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Grade 10 EM Science 18/06/2020
Chemical bonds part II Study pack 08
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Atomic Lattice
• Some atoms are organized as a lattice
• In the lattice atoms are covalently bonded
• Example – Carbon
• Carbon has two forms of atomic lattices
• Graphite and Diamond – Allotropic forms of
carbon
2020-06-11 Prepared by:BSG Chandrasekera (BSc,
MSc) 2
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Allotropic forms of Carbon
• Differ in the way the carbon atom forms covalent bonds with one another
• Graphite
2020-06-11 Prepared by:BSG Chandrasekera (BSc,
MSc) 3
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Graphite
• Consists of layers of Carbon atoms by joining of one carbon atom with three another carbon atoms by single bonds
• Layers are superimposed on one another
• Forces between them are weak
• One layer easily slide over
• Thus Graphite behave as a lubricant
2020-06-11 Prepared by:BSG Chandrasekera (BSc,
MSc) 4
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Diamond • Three dimensional lattice
• Every Carbon atom forms four single bonds with four other carbon atoms
• The hardest substance in nature
2020-06-11 Prepared by:BSG Chandrasekera (BSc,
MSc) 5
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Polarity of Bonds
• Electronegativity – an atom to attract electrons of
a chemical bond
• Equal electronegativity
– Hydrogen molecule (H-H)
– Distribution of electrons in the bond pair is equal
– H2 is a non – polar molecule
2020-06-11 Prepared by:BSG Chandrasekera (BSc,
MSc) 6
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Polarity of bonds
• When two atoms in bond pair is different
– Ex - HF (Hydrogen fluoride)
– Fluorine is more electronegative than Hydrogen
– Bond pair is more displaced towards Fluorine
– Electron distribution is asymmetrical
– Fluorine bears a small negative charge
– This is known as POLARIZATION
– HF whole is a neutral molecule
2020-06-11 Prepared by: BSG Chandrasekera (BSc, MSc) 7
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Polar covalent bonds • Two atoms of unequal electronegativity are joined
by a covalent bond
• Gets polarized due to asymmetric distribution of electrons
• Eg – Water (H2O) molecule
2020-06-11 Prepared by:BSG Chandrasekera (BSc,
MSc) 8
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Intermolecular bonds
• H2O – H atom with a small positive charge form
attractive bonds with O atom in neighbouring H2O
molecule
• Not strong
• H2O get special properties due to these bonds
2020-06-11 Prepared by:BSG Chandrasekera (BSc,
MSc) 9
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Fill the following table Ionic compounds Covalent compounds
Examples
Characters 1 2 3 4 5 6
2020-06-11 Prepared by:BSG Chandrasekera (BSc,
MSc) 10
Please read the page from 184 and 185 and fill this table. Please read the summary in page no – 186 carefully Do the exercises (page 187)
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Lesson 11 -Turning effect of a force
• Applying forces on object
– Push
– Pull
– Lift
– Move
– Rotate the object
– More attention – rotation of an object around a given point
2020-06-11 Prepared by:BSG Chandrasekera (BSc,
MSc) 11
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Turning effect of a force
• Read the activity 1 (page 189)
• You can do this activity without a Newton balance
• Try to open the door at different distances from the hinge
• Please refer figure 11.1
•
2020-06-11 Prepared by:BSG Chandrasekera (BSc,
MSc) 12
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Turning effect of a force
• Read the activity 1 (page 189)
• You can do this activity without a Newton balance
• Try to open the door at different distances from the hinge
• Please refer figure 11.1
• Door rotates around an axis passing through the hinge – axis of rotation
2020-06-11 Prepared by:BSG Chandrasekera (BSc,
MSc) 13
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Turning effect of a force • It is easier to open the door when the force
applied is far away from the rotation axis
• It is difficult to open the door when force applied is closer to the rotation axis
• Example -
2020-06-11 Prepared by:BSG Chandrasekera (BSc,
MSc) 14
Perpendicular distance from rotation axis to the force
Newton Balance reading (N)
A 5
B 10
C 15
D 20
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Turning effect of a force
• In order to rotate an object around a given axis, what
is required is not just a force but a moment
• A moment required to rotate an object is created by
applying a force at a certain distance from the rotation
axis
• Rotation due to the action of a force - turning effect of
the force
2020-06-11 Prepared by:BSG Chandrasekera (BSc,
MSc) 15
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Moment
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MSc) 16