Int Chem Chap 4

8/14/2019 Int Chem Chap 4

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44 PERIODICPERIODICTABLETABLE

4.14.1 Periodic table ofPeriodic table of

elementselements


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Contribution by AntoineContribution by AntoineLavoisier (1743 - 1794)Lavoisier (1743 - 1794)

1. Antoine Lavoisier, a French chemist,was the first person to classifyelements into groups.

2. In the year 1789, the knownelements at that time were classifiedinto four groups as shown in Table 4.1.

3. In his table, elements wereclassified into metals and non-metals.


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Contribution by AntoineContribution by AntoineLavoisier (1743 - 1794)Lavoisier (1743 - 1794)


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Contribution by Johann W.Contribution by Johann W.Dobereiner (1780 - 1849)Dobereiner (1780 - 1849)

1. In the year 1829, Johann W. Dobereiner, aGerman chemist, divided the elements intogroups. Each group consisted of three elementswith similar chemical properties. He named eachof these groups as triad.


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Contribution by JohnContribution by JohnNewlands(1837-1898)Newlands(1837-1898)

1. In the year 1863, John Newlands, a Britishchemist, arranged all the known elementsaccording to the ascending order of their atomicmasses.


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Contribution by LotharContribution by LotharMeyer(1830-1895)Meyer(1830-1895)

1. In the year 1870, Lothar Meyer, a Germanchemist, plotted- a graph of the atomic volumeagainst the atomic mass for all the knownelements as shown in Figure 4.1. (The atomicvolume of an element is the volume of one mole

atom of that element).


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Contribution by DmtriContribution by DmtriMendeleev (1839-1907)Mendeleev (1839-1907)

1. Dmitri Mendeleev, a Russian chemistry professor,had shown that the properties of elements changedperiodically with their atomic masses.

2. In the year 1869, he arranged the elements in the

same way as Newlands but made a few changes asbelow.

(a) Elements with similar chemical properties wereplaced in the same column called a group.

(b) Empty spaces were left in the Periodic Table forthose undiscovered elements at that time.


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Contribution by H.J.G. MoseleyContribution by H.J.G. Moseley(1887 - 1915)(1887 - 1915)

1. In the year 1914, H.J.G. Moseley, a Britishphysicist, investigated the X-ray spectrum ofelements.

2. He plotted a graph of the square root of thefrequency of X-ray from the elements againsttheir proton numbers. A straight line wasobtained.

3. He concluded that the proton numbers shouldbe used as a basis for the periodic changes in thechemical properties of elements.

4. Therefore, Moseley arranged the elements inincreasing order of their proton numbers. Heproduced a Periodic Table similar to Mendeleev'sPeriodic Table.


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Arrangement of elements inArrangement of elements inthe Periodic Tablethe Periodic Table

1. Figure 4.2 shows the Periodic Table.


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Elements with the same number ofvalence electrons will exhibit

similar chemical properties.


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4.24.2 Group 18 ElementsGroup 18 Elements

1. Elements in Group 18 of thePeriodic Table are - helium, neon,argon, krypton, xenon and radon.

They are known as noble gases.

2. Our air consists of approximately1% of noble gases.


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Physical PropertiesPhysical Properties

1. Table 4.9 lists the physicalproperties of Group 18 elements.


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Physical PropertiesPhysical Properties

Solubility

All noble gases are insoluble in

water. Electrical and heat conductivity

All noble gases cannot conduct

electricity and are poor conductorsof heat.


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Unreactive properties of nobleUnreactive properties of noblegasesgases

1. Table 4.10 shows the electronarrangements for the atoms of noblegases.


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Unreactive properties of nobleUnreactive properties of noblegasesgases

2. The outermost shell of helium atom has 2electrons, called the duplet electron arrangementwhereas the outermost shells of the other noblegases have 8 electrons, called the octet electronarrangement.

3. The duplet electron arrangement for helium andthe octet electron arrangement for the other noblegases are very stable.

4. Hence, atoms of noble gases do not releaseelectrons, accept electrons or share electrons among

each other or with other atoms. 5. Therefore, all noble gases do not react with otherelements or compounds.


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Uses of Group 18 elementsUses of Group 18 elements Helium

(i) Helium gas is very light and non-flammable (unreactive).

(ii) These properties enable helium gas to be used in filling weatherballoons and airships.

Neon

Neon gas is used to fill neon lights which are used to light up

advertisement boards. It glows with a reddish-orange colour. Argon

Argon gas is used td fill electrical bulbs. This is because the hot tungstenfilament in the bulb does, not react with inert argon gas. Apart from that,argon gas prevents the oxidation of the filament.

Krypton

The inert krypton gas is used to fill high speed photographic flash lamps.

Radon Radon gas is used to treat cancer because it is radioactive.


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Group 1 elements are lithium,sodium, potassium, rubidium,caesium and francium. They are

known as alkali metals.


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Physical propertiesPhysical properties


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Physical propertiesPhysical propertiesGeneral physical properties for Group 1 elementsare as follows.

(a) All alkali metals are grey solids with shinysurfaces at room conditions.

(b) All alkali metals are soft solids and can beeasily cut. (c) All alkali metals have low densities compared

to heavy metals such as iron and copper. (d) All alkali metals can conduct electricity and

heat. (e) All alkali metals have low melting and boilingpoints compared to heavy metals.


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Chemical propertiesChemical properties


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1. All the atoms of alkali metals have onevalence electron. Hence, alkali metals exhibitsimilar chemical properties.

2. Although the alkali metals have similarchemical properties, the reactivity increases whengoing down Group 1.


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When going down Group 1, the size ofalkali metals increases. Hence, the singlevalence electron become further away

from the nucleus. Thus, the single valenceelectron become more weaklypulled bythe nucleus.This causes the single valence electron

released more easily to form ionsY Y+ +e-


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2Li(s) + Cl2(g) 2LiCl(s)

Lithium chlorine Lithium Chloride

2Na(s) + Br2 (g) 2NaBr(s) Sodium Bromine Sodium Bromide


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Experiment: Investigating theExperiment: Investigating thechemical properties of Group 1chemical properties of Group 1

elementselements


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Experiment: Investigating theExperiment: Investigating thechemical properties of Group 1chemical properties of Group 1

elementselements

Discussion: 1. Lithium, sodium and potassium react with water to

produce a colourless gas ('hissing' sound) and alkalinesolution that turns red litmus paper blue. Hence, lithium,

sodium and potassium exhibit similar chemical properties. 2. The reactivity of alkali metals in their reactions with

water increases from lithium sodium potassium.

xper men : nves ga ng exper men : nves ga ng e


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xper men : nves ga ng exper men : nves ga ng echemical properties of Group 1chemical properties of Group 1

elementselements

B. Reactions of alkali metals with oxygen .



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elementselements

Observation:



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elementselements

Discussion:

1. Lithium, sodium and potassium burn in

oxygen gas (air) to produce a white solidwhich is alkaline when dissolved in water.So, lithium, sodium and potassium exhibitsimilar chemical properties.

2. The reactivity of the alkali metals intheir reactions with oxygen (air) increasesfrom lithium sodium potassium.



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elementselements


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1. Elements in Group 17 are fluorine,chlorine, bromine, iodine and astatine.They are known as halogens.

2. All halogens exist as diatomic covalentmolecules. They are written as F

2, Cl

2, Br

2,

I2and At

2.

3. Halogens are reactive non-metals.They exist in various mineral salts in theearth's crust and sea water.


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(a) The colour of halogens becomesdarker when going down Group 17.Table 4.20 shows the physical states

and colours of various halogens.


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Physical propertiesPhysical properties (b) All halogens do not conduct electricity.

(c) All halogens are weak conductors of heat.

(d) All halogens have high electronegativity which meansthe strength of its atom in a molecule to pull electronstowards its nucleus is strong. However, theelectronegativity of halogens decreases when goingdown Group 17 due to the increase in the number ofshells occupied with electrons. This causes theoutermost occupied shell to become further away fromthe nucleus.


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1. Table 4.21 shows the electronarrangements of all halogens fromGroup 17 of the Periodic Table.


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(a) All atoms of halogens have sevenvalence electrons.

(b) Each. of these halogen atoms will

receive one more electron, eitherthrough the transfer of electrons orsharing electrons, to achieve a stableoctet electron arrangement duringreactions.


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(a) All atoms of halogens have sevenvalence electrons.

(b) Each. of these halogen atoms willreceive one more electron, either throughthe transfer of electrons or sharingelectrons, to achieve a stable octet electronarrangement during reactions.

(c) The reactivity of a halogen is measuredby the ease of that halogen atom to receiveelectrons.



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elementselements

A. Reactions of halogens with water

I. Chlorine with water



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elementselements

Method: B Reaction of halogens with iron I Chlorine with iron



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elementselements

Results:



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elementselements

Discussion: A Reaction of halogens with water 1. The solubility of halogens in water

decreases when going down Group 17.

2. All halogens react with water toproduce acidic solutions.



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elementselements

A Reaction of halogens with water



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elementselements

Discussion:

B Reactions of halogens with iron



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elementselements

C Reactions of halogens with sodiumhydroxide solution


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Elements in a PeriodElements in a Period 1. Period is the horizontal row of elements in the

Periodic Table. 2. The Periodic Table consists of seven periods

from Period 1 to Period 7. 3. The period_ number of an element is the

number of shells occupied with electrons in an,atom of the element. For example, all the atomsof Period 3 elements have three shells occupiedwith electrons.

4. When going across a period from left to right,

each atom has one proton more than theprevious element. Hence, the proton numberincrease by one from one element to the next.


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Elements in a PeriodElements in a Period

Ch i tiCh i ti


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Change in properties acrossChange in properties acrossPeriod 3Period 3

2. Atomic radius (atomic size)

3. Electronegativity

4. Physical states

5. Metallic properties (electropositivity) of elements

6. Electrical conductivity

P ti f id fP ti f id f


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Properties of oxides ofProperties of oxides ofelements in Period 3elements in Period 3

(a) Metals form oxides with basicproperties only.

(b) Some metals can form oxideswith both basic and acidic propertieswhich are known as amphotericproperties.

(c) Non-metals form oxides withacidic properties only.

U f i t lU f i t l


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Uses of semi-metalsUses of semi-metals(metalloids) in industry(metalloids) in industry

1. Silicon is widely used in the microelectronicindustry. It is used in making diodes, transistorsand other electronic components.

2. These electronic components are joinedtogether on a thin piece of silicon wafer to form

an integrated circuit called microchip. 3. Microchips are used in the manufacture of

computers, calculators, cellphones, videocameras, video recorders, televisions and others.

4. Germanium is also used as a semi-metal

(metalloid) in the microclectronic industry.


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44 PERIODICPERIODIC

TABLE OFTABLE OFELEMENTSELEMENTS

4.64.6 Transition ElementsTransition Elements

Th iti i th P i diTh iti i th P i di


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The position in the PeriodicThe position in the PeriodicTableTable

1. Transition elements are located inGroup 3 to Group 12 of the Periodic Table

Properties of transitionProperties of transition


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Properties of transitionProperties of transitionelementselements

2. The properties of transition elements do notchange much when going across the period.

(a) The atomic atomic sizes for the first seriesof transition elements are almost the same.

(b) All transition elements are metals. 3. Although zinc is located in the first series oftransition elements, it does not exhibit thecharacteristics of transition elements. Thus, it isnot a transition element.

S i l h t i ti fSpecial characteristics of


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Special characteristics ofSpecial characteristics oftransition elementstransition elements

All transition elements exhibit four specialcharacteristics as follows.

1. Form coloured ions/compounds

2. Exhibit different oxidation numbers incompounds

3. Form complex ions [Cr(NH3)6]3+

4. Act as catalysts

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Int Chem Chap 4