كيمياء لغات Physical properties للصف الثالث الثانوى 2016

Physical properties of transition elements

:Atomic mass -

.Atomic masses of these elements increase gradually by increasing the atomic number

­:Atomic volume -

.(We notice that, there is a gradual decrease in the atomic size from ₂₁Sc till ₂₉Cu, (relatively constant

:G.R:Atomic radius of the transition elements is relatively constant

:Due to two opposite factors

 When the atomic number increase, the number of positive charges increase and the attraction force also increase, while the radius decrease

 When the atomic number increase, the number of negative charges (electrons) increase and the repulsive force increase, and also the radius increase

NB: a- Transition elements have small atomic size and variation in atomic size is small, so, oxidation of these elements is difficult, i.e. I.P increases

.G.R:On moving in the first transition series from left to right it becomes more difficult to oxidize the elements

.Due to the slight decrease in radius and the increase of the nuclear attraction force to the valency electrons

.b- Due to the atomic radius is relatively constant, these elements are used in alloys industry

c- When the atomic radii are the same, the properties are similar, and this explains the similarity in properties in iron triad (Fe,Co,Ni

:Density -

.G.R:1- Transition elements have high density

.(Density of iron (7.87 gm/cm3) is less than that of cobalt (8.8 gm/cm3

     = Because density  

  .and the atomic mass of iron is less than that of cobalt and atomic volume of (Fe & Co) is nearly equal,

:Boiling and Melting points -

Melting point and boiling point are high because they have strong metallic bonds due to the increase of the valence electrons in 3d, 4S sublevels

(Number of free valence electrons α strength of the metallic bond α Melting point and boiling point)

NB: Cu and Zn are relatively soft and of lower boiling points as their metallic bonds are weaker, since they involve the participation of 4S electrons only

.G.R:Transition elements are harder than representative elements

NB: The transition elements have some properties which differentiate them from the representative elements, these properties are

.Magnetic properties -

.The coloured compounds -

.Catalytic activity of the elements and their compounds -

:Complete

………, ………, ………  Transition elements differ from representative elements in 

:Magnetic properties -

Magnetic moment = Number of unpaired electrons in d sublevel

:Transition Elements classified into

:paramagnetic Substance *

It is the substance which is attracted to the external magnetic field due to the presence of unpaired electrons in the d sublevel, which spin in one direction forming magnetic field

:Diamagnetic substance *

It is the substance which repels with the external magnetic field due to the presence of paired electrons in the d sublevel, which spin in opposite direction

:Question

.compare between para magnetism and diamagnetism

?2-   Which of the following is paramagnetic and which is diamagnetic Zn⁺² , Cu⁺² , Fe⁺²

.G.R:1- Measuring the magnetic moment helps in determination the electronic configuration

Because when the magnetic moment = Zero, this means that all electrons are coupled, when it has a certain value this means the presence of a number of unpaired electrons and the magnetic moment is directly proportion to the number of unpaired electrons

.FeCl₃ is attracted to the magnet more than TiCl₃

Because Fe⁺³ has 5 unpaired electrons, while, Ti⁺³ has only one electron, accordingly, magnetic moment of Fe⁺³ is more than Ti⁺³, so, FeCl₃ is attracted to the magnet more than TiCl₃

.FeCl₃is attracted to the magnet more thanFeCl₂

:Question

Arrange the following compounds in an ascending order according to their magnetic moment: CuSO₄ , ZnCO₃ , FeSO₄ , Fe₂(SO₄)₃

:The coloured compound -

.The colour of a substance results from the absorption of visible light

The light is a form of energy and each compound of transition elements especially which has unpaired electrons in the d sublevel when exposed to light their electrons are excited by a certain colour of white light, (white light consists of 7 colours), so, the substance absorbs it and does not absorb others (complementary), which we see substance by it

.NB: If the substance absorbs all the colours of the visible light it appears black

     If the substance does not absorb any colours of the visible light it  appears white (colourless), and it takes place in the following cases

.a- In case of d⁰ and d¹⁰

b- In case of ions of representative elements, where they have unpaired electrons in the sublevel S and P where the energy of the visible light can not excite them to higher energy levels, so they are colourless

    .If the substance absorbs a part of light colours, it appears in the complementary colour

:Complementary colour

It is the net of colours which are not absorbed by the substance, it is the colour seen

.G.R:Cobalt compounds appear with blue colour

Because the energy required exciting the unpaired electrons in the 3d- sublevel is equal to the energy of the orange colour, so, it appears with the complementary colour which the blue colour

.NB: 1- Compounds are coloured in case d^1-9

     . Compounds are coloures in case d⁰ or d¹⁰

(e.g.: 1- Sc⁺³ is colourless because the sublevel d is empty (d⁰

      ( 2- Cu⁺¹ is colourless because the sublevel d is complete (d¹⁰

      (3- Cu⁺² is coloured because the sublevel d is not complete (d⁹

        (4- Zn⁺² is colouress because the sublevel d is complete(d¹⁰

.G.R:1- Cu⁺¹ is colourless, while , Cu⁺² is blue

Because ₂₉Cu: ₁₈[Ar], 4S¹ , 3d¹⁰

. Ti⁺³ is reddish purpule, while, Ti⁺⁴ is colourless

.Solution of cobalt are coloured, whereas, solution of Zinc salts is colourless

:Solutions of cobalt salts are coloured because 3d⁷ sublevel is partially filled

Which means, there is a number of unpaired electrons in the d-sublevel, so it absorbs a colour from the white light and complementry colour is seen

:But solutions of zinc salts are colourless because 3d¹⁰ sublevel is completely filled

.Which means, there is no unpaired electrons in the d-sublevel, so it doesn’t absorbs any colour, i.e., it is colourless

NB: There are some compounds although the (d) sublevel is d⁰ or d¹⁰ but they are coloured such as: KMnO₄ is violet although Mn⁺⁷

:Choose

:The compound FeCl₂ is

.a- paramagnetic colourless.                    b- paramagnetic coloured

.c- Diamagnetic colourless.                      d- Diamagnetic coloured

:Catalytic Activity -

:”G.R “V.I

.Elements of the 1^st transition series are good catalysts *

.Finally divided nickel is used as a catalyst for hydrogenation of vegetable oil*

.Iron is a good catalyst*

.Vanadium pentaoxide is used as a catalyst in the production of sulphuric acid*

.Chromium compounds are used as a catalyst in polymerization of ethene*

,Chromium oxides or colloidal platinum on asbestos are used in many industries such as sulphuric acid*

production, and ammonia production by Haber method

Due to the presence of the 3d and 4S electrons which form bonds between the reacting molecules and the surface of the catalyst which leads to

.a-   increasing the concentration of the reactants at the surface of the catalyst

.b-   Rate of collision between the reacting molecules increase

.c-   The bonds in the molecules of the reactants become weak

.d-   The activation energy decreases and the speed of the reaction increases

:Question

:Write one use for each of the following

.a- colloidal platinium on asbestos.                            b- Chromium oxide