Grade 10 EM Science 18/06/2020 · Polar covalent bonds •Two atoms of unequal electronegativity are joined by a covalent bond •Gets polarized due to asymmetric distribution of

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Grade 10 EM Science 18/06/2020

Chemical bonds part II Study pack 08

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

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

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

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

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

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

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

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

Fill the following table Ionic compounds Covalent compounds

Examples

Characters 1 2 3 4 5 6

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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)

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

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

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

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

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

Moment

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MSc) 16