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

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Why is Iron (Fe) difficult to reduce?

$\ce{Fe^3+ + e- -> Fe^2+} \quad +0.77$ $\ce{Fe^3+ + 3e- -> Fe} \quad -0.04$ $\ce{Fe^2+ + 2e- -> Fe} \quad -0.41$ $\ce{Zn^2+ + 2e- -> Zn} \quad -0.76$ $\ce{Co^2+ + 2e- -> Co} \quad ...
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Transition metals [closed]

Transition metals have the ability to cause heterogenous and homogenous catalysis, what property of it causes this ability at the microscopic level. Why do transition metals specifically show this ...
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27 views

In the periodic table, why doesn't the 2nd row have exactly 2 elements?

Rows 2 and 3 have 8 elements each. Rows 4 and 5 have 18 elements each. Rows 6 and 7 have 32 elements each. So there's a pattern of two rows having the same number of elements. Why don't the first ...
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Difference in the change in oxidation states of transition elements and p-block elements

In transition elements the oxidation states differ by one (+2 to +7 in Mn). However, in the p-block elements, the oxidation states differ by two (-1,+1,+3,+5 in the halogen group). Why is this so?
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Increasing Covalent character increases Colour intensity

I observed some trends as follows PbCl2 white and PbI2 yellow SnCl2 white, SnCl4 red and SnI4 black AgCl white, AgI,AgBr and AgCO3 yellow In all these cases as the size of anion increases ( ...
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50 views

Why is the periodic table periodic?

I am not a chemist, but I am interested in Science in a general sense. Can anybody explain why the periodic table is periodic in nature? I would appreciate links for further reading.
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25 views

Why does ionization increase from Li to Be? [duplicate]

If ionization energy decreases from $\ce{N}$ to $\ce{O}$ due to the pairing of electrons (causing electric repulsion and greater potential energy) in the $\mathrm{2p}$ orbital in the $\ce{O}$ atom, ...
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35 views

Why is Aluminum's 2nd ionization energy higher than Silicon's?

According to the periodic table trend for I.E. Silicon should have a higher 2nd ionization energy than Aluminum so I'm confused.
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Why is Mo(VI) more stable than Cr (VI)?

Acids with $\ce{Mo}^\mathrm{VI}$ are more stable than those of $\ce{Cr}^\mathrm{VI}$ in terms of redox reactivity. In p-block elements, as we go down the groups, the stability of lower oxidation ...
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Why is fluorine more reactive than iodine despite the weaker I-I bond?

The atomic radii of halogen increases as we go down the group due to addition of new shells. As a result, bond length of halogen $\ce{X-X}$ increases down the group. so, less energy is required to ...
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230 views

How long the block starting with element 121 will be?

I remember from my chemistry classes that (after the initial irregularities) a new block of elements starts every two periods. After the initial s-block and p-block following it shortly, we have ...
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243 views

Why does tin form tin (II) compounds?

The stability of the +II oxidation state in lead has been widely attributed to the so-called “inert pair effect”: the 6s subshell is stabilized through relativistic contraction due to the near-c speed ...
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53 views

Why does the boiling and melting point 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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87 views

Why ionic radii of Cu2+ is less than Zn2+?

Fully filled orbital has more effective nuclear charge than incompletely filled orbital. So atomic or ionic radii of elements or ions having fully filled orbitals should be less than that of elements ...
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43 views

How to tell which compound has the biggest ionization energy?

I am preparing for my final exam, and I am very confused about ionization energy. An example question would be: Between the species $\ce{Ne, Na+, Mg^2+, Ar, K+, \&~Ca^2+}$, which one has the ...
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49 views

Electron affinity of Group 15 elements

The electron affinities of elements in the same group should decrease as you go down the group, but in the Group 15 elements the values generally increase: $$\begin{array}{cc} \hline \text{Element} ...
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How does the electron configuration of platinum relate to its stability?

Does platinum's electron configuration, [Xe] 4f14 5d9 6s1, influence its reactivity and stability? Is the electron configuration the primary contributing factor to platinum's relative inertness? ...
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Why is ionisation energy of bismuth lower than lead?

Why is ionisation enthalpy of Bismuth less than that of Lead for it just comes after the latter in periodic table? First ionisation energy of bismuth is 703 kg/mol while that of lead is 715 kg/mol. I ...
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Why are the 6d and 7s electronic shells are filled in actinium and thorium and not 5f shell?

According to me, lanthanides and actinides form the f-block elements because they have a f orbital. So, while writing the electronic configuration of lanthanides and actinides, electron should ...
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86 views

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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Periodic table- quantum numbers

I have come across many questions like: "if electron had 3 spins (-1/2,0,+12) then what change will be there in the periodic table?", also sometimes " if the capacity of each orbital becomes 5 then in ...
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89 views

Ionization energy and Electron Affnity

Which of the following statements correctly interprets the relationship between ionization energy, atomic radius Electron affinity when comparing two atoms. The correct choice as per my instructor ...
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102 views

What is the lattice structure of manganese?

A transition element is defined as the one which has incompletely filled d orbital in its ground state or in any one of its oxidation state. Zinc , cadmium and mercury are not typical transition ...
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329 views

Memorizing polyatomic ions? Using Periodic Table

In my Chemistry course, we must memorize a list of common polyatomic ions. Is their an easy way of memorizing ions such as Sulfate $\ce{SO4^2-}$ by looking at just the periodic table. I listed the ...
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158 views

Is it possible that atoms with 120 protons are possible, but that atoms with 119 protons aren't possible?

We currently know that there are atoms with atomic number up to 118 are possible. Is it possible that atoms with 120 protons are possible, but that atoms with 119 protons aren't possible? Or are ...
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856 views

Why does electronegativity increase as effective nuclear charge increases?

I know that electronegativity is the ability to attract shared electrons and that effective nuclear charge is the pull of the nucleus on outer electrons based on my notes. But I'm not really sure ...
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Why can't element with paired electron have colour

I know that element with unpaired electrons give out colour especially the d-block element which can be explained by crystal field theory. But, why can't element with paired electrons give colour, is ...
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Anomalous behavior of 1st member of s and p block

Why do the first member of each group of s and p-block elements show anomalous behavior? Is it because of their small size or high electronegativity ??
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1k views

Reactivity and the periodic table

I cannot seem to help find research to support that the answers selected on a multiple choice test were wrong and need help explaining the correct answers. Which is more reactive, aluminum or ...
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Why do some elements such as polonium not follow the trend of decreasing atomic radius?

Most of the periodic table follows the trend of increasing radius as you move down a family and decreasing radius as you move across a period. Why is this trend not observed for polonium?
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Why is lutetium part of the lanthanide series?

I’ve been looking at the periodic table and began to wonder - why is lutetium part of the lanthanide series? Or, for that matter, why is lawrencium part of the actinide series? This isn’t readily ...
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55 views

Instability of heavy hydrides

Question: Why do hydrogen compounds from the third period down (that are electron deficient or have completed octets) readily decompose? Thoughts: Apparently, heavier group 14 elements form ...
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Why there is an exception in melting and boiling point in p block?

Why is the boiling point and melting point of 15th group and 16th group has an exception? As we know that as molecular mass increases boiling point and melting point will also increase. So on going ...
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558 views

Why is BCl3 a monomer whereas AlCl3 exists as a dimer?

What makes dimerization possible in $\ce{AlCl3}$? Are there 3c-2e bonds in $\ce{AlCl3}$ as in $\ce{BH3}$?
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678 views

Why does density decrease across the period 4 and 5 transition metals?

I know that density decreases across period 4 because the last two elements are liquids and gases which means that their densities are less but why are the densities increasing and then decreasing ...
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370 views

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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450 views

Why are the atomic radii of iron, cobalt, nickel, and copper almost the same?

So we have to select the set of elements which will have almost the same atomic radii: O, S, Se, Te Li, Be, B, C Fe, Co, Ni, Cu Now I googled the atomic radii of the third set and found them to be ...
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Which element has a greater second electron affinity, sulfur or oxygen?

I found a question asking the above which states that sulfur has a lesser second electron affinity than oxygen. But since the inter-electronic repulsion in sulfur is lesser, shouldn't it be willing to ...
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202 views

Color of halogens

Why does the color of the halogens deepens as we go down the group? also why there is a change in physical state of halogens down the group? \begin{array}{c|c} \mathbf{Gas} & \mathbf{Color} ...
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378 views

Bond angles for the hydrides

I noticed the fact that all the hydrides of the elements belonging to group IV has bond angle 109.5° while in group V it varies from 107.3° for $\ce{NH3}$ to 91.3° for $\ce{SbH3}$. Similarly we see in ...
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764 views

Trend in the melting point down the group

We know the the atomic radii increase down the group. So less energy is required to pull the outermost electron as we go down the group and gradually melting points decreases down the group. The ...
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723 views

Does caesium or francium have a lower ionization energy?

$\ce{Cs}$ and $\ce{Fr}$ are in the same group of lowest first ionization energy, but which element has the lowest ionization energy, and why?
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Why are there peaks in electronegativities in d-block elements?

Looking at the Pauling electronegativities in the Periodic Table (below, from ChemWiki): Asides from the overall trend of increasing electronegativity across and up the Periodic Table (towards ...
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Relation Between Degree of Hydration and Electropositivity

Why are salts of strongly electropositive elements less heavily hydrated in aqueous solution than the those of less electropositive elements? Shouldn't it be the other way round as the salts of ...
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2k views

Diagonal relationships in the Periodic Table

I have often wondered about diagonal relationships between elements on the periodic table, and the most often cited explanations revolve around charge-density considerations. But other than that, ...
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Electron affinities of the chalcogens and halogens

Here are the electron affinities of the 17th and 18th groups. The general trend for electron affinity down the group is that it decreases because of the increase in atomic radius.The exception of ...
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774 views

Anomalous trends in ionization energy

I want to address two exceptions in the trend of ionization energy across the period, that are causing me problems: Taking the second period as an example : The two exceptions from the general trend ...
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597 views

Is there a function to approximate atomic mass from the atomic number?

The product of $2Z$ generally approximates the value of $m_\mathrm{a}$ of atoms that comprise relatively few protons. Whereas, the product of $2.5Z$ generally approximates the value of $m_\mathrm{a}$ ...
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654 views

Variation in atomic radii of elements in different blocks?

If we look at the values for the atomic radii (look at the table here), we can see that they rapidly decrease across the period initially. Looking at the first period, The graph is pretty steep ...
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Available orbitals for promotion

I am under the impression that elements from the third period onwards can promote electrons into d orbitals to form hybridised orbitals. Why would an element in the third period promote an electron to ...