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Chemistry Experiment¶s Report

MOLECULE¶S SHAPE

Written by:

Name :

No Absent : 15

Class : XI Ns. 3

Teacher : Mrs. Tuti Purwaningsih

Subject : Chemistry

PEMERINTAH KABUPATEN TEGAL

DINAS PENDIDIKAN, PEMUDA DAN OLAHRAGA

UPTD SMA NEGERI 1 SLAWIJl. K.H Wahid Hasyim No, Kotak Pos 6, Telp. 0283 3317173, Fax. 0283 491164, Kode Pos :

52415



MOLECULE¶S SHAPE

A. Objectives:

1. Predicting molecular geometries using the Electron Domain Model.

2. Understanding the properties of molecules, and correspondingly the

substances which they comprise, should depend on the details of the structure

and bonding in these molecules.

3. Understanding the relationship between molecular structure and chemical

bonding.

B. Tools and Materials:

1. Molymod with each color and size that representative atom.

C : black (3 pieces)

H : white (11 pieces)

N : blue and small ( 1 piece)

B : blue and big (1 piece)

F : green and small (3 pieces)

O : red (2 pieces)

2. Connected stick:

Short (9 pieces)

Long (3 pieces)

C.

Work Methods:

1. Identified the electron domain and geometrical form of CH4 molecule, then

indentify the molecular shape.

2. Make the molecular shape model of CH4. Set the connected stick with C

atom, and set the other into H atom.

3. Investigate and draw the molecular shape of CH4.

4. Do step 1-3 for NH3, H2O, BF3, and C2H2 molecules.

D. Base Principle:

Valence Shell Electron Pair Repulsion (VESPR) theory states that the pairs of

electron that are negatively charged will keep their distance as far apart as

possible, thus minimizing the repulsion between them.

Molecular geometry is determined by minimizing the mutual repulsion of the

valence shell electron pairs. The pairs of valence shell electrons are arranged in



bonding and non-bonding domains, and these domains are separated in space to

minimize electron-electron repulsions. This electron domain arrangement

determines the molecular geometry. As such, this model of molecular geometry isoften referred to as the valence shell electron pair repulsion (VSEPR) theory. For

reasons that will become clear, extension of this model implies that a better name

is the Electron Domain (ED) Theory .

The geometry of a molecule includes a description of the arrangements of the

atoms in the molecule. At a simple level, the molecular structure tells us which

atoms are bonded to which. At a more detailed level, the geometry includes the

lengths of all of these bonds, that is, the distances between the atoms which are

bonded together, and the angles between pairs of bonds.

Electron domain can be distinguished into:

1. Bonding Electron Domain (BEP), which contains pairs of bonding electrons.

2. Non-Bonding Electron Domain (NBEP), which contains pairs of non-bonding

electron.

The form of molecular shapes are state:

With:

A: central atom

n: the sum of BEP

m: the sum of NBEP

X: Bonding electron domain

E: Non-Bonding electron domain



Predicting Shape using The Electron Domain Theory

Geometrical form Geometrical shape Bond angle

AX2 Linear 180o

AX3 Triangular planar 120o

AX2E V-Shaped <120o

AX4 Tetrahedral 109,5o

AX3E Trigonal pyramid 107o

AX2E2 V-Shaped 104,5o

AX5 Trigonal bipyramid

Ax-Ax= 180o

Equ-Equ= 120o

Ax-Equ= 90o

AX4E Distorted tetrahedral

Ax-Ax= 180o

Equ-Equ= <120o

Ax-Equ= 90o

AX3E2 T-ShapedAx-Ax= 180

o

Ax-Equ= 90o

AX2E3 Linear 180o

AX6 Octahedral Axial= 90

o

Equatorial= 90

o

AX5E Square pyramid Ax-Equ= 90o

AX4E2 Square planar 90o

AX3E3 - -

AX2E4 - -



E. Experiment¶s Result:

Molecule Bond Angle Molecule¶s Shape Molecule¶s Shape Picture

CH4 109,5o

(H-C-H) Tetrahedral

NH3 107o

Trigonal pyramid

H2O 104,5o

V-Shaped



BF3 120 o Triangular planar

C2H2 180o

Linear

F. Analysis and Question:

a. Question:

1. From the experiment¶s result, there are different molecule¶s picture in the different

elements. What did caused that differences?

Answer :

The differences of the molecule picture are caused by the number of BEP (Bonding

Electron Pair) and NBEP (Non-Bonding Electron Pair) of that molecule. This differences

caused the different bond angle for each molecule and caused a different shapes.

2. Explain the influence of NBEP for NH3 and H2O molecule¶s shapes?

Answer:

3. Why did the molecule¶s shape of NH3 is not flat like BF3, even the sum of the atom are

same?

Answer:

Valence electron from N = 5

Electron from H = 3 +

Sum of the electron = 8 (4 pairs)



BEP = 3

NBEP = 1

Valence electron from B = 3

Electron from F = 3 +


BEP = 3

NBEP = 0

The molecule¶s shape of NH3 is not flat like BF3, because NH3 have 2 NBEP and BF3

don¶t have any NBEP. This difference make NH3¶s shape is different from BF3¶s.

4. According to the form, identify the valence electron, BEP, and NBEP for central atom N

in NH3 molecule (atomic number of N is 7)

Answer:

Valence electron from N = 5

Electron from H = 3 +


BEP = 3 NBEP = 1

b. Analysis:

Molecular geometry is determined by the sum of BEP (Bonding Electron Pair) and NBEP

(Non-Bonding Electron Pair) of that molecule. This differences caused the different bond

angle for each molecule and caused a different shapes.



G. References:

Johari, J.M.C. Chemistry for Senior High School Grade XI Semester 1. 2010.

Jakarta: ESIS

www.chemi4kids.com

www.google.com

www.teachersdomain.com

www.vias.org

www.wikipedia.org

Slawi, September 2010

Guide teacher Practician

Mrs. Tuti Purwaningsih

NIP.