revision for h y gr. viii

8/9/2019 Revision for H Y Gr. VIII

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Revision plan for Gr. VIII

Topic 01: The Particulate Nature of Matter

Sub-topics: a) Properties of matter in the solid, liquid and gaseous states, c) Kinetic Particle Theory, d) Inter-conversion ofthe states of matter, e) iffusion

Key !ords: "atter, States of matter, #hange of states, "elting, $oiling, %vaporation, #ondensation, Sublimation,&ree'ing, (eating curve, #ooling curve, iffusion

a) Properties of matter in the solid, liquid and gaseous states:

States of "atter Solid iquid *as

Shape &i+ed ot fi+edTaes shape of container

ot fi+edTaes shape of container

.olume &i+ed &i+ed ot fi+edSame as volume of container

ensity (igh "oderate o!

#ompressibility #an not be compressed #an not be compressed (ighly compressible

b) Particulate nature:

Kinetic Particle Theory: /ll matter is made up of tiny particles and that these particles are in constant, random motion0

hange of state: Solid iquid, *ases

!eating ur"e:

ooling ur"e:

Melting Point: The temperature at !hich a pure solid turns into liquid0 Ice- m0p0 1o#

#oiling Point: The temperature at !hich a pure liquid turns into gas0 2ater - b0p0 311o#

$iffusion: is the movement of particles from a region of higher concentration to a region of lo!er concentration0

%actors: a) Temperature: (igher the temperature higher the diffusion, b)Molecular mass: ighter particles diffuse faster

States of "atter Solid iquid *as

/rrangement ofparticles

4rderly#losely paced

isorderlyoosely paced

5andom.ery far apart

/ttractive forces .ery strong Strong .ery !ea

Particle motion .ibrate about afi+ed position

5oll 6 slide past each other5andom motion

"ove about at great speed5andom motion

%nergy content o! "oderate (igh


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Topic 0&: '(perimental Techniques

Sub-topics: A) Experimental design, B) Identification and function of apparatus

Key Points: Time, Temperature, "ass, .olume, /pparatus, #ollecting gases, Solubility, ensity, rying agent, etermining Purity

Measuring Time: Stop!atch: a) /nalogue Stop!atchb) igital Stop!atch S0I0 7nit: econd *s)

Measuring Temperature: Thermometer: a) "ercury Thermometer, b) /lcohol Thermometer, c) igital Thermometer0 S0I0 7nit:Kel"in*K)

Measuring Mass: a) $eam $alance b) %lectronic balance0 S0I0 7nit: +ilogram*+g)

Measuring olume: a) "easuring cylinder: "ore accurate than a beaer and "easure up to nearest cm80 %g 99 cm8

b) #onical flas: 5ough measurement

c) $eaer: 7sed to estimate the volume of a liquid0 %0g0 appro+imately 311 cm8

d) Pipette: /ccurately measures out fi+ed volumes of liquids, e0g 101 cm8or ; cm8

e) $urette: /ccurately measures out fi+ed volumes of liquids to the nearest 103 cm8

ollection of -asesThe method of gas collection depends on properties of the gas:


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Drying of Gases

The prepared gas is then bubbled into a drying agent in order to be dried.

A drying agent is a substance which has a great liking for water molecules.

Common examples of drying agents

(1)Concentrated H2SO4: Used to dry Chlorine, Hydrogen chloride

(2)Quck lime(CaO): Used to dry Ammonia

(3)Fused Calcium chloride: Used to dry hydrogen

Determining Purity1.hat is a pure su!stance"

A pure substance is a single substance not mixed with anything else.

#. hat is a mi$ture"

A mixture contains two or more substances not chemically combined together.

%. hat is puri&cation"

Itis the process of separating mixtures into pure substances.

'. (tate one characteristic of a pure solid.

Fixed melting point

). *o+ do impurities a,ect a solid-s melting point"

Impurities lower the melting point.

Impurities cause the solid to melt over a range of temperature.

. (tate one characteristic of a pure li/uid.

Fixed boiling point

0. *o+ do impurities a,ect a li/uid-s !oiling point"

Impurities raise the boiling point. Impurities cause the liquid to boil over a range of temperature.

. hat is the relationship !et+een the amount of impurities in a su!stance and thesu!stance-s melting 2 !oiling point"

The greater the amount of impurities, the lower the melting point.

The greater the amount of impurities, the higher the boiling point.

3. (tate three methods that can !e used to determine +hether a su!stance is pure.

Melting point comparison

oiling point comparison

!hromatography


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Topics 03: Elements, Compounds and Mixture

Key words: Atom, Molecule, Elements, Metal, non-metals, Alloy, Compounds and Mixtures

.tom:Smallest particle of an element

Molecule: #ombination of t!o or more atoms of the same element

'lement:#omposed of only one type of atom and cannot be broen do!n into simpler substances by chemical methods

%lements can be classified into

Metals and Non metals

Metals

hiny solids

Malleable

onorous

$uctile

!igh melting points and boiling points

-ood conductors of heat

-ood conductors of electricity

Non/metals

-ases, "olatile liquids or dull solids ith lo

melting points

#rittle

o melting points and boiling points

Poor conductors of electricity

Poor conductors of heat

ompound:a substance containing t!o or more elements chemically =oined together


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Pure metals are !ea as the layers of atoms slide over each other easily0 in alloy of metals, they have different

si'es of atoms so this distrupts the orderly layer of atoms maing it difficult for atoms to slide over0

%g of alloys

o Steel: iron and carbon

o bron'e: copper and tin

o brass: copper and 'inc

o duralumin: aluminium, copper, magnesium

7ses of duralumin: it is light but strong and durable so used for aircraft parts, greenhouse frames,

overhead cables, curtain !alling in high-rise buildings etc0

Topics 02: .tomic tructureKeyords: Nucleus, louds of electrons, %undamental particles, Nucleon number, .tomic number,'lectron configuration, 3sotropes, alence electrons

Nuclear model of an atom

Particle ymbol4elati"e

massharge

proton p 3 ?3

neutron n 3 1

electron e 3@3A8B -3

Proton number: number of protons in an atom

Nucleon number: number of protons ? number of neutrons


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Number of electrons 5 number of protons

3sotopes: atoms of the same element !ith same proton number but different number of neutrons

o isotopes have slightly different physical properties but have identical chemical properties as they

have the same number and arrangement of electrons

alence electrons:the electrons in the outermost shell

o used to form chemical bonds

%lectronic #onfiguration

%lectrons are placed in orbits0

&irst shell contains ma+imum electrons0 Second shell and so and so for has ma+imum of A electrons0

To !rite electronic configuration !e !rite as n0n0n0000 !here first n denotes the first shell, second the

second shell and so and so for0

o %0g0 Sulfur has electronic configuration of 0A0B

The valence electrons is the number of electrons of the outermost shell0

o Sulphur has B valence electrons0

5elation !ith Periodic Table

%lements in same hori'ontal ro!: Period

%lements in same vertical column: -roup

o *roup 3 has 3 valency

o *roup has valency

o *roup 8 has 8 valency and so on0

o *roup 1 has full valency !hich maes it having stable electronic configuration0

o!n the group the number of shells increases0


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Topics 1;: hemical #onding: The tructure of Matter

Keyords: #onding, %ormation of ions, 3onic bond, o"alent bond, Metallic bond, attice, -iant co"alentstructure, imple co"alent structure

The =oining together of atoms Is calledbonding6 There are three types bonding:

3onic #onding

o"alent #onding

Metallic #onding

Ionic bond

Ionic bonding is the transfer of electrons from one atom to another to become achieve an inert gas

configuration, forming ions0

Ionic bonds are formed bet!een "%T/I# and 4- "%T/I# /T4"S 4C0

"etals lose electrons to form positive ions


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on-metals gain electrons to form negative ions


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Structure and Properties of ionic bond

tructure

Ionic substances appear as giant lattice structures !hich the ions are held together by electrostatic

force bet!een oppositely charged ions0

To find the formula of ionic bond, say sodium chloride bond, by looing at lattice structure, !e count the

ratio of amount of metal ions to non-metal ions0

o %0g0 in sodium chloride, the ratio a:#l is 3:3, therefore the ionic formula is a#l0

Properties

o #ontain ions

o (igh melting and boiling points

o on-volatile

o 7sually soluble in !ater but insoluble in organic solvent

o #onduct electricity !hen molten or !hen dissolved in !ater

#ovalent bond

#ovalent bonding is the sharing a pair of electrons to gain electronic configuration of an inert gas,

usually for molecules0

#ovalent bonds occur bet!een 4-"%T/I# /T4"S 4C0

In covalent bond, !e try to substitute the short of electrons of t!o or more atoms bet!een each other to

form the or A valence electrons0

The shared electrons appear in pairs

'(ample: !&molecule


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(ydrogen atom has one valency0

To become stable !ith hydrogen atom, it needs one more electron, =ust lie helium !hich has valency0

2hen hydrogen atoms =oin, they share their electrons, on !hich, the share becomes electrons,

!hich is no! a noble gas configuration, being shared bet!een these atoms0

2e !rite the bond as ( E ( single bond, !hich means they share an electron pair


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/part from o+ygen sharing bet!een o+ygen atoms, it can have electrons !ith other atoms0

4+ygen needs electrons and !hen bonded !ith hydrogen, !hich need an atom each, they combine

to provide electrons on both sides of o+ygen bonded !ith hydrogen atoms0

%ach hydrogen !ith o+ygen atom form a single bond: 4 E (0

'(ample: 9&molecule

#arbon needs D, o+ygen needs 0

2e share t!o from o+ygen part, 2(I#( (/S T(% S"/%ST 7"$%5 4& S(45T %%#T54S,

T4 S(/5% T(% /"47T 4& %%#T54S T(/T /T4" %%S, to form D shared atoms0

o! o+ygen is stable but carbon needs more, !hich !e no! no! they can get from another o+ygen

atom0

The atoms are no! stable and since each bond has pairs of electrons, !e call this double bond: # H

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Structure and Properties of covalent bond


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tructure

a6 -iant o"alent #ond

$iamond

o iamond has carbon atoms bonded !ith another carbon atoms in a tetrahedral arrangement

!hich each carbon atom uses all its valence electrons to form D single covalent bonds !ith

other D carbon atoms0

ilicon $io(ide

o Silicon dio+ide, Si4, has silicon atoms bonded !ith another o+ygen atoms in a tetrahedral

arrangement !hich each silicon atom uses all its valence electrons to form D single covalentbonds !ith other D o+ygen atoms0

-raphite

o *raphite has flat layers of carbon atoms bonded strongly in he+agonal arrangement in !hich

the layers are bonded to each other !ealy0

Properties

It is a hard solid because it consists of many strong covalent bonds bet!een atoms0 This property

maes it suitable as abrasives0

It has very high melting and boiling points0

It does not conduct electricity


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"etals conduct electricity as it has free electrons !hich carries current0

"etals conduct heat as it has free electrons !hich gains energy !hen heated and moves faster to

collide !ith metal atoms, releasing heat in collisions0

"etals have high melting and boiling points because the bonds bet!een metals is very strong0 (ence

very high heat energy needed to brea the bonds0

Simple "olecular Substances

Simple molecular substances are usually liquids@gases at r0t0p0 because the molecules are not tightly

bonded lie in solids, hence free to move0

They have lo! melting and boiling points because the force of attraction is !ea that they can be easily

broen by heat0

Since they have lo! boiling points, they evaporate easily0

They donJt conduct electricity because they donJt have free electrons@ions !hich helps to conduct

electricity0

"ost of these are insoluble in !ater but soluble in organic solvent0

oble gases

- oble *ases lie helium and argon are unreactive0

- do not form chemical bonds !ith other atoms as they have a stable electronic configuration0

- /toms of other elements form chemical bonds so that they attain the electronic configuration of a noble gas

revision for h y gr. viii

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