ASSIGNMENT OF GMCS CHEMISTRY

P-block Elements:

We know that electrons are arranged in the shells of atoms around the nucleus. These shells are arranged according to their energy and can be represented as K, L, M, and N.... The atomic shells can be further classified as s, p, d and f sub-shells. Each sub-shell is divided into orbitals which are denoted as s, p, d, and f-orbitals. The long form of the periodic table is also based in these orbital and sub-shells.

The periodic table can be divided into blocks; s, p, d and f according to their valence shell electronic configuration. The elements of s-block have their valence electron in s-sub shell. A first and second group of the periodic table is part of s-block. From 3rd group, the valence electrons are filled in d-sub shell therefore these elements are part of d-block and continue till 12th group of the periodic table. Form 13th group, again valence electrons are again filled in p-sub shell, therefore these elements are known as p-block elements. p-block elements are placed from 13th to 18th group of the periodic table. They include metals, non-metals and metalloids. This block is better explained group wise and each group is known with its 1st element such as carbon family, nitrogen family, boron family etc. Let’s have a look at some more features of p-block of elements.

In these elements p-orbitals are in the process of being filled up.

Properties of P- block Elements

P block chemistry is a little complicated compared to the s block chemistry. The reason behind this is that P block not only has non metals, but metalloids and metals too. 

Every group, the boron group, Carbon group, Nitrogen group, Chalcogens, halogens and the noble gases have different physical and chemical properties.

Some of the common properties of 'P' block elements are

1. Atomic size

Atomic size of all elements in the 'P' block, decreases as we move from IIIA to VIIA.When we move down a group, say, for example, from carbon to lead in group IV A, the elements increase in size, due to the additional shell added.

2. Ionization energy

Ionization energy, or the energy to remove an electron from the outermost shell of an element, increases as we move along from IIIA to VIIA. It is maximum for a noble gas because noble gases have completely filled configuration. Ionization energy decreases as we move down a group. Some elements at the bottom of a group like Lead, tin, Thallium, Bismuth, etc. behave almost as like metals with very low ionization energies.

3. Electronegativity

The property of acquiring an electron or the ability to withdraw electrons from an electropositve element increases as we move from III A to VII A. Elements of VII A have maximum electronegativity, with fluorine being the most electronegative atom present, due to its smaller size.

4. Allotropy

Allotropy is a phenomenon by which one element can exist in many forms. Most elements of IV A, V A, and VI A show allotropy.

For example, phosphorus exist in many forms like red phosphorus, white phosphorus, etc. Similarly, many forms of sulfur like monoclininc sulfur, rhombic sulfur, etc., are known. There are many forms of carbon too, like graphite, diamond, etc. Halogens do not show allotropy.

5. Catenation

1. Catenation is the ability to form compounds in which the atoms are linked to each other in chains or rings.
2. Carbon has the greater tendency to combine with other carbon atoms to form quite large carbon structures.
3. Other elements like silicon undergo catenation in IV A group. V A group also exhibits this property. Nitrogen and phosphorus have a tendency to form M-M links.
4. Catenation can be seen in the case of Oxygen group too. S₈ is an example of catenation.
5. Catenation is not shown among halogens and noble gases.

6. Chemical Properties of P block elements

Since P block elements are all non metals, covalent bond is seen in compounds such as hydrides, oxides, halides, etc. 

Interhalogens:

The halogens react with each other to form interhalogen compounds. The general formula of most interhalogen compounds is XY_n, where n = 1, 3, 5 or 7, and X is the less electronegative of the two halogens. The compounds which are formed by the union of two different halogens are called inter halogen compounds.

Introduction

There are never more than two types of halogen in ainterhalogen molecule, which are of 4-types.

1.    AX- type : ClF, BrF, BrCl, ICl, IBr,

2.    AX₃-type: ClF₃, BrF₃, (ICl₃)₂,

3.    AX₅-type: ClF₅, BrF₅, IF₅,

4.    AX₇-type: IF₇.

The interhalogen compounds of type AX and AX₃ are formed between the halogen having very low electronegative difference (e.g., ClF, ClF₃). The inter halogen compounds of type AX₅ and AX₇ are formed by larger atoms having low electronegativity with the smaller atoms having high electronegativity. This is because it is possible to fit the greater number of smaller atom around a larger one (e.g. BrF₅, IF₇).

Interhalogen are all prone to hydrolysis and ionize to give rise to polyatomic ions. The inter halogens are generally more reactive than halogens except F. This is because A-X bonds in interhalogens are weaker than the X-X bonds in dihalogen molecules. Reaction of inter halogens are similar to halogens. Hydrolysis of interhalogen compounds give halogen acid and oxy-acid.

Nomenclature

To name an Interhalogen compound, the less electronegative element is placed on to the left in formulae and naming is done straight forward.

Properties

1.    All Interhalogens are volatile at room temperature

2.    All are polar due to difference in their electronegativity.

3.    These are usually covalent liquids or gases due to small electronegativity difference among them.

4.    Some compounds partially ionize in solution. For example:

2ICl→I++ICl−22ICl→I++ICl2−

5.    Interhalogen compounds are more reactive than normal halogens except fluorine.

Diatomic Interhalogens (AX)

The interhalogens of form XY have physical properties intermediate between those of the two parent halogens. The covalent bond between the two atoms has some ionic character, the less electronegative element, X, being oxidised and having a partial positive charge. Most combinations of F, Cl, Br and I are known, but not all are stable.

·         Chlorine monofluoride (ClF): The lightest interhalogen compound, ClF is a colorless gas with a normal boiling point of -100 °C.

·         Bromine monofluoride (BrF): BrF has not been obtained pure and dissociates into the trifluoride and free bromine.

·         Iodine monofluoride (IF): IF is unstable and decomposes at 0 C, disproportionating into elemental iodine and iodine pentafluoride.

·         Bromine monochloride (BrCl): A red-brown gas with a boiling point of 5 °C.

·         Iodine monochloride (ICl): Red transparent crystals which melt at 27.2 °C to form a choking brownish liquid (similar in appearance and weight to bromine). It reacts with HCl to form the strong acid HICl₂. The crystal structure of iodine monochloride consists of puckered zig-zag chains, with strong interactions between the chains.

·         Iodine monobromide (IBr): Made by direct combination of the elements to form a dark red crystalline solid. It melts at 42 °C and boils at 116 °C to form a partially dissociated vapor.

Tetra-atomic Interhalogens (AX₃)

·         Chlorine trifluoride (ClF₃) is a colorless gas which condenses to a green liquid, and freezes to a white solid. It is made by reacting chlorine with an excess of fluorine at 250 °C in a nickel tube. It reacts more violently than fluorine, often explosively. The molecule is planar and T-shaped. It is used in the manufacture of uranium hexafluoride.

·         Bromine trifluoride (BrF₃) is a yellow green liquid which conducts electricity and ionizes to form [BrF₂⁺] + [BrF₄^-]. It reacts with many metals and metal oxides to form similar ionized entities; with some others it forms the metal fluoride plus free bromine and oxygen . It is used in organic chemistry as a fluorinating agent. It has the same molecular shape as chlorine trifluoride.

·         Iodine trifluoride (IF₃) is a yellow solid which decomposes above -28 °C. It can be synthesized from the elements, but care must be taken to avoid the formation of IF₅. F₂ attacks I₂ to yield IF₃ at -45 °C in CCl₃F. Alternatively, at low temperatures, the fluorination reaction I₂+ 3XeF₂ --> 2IF₃ + 3Xe can be used. Not much is known about iodine trifluoride as it is so unstable.

·         Iodine trichloride (ICl₃) forms lemon yellow crystals which can be melted under pressure to a brown liquid. It can be made from the elements at low temperature, or from iodine pentoxide and hydrogen chloride. It reacts with many metal chlorides to form tetrachloriodides, and hydrolyses in water. The molecule is a planar dimer, with each iodine atom surrounded by four chlorine atoms.

Hexa-atomic Interhalogens (AX₅)

·         Chlorine pentafluoride (ClF₅) is a colorless gas, made by reacting chlorine trifluoride with fluorine at high temperatures and high pressures. It reacts violently with water and most metals and nonmetals.

·         Bromine pentafluoride (BrF₅) is a colorless fuming liquid, made by reacting bromine trifluoride with fluorine at 200Å C. It is physically stable, but reacts violently with water and most metals and nonmetals.

·         Iodine pentafluoride (IF₅) is a colorless liquid, made by reacting iodine pentoxide with fluorine, or iodine with silver fluoride. It is highly reactive, even slowly with glass. It reacts with elements, oxides and carbon halides.The molecule has the form of a tetragonal pyramid.

Octa-atomic interhalogens (AX₇)

·         Iodine heptafluoride (IF₇) is a colourless gas. It is made by reacting the pentafluoride with fluorine. IF₇ is chemically inert, having no lone pair of electrons in the valency shell; in this it resembles sulfur hexafluoride. The molecule is a pentagonal bipyramid. This compound is the only interhalogen compound possible where the larger atom is carrying seven of the smaller atoms

·         All attempts to form bromine heptafluoride (BrF₇) have failed and instead produce bromine pentafluoride (BrF₅) gas.

 

Pseudohalogen

The pseudohalogens are polyatomic analogues of halogens, whose chemistry, resembling that of the true halogens, allows them to substitute for halogens in several classes of chemical compounds. Pseudohalogens occur in pseudohalogen molecules, inorganic molecules of the general forms Ps–Ps or Ps–X (where Ps is a pseudohalogen group), such as cyanogen; pseudohalide anions, such as cyanide ion; inorganic acids, such as hydrogen cyanide; as ligands in coordination complexes, such as ferricyanide; and as functional groups in organic molecules, such as the nitrile group. Well-known pseudohalogen functional groups include cyanide, cyanate, thiocyanate, and azide.

Examples of pseudohalogen molecules:

Examples of symmetrical pseudohalogens (Ps–Ps) include cyanogen (CN)2, thiocyanogen (SCN)2, selenorhodane (SeCN)2, azidodithiocarbonate (N3CS2)2. Another complex symmetrical pseudohalogen is dicobalt octacarbonyl, Co2(CO)8. This substance can be considered as a dimer of the hypothetical cobalt tetracarbonyl, Co(CO)4.

Examples of non-symmetrical pseudohalogens (Ps–X) are cyanogen halides (ICN, ClCN, BrCN), and other compounds. Sometimes nitrosyl chloride NOCl also is considered as pseudohalogen.

Not all combinations are known to be stable.

                                                            

Pseudohalides:

Pseudohalides are the anions (or functional groups) of corresponding pseudohalogen groups such as cyanides, cyanates, isocyanates, rhodanides (i.e. thiocyanates and isothiocyanates),selenocyanogens, tellurorhodanides and azides.

A common complex pseudohalide is tetracarbonylcobaltate (Co(CO)₄⁻). The acid HCo(CO)₄ is in fact quite a strong acid, though its low solubility renders it not as strong as the true hydrohalic acids.

The behavior and chemical properties of the above pseudohalides are identical to that of the true halide ions. The presence of the internal double bonds or triple bonds do not appear to affect their chemical behavior. For example, they can form strong acids of the type HX (compare HCl to HCo(CO)₄), and they can react with metals to form compounds like MX (compare NaCl to NaN₃).

Nanoclusters of aluminium (often referred to as superatoms) are sometimes considered to be pseudohalides since they, too, behave chemically as halide ions, forming Al₁₃I₂⁻ (analogous to I₃⁻) and similar compounds. This is due to the effects of metallic bonding on small scales.

Polyhalide Ions

Polyhalide ions

Halogens or interhalogens combine with halide ions to form polyhalide ions. The most common example of polyhalide ion formation is furnished by the increase in solubility of iodine in water in the presence of which is due to the formation of tri iodide ion, I^–₃

                 I^– + I₂ ———> I^–₃

Many other examples of polyhalides ions are

         (i) Cl₃^–, Br^–₃, ICI^˜₂, IBr^–₂ including I₃^–. In these ions, one of the halogen atoms (in case of similar atoms) or halogen atom larger in size undergoes sp³d-hybridization giving a linear shape with three lone pairs at equatorial positions.

         (ii) Cl₃⁺, Br₃⁺, I₃⁺, ICI₃⁺, IBr₂⁺ Here we find central atom sp³ hybridized giving a bent shape with two lone pairs of electrons on the central atom.

         (iii) ICI₄^–, BrF₄^–, I₃^–. Here central atom involves sp³d² hybridization giving square planar shape with two lone pairs of electrons on axial positions.

         (iv) ICI₄^–, BrF₄^–, I₅^–. In these ions central atom involves sp³d hybridization giving a distorted tetrahedral structure with one lone pair of electrons on equatorial position.

         (v) I₇^–, IF₆⁺. The central I atom  undergoes sp³d³ hybridization giving a distorted octahedral structure with one lone pair of electrons.

         (vi) I₇⁺, Here central I atom involves sp³d² hybridization giving an octahedral structure.

Fluorine due to its highest electronegativity (and only –1 oxidation state) does not form polyhalide ions where it acts as a central atom.

Polyhalides

 Polyiodides are specific polyhalides containing species such as I3", I7", Iq". Polyhalides often dissociate on heating the solid complexes. [c.320]

 INTER HALOGEN COMPOUNDS AND POLYHALIDES There are four types of interhalogen compound [c.345]

 The best known polyhalide is the triiodide ion, Ij", found when iodine dissolves in the aqueous solution of the iodide of a large unipositive cation (usually K ) [c.346]

 Alkyl Halides, Polyhalides, a-Halo Ketones and Esters [c.261]

 Iodine Halides and Polyhalides. Iodine forms six weU-defined compounds with the other haUdes (115,116). These compounds are readily formed by direct reaction of the two halogens (117). [c.365]

 It follows from the preceding discussion that the unbranched H bond can be regarded as a 3-centre 4-electron bond A-H B in which the 2 pairs of electrons involved are the bond pair in A-H and the lone pair on B. The degree of charge separation on bond formation will depend on the nature of the proton-donor group AH and the Lewis base B. The relation between this 3-centre bond formalism and the 3-centre bond descriptions frequently used for boranes, polyhalides and compounds of xenon is particularly instructive and is elaborated in [c.63]

 The linear polyhalide anion [F-C1-F] and the [c.827]

 The preparative utility of such reactions is, however, rather limited, and neither ICl or IBr has been much used except to form various mixed polyhalide species. Compounds must frequently [c.827]

 Typical examples of linear (or nearly linear) triatomic polyhalides are in Table 17.15 the structures are characterized by considerable variability of interatomic distances and these distances are individually always substantially greater than for the corresponding diatomic interhalogen (p. 825). Note also that for [c.835]

 Ref. 23, pp. 1534-63 (Polyhalide anions) and references therein. [c.835]

 Polyhalide Cations Structure Dimensions x/pm, y/pm Angle [c.836]

 The propensity for iodine to catenate is well illustrated by the numerous polyiodides which crystallize from solutions containing iodide ions and iodine. The symmetrical and unsymmetrical 13 ions (Table 17.15) have already been mentioned as have the I5- and anions and the extended networks of stoichiometry (Fig. 17.12). The stoichiometry of the crystals and the detailed geometry of the polyhalide depend sensitively on the relative concentrations of the components and the nature of the cation. For example, the linear ion may have the following dimensions [c.838]

 Other polyhalides, all singly charged, are formed from one halide ion together with other halogen or interhalogen molecules adding on, for example [ClIBr] , [IClJ . Many of these ions give salts with the alkali metal cations which, if the metal ion is large (for example the rubidium or caesium ion), can be crystallised from solution. The ion ICI4 is known in the solid acid, HICI4. dHjO, formed by adding iodine trichloride to hydrochloric acid. Many other polyhalide ions are less stable and tend to dissociate into the halide and interhalogen compound. [c.346]

 Cl-I-Br] the I-Cl distance is greater than the I-Br distance, and in [Br-I-I] I-Br is greater than I-I. On dissociation, the polyhalide yields the solid monohalide corresponding to the smaller of the halogens present, e.g. CsIClj gives CsCl and ICl rather than Csl + Clj. Likewise for CsIBrCl the favoured products are CsCl(s) + IBr(g) rather than CsBr(s) + ICl(g) or Csl(s) + BrCl(g). Thermochemical cycles have been developed to interpret these results. [c.836]

 Penta-atomic polyhalide anions [XY4] favour the square-planar geometry (D4h) as expected for species with 12 valence-shell electrons on the central atom. Examples are the Rb+ and Cs+ salts of [C1F4], and KBrp4 (in which Br-F is 189 pm and adjacent angles F-Br-F are 90 ( 2°). The symmetry of the anion is slightly [c.836]

Ionic Compound Propertie

Here are the properties shared by the ionic compounds. Notice that the properties of ionic compounds relate to how strongly the positive and negative ions attract each other in an ionic bond.

·         Ionic compounds form crystals.
Ionic compounds form crystal lattices rather than amorphous solids.Although molecular compounds form crystals, they frequently take other forms plus molecular crystals typically are softer than ionic crystals.

·         Ionic compounds have high melting points and high boiling points.
High temperatures are required to overcome the attraction between the positive and negative ions in ionic compounds. Therefore, a lot of energy is required to melt ionic compounds or cause them to boil.

·         Ionic compounds have higher enthalpies of fusion andvaporization than molecular compounds.
Just as ionic compounds have high melting and boiling points, they usually have enthalpies of fusion and vaporization that may be 10 to 100 times higher than those of most molecular compounds. The enthalpy of fusion is the heat required melt a single mole of a solid under constant pressure. The enthalpy of vaporization is the heat required for vaporize one mole of a liquid compound under constant pressure

·         onic compounds are hard and brittle.
Ionic crystals are hard because the positive and negative ions are strongly attracted to each other and difficult to separate, however, when pressure is applied to an ionic crystal then ions of like charge may be forced closer to each other. The electrostatic repulsion can be enough to split the crystal, which is why ionic solids also are brittle.

                            

·         Ionic compounds conduct electricity when they are dissolved in water.
When ionic compounds are dissolved in water the dissociated ions are free to conduct electric charge through the solution. Molten ionic compounds (molten salts) also conduct electricity.

·         Ionic solids are good insulators.
Although they conduct in molten form or in aqueous solution, ionic solids do not conduct electricity very well because the ions are bound so tightly to each other.

Covalent Compound or Molecular Compound Properties

These are properties of covalent compounds, also known as molecular compounds. Covalent compounds are a diverse group of molecules, so there are several exceptions to each 'rule'. When looking at a compound and trying to determine whether it is an ionic compound or a covalent compound, it's best to examine several properties of the sample.
 

·         Most covalent compounds have relatively low melting points and boiling points.
While the ions in an ionic compound are strongly attracted to each other, covalent bonds create molecules that can separate from each other when a lower amount of energy is added to them. Therefore, molecular compounds usually have low melting and boiling points.

·         Covalent compounds usually have lower enthalpies of fusion and vaporization than ionic compounds.
The enthalpy of fusion is the amount of energy needed, at constant pressure, to melt one mole of a solid substance. The enthalpy of vaporization is the amount of energy, at constant pressure, required to vaporize one mole of a liquid. On average, it takes only 1% to 10% as much heat to change the phase of a molecular compound as it does for an ionic compound.

·         Covalent compounds tend to be soft and relatively flexible.
This is largely because covalent bonds are relatively flexible and easy to break. The covalent bonds in molecular compounds cause these compounds to take form as gases, liquids and soft solids. As with many properties, there are exceptions, primarily when molecular compounds assume crystalline forms.

·         covalent compounds tend to be more flammable than ionic compounds.
Many flammable substances contain hydrogen and carbon atoms which can undergo combustion, a reaction that releases energy when the compound reacts with oxygen to produce carbon dioxide and water. Carbon and hydrogen have comparable electronegativies so they are found together in many molecular compounds.

·         When dissolved in water, covalent compounds don't conduct electricity.
Ions are needed to conduct electricity in an aqueous solution. Molecular compounds dissolve into molecules rather than dissociate into ions, so they typically do not conduct electricity very well when dissolved in water.

·         Many covalent compounds don't dissolve well in water.
There are many exceptions to this rule, just as there are many salts (ionic compounds) that don't dissolve well in water. However, many covalent compounds are polar molecules that do dissolve well in a polar solvent, such as water. Examples of molecular compounds that dissolve well in water are sugar and ethanol. Examples of molecular compounds that don't dissolve well in water are oil and polymerized plastic.

Note that network solids are compounds containing covalent bonds that violate some of these "rules". Diamond, for example, consists of carbon atoms held together by covalent bonds in a crystalline structure.

           Assignment : CHEMISTRY

NAME : KABIR HUSSAIN

 

ROLL:  03

 

CLASS: BS (HON) BOTANY 1^ST semester

 

SUBJECT: CHEMISTRY

 

SUBMITTED BY: KABIR HUSSAIN

 

SUBMITTED TO: SIR IMRAN

 

GOVT MURRAY COLLEGE  SIALKOT

RFERENCE

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                          TITLE

PROPERTIES OF P BLOCK ELEMENTS

INTERHALOGENS

PSUDOHALOGENS

POLYHALIDE IONS

POLYHALIDS

PROPERTIES OF IONIC COMPOUNDS

PROPERTIES OF COVALENT COMPOUNDS