LESSON PLAN
PUTU EKA SURYA PUTRA
CHEMISTRY EDUCATION DEPARTMENT
GANESHA UNIVERSITY OF EDUCATION
I. Identity
| School | : | SMA ................ |
| Subject | : | Chemistry |
| Year/Semester | : | XI IA/1 |
| Time Allotment | : | 2 Hours (2 x 45 menutes) |
II. Standard Competence
Understanding atomic structure to predict periodicity of elements, molecular structure, and properties of compounds.
III. Basic Competence
1.3 Explain interaction between molecules (intremolecular force) and their properties
IV. Indicators
1.3.1 Explain physical properties different (boiling point, freezing point) based on intermolecular force different (Van Der Waals force, London force, and Hydrogen bond)
V. Learning Outcomes
Students be able to Explain physical properties different (boiling point, freezing point) based on intermolecular force different (Van Der Waals force, London force, and Hydrogen bond)
VI. Teaching and Learning Topics
- Van der waals forces
- Hydrogen bonds
- The influences of intermolecular force and size of molecule to boiling point (Tb) and freezing point (Tf)
Contents
Intermolecular forces are forces of attraction and repulsion between molecule of matter. A study of these intermolecular forces has been an important part of the development of physical chemistry in 20-th century. The following are explanations about intermolecular forces dealing with Van der Waals forces and hydrogen bonds.
1. Van der Waals Forces
Because atoms and molecule were surounded by electrons which alectrically charged, then the molecule in a substance might be in an repulsion of each other, but it never happens. This phenomenon has been explained by a dutch physicist, Johannes Diderik van der Waals. According to him, molecules in a substances does not in repulsion of each other because betweenthe molecule there is a weak attraction force. The forces is called Van der Walls force, which can hold the molecule to stay in a certain susbtance.
The occurrence of Van der Waals force was believed because of there forces, those are dipole-dipole attraction, induction force, and London Force or dispersion force.
a. Dipole-dipole Attraction
Dipole-dipole attraction occurs between polar molecule. In a polar molecule, one pole of the molecule is positively charged and the other pole is negatively charged. These two oppositely charged poles form a dipole. The dipole plays role in happening of dipole-dipole attraction between the polar molecule in a substance. The positive part of each polar molecule attracts the negative part of its neighbouring molecule, and the negative part of each polar molecule attract the positive part of its neighbouring molecules, so dipole-dipole attractions are formed, such as shown in the following figure.
Based on the explanation above, the Van der Waals force in polar molecule is produce from the dipole-dipole attractions between the molecule. In this case, the more polar the molecule, the stronger the dipole-dipole attraction between them and the harder it is to separate them. Molecule that are more polar tend to have higher melting points and boiling points than those of molecule that are less polar. Polar molecule which have dipole-dipole attractions, among other are water, methanol, and amonia.
a. Induction Force
Induction force occurs between a polar molecule and a nonpolar molecule. It is because the polar molecule induces its dipole to the nonpolar molecule, so the negative charges at the nonpolar molecule will be accumulated at a certain side of the nonpolar molecule near the positive side of polar molecule. This condition can produce a temporary dipole, which produces an attractions between the two molecules called induction force. Consider the following figure illustrating the occurence of an induction force between a polar molecule a nonpolar molecule.
b. London Force (Dispersion force)
Basically, London force is a weak form of dipole-dipole attraction. London force occurs when a nonpolar molecule becomes polar for a short time. Nonpolar molecules can briefly become polar because their electron are in constant mition. This motions is usually balance around a nonpolar molecule. If the molecule is briefly disturbed, its electron may accumulate at one part of the molecule. And its produce a positive charge on another part of the molecule.
Base on the case above, the molecule a temporary dipole until the electrons rebalance. As long as the molecule has a dipole, the charge can disturb electrons in neighbouring molecules, so these neighbouring molecules have also a temporary dipole. These temporary dipoles attract each other using a force called London force.
Non polar molecules such as methane (CH4) and nitorgen (N2) molecules have only the intermolecular attraction force in the form of London forces. These force are very week, so the nonpolar substance have low melting and boiling points and usually they are found in the form of gaseous at room temperature.
1. Hydrogen Bonding
Hydrogen bonds are chemical bonds formed between molecules containing a hydrogen atom bound to a strongly electronegative atom, such as fluorine (F), oxygen (O), and nitrogen (N). because the electronegative atoms pull the electron from the hydrogen atom, the atom form a very polar molecule, meaning one side a negatively charged and the other side is positively charged. Hydrogen bonds form between these molecules because the negative sides of the molecule are attracted to the positive side of other molecules, and vice versa. These hydrogen bond are stronger than the bonds formed by Van der Waals forces. Hydrogen bonds play an important role in influencing the compound properties. Pay attentiont to the following explanation.
In daily live we find water in liquids phase. Whereas, the relative molecular mass of water is relatively small (Mr = 18g/mole) and between those water molecules there are Van der Waals forces, theoretically at very low temperature (about -750C), water will be found in gaseous phase. Scientists believe that, the presence of water in liquid phase at normal temperature in earth is caused by the presence of hydrogen bonds between those water molecules. 1. The influences of intermolecular force and size of molecule to boiling point (Tb) and freezing point (Tf)
The power of intermolecular force influences of the combination between kinds of intermolecular force and size of molecule. The power of intermolecular force as follow : hydrogen bonding > dipole-dipole attraction > London Force. The hydrogen bonds formed between water molecules influence some of properties of water. The attraction created by hydrogen bonds keeps water in liquids phase over a wide range of temperature and water has a high heat of vaporization. The heat of vapourization is an amount of energy needed the convert water from liquid to gaseous phase (water vapor).a. When intermolecular of substance there is not found the hydrogen bonding, the power of intermolecular can predict using the sizes of molecule. For compound that have similar of relative molecule mass, the power of intermolecular force hanging on the kind of intermolecular force.
b. For compounds that have a similar intermolecular force and size of molecule, the power of intermolecular force influences of the polarisability of electron. The compound that have higest polarisability will have intermolecular force stronger than compound that have lower polarisability.
II. TEACHING-LEARNING METHOD
- Inductive : ask and question method, giving information, groups discusion
III. TEACHING AND LEARNING PROCESS
1. Preparation (± 15 minute)
§ Greetings and Introductions
§ Checking students attendance
§ Presenting the learning outcomes and the assessment procedure
§ Apperception and motivation (focusing) about hybridization theory and the basic concepts of intermolecular force there is about how the oxygen molecules can to be found in water.
2. Mains Activities (± 75 minute)
| Teacher Activities | Student Activity | Time Allocation | Location |
| Exploration | Class room | ||
| Motivate the student with some questions related to the topics that will learn. | Students answer the teacher question. | 15 minutes | |
| Elaboration | |||
| - Presenting the topics, collecting information and problem that have students - Guiding the students to investigate understanding the shape of molecule affect the intermoecular forces - Observing the student’s activity | Paying a good attention to the teacher’s explanation, Give information answer the teacher’s question | 30 minutes | |
| Confirmation | |||
| - Giving some exercises - Giving a comment about the asks and giving a explanation if there is misconception - Post test | - Doing exercises given by teacher - Correcting the ask according to the teacher’s comment | 30 minutes | |
3. End Activities (± 5 minutes)
a. Giving a chance for students to asking a question about the topic
b. Giving homework
c. Giving information of the next topic
d. Greetings
IV. TEACHING AND LEARNING RESOURCES
1. Chemistry book :
Chang, Raymond. 2004. Kimia Dasar Konsep-Konsep Inti Jilid 1 Hal 290-316. Jakarta : Erlangga
Haryanto, Untung Tri. ......... Kreatif Kreasi Belajar Siswa Aktif Kimia Xia. Klaten : Viva Pakarindo
Parning. 2008. Kimia SMA Kelas XI Semester Pertama. Hal: 23-38 Jakarta : Yudhistira
Rahardjo, Sentot Budi. 2008. Kimia Berbasis Eksperimen 2. Hal 28-35. Solo : Platinum
Sunardi. 2008. Kimia Bilingual untuk SMA Kelas XI. Hal 64-83. Bandung : Yrama Widya
2. Dicussion worksheet (Exercise)
3. Power Point Slide Show
V. INSTRUMENTS AND MEDIA
Spidol, white board, laptop, LCD
VI. ASSESSMENT PROCEDURE
1. Evaluation Method: Cognitive using posttest, and discussion worksheets. Affective using affective rubrics
2. Istrument: cognitive and affective assessment rubrics
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