26 votes

Which molecule is more acidic: CHF3 or CHBr3?

The following table contains some relevant data, the $\mathrm{p}K_\mathrm{a}$'s of the various haloforms along with the Pauling electronegativity of the corresponding halogen. \begin{array}{|c|c|c|} \...
ron's user avatar
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16 votes
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Why a higher s character increases a carbon atom's electronegativity?

Electronegativity is the power of an atom to attract bonding pairs of electrons to itself. It clearly depends on the nuclear charge: the larger it is, the more strongly the nucleus attracts electrons ...
Wildcat's user avatar
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15 votes
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Why does C=O have a larger dipole moment than C-O?

According to Wikipedia, bond dipole moment depends on: Distance between atoms and Overall charge difference, not just electronegativity difference. Resonance tells us that there is some amount ...
Dennis Cao's user avatar
11 votes

Strongest negative inductive effect group between trimethylammonium, ammonium and dimethylsulfonium groups

The inductive effect can be quantitatively measured by the Hammett equation $$\sigma(\ce{X}) = \mathrm{p}K_\mathrm{a}(\ce{H}) - \mathrm{p}K_\mathrm{a}(\ce{X})$$ where $\mathrm{p}K_\mathrm{a}(\ce{X})$...
orthocresol's user avatar
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10 votes
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Does 1-bromo-4-chlorobenzene have a permanent dipole moment?

As others have stated before in the comments, the molecule itself has a dipole moment, but it is indeed very, very small, to the point where you would say it is negligible. To illustrate this, I have ...
Martin - マーチン's user avatar
10 votes
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Strongest negative inductive effect group between trimethylammonium, ammonium and dimethylsulfonium groups

Methyl groups are great at stabilising carbenium ions via an inductive effect — which should actually be considered a resonance effect — known as hyperconjugation. This effect, which is actually due ...
Jan's user avatar
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10 votes

Which molecule is more acidic: CHF3 or CHBr3?

Experimentally, according to The Relative Rates of Formation of Carbanions by Haloforms J. Am. Chem. Soc., 1957, 79 (6), pp 1406–1412 the rates of formation of the corresponding anions from the ...
DavePhD's user avatar
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9 votes

Why is solid sodium hydride a base and not an acid when reacted with water?

The answer lies in electronegativity. Sodium has a significantly lower electronegativity ($\approx 1.0$) than hydrogen ($\approx 2.1$) meaning that hydrogen pulls electron density towards itself, away ...
Jan's user avatar
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9 votes

Why does NF3 have a smaller bond angle than NH3?

This can be argued on the basis of Bent's rule; concisely stated Atomic s character concentrates in orbitals directed toward electropositive substituents What follows below is a crude explanation. ...
getafix's user avatar
  • 8,475
9 votes

Is there a mathematical formula for electronegativity?

Electronegativity cannot be calculated from the number of subatomic particles in an atom. However, using Ionization Energy and Electron Affinity, one can calculate the Electronegativity of an atom ...
Ciambro's user avatar
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8 votes
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IChO problem involving the condensation point of NF3, NHF2, NH2F

The interactions do not limit to only dipole-dipole, which means positive charge is not everything. What's special about $\ce{NF3}$? It has no hydrogens. As a result, it cannot form hydrogen bond, ...
Huy Ngo's user avatar
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8 votes
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Li2O + 2KCl =2 LiCl +K2O: Is it a feasible Reaction?

Although every reaction is reversible in nature, let's try to understand where the equilibrium might be biased, i.e. whether the reactant side favoured or the product side. A rule of thumb while ...
Berry Holmes's user avatar
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8 votes

Does the dipole moment increase or decrease by increasing the bond length?

Strictly speaking, you can neither decrease nor increase the bond length a slightest bit.$\dagger$ All molecules of a given compound are equal. It is not like you may grab one with tiny pincers of ...
Ivan Neretin's user avatar
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8 votes

Confusion between electronegativity and electron affinity

I wouldn't shoot this down so quickly - consider, e.g. Mulliken electronegativity, defined as the average of the electron affinity and ionisation energy. If you think about it, electronegativity ...
orthocresol's user avatar
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7 votes
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Why does NF3 have a smaller bond angle than NH3?

The bond angle difference between $\ce{NH3}$ and $\ce{NF3}$ is not easily explained — but that is primarily because ammonia’s bond angles already violate the simple theories that work so well for ...
Jan's user avatar
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7 votes

Why an atom is more stable when only sublevels s and p are full?

Supposedly when explaining electronegativity and stability of an element, they tell you that it is more stable if the last level is full. No "supposedly" about it. That concept is ...
John Bollinger's user avatar
7 votes
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Why does ammonium chloride form an ionic bond?

Quick Answer Explicit valence of $\ce{N}$ is four, $\ce{N}$ of $\ce{NH4+}$ cannot form another (covalent) bond with $\ce{Cl-}$. The chemistry of $\ce{NH4+}$, owing to similar size, charge, and ...
ananta's user avatar
  • 2,299
6 votes

How is Al2Cl6 covalent and Al2O3 ionic?

You are right that the difference in electronegativity is responsible for the ionic bonds in aluminum and oxygen, and normally that would be the case with chlorine too, but $\ce{Al2Cl6}$ is a special ...
AS_1000's user avatar
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6 votes

Difference between electropositivity and electronegativity

Background: Electropositive implies having tendency to lose electrons to form positive ions. Electronegative implies having tendency to gain electrons to form negative ions. Electronegativity is a ...
JM97's user avatar
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6 votes

Is the inductive effect always measured relative to hydrogen?

Your definition is falling apart because you are over-applying it. In the definition, you can see that it says: ...transmission of charge through a chain of atoms in a molecule... It doesn't make ...
ringo's user avatar
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6 votes

Why does NF3 have a smaller bond angle than NH3?

When you're comparing bond angles between $\mathrm{NH_{3}}$ and $\mathrm{NF_{3}}$, you'd want to take the electronegativities the of hydrogen and fluorine into consideration. Fluorine hits a 3.98 on ...
paracetamol's user avatar
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6 votes
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What is the most polar covalent bond?

There are various electronegativity scales. Electronegativity vales from Wikipedia $$\newcommand{\d}[2]{#1.&\hspace{-1em}#2} \begin{array}{lrl} \hline \text{Element} & \text{Pauling} & \...
MaxW's user avatar
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6 votes

Bond angles in NH3 and NCl3

As Tan Yong Boon stated, it is Bent’s Rule with which we can explain the lower bond angle of $\ce{NF3}$ when compared to $\ce{NH3}$. The rule as stated by Henry Bent: Atomic s character ...
MollyCooL's user avatar
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6 votes

Reference for electronegativities of different metal oxidation states

Pearson conveniently lists cumulative experimental data in the 1988 paper [1], referrring to the earlier work of Moore [2]. Selected values of $I$ (ionization potential), $A$ (electron affinity), $χ$ (...
andselisk's user avatar
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6 votes
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Why are Tyrosine and Tryptophan considered hydrophobic?

Unlike that in organic chemistry, polar and non-polar compounds determination is done differently in biochemistry, probably because most biochemical reactions are done in aqueous medium. Therefore, ...
Mathew Mahindaratne's user avatar
6 votes
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Why is a sodium chloride molecule stable?

What you have calculated is the energy required to make two separated ions out of two separated $\ce{Na}$ ad $\ce{Cl}$ atoms. When they are separated, these ions do not make a molecule or a crystal of ...
Maurice's user avatar
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5 votes
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Allred-Rochow vs Pauling Electronegativity scale

Neither scale is 'more accurate'. As The_Vinz said, each scale may be applied in different areas, and there is a moderately good correlation between the two scales once conversion factors are ...
gannex's user avatar
  • 2,334
5 votes

Does the dipole moment increase or decrease by increasing the bond length?

If the same point charges are separated by a larger distance, that's a higher dipole moment. In the real world, you have to regard the distance and the actual charge difference and distribution. In ...
Karl's user avatar
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5 votes
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Bond angles in NH3 and NCl3

The bond angle of a molecule depends on several factors. We have to look at all the factors and then decide the result according to them. The difference in bond angles in $\ce{NF3}$ and $\ce{NH3}$ is ...
Soumik Das's user avatar
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