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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Relation between Ionization energy and reactivity

So I was learning about the periodic table where I came across the topic of ionization energy. As a general trend the Ionization energy decreases as we move down a group with a few exceptions such as ...
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Which has the largest bond angle between water, oxygen difluoride and dichlorine oxide?

Which one out of $\ce{H2O}, \ce{Cl2O}, \&\ \ce{F2O}$ will have largest bond angle? I think it should be $\ce{H2O}$ because oxygen is most electronegative in this case so electrons will be more ...
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How to explain the periodic trends in boiling points in groups?

Observing the trend of boiling points of the compounds listed, choose the appropriate terms to fit into the blanks: \begin{array}{lr} \hline \text{Compound} & \text{b.p.}/\pu{°C}\\ \hline \ce{H2Te}...
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Why are the melting and boiling points of the group 1 metals lower than the group 2 metals in the same period?

I thought it was because the group 1 metals are smaller than the group 2 metals but the answer sheet says it's because there are more valence electrons and a stronger positive charge in group 2 metals....
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Periodic Trends of Zeff and Electronegativity

The effective nuclear charge $Z_\mathrm{eff}$ increases from left to right and from top to bottom. Can you explain why it increases from top to bottom? Also can we explain the periodic trend of ...
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Why do selenium , tellurium and polonium have more negative electron gain enthalpy than oxygen?

In my book(NCERT Chemistry Part I, Textbook for Class XI[1]) a list of values of electron gain enthalpies of various elements is given. According to that list, oxygen has less negative electron gain ...
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Which oxidation states were used when Pauling developed his electronegativity scale?

Paulings electronegativity is a relative scale, based on the difference in electronegativity between X and Y, $\Delta EN = 0.102 \sqrt {\Delta}$, where $\Delta = (X-Y)_{measured}-(X-Y)_{theoretical}$ ...
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Do organopolonium compounds exist?

Analogues of alcohols exist for all the heavier Group 16 elements, namely sulfur, selenium, and tellurium. Would polonium also be able to form a "polonol" like $\ce{CH3PoH}$?
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Why is strontium(II) ion bigger than krypton atom?

$\ce{Sr^2+}$ is exactly the same as $\ce{Kr}$, in terms of electrons and orbitals. The only difference between the two, is that $\ce{Sr^2+}$ has a couple of extra protons in the nucleus (and probably ...
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Acidic character and anion stability across periods and groups of the periodic table [duplicate]

I understand that to compare relative acidity one must consider the stability of the conjugate bases. Across a period the electronegativity of an element increases. And that is for example why $\ce{HF}...
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Why H2S2 is hydrogen disulfide and not hydrogen persulfide?

Context: I was checking this question and in the answer, the compound $\ce{FeS2}$ was named "iron disulphide" (it was previously named "iron persulfide" but later changed after ...
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Electron Affinity of Lead as compared to Bismuth

For "nitrogen family" and "carbon family" the trend goes that in a period, the electron affinity in case of group 15 is less than that of group 14. This is attributed to the half-...
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Why do the boiling and melting points decrease as you go down group 1 and vice versa for group 7?

I used to think that because an alkali metal needs to lose one electron to complete its outer shell, when the atom increases in size (atomic radius), the electron would be easier to lose as the ...
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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 are group 1 elements so low in density?

I was studying the s-block elements and found that they extremely low in density. Lithium is said to be the least dense solid in the entire periodic table and their Cohesive Energies are also very low....
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S(p)-C(p) vs. O(p)-C(p) overlap

In Grossman, The Art of Writing Reasonable Organic Reaction Mechanisms, he provides the following explanation. The question asks to explain why the difference in pKa values between PhSH and EtSH is ...
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Is there an enolate equivalent for enamines?

I'm learning that enolates are stronger than enamines are stronger than enols in terms of general nucleophilicity. Makes sense. But what I can't find any explanation for online is why the trend ...
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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 is fluorine more reactive than iodine despite the weaker I-I bond?

The atomic radius of halogens increases as we go down the group due to the addition of new shells. As a result, the bond length of halogen $\ce{X-X}$ increases down the group. So, less energy is ...
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Why is the increase in covalent radius from As to Bi not as big as from N to P?

The following is the radius of Group $15$ elements: $$\begin{array}{c|c} \hline \text{Element} & \text{Covalent Radius }(\pu{pm}) \\ \hline \ce{N} &75 \\ \ce{P} &110 \\ \ce{As} &...
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Color of Flame Test for Alkali Metals

Lithium is known to have the highest ionization energy among Group 1 elements. Also, characteristic colours in the flame test arise due to the excitation and de-excitation of electrons. Then why ...
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Why is magnesium sulfate more soluble in water than that of strontium and calcium sulfates?

Magnesium sulfate is soluble in water. Its solubility is $\pu{26.9 g}/\pu{100 mL}$ at $\pu{0 ^\circ C}$ $(\pu{35.1 g}/\pu{100 mL}$ at $\pu{20 ^\circ C})$.[1] However, both calcium sulfate $(\pu{0.21 g}...
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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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Out of KCl, CaCl2, MgCl2, NaCl, which causes the greatest corrosion rate of iron and why?

I know that salts act as an electrolyte in a redox process and rusting of iron, where iron loses electrons and oxidizes, and oxygen gains electrons and reduces. I did an experiment with KCl, NaCl, ...
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Predict the valence configuration of this element using the first five ionization energies [closed]

If the first five ionization energies of an element are, respectively: $\pu{1.09 kJ/mol}$, $\pu{2.35 kJ/mol}$, $\pu{4.62 kJ/mol}$, $\pu{6.22 kJ/mol}$ and $\pu{37.83 kJ/mol}$, to which group of the ...
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Density of d-block elements

Something that confuses me slightly is the trends in density when comparing periods 4, 5, and 6 in the d-block. Looking at periods 5 and 6, the density peaks at group 8, with ruthenium and osmium, ...
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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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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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Why is fluorine a oxidising agent? [closed]

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 that ...
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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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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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Why does the second electron affinity has an opposite sign of the first one?

Many first electron affinities are positive, indicating a favourable process, but the corresponding second electron affinities are negative. For example, the first and second electron affinities of ...
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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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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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Halogen Oxyacid Trend (acid strength)

Why is $\ce{HClO4}$ more acidic than $\ce{HBrO4}$? But $\ce{HCl}$ is less acidic than $\ce{HBr}$? What determines the acidity? Is it the concentration of $\ce{H+}$? If so, how do these trends develop ...
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Why is the melting point of magnesium oxide higher than aluminium oxide?

There's a graph of the melting points of period three oxides. The melting point of magnesium oxide is several hundred Kelvin higher than aluminiumoxide. I can't find any explanations for this on the ...
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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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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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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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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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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 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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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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How do atomic radius and nuclear charge influence ionisation energies?

This is actually a multiple choice question. Why is the first ionisation energy of neon higher than that of fluorine? A: Fluorine is more electronegative than neon B: Neon has a complete octet, but ...
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Why is the boiling point of heavy water more than that of normal water?

In class we learnt that the London forces become stronger as the relative molecular mass increases. Not just as in organic chemistry but in things like the halogens. However, as I understand, the ...
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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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Why do the melting points of Group 15 elements increase upto Arsenic but then decrease upto Bismuth?

The boiling points of group 15 elements increase on going down the group (or, as size increases) but the same is not true for the melting points. The melting points increase from $\ce{N}$ to $\ce{As}$ ...
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Why is lithium the most reducing alkali metal, and not caesium?

Caesium has a larger size, and the effective nuclear charge that the valence electron experiences will be far less compared to that of lithium's, right? But lithium is still considered the strongest ...
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Trend in reducing property of dioxides

I am not sure of the explanation for the following statement: The reducing property of dioxides of group 16 elements decreases from $\ce{SO2}$ to $\ce{TeO2}$. Is the statement valid? If yes, how ...

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