Zero group elements

Description,general properties and reaction of zero group elements

1. ZERO GROUP ELEMENTS BY, MS. LIPSA SAMAL ASST. PROF. ( PA & QA) SCHOOL OF PHARMACY AND LIFE SCIENCES, CENTURION UNIVERITY OF TECHNOLOGY AND MANAGEMENT, BHUBANESWAR, 2020

2. INTRODUCTION The  elements  which have a stable electronic configuration(octet in nature which makes them stable and unable to gain or lose electrons) and have very little or  zero  tendency to react with other  elements  are called  zero group elements  or inert gases or  zero   valent gases.   Elements  included under this  group  are helium, neon, argon, krypton, xenon and radon.

3. General Properties 1. Electronic Configuration : All noble gases have general electronic configuration ns2np6 except helium which has 1s2. Many properties of noble gases including their inactive nature are ascribed to their closed shell structures. 2. Ionisation Enthalpy (amount of energy that an isolated gaseous atom requires to lose an electron in its ground state) Due to stable electronic configuration these gases exhibit very high ionisation enthalpy. However, it decreases down the group with increase in atomic size. 3. Atomic Radii: (measure the size of atom) (by measuring the nucleus of two touching atom) Atomic radii increase down the group with increase in atomic number. 4. Electron Gain Enthalpy (amount of energy released when an electron is added to an isolated gaseous atom) • Since noble gases have stable electronic configurations, they have no tendency to accept the electron and therefore, have large positive values of electron gain enthalpy.

4. Physical Properties • Monoatomic - colourless , odourless & tasteless. • Sparingly soluble(100 to 30) in water. Have very low m.p . and b.p . because the only type of interatomic interaction in these elements is weak dispersion forces. • Helium has the lowest b.p . (4.2 K) of any known substance. • It has an unusual property of diffusing through most commonly used laboratory materials such as rubber, glass or plastics.

5. Chemical Properties In general, noble gases are least reactive. Their inertness to chemical reactivity is attributed to the following reasons: ( i ) Noble gases except helium (1s2) have completely filled ns2np6 electronic configuration in their valence shell. (ii) Have high ionisation enthalpy and more + ve electron gain enthalpy. The noble gases have weak  interatomic force , and consequently have very low  melting  and  boiling points . They are all  monatomic   gases  under  standard conditions , including the elements with larger  atomic masses  than many normally solid elements.

6. Helium has several unique qualities when compared with other elements: its boiling point at 1  atm is lower than those of any other known substance; it is the only element known to exhibit   superfluidity (flow with out viscocity and with out the loss of energy) it is the only element that cannot be solidified by cooling under standard conditions—a  pressure  of 25  standard atmospheres  (2,500  kPa ; 370  psi ) must be applied at a temperature of 0.95 K (−272.200 °C; −457.960 °F) to convert it to a solid. The noble gases up to xenon have multiple stable  isotopes . Radon has no  stable isotopes ; its longest-lived isotope,  222 Rn , has a  half-life  of 3.8 days and decays to form helium and  polonium , which ultimately decays to  lead .

7. Uses of Noble gases: Helium is a non-inflammable and light gas. Hence, it is used in filling balloons for meteorological observations. It is also used in gas-cooled nuclear reactors. Liquid helium finds use as cryogenic agent for carrying out various experiments at low temperatures. • It is used to produce and sustain powerful superconducting magnets which form an essential part of modern NMR spectrometers and Magnetic Resonance Imaging (MRI) systems for clinical diagnosis. • It is used as a diluent for oxygen in modern diving apparatus because of its very low solubility in blood. Ne is used in discharge tubes and fluorescent bulbs for advertisement display purposes. Ne bulbs are used in botanical gardens and in green houses. • Ar is used mainly to provide an inert atmosphere in high temperature metallurgical processes (arc welding of metals or alloys) and for filling electric bulbs. It is also used in the laboratory for handling substances that are air-sensitive.

8. Xenon has various applications in incandescent lighting, x-ray development, plasma display panels (PDPs), and more. Nuclear fission  products may include several radioactive isotopes of xenon, which absorb neutrons in nuclear reactor cores. The formation and elimination of radioactive xenon decay products are factors in nuclear reactor. Radon is reported as the second most frequent cause of lung cancer, after cigarette smoking. However, it also has beneficial applications in radiotherapy, arthritis treatment, and bathing. In radiotherapy, radon has been used in implantable seeds, made of glass or gold, primarily used to treat cancers. krypton can be found in energy efficient windows. Because of its superior thermal efficiency, krypton is sometimes chosen over argon for insulation. Krypton is also found in fuel sources, lasers and headlights. In lasers, krypton functions as a control for a desired optic wavelength Krypton is used for high performance light bulbs, which have higher color temperatures and efficiency because the krypton reduces the rate of evaporation of the filament.

9. Xenon is an element under the Noble gases group and is on period 7 of the periodic table. This element is most notable for its bright luminescence in light bulbs. Xenon is unique for being the first noble gas element to be synthesized into a compound. Isotopes Nine naturally occurring isotopes of xenon exist. They are xenon-124, xenon-126, xenon-128, xenon-129, xenon-130, xenon-131, xenon-132, xenon-134, and xenon-136.

10. Crystal Lattice Structure As a solid noble gas, solid xenon is structured as face centered cubic (FCC). This is also known as the CCP, which is the cubic closest packing. This crystal lattice structure is the closest that atoms can be packed into a cube. In the FCC structure, there is one atom at each corner and one atom at each face of the cube. The structure fits four atoms in each lattice cube. Face centered cubic structures are the most dense. Atomic radii :  Increases down the table. Reason : The radii is constantly increasing because the nucleus is gaining more protons, therefore affording to attract more electrons. For example, with an atomic number of 2, helium can only hold 2 electrons. On the other hand, Xenon has an atomic number of 54, which allows the element to hold 54 electrons. This brings the electron cloud to the 5p orbital. Boiling point:   Increases down the table. As you go down the periodic table of the noble gases, there are more electrons, creating more Van Der Waals forces. We know that boiling points depend on the strength of the bonds. The stronger the bonds, the more energy it needs to drive structure to entropy, therefore having a higher boiling point. Ionization energies :  Increases going up the table because it's harder to remove electrons from smaller atoms.

11. Crystal Lattice Structure structure is a description of the ordered arrangement of  atoms ,  ions  or  molecules  in a  crystalline material . Each point represents one or more atoms in the actual  crystal , and if the points are connected by lines, a  crystal lattice  is  formed ; the  lattice  is divided into a number of identical blocks, or unit cells. This is called a  body-centered cubic (BCC) solid . Atoms in the corners of a BCC unit cell do not contact each other but contact the atom in the center. Any atom in this structure touches four atoms in the layer above it and four atoms in the layer below it. Thus, an atom in a BCC structure has a coordination number of eight.

12. Xenon-fluorine compounds Xenon reacts directly with  fluorine  because  fluorine  is a very powerful oxidizing agent (electron acceptor) (hence it gets reduced and it gains an electron from Xenon). Xenon forms three binary fluorides, XeF2, XeF4 and XeF6 • Xe (g) + F2 (g) → XeF2(s) (xenon in excess) • Xe (g) + 2F2 (g) → XeF4(s) (1:5 ratio) • Xe (g) + 3F2 (g) → XeF6(s) (1:20 ratio) • XeF6 can also be prepared by the interaction of XeF4 and O2F2 at 143K. XeF4 + O2F2 → XeF6 + O2 • XeF2, XeF4 & XeF6 are colourless crystalline solids and sublime readily at 298 K. They are powerful fluorinating agents. They are readily hydrolysed even by traces of water. For example, XeF2 is hydrolysed to give Xe , HF and O2. 2XeF2 (s) + 2H2O(l) → 2Xe (g) + 4 HF( aq ) + O2(g) Xenon-fluorine compounds  

13. in XeF2, Xenon  is sp3d hybridised and the molecule has linear  structure. Xe has 8 valence electrons. That is, s2 p6 configuration. Each Fluorine atom has 1 unpaired electron. Xe : s2 p6 (ground state) Xe : s2 p5 d1 (excited state, with 2 unpaired electrons) The 2 unpaired electrons of Xe are paired by the unpaired electrons of 2 F atoms. So, totally 5 electron pairs { 2 bond pairs(axial),3 lone pairs(equatorial)}. Thus, 5 sp3d hybridized orbitals are formed. Hence, Hybridisation : sp3d and Shape: Trigonal bipyramidal in XeF4, Xenon  is sp3d2 hybridised and the molecule having geometry Square Planar. in XeF6, Xenon  is sp3d3 hybridised and the molecule having distorted octahedral structure.

14. • XeF2 and XeF4 have linear and square planar structures resp. • XeF6 has 7 electron pairs (6 bonding pairs and one lone pair) and would, thus, have a distorted octahedral structure as found experimentally in the gas phase. Xenon-fluorine compounds • Xenon fluorides react with fluoride ion acceptors to form cationic species(+ ve ) and fluoride ion donors to form fluoro anions(- ve ). XeF2 + PF5 → [ XeF ]+ [PF6]– XeF4 + SbF5 → [XeF3]+ [SbF6]– XeF6 + MF → M+ [XeF7]– (M = Na, K, Rb or Cs) Xenon-fluorine compounds

15. Xenon-oxygen compounds • Hydrolysis of XeF4 and XeF6 with water gives Xe03. 6XeF4 + 12 H2O → 4Xe + 2Xe03 + 24 HF + 3 O2 XeF6 + 3 H2O → XeO3 + 6 HF • Partial hydrolysis of XeF6 gives oxyfluorides , XeOF4 and XeO2F2. XeF6 + H2O → XeOF4 + 2 HF XeF6 + 2 H2O → XeO2F2 + 4HF • XeO3 - colourless explosive solid - pyramidal molecular structure. XeOF4 - colourless volatile liquid - square pyramidal molecular structure

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