Classification of Elements 4 Flashcards
what is electron gain enthalp
When an electron is added to a neutral gaseous
atom (X) to convert it into a negative ion, the
enthalpy change accompanying the process is
defined as the Electron Gain Enthalpy (∆egH).
Electron gain enthalpy provides a measure of
the ease with which an atom adds an electron
to form anion
X+ e- —-> X-
are e- gain enthalpies +ve or -ve
Depending on the element, the process of
adding an electron to the atom can be either
endothermic(+ve) or exothermic(-ve) . For many elements
energy is released when an electron is added
to the atom and the electron gain enthalpy is
negative.
what is the e-gain enthalpies of halogens and that of noble gases
group 17 elements (the
halogens) have very high negative electron gain
enthalpies because they can attain stable noble
gas electronic configurations by picking up an
electron.
On the other hand, noble gases havelarge positive electron gain enthalpies because
the electron has to enter the next higher
principal quantum level leading to a very
unstable electronic configuration.
How does electronegativity vary across a period
electron gain enthalpy becomes more negative with increase in the atomic number across a period. The effective nuclear charge increases from left to right across a period and consequently it will be easier to add an electron to a smaller atom since the added electron on an average would be closer to the positively charged nucleus
How does electron gain enthalpy vary down a group
We should also expect electron gain enthalpy to become less negative as we go down a group because the size of the atom increases and the added electron would be farther from the nucleus.
The electron gain enthalpy of O/F is more than in S/Cl why
electron gain enthalpy of O or F is less negative than that of the succeeding element. This is because when an electron is added to O or F, the added electron goes to the smaller n = 2 quantum level and suffers significant repulsion from the other electrons present in this level. For the n = 3 quantum level (S or Cl), the added electron occupies a larger region of space and the electron-electron repulsion is much less.
Which of the following has the most negative electron gain enthalpy and which the least negative?
P,S,Cl,F.
Explain your answer.
Electron gain enthalpy generally becomes more negative across a period as we move from left to right. Within a group, electron gain enthalpy becomes less negative down a group. However, adding an electron to the 2p-orbital leads to greater repulsion than adding an electron to the larger 3p-orbital. Hence the element with most negative electron gain enthalpy is chlorine; the one with the least negative electron gain enthalpy is phosphorus because it has half filled orbitals and has extra stability
Would you expect the second electron gain enthalpy of O as positive, more negative or less negative than the first? Justify your answer.
When an e- is added to an oxygen atom, energy is released ie ΔegH 1 is -ve and large.
O +e- ——> O-
When an e- is added to the O- ion, energy will be absorbed due to overcome the large electrostatic force of repulsion between the electron and the negatively charged ion.
O- + e- ——>O2-
What is electronegativity
A qualitative measure of the ability of an atom in a chemical compound to attract shared electrons to itself is called electronegativity. Unlike ionization enthalpy and electron gain enthalpy, it is not a measureable quantity.
How can electronegativity be measured
a number of numerical scales of electronegativity of elements viz., Pauling scale, Mulliken-Jaffe scale, Allred-Rochow scale have been developed. The one which is the most widely used is the Pauling scale.
How does electronegativity vary across a period
Electronegativity increases as we move from left to right across a period. The attraction between the nucleus and electrons increases as the atomic radius decreases . Hence electronegativity also imcrease
How does electronegativity vary down a group
The electronegativity decreases down a group because atomic radius increases and attraction b/w nucleus and electrons decrease
How is electronegativity related to non-metallic and metallic character
Non-metallic elements have strong tendency to gain electrons. Therefore, electronegativity is directly related to that non-metallic properties of elements. It can be further extended to say that the electronegativity is inversely related to the metallic properties of elements. Thus, the increase in electronegativities across a period is accompanied by an increase in non-metallic properties (or decrease in metallic properties) of elements. Similarly, the decrease in electronegativity down a group is accompanied by a decrease in non-metallic properties (or increase in metallic properties) of elements.
