2] Answer the questions (a)-He) referring the diagrams (Figs 1 and 2) and the te

Question

2] Answer the questions (a)-He) referring the diagrams (Figs 1 and 2) and the terms given below 20 20 Fig.1 First ionization energy in eV (ordinate) vs Fig 2 Atomic radius in 100 m (ordinate) vs atomic atomic number Z(abscissa) number Z (abscissa). Terms: nuclear charge, Coulomb (electrostatic) attracive force, Coulomb potential energy, electron shells, distance from the nucleus, shielding effect of electrons (a) Give the definition of the first ionization energy (first ionization poterbial, h) b) Discuss the trend in the first i onization energy with increase in the atomic number (i.e., on going to the right hand side) for the Period 2 elements c) Electron affnties (EA) of He, Ne. A, Kr, and Xe are 05,1210, 10,and-0.8 eV. respectively, Account for the trend Iin the glectronegathvity on going down the Group 18 (d) The ionization energy of H is 13.6 eV Calculate this energy per mole of H atoms in the unit of kJ molr ()Calculate the wavelength (in nm) of a photon that is able to ionize a H atom

Explanation / Answer

1)First Ionization Energy:The first ionization energy is the energy required to remove one mole of most loosely held electrons from one mole of gaseous atoms to produce 1 mole of gaseous ions each with a charge +1.

2)Normal trend of ionisation energies is to increase across a period.Ionisation energy is the energy needed to pull away an electron from the nucleus.In period 2 the outer electrons are in 2s ans 2p orbitals screened by 1s orbital.From lithium to neon the number of protons and electrons increase.it causes greater attraction between the electrons and nucleus,so increases the ionisation energy.Increasing nuclear charge attracts the outer electrons closer to the nucleus.But there is a drop between Be to B and there is another drop between N to O.

Be 1s22s2 1st ionisation energy =900kj

B 1s22s22p1 1st ionisation energy=799kj

first ionisaion energy of Be is more than B .because boron's outer electron is in 2p orbital but beryllium's outer electron is in 2s orbital.The increased distance causes lesser attraction so reduced ionisation energy.2p orbital screened by both 2s and 1s orbital.so reduce the pull from the nucleus so reduced ionisation energy.

N 1s22s22p3 1st ionisation energy1400 kj

O 1s22s22p4 1st ionisation energy 1310 kj

Now half filled orbitals and full filled orbitals are stable than any other electron configuration.here N have half filled orbital but O dont have .but after 1st ionisation oxygen will get stable half filled configuration,so O loose its outer electron more readily than N so O have lesser 1st ionisation energy

3.electronegetivity describes the tendency of an attom to attract electrons towards itself.electron affinity is the amount of energy released when an electron added to atom or molecule.

so from the electron affinity value we can understand,

from He to Ne electronegetivity increase.from Ne to Ar electronegetivity decrease,Ar and kr have almost same electronegetivity,from kr to xe electronegetivity decrease.

d)1ev=1.602*10-19 joule

13.6eV=2.18*10-18joule

this is the energy needed to remove 1 electron from 1 hydrogen atom.for 1 mol we need to multiply with avogadro number

E=2.18*10-18*6.02*1023=13.123*105J/mol=1312kj/mol

e)E=13.6*1.60*10-19=2.18*10-18J

E=hc/lambda

wave length(lambda)=hc/E=6.63*10-34*3*108/2.18*10-18=9.12*10-8m=.91.2nm

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