Theory Flashcards
Bonding, what? And valency?
Lattice energy is nothing but bonding energy (energy req to form/break the bond, both are equivalent)
Force of attraction that exists between 2 atoms which is responsible for combining them.
Valency is the combining power of an atom.
Electrovalent compounds are good conductors of electricity. True/False.
False.
Ioniccompoundsdon’t conduct electricityvery well because the charge carriers can’t move through the crystal. They canconductheat because the kinetic energy itself is the “heat carrier” - it can be transferred without moving ions too far from their mean positions.
We can say that Electrovalent compounds conduct electricity in fused state.
Ionic compounds are easily available and are hard and brittle in nature. Edit. Also, give other characteristics.
Ionic compounds are in fact hard and brittle in nature but not so easily available.
~Formed between electropositive and electronegative elements.
~They have a high dielectric constant.
~Soluble in water but insoluble in organic solvent.
~High MP and high BP.
~Do not show isomerism.
~high polarity
Dielectric constant
In chemistry and this chapter specifically, dielectric constant reveals certain properties of the solvent Eg. Whether it is polar or non polar.
Dielectric constant increases with increase in polarity.
P h y j e e k s
dimension less, ratio of permittivityof a substance to thepermittivityof free space. Dielectric constantis proportional to the ratio of polarization density (P) and electric field (E) which meansdielectric constantis inversely proportional to electric field. The Electric field (E) inside aconductoris always zero under the static situation so thedielectric constantforconductoris infinite.
Ionic compounds/solids have a higher MP/BP than Covalent compounds or solids?
Cov. Solids > Ionic > Cov. Compounds
Discuss properties of ionic compounds.
Ionic compounds are in fact hard and brittle in nature but not so easily available.
~Formed between electropositive and electronegative elements.
~They have a high dielectric constant.
~Soluble in water but insoluble in organic solvent.
~High MP and high BP.
~Do not show isomerism.
~high polarity
1) . Ionic crystals dissolve in water? How come?
2) . Is it necessary for all ionic comp to dissolve in water? Why/why not?
2) . S o l u b i l i t y , say whaaaaat? Factors.
Bring Lattice energy, hydration energy into discussion.
“Water decreases the interionic attraction in Crystal lattice due to solvation”
No, not necessary for all ionic comp to dissolve in water. Solubility depends on many other factors like lattice energy and hydration energy.
When put in a solvent say water, the solute-solute interaction weakens and solute-solvent interactions pop up (“mixing” and thereby forming a solution, “Water decreases the interionic attraction in Crystal lattice due to solvation”). The amount of energy released in these solute-solvent reactions is known as hydration energy/solvation energy.
MORE IMPORTANTLY,
IF LE > HE : i n s o l u b l e
IF LE < HE : s o l u b l e
Arrange the following in increasing % ionic character and increasing ionic strength:
AlN , Al₂O₃ , AlF₃
% ionic character/ionic nature is decided by EN (charge and radius ratio q/r)
16(Xₐ - Xᵥ) + 3.5(Xₐ - Xᵥ)²
EN difference increases, ionic character increases
% AlN < Al₂O₃ < AlF₃
Whereas the stability and strength is dependent on lattice energy (which depends on charge)
~ AlN > Al₂O₃ > AlF₃
Here charge on EN atoms: -3, -2, -1
Greatest charge on N, hence highest stability
Another example: NaF , MgO , AlN
Out of these three the lattice energy of AlN will be the highest hence maximum stability.
Why is attraction always associated with decrease in energy?
It involves work being done by the system, hence decrease in energy and increased stability.
Question: solubility order.
BeSO₄ , MgSO₄ , SrSO₄ , BaSO₄ , CaSO₄
(What is constant, what is considered? A/c to what rule?)
NaCl , KCl , CsCl , RbCl
In the first case, the charge is same on all so LE is almost same so HE is considered.
As a principle for solubility, if one of the two ions is large, the other has to be small.
So here, since SO₄²⁻ is large, the cation has to be small.
Accordingly, BeSO₄ > MgSO₄ > CaSO₄ …
Opposite in Crystal halites, since Cl⁻ is a small anion so we look for a big cation
CsCl > RbCl > KCl > NaCl
Give some examples of ionic compounds for all three states. Why isn’t it considered as a real bond?
Just solids. Don’t exist in gaseous or aqueous state. But molten/fused state, yes.
Ionic bond is in essence just electrostatic force of attraction at play, no overlapping, no sharing; just a mere exchange of electrons. In this aspect, Covalent bond would be called a (real) bond in the truest sense of the word.
Why don’t ionic compounds exhibit isomerism?
Why are we able to measure the reaction rate for reactions involving Covalent comp/solids but not ionic ones?
1) . Because of their non directional nature
2) . Because the reaction rate of both differs greatly. Ions react at a greater speed and we’re unable to measure the rate at which they do so. Atoms on the other hand react at a comparatively lesser speed.
Sodium chloride’s Crystal is actually one cation/anion surrounded by its counter ion. Why still do we use NaCl and not Na₆Cl₆ ? And it isn’t like another of such doesn’t exist, say C₆H₆?
Formula of ionic compound requires empirical formula, not molecular formula. Whereas no such rule is there for Covalent compounds, lime benzene, where molecular formulae are required.
What determines the relative strength of sigma and pi bonds?
1) . Type of overlapping
2) . Axis across orbital
