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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Chemistry grade 11, Periodic trends

Which of the series below is ordered in ascending order? A) Radius of: H-, H and H + B) First ionization energy of: oxygen, fluorine and neon C) The electronegativity of: chlorine, bromine and iodine ...
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enthalpy of formation group 2 oxides

i understand the the trend for enthalpy of formation of alkaline earth metal oxides should become less exothermic moving down the group as the positive charge density decreases and the strength of the ...
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Why does the ionization enthalpy of elements across a period not follow a regular pattern while the atomic size always decreases?

First of all, I would like to mention that I am only talking about elements that aren't from the d or f blocks. In order to further elaborate on my question, I would like to take the third period as ...
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56 views

The quantum mechanics behind periodicity of elements

Especially in high school/first-year undergraduate chemistry courses, we learn with great dedication the periodicities along groups and periods. There are various useful and interesting trends. I ...
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46 views

Why is boiling point of Ammonia greater than Arsine?

I have previously read that the boiling point of Stibane(SbH3) is greater than Ammonia(NH3) as ammonia is gas at room temperature and no hydrogen bonding exists in the gaseous form of NH3. Hence, as ...
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745 views

Why doesn't ionization energy decrease from O to F or F to Ne?

I know that in general, the first ionization energy increases across a period due to increasing nuclear charge, reasonably constant shielding & decreasing atomic radius. From N to O, however, the ...
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41 views

Tendency of formation of complexes in Group-1 elements

My book states the following: Down the group(Group-1), tendency to form complexes decreases due to decrease in charge density$\bigg(\frac{\text{charge}}{\text{radius}}\bigg).$ This results in ...
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47 views

Why does this formula work?

My teacher gave us a formula for determining if a M-O-H like compound will act like a base or not.without explaining much. Base if:$$|\chi_o-\chi_M|\gt|\chi_o-\chi_H|$$ Flipped inequality if acid. I ...
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105 views

Question on d block contraction

For size trend down a group, it is known that:$$Al\gt Ga$$ Due, to d block contraction of gallium. Why isn't this the case when it comes to silicon and germanium? Won't the poor shielding effect from ...
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Why can’t lanthanum through lutetium and actinium through lawrencium all be in group 3?

In 2015, IUPAC established a task force to “deliver a recommendation in favor of the composition of group 3 of the periodic table.” Not much about their decision-making process has been made known to ...
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Find the Ionisation Potential and Electron affinity of X

$N_0/2$ atoms of $X_{(g)}$ are converted into $\ce{X^+_{(g)}}$ by energy $E_1$. $N_0/2$ atoms of $X_{(g)}$ are converted into $\ce{X^-_{(g)}}$ by energy $E_2$. Hence ionisation potential and electron ...
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Reactivity Dilemma of elements [closed]

While learning Periodic Properties, I stumbled upon a doubt regarding reactivity of elements of period 2 and period 3. (I am denoting reactivity, of any $X$ element as $R_{X}$.) For reactivity of $s-...
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505 views

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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369 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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430 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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733 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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1answer
303 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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287 views

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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236 views

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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192 views

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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262 views

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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80 views

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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314 views

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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241 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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897 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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551 views

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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1k 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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510 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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506 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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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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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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824 views

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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222 views

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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323 views

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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437 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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549 views

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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9k views

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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2k 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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