#### Discussions:

Main shell electron configuration

N = 2 . 5

H = 2

The N atom requires 3 electrons to achieve octet stability.

The H atom requires 1 electron to achieve duplet stability.

In ammonia or NH₃ compounds, the N atom acts as the central atom bonded to 3 H atoms. As non-metals and sharing electrons, the type of bond that occurs is a covalent bond.

After the central atom N reaches the octet, there is still a pair of lone electrons belonging to N. Consider the next mechanism.

• The bonding electron domain or also called the bonding electron pair (PEI) = 3. Occurs between the central N atom which is bonded to 3 H atoms.
• The lone electron domain or also called the lone pair (PEB) = 1, is a lone pair of electrons belonging to the central atom of N.
• Between the lone pair of electrons on the central N atom and the three pairs of bonding electrons on the H atom, a repulsive interaction occurs.

The type of molecule is

• A = central atom N
• X = bonding electron pair (PEI)
• m = number of PEI 3 (or bonded to 3 H atoms)
• E = lone pair of electrons (PEB)
• n = number of PEB 1

Thus the type of molecule is

The shape of the molecule is a trigonal pyramid or it may also be called a triangular pyramid.

Answer : D

#### Also Read: 50+ Multiple Choice Chemical Bond Questions [+ Pembahasan Lengkap]

6. Total PEI and PEB of H molecule2O (1H and 8O) is…

A. 1 and 2

B. 1 and 3

C. 2 and 1

D. 2 and 2

E. 2 and 3

Discussions:

H2O has 2 bonding electron pairs/PEI and 2 lone pairs so the type of molecule is AX2E2

7. The atomic number of the element X = 5 and the atomic number of the element Y = 17, both form the compound XY3. The molecular shape of the compound is

a. linear

b. equilateral triangle

c. trigonal pyramid

d. corner

e. octahedron

Answer: B

The molecular shape of the compound XY₃ is an equivalent triangle (planar triangle). It begins with knowing the electron configuration, the tendency to achieve stability, the number of bound and free domains, and the type of molecule.

#### Discussions:

Electron configuration based on main shell and group and period

X = 2 . 3 Group IIIA and Period 2

Y = 2 . 8 . 7 Group VIIA and Period 3

We certainly still remember that the group is determined by the number of electrons in the outermost shell while the period is based on the number of shells.

The number of electrons in the outermost shell or valence electrons of atoms of elements X and Y are 3 and 7, respectively.

For an atom of element Y it takes 1 electron to achieve stability or an octet state (8 electrons) in the outer shell.

What about the atoms of element X? Note, element X is not a metal but a metalloid. On the periodic table, element X is boron (B) and element Y is chlorine (Cl). If the element number 5 is involved in a bond, there will be a deviation from the octet rule.

In the Lewis structure of the compound XY₃, each of the three Y atoms captures 1 valence electron belonging to the central atom X so that they reach an octet/stable. While the central atom X, which also uses 1 electron from each of the three Y atoms, has not yet reached an octet because the total is only 6 electrons. This is called the deviation of the octet rule.

8. If the atomic number S = 16 and the atomic number F = 9, then the molecular shape is SF4 is…

A. Flat triangle

BV shape

C. Tetrahedral

D. Distorted tetrahedral

E. Linear

#### Discussions:

is known :

S = 2 8 6
F = 2 7

Dit : Type SF4 ?

Answer
SF4 has:
PEI = 4
PEB = 1

So the type of molecule

AX4E1 (Tetrahedral)

Answer: C

9. Which of the following molecules has the largest bond angle?

A. H2O

B. NH₃

C. BF₃

E. IF₃

D.BeCl2

Discussions:

• H2O = AX2E2 = 104.5 degrees
• NH3= AX3E = 107.5 degrees
• CH4 = Ax4 = 109.5 degrees
• SF6= AX6 = 90 degrees
• BeCl2= AX2 = 180 degrees

10. The bond angle in the H2O molecule is 104.5 degrees , even though the electron pairs occupy the space position of the tetrahedron. This is caused by

A. have 2 lone pairs of electrons

B. the presence of 2 bonding electron pairs

C. the electron pair is far from the central atom

D. the presence of hydrogen bonds in H2O

E. the presence of a permanent dipole on H2O

Discussions:

The bond angle in the H2O molecule is 104.5 degrees , even though the electron pairs occupy the space positions of the tetrahedron. This is caused by the presence of 2 lone pairs of lone electrons here requires a larger space (larger angle) of the bonding electrons. In the H2O molecule there are 2 PEB, so the angle is 104.5 degrees.

Answer: A

11. A molecule has 5 electron pairs around the central atom, two of which are lone pairs. The most likely shape of the molecule is…

A. Flat triangle

B. Tetrahedral

C. Triangle pyramid

DV shape

ET shape

Discussions:

Sumber

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