Questions tagged [periodic-trends]

Trends which are observed in the properties of elements as you move along the periodic table in a given direction.

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When the basicity of hydroxides of group 1A and group 2A increase down the group, why do we have NaOH as the strongest base?

When the basicity of hydroxides of group 1A and group 2A increase down the group, why do we have $\ce{NaOH}$ as the strongest base located at the top of group 1A? Shouldn't, if the trend is followed, ...
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Why is the electronegativity of potassium and rubidium same?

The electronegativity of potassium and rubidium is reckoned at 0.82 for both. Why is it same for both of them? Shouldn't it be less for rubidium as compared to potassium owing to the addition of one ...
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284 views

Covalent atomic radii: oxygen vs nitrogen

Many books state that $R_\ce{N} > R_\ce{O}$ which is in accordance with the general trend. However, some books say that $R_\ce{O} > R_\ce{N}$ because of repulsion caused by pairing of electrons. ...
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Is there an opposite to shielding effect? [closed]

I recently read about shielding effect and lowering of effective nuclear charge due to penetration of other electrons. I wonder while doing calculations involving Slater's rules the electrons from ...
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why lawrencium is placed in f-block elements although its last electron enters in 6d-subshell?

The electronic configuration of lawrencium ($\ce{Lr}$) is $\mathrm{[Rn] 7s^2 5f^{14} 6d^1}$. As its last electron enters the $\mathrm{6d}$ sub shell, it should be a part of $\mathrm{d}$-block elements,...
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86 views

Trend in atomic volume across a period [closed]

"Atomic volume decreases along a period, reaches a minimum at the middle, and then increases for the rest of the period" Why does the atomic volume, along a period, initially decrease, ...
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Why does solubility of Carbonate salts of Alkali metals in water increase down the group?

Carbonate salts have a very large anion so hydration energy should dominate over lattice energy. Since hydration energy is inversely proportional to radius of ion, I would expect Lithium to release ...
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147 views

What is the structure of CF3 radical? [duplicate]

In the class, I was told that $\ce{H3C^.}$ has a trigonal planar structure with the unpaired electron in $\mathrm{2p_z}$ orbital. But $\ce{H3C -}$ has a trigonal pyramidal structure. But why does ...
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Why doesn't core charge increase down a group? [closed]

Atomic radius increases down a group because the electrons feel a lesser attraction to the positive nucleus (due to shielding from inner shells). Why then, doesn't core charge decrease seeing as core ...
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87 views

Why is ionization energy of indium less than gallium?

In group 13 we observe an irregular trend in ionization energy: B > Tl > Ga > Al > In. Gallium has a filled 3d subshell, but indium has a filled 4d and 3d subshell. Thus it should have more poor ...
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Why is the strontium ion smaller than the potassium ion? [closed]

The ionic radius of the $\ce{Sr^2+}$ ion is $\mathrm{132\,pm}$, while the ionic radius of the $\ce{K^+}$ ion is $\mathrm{152\,pm}$. Why is this the case? I would have thought that since $\ce{K^+}$ has ...
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Is the magnitude of ionisation enthalpy and ionisation energy is same?

In my textbook it is written that ionisation energy and ionisation enthalpy are two different quantities. ionisation energy is the amount of energy provided to extract an electron from the outermost ...
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Why is platinum denser than gold?

The atomic masses of gold and platinum are 196.96657 u and 195.084 u respectively, meaning that (on average) an individual gold atom is heavier than an individual platinum atom. At the same time, the ...
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Scale to be considered for comparing electronegativities of nitrogen and chlorine

The Pauling scale gives the $\chi$ values of $\ce{N}$ and $\ce{Cl}$ to be $3.04$ and $3.16,$ respectively, but the Allen scale gives the $\chi$ values of $\ce{N}$ and $\ce{Cl}$ to be $3.066$ and $2....
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Why is phosphorus trifluoride the strongest Lewis acid among the phosphorus trihalides?

I had read that for the trihalides of boron, boron trifluoride is the weakest Lewis acid due to backbonding. The order I had seen was - $\ce{BI3 > BBr3 > BCl3 > BF3}\$ $$\ce{}$ $- order of ...
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Comparing Electron affinity and electron gain enthalpy at 0 K

In my book it is given that first electron gain enthalpy is greater than second for elements. Should we compare the magnitudes in such cases or the actual numbers with signs? Does the same comparision ...
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why is lithium oxide so different from water [closed]

Take water and replace hydrogens with the next element down in the periodic table, and you get a white solid, nothing like water. https://en.wikipedia.org/wiki/Lithium_oxide Lithium itself is very ...
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Why does the electron affinity increase become more exothermic down group 2 and group 5?

It is generally true that the electron affinity becomes less exothermic down a group, because of the increase in atomic radius. There is a well-known exception that the electron affinity of Cl is ...
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Why aren't Boron and Aluminium assigned to group 3 of periodic table? What determines the group? [closed]

I've been curious about this 3D representation of the periodic table "Mendeleev's Flower" and was trying to study it, wondering if it reveals any regularities that are not obvious from classic ...
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109 views

Why is the first energy of ionization of oxygen lesser than that of nitrogen? [duplicate]

The following question arises from a question I found in my book. Experimentally it has been determined that the value of the first energy of ionization of oxygen is lesser than the first energy ...
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Is strontium more metallic than sodium? If yes then why?

I got an MCQ in my examination, "Which one of the following is more metallic?" and the options were Sr, Na, Be or Aluminium. I know that sodium is more metallic than Be or Al but my mind stuck on ...
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Why Zn has highest ionisation enthalpy in 3d series?

Zn which has the highest ionisation enthalpy in 3d series.The reason given in my textbook is: The value of zinc is higher because it represent ionisation from 4s level. This is not correct because ...
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515 views

Reorganization during ionisation for d block elements

This is a quote from my textbook: The irregular trend in the first ionisation enthalpy of 3d lmetals,can be accounted for by considering that the removal of one electron alters the relative ...
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Shielding effects and atomic size [closed]

The atomic size on going from aluminum to gallium decreases because of poor shielding effect of the $(n-1)d$ electrons, but on going from copper to zinc, the size increases due to the same shielding ...
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Why does hydrogen have a lower ionization energy than fluorine?

I found here that the ionization energy of hydrogen is $\pu{1312kJ/mol}$ and for fluorine, it is $\pu{1681kJ/mol}$. Now clearly, from the data, we can see that hydrogen has a lower ionization energy ...
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423 views

What do you mean by “periodic” in the periodic table? [closed]

Modern periodic law states: “The physical and chemical properties of the elements are periodic functions of their atomic numbers”. But I don't think this is so! (Forgive me for my stupidity. But ...
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How ion size/electronegativity influences strength of an acid

My prof was explaining how we can use the structure of acids and bases to rationalize relative strengths (ie: acid X is stronger than acid Y because ...). He then went on to explain how when ...
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313 views

Is acidic character related to reducing power?

My book says that the acidic character of halogen acids increases on going down the group because the bond strength decreases, making it easier to release the $\ce{H+}$. But I also know that $\ce{HI}$...
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296 views

Electronegativity of heavier elements of Group 15

While reading about p-block I got to know that in Group 15 elements electronegativity value decrease down the group but amongst the heavier elements difference is not that much pronounced. I ...
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316 views

Why do atomic radii decrease across a period? [closed]

It's said that atomic size/radius decreases across a period, in spite of addition of electrons. But how does this actually work?
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666 views

Why is Aluminium oxide amphoteric?

I was reading my book, in which it mentioned that aluminium and gallium oxides are amphoteric and and indium and thalium oxide are basic in their properties. But no explanation was given. My main ...
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Effective nuclear charge and Ionization energy

A common reason given on why 3rd ionization energy > 2nd > 1st is because of increasing effective nuclear charge. As per my book $Z_\mathrm{eff}$ = Atomic number $-$ Number of inner electrons. Now ...
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How would one determine an element simply by looking at its binding energy?

I am self studying MIT OCW chemistry 5.111 2014, one of the lecture questions states the following: Consider a neutral atom with 8 distinct electron binding energies: −14 eV, −28 eV, −94 eV, −218 ...
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Standard Reduction Potentials and Electropositivity

I was looking through a table of standard reduction potentials and the trend seemed like it correlated with electropositivity. Is it reasonable to qualitatively compare two metals to see which has a ...
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220 views

Why does Calcium have a higher ionization energy than Aluminium?

Given their places on the periodic table I'd assume Aluminium has a higher ionization energy, because it has fewer energy levels, and is on a "righter" row on the periodic table, but in reality it is ...
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Why does the emission wavelength of sodium appear to be an exception despite the trend for ionisation enthalpies among alkali metals?

The wavelengths for emissions in the visible region for Group 1 elements is as follows: $$ \begin{array}{lc} \hline \text{Element} & λ/\pu{nm} \\ \hline \ce{Li} & 670.8 \\ \ce{Na} & 589.2 ...
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Ionization energy of neon vs its cationic counterpart

Which requires more ionization energy: $\ce{Ne}$ or $\ce{Ne+}?$ It seems to me like it should be neon because of noble gas configuration, but the answer given is $\ce{Ne+}.$ Does this anything to do ...
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Predicting atomic weight and density of calcium [closed]

I have a question from school: Assuming that the element Ca had not been discovered, predict using the properties of the known element surrounding Ca its own properties such as its atomic weight ...
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Ionization enthalpy for group 13 elements

The ionization enthalpy for elements along a group generally reduces. But there is an exception for group 13 elements and the order is not uniform. The order is: B>Tl>Ga>Al>In According to ...
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789 views

why lithium is less reactive than sodium? [duplicate]

Lithium lies above sodium in a group and is also smaller in size. According to periodic trend reactivity decreases from left to right in period and down the group.
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Relationship between electronegativity and atomic radius [closed]

Would someone please explain in detail the relationship between the two? I understand that atomic radius is related to ionisation energy but I can't see how atomic radius may be related to ...
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398 views

Which is more metallic: boron or silicon?

I read somewhere that boron is more metallic. Is it correct? If so, can you please elaborate? The reason why I'm confused is because 2 factors come into play here: When you move towards right, ...
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Change in electronegativity order down a group from groups 13-16 to group 17

In general, going down a group Zeff initially increases but then becomes approximately constant, while electrons are in higher n orbitals, hence valence electrons on average further from nucleus, ...
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Exception in trend of increasing ionisation energy across a period

One exception to the trend of increasing ionisation energy across a period in e.g. period 2 is going from N to O. There is no loss of exchange energy in I1 of O, but there is 2K lost in I1 of N, hence ...
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469 views

Why do metals form cations?

metals that have a low number of occupied shells such as lithium and potassium should have a stronger electrostatic attraction to their nuclei, so what causes them to always lose their electrons ...
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Ionisation energies of Carbon and Boron

The first ionisation energy of Carbon atom is greater than that of Boron atom whereas, the reverse is true for the second ionisation energy. In order to explain the above statement I considered the ...
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Thermal stability order of NaF, MgF2 and AlF3

I came up with a question to arrange thermal stability order of $\ce{NaF}$, $\ce{MgF2}$ and $\ce{AlF3}$ and I think the answer is $\ce{NaF>MgF2>AlF3}$ because $\ce{Na+}$ has largest ionic radius ...
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Why is fluorine a oxidising agent?

An oxidizing agent pulls the electron cloud of the substance being oxidized towards itself, for example: $$\ce{F2 + 2 X- -> 2F- + X2}\qquad (\ce{X} = \ce{Cl}, \ce{Br}, \ce{I})$$ We also know ...
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Lanthanoid Contraction

Why is the radius of Europium so unusually high and out of the general trend ? Moreover, at different sources I am getting different values of radii. In some (e.g., Wikipedia) the radii are following ...
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471 views

How can an electron shield another electron of the same subshell?

While I was preparing for my upcoming exams, I stumbled upon this sentence which is bothering me quite a bit: The contraction of the lanthanoids is due to the imperfect shielding of one electron by ...

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