30 votes
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What should be the oxidation state of oxygen in HOF (hypofluorous acid)?

Until the (recent) redefinition of the IUPAC, the concept of oxidation states was not as well defined as one would expect. I have discussed the issues of the old version and outlined the new ...
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24 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|} \...
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Is KF the most ionic compound?

Yes, this is a subtle thing. Using the Pauling electronegativities, one would expect CsF to have the larger electronegativity difference (3.2). So in principal, it should be "more ionic." ...
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Is HF the least acidic hydrogen halide?

First of all as @chipbuster says $\ce{HF}$ in diluted solutions in water is nearly completely dissociated and therefore shouldn't be called weak. Wikipedia describes this nicely and cites several ...
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Why is carbon dioxide nonpolar?

so wouldn't it be that you would have an even more positive carbon and 2 partially negative oxygens Yes, your analysis is correct to this point. A chemist would say that the bonds in $\ce{CO2}$ ...
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16 votes

How fast do electrons move around the nucleus?

The ratio of the speed of an electron traveling in the first Bohr orbit to the speed of light is given by the handy equation $$\mathrm{V_{rel}=\frac{[Z]}{[137]}}$$ where Z is the atomic number of ...
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15 votes

Electronegativity in krypton and xenon?

Why do Krypton and Xenon have high electronegativity? As you point out, krypton ($\ce{Kr}$) and xenon ($\ce{Xe}$) are members of the Noble gas family. They are generally unreactive (noble) because ...
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What happens if the electronegativity difference is exactly 2.1?

As mentioned above there is no hard line between an ionic and a covalent bond, they are just two ends of a spectrum where a bond can have a certain degree of ionic or covalent character. At the lower ...
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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 ...
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Why is zinc more reactive than copper?

You have to think about the whole process. When a metal loses electrons to make a metal ion the following happens: The metallic bonds holding the metal atoms together are broken. The metal atom ...
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What happens if the electronegativity difference is exactly 2.1?

Based on the the answer to this question: Why electronegativity difference greater than 1.7 are ionic? Here is a very nice graph of percent ionic character as function of electronegativity ...
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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 ...
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11 votes

Why is carbon dioxide nonpolar?

In understanding molecular polarity you need to take the whole structure into account. Your reasoning is correct as far as the parts of the molecule are concerned. The individual bonds are polar. ...
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Inductive effect and hyperconjugation - one elephant, different parts?

Are the inductive effect and hyperconjugation both different ways of looking at the same phenomenon I think so, both inductive and resonance (that's what hyperconjugation is after all) effects move ...
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11 votes
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Percentage ionic character when electronegativity is given

Linus Pauling proposed an empirical relationship which relates the percent ionic character in a bond to the electronegativity difference $\Delta \chi$. Percent ionic character $= (1-e^{-(\Delta \chi/...
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What is the explanation of the changes in stability going down a group for carbonates, bicarbonates, fluorides, and chlorides?

Carbonates The quote from your text: Carbonates of alkaline earth metals are insoluble in water and can be precipitated by addition of a sodium or ammonium carbonate solution to a solution ...
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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 $\mathrm{p}K_\mathrm{a}(\ce{X})$...
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Why is electronegativity increasing with oxidation state increase?

Yes absolutely, electronegativities are hardly static values when you start combining elements and forming ions or molecules. Electronegativity is simply a measure of an ability of an atom to ...
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Inductive effect of phenyl ring

As the $\mathrm{s}$ characteristic of an atom increases, so too does its electronegativity. Proof of this can be seen when comparing the $\mathrm{p}K_\mathrm{a}$'s of 2-carbon hydrocarbons. The $\...
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Is HF the least acidic hydrogen halide?

Hydrofluoric acid is the least acidic hydrogen halide because of fluorine's electronegativity. Because of the fluoride ion's small size, it cannot disperse the negative charge over a larger space and ...
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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 ...
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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 ...
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9 votes
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Electron distribution in a C-S bond

I think your lecturer would have been more correct had he said that the carbon-sulfur bond reacts as if the sulfur is slightly $\delta^{-}$ and the carbon slightly $\delta^{+}$. Sulphur is a larger ...
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9 votes

Why is carbon dioxide nonpolar?

The formula for the net dipole moment $\vec{\mu_{net}}$ of an overall neutral system of $n$ charged point particles is given by: $$ \vec{\mu_{net}} = \sum\limits_{i}^{n} q_i\vec{r_i} $$ where $q_i$ ...
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Hydrogen halide acidity

Yes, you are on the right track, let's look at the situation in more detail. In the haloacid equilibrium $$\ce{HX <=> H+ + X-}$$ anything that stabilizes HX will push the equilibrium to the ...
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9 votes
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Structures for NO+ (Nitrosonium)

Which is a better Lewis structure? There is no such thing as a better or a worse Lewis structure. They should be properly referred to as major or minor resonance contributors/forms. I looked up a ...
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Why is OH group activating towards electrophilic aromatic substitution?

The oxygen in the $\ce{-OH}$ group in phenol has unpaired electrons that are capable of being donated to the ring. Although oxygen is electronegative and does exhibit some I- effects, the electron ...
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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 ...
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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 ...
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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. ...
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