360 scientific reasons

8/12/2019 360 Scientific Reasons

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Scientific ReasonsGive the scientific reasons of the following: (Answers in the end.)

1. Transition elements form complex compounds.

. !itric acid is a strong oxidi"ing agent.

#. !a$ ion is smaller than !a atom.

%. Sulphuric acid has higher &oiling point and viscosit'.

. %s or&ital is filled prior to #d &ut on ioni"ation the %s electrons are lost first.

. Anh'drous *uS+% is white while h'drous *uS+% is &lue.

,. The heat of h'dration of -i$ ion is greater than *s$ ion.

. /iamond does not conduct electricit' while graphite does.

0. !ascent h'drogen is more reactive than ordinar' molecular h'drogen.

1. 2lements of group 3A and group 33A readil' loses their valence electrons.

11. Transition elements are paramagnetic.

1. 4elting and &oiling point of 3A group elements are ver' low.

1#. -igands are generall' called -ewis &ase.

1%. 5romine is displaced from its salts &' chlorine.

1. (!6%)$ and 6#+$ ions donot act as ligands though 6+ and !6# act as ligands.

1. The salts of al7aline earth metals are h'drated than al7ali metal salts.

1,. 8n(+6) is solu&le in excess of !a+6 solution.

1. 9h' do chromium (%) and copper (0) shows an electronic configuration which is out oforder.

10. Assign reasons for formation of coloured ion in case of transition elements except "inc.

. 3oni"ation enthalpies of 33A group elements are higher than 3A group elements.

1. Graphite is used as -u&ricant.

. 4etallic character of Aluminium is greater than 5oron.

#. lastic sulphur is elastic.

%. Al7aline earth metals are harder than al7ali metals.

. +rdinar' h'drogen called as molecular h'drogen.

. 2lectropositivel' increases from top to &ottom.

,. Transition elements show varia&le oxidation state.. !a$ ions are discharged at the cathode in preference to 6$ in the manufacture !a+6 in*astner ;elner cell.

0. -i$


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Transition elements have small highl' charged ions and vacant d=or&itals of suita&le energ'.These vacant d=or&itals form coordinate &ond &' accepting lone electron pairs from ligands. Thisis the reason wh' transition elements form coordination compounds.

.

The oxidi"ing properties of nitric acid is due to the sta&ilit' of its molecule and &ecause nitrogen ispresent in its highest oxidation state> i.e. . The degree of oxidation depends upon theconcentration of acid and nature of element.

#.

The num&er of protons in !a$ ion are greater than the num&er of electrons due to which thenuclear attraction increases. And !a$ has one shell less than !a atom> &ecause the last shellconsists of onl' one electron> which is not present in !a$ ion. These are the reason due to which!a$ ion has smaller radii than !a atom.

%.

Sulphuric acid has higher &oiling point and viscosit' due to the presence of h'drogen &ondingwhich lin7 the molecules in larger aggregates.

.

According to Auf&au principle and n$l rule> the se?uence of filling in atomic or&itals in dependenton the value of n $ l.

Since>

n $ l for %s @ % $ @ %

and>

n $ l for #d @ # $ @ s

Therefore> electron goes in the or&ital having lowest energ' i.e. %s. 3n the same wa'> the electronin %s or&ital have less energ'> therefore the' are lost first during ioni"ation.

.

6'drated *uS+%.6+ contains molecules of water of cr'stalli"ation and water act as ligand.The lone pair of electron of water molecules influence the #d or&ital of *u &' splitting it into egand tg. Thus &' a&sor&ing visi&le light an electron can ump from lower energ' set (tg) tohigher energ' set (eg). 3n doing so some of the component wavelength of light is removed> so theremaining component wavelength of light reflected shows the &lue colour. An h'drous *uS+% iscolourless due to the a&sence of water molecule.

,.

The atomic si"e of -ithium is much smaller than that of *esium> therefore its charge densit' ismore. /ue to more charge densit'> the electrons are attracted with a greater force of attraction.This is the reason more amount of heat is li&erated when one mole of -i$ ion is dissolved inwater. This is the reason wh' heat of h'dration decreases down the group.

.

3n diamond> each car&on atom is sp# h'&eridi"ed and is strongl' &onded to four other car&on

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atoms. 3t utili"es its four unpaired electrons in the formation of four covalent &onds. Since> it hasno free electronsB it is a poor conductor of electricit'.

9hereas> in graphite> each car&on is sp h'&ridi"ed and covalentl' lin7ed with three other car&onatoms to give &asic hexagonal ring. These hexagonal rings are #.# AC awa' from each other andare held together &' wea7 Dander 9aalEs forces. The fourth electron of each car&on formsdelocali"ed p &onds> which are spread uniforml'. This is the reason graphite conducts electricit'.

0.

4olecular h'drogen is composed of two atoms of h'drogen. The' are held together &' a covalent&ond. The &ond energ' of this covalent &ond is 1% 7cal themolecular h'drogen needs an energ' to over come the &onding energ' i.e. greater than 1%7cal the nuclear charge decreases> which increases the

atomic si"e and reduces the force on valence electron. This is the reason wh' elements of group3A and 33A readil' lose their electrons.

11.

The paramagnetic propert' of an element depends upon the availa&ilit' of free electrons. 4an'compounds of the transition elements are paramagnetic. This is &ecause the' have unpairedelectrons in their d=or&itals> which &ecomes active in a magnetic field.

1.

The elements of group 3A have large atomic radii and small nuclear charges. This is the reasonwh' melting point> &oiling points are lower than other elements in the periods.

1#.

-igands are atoms> molecules or ions that donate a lone pair of electron to metal and formcoordinate &ond with them. According to -ewis> &ases are su&stances that donate a lone pair ofelectrons. This is the reason wh' ligands are called -ewis &ase.

1%.

The electronegativit' of chlorine is greater than that of &romine. 5ecause it decreases down thegroup. Since> chlorine is more electronegative than &romine> it displaces &romine from its salts.

1.

3n case of !6#> the central atom nitrogen contains a lone pair of electron> which it can donate tometal. 9hereas incase of !6%$> the central atom nitragen has alread' donated its lone pair toh'drogen so it does not act as ligand. Similarl' 6+ act as ligand &ut 6#+$ does not act asligand.

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6'dration of cations depend upon the nuclear charge and ionic radii. Smaller the ionic radii>greater would &e the nuclear charge and more the salt will show the tendenc' for h'dration.Since> the al7ali earth metals have a greater nuclear charge and a stronger electric field than theal7ali metals> therefore> the' are more h'drated than al7ali salts.

1,.

8inc h'droxide 3 an emphotric su&stance> i.e. it shows &oth acidic and &asic properties.Therefore> when 8n(+6) is dissolved in excess of !a+6 solution it does not precipitate out &utforms a complex ion and redissolves.

8n(+6) $ !a+6 F 8n(+6)%H= $ !a$

Tetra Hydroxozincate

1.

%*r @ %s#d% F (%s1#d)0*u @ %s#d0 F (%s1#d1)

The half filled or completel' filled or&itals are more sta&le than other wise filled or&itals. 3n case of*romium the one electron of %s or&ital umps into #d or&ital> as a result %s and #d or&itals are halffilled and sta&i"ed. Similarl' in copper one electron of %s or&ital umps into #d or&ital> as a result%s is half filled whereas #d is completel' filled.

6ence electronic configuration of *romium (*r) is %s1#d instead of %s#d% and configuration ofcopper (*u) is %s1#d1 instead of %s#d0.

10.

The formation of coloured ion in case of transition elements can &e explained &' *r'stal Iield

Theor'. According to the theor' (*.I.T) the &onding &etween ligand and a metal ion iselectrostatic. The ligands surrounding the metal ion create an electrostatic field around its d=or&ital. This field splits five degenerated d=or&itals into two sets with different energies.

The energ' difference &etween two sets (eg and tg) of d or&ital is e?uivalent to a wavelength ina visi&le region. Thus &' a&sor&ing visi&le light> an electron ma' &e a&le to move from lowerenerg' set (tg) to higher energ' set eg of d or&itals. 3n doing so some of the componentwavelength of white light is removed> so the remaining component wavelength of light reflected ortransmitted shows the colour of ion.

6ence the colour of the ion is due to the half filled #d or&ital> the electron can ump from d or&italof lower energ' &' the a&sorption of small amount of energ' of a particular wavelength in a visi&leregion. Since in case of "inc> the #d or&ital is completel' filled therefore the compounds of 8incare white or colourless.

.

The ioni"ation enthalpies 33A (al7aline earth elements) is higher than the corresponding ioni"ationenthalpies of 3A group (al7ali metals> &ecause elements of 33A group has an extra nuclear protonwhich causes an increase in the electrostatic 5eautiful force &etween the nucleus and the outermost electron.

1.

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3n Graphite> each car&on is Sp h'&eridi"ed and covalentl' lin7ed with three other car&on atomsto give &asic hexagonal ring. These hexagonal rings then form la'ers in graphite. These la'ersare #.# AC awa' from one another and held together &' wea7 Dander 9aalEs forces of attraction./ue to large inter planner distance (#.#AC)> the la'ers slide easil' over one another that is wh' itis soft and used as -u&ricant.

.

The maximum capacit' of electron accomodation of &oron in its outer most shell is eight electronsand that of Aluminium is eighteen electron.

5 @ 1s> s> p1

1#Al @ 1s> s> p> #s> #p1

3t means electron population of aluminium is less than &oron. /ue to less electron population> thenum&er of neigh&ouring atoms in the lattice increases> that is wh' metallic character of aluminiumis greater than &oron.

#.

The plastic sulphur or g=sulphur is composed of long chains of sulphur atoms. The elasticit' ofplastic sulphur is due to uncoiling of long sulphur chains and then recoiling of chains &' therelease of tension.

%.

The al7aline earth metals (33 group metals) are apprecia&l' harder than al7ali metals (3 group)&ecause the presence of divalent cations in their metallic structure produce greater &ondingforces.

.

+rdinar' h'drogen exist as diatomic molecule (6) therefore it is also 7nown as molecularh'drogen.

.

The tendenc' of atom to give out electrons is 7nown as electropositivit'. 2lectropositivit' isinversel' proportional to ioni"ation potential and electron population. 5oth the factors decreasesdown the group> hence electropositivit' increases from top to &ottom.

,.

The transition elemenets show varia&le oxidation states in their compounds. This variation is dueto the ver' small energ' difference in &etween #d and %s or&itals. As a result> electrons of #d as

well as %s ta7es part in the &ond formation..

3n castner=7ellner cell> 6$ ions are not easil' discharged due to high voltage of 6$ ion> on thecontrar' !a$ ions are easil' discharged over mercur' surface.

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360 scientific reasons

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