Questions tagged [periodic-table]

This tag should be applied to questions about the layout, history and interpretation of the periodic table, not to questions relating to specific elements or trends within the table. For these, the tags 'elements' or 'periodic-trends' should be used where appropriate.

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40 views

Why is the product of the reaction “Bi + O2” Bi2O3 instead of Bi2O5?

I am stuck on a homework question that states: A piece of solid bismuth is heated strongly in oxygen. The answer key states the answer as $\ce{Bi + O2 → Bi2O3}$. However, it is to my understanding ...
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1answer
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The reaction of Group 14 to get its full shell

I was learning about group 14 of the periodic table and in the course, on Alison (link at the bottom), it said a reaction of the elements in group 14, they use group 4, would consist of sharing ...
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112 views

Why is Thorium (At. no. 90) an f-block element at all?

Being an exception of the Aufbau principle, Thorium has an electronic configuration of $\ce{[Rn]}\mathrm{7s^25f^06d^2}$ instead of the expected $\ce{[Rn]}\mathrm{7s^2 5f^2 6d^0}$. Two other elements, ...
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57 views

Why does period 3 of the periodic table contain 8 elements instead of 18?

Period 1 of the periodic table contains 2 elements ($1s^1$ and $1s^2$). Period 2 contains 8 elements ($2s^1$, $2s^2$, $2p^1$, $2p^3$, ..., $2p^6$). By the same argument, period 3 might contain 18 ...
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1answer
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Why is the valency of the Calcium (Ca) Bohr model, set to 2 electrons, instead of 1 electron for stability? [duplicate]

This is an Ascii table for the elements on the 4th period (row) of the periodic table, and distribution of electrons in each orbit. ...
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25 views

Why is the Ionization Energy of Germanium less than that of Silicon?

I've read that in the 13th period, Ga has higher I.E. than Al because of the filling of the d-orbitals in Ga. The text said they have low penetration,hence they don't shield well and the effective ...
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n+l rule for first member of lanthanide and actinide series

as we all know that if the value of $n+l$ is same then the orbital with lower value of $n$ will get filled first so in case of first member of lanthanide series the configuration is $(\ce{Xe})\mathrm{...
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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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28 views

Comparing the EA [duplicate]

What is the electron affinity trend for the oxygen family? I am interested in the question above. I am aware that EA of O $>$ EA of S, but what about the others? Which is having more EA: O or Se? ...
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1answer
53 views

What is the electronic configuration of La⁺? [closed]

Second IP of La is most likely to second IP of which element: (1) Be (2) Ba (3) Ca (4) Zn The given answer is calcium. I don't understand if the 6s electron or the 5d electron leaves on ...
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1answer
198 views

Effective nuclear charge of oxygen atom (O) vs oxygen anion (O2-)

The size of an anion is greater compared to its parent atom because former's effective nuclear charge is lesser than that of latter. I found on wikipedia that the effective nuclear charge can be ...
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1answer
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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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Definition of early vs. late transition metal

Is there an accepted definition of an early or late transition metal? I think the late transition metals start at Group 8 (including Fe), but others have said Fe is not a late transition metal. I'm ...
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2answers
107 views

How will the periodic table change due to redefinition of the kilogram (May 2019)?

The definition of a kilogram has recently been changed. What effect, if any, will this change have on data on the periodic table?
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Difference in Periodic Tables in Block Formation (split in d-block) [duplicate]

I had a question. When I was learning Chemistry and blocks in the periodic table, my professors always broke the table down like the image below Recently, when I looked up the periodic table (in ...
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3answers
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Confused by notation of atomic number Z and mass number A on periodic table of elements

I'm totally confused by the different conventions and when to use what. In the Periodic Table I see $$\ce{^{6}_{12}C}$$ However, in books when talking about isotopes I see $$\ce{^{12}_{6}C}$$ I ...
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2answers
289 views

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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1answer
219 views

Two different electronic configurations for cerium

Depending on the textbook there are two different electronic configurations stated for cerium. On the one hand $$[\ce{Xe}]\mathrm{4f^15d^16s^2}\quad$$ and on the other hand $$[\ce{Xe}]\mathrm{4f^...
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59 views

Mendeleev periodic table [closed]

Mendeleev accurately predicted the properties of gallium(eka aluminium). In his justification of properties he says(according to image given) the melting point of the element would be low. What could ...
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1answer
112 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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178 views

Why ionisation enthalpy of early lanthanides are expected to be greater than early actinides?

In my book Chemistry Part I (NCERT XII), a statement on p. 232 goes like this: It is evident from the behaviour of the actinoids that the ionisation enthalpies of the early actinoids, though not ...
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1answer
686 views

Which has a higher lattice energy CaO or NaCl? [closed]

I know that as charge increase the lattice energy increases as well. However when the size increases, the lattice energy decreases. Can you please explain this to me? I think it is CaO but i'm not ...
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What are Technetium's physical stress characteristics?

I've looked at periodic and data tables from several sources, but none give mechanical / engineering property data on Technetium. Why is this?
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Is there a definitive model of the Elements as a Periodic Tetrahedral [closed]

i.e. Is there a specific reason why these diagrams exist? Is the "neatness" of the design simply a graphical representation of the mathematical constants, or is there some underlying reason why a ...
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1answer
49 views

What does it mean that an electron quantum numbers are n1= 4 - l1?

I'm trying to solve some exercises from the 2017 IChO, and the problem 6-A1 states that in first ionization, an electron with the quantum numbers $n_1 = 4 - l_1$ is removed. Now, I've never seen ...
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3answers
471 views

Calling Diamond an element?

Is it scientifically correct to call Diamond an element? Carbon has a wide range of allotropes, so would it be correct to actually just call graphite, diamond etc an element. For that matter, could we ...
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1answer
990 views

How to quickly predict the group of elements with atomic numbers 117 and 120?

The elements Z (atomic number) = 117 and 120 have not yet been discovered. In which group would you place these elements? I tried to write their electronic configurations but it was too tedious and I ...
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2answers
289 views

What is the true depiction of the periodic table?

Normally with the periodic table the lanthanide series is separated out because it's long and would make the table wide. I looked for an expanded version and found this: I found it kind of strange ...
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1answer
3k views

Rule to determine the total number of elements in a period [closed]

If each orbital can take maximum of 3 electrons, then total number of elements in 2nd and 4th periods respectively are = ? I am not aware of the rule which helps to determine the total number of ...
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1answer
4k views

Why does oxygen have less negative electron gain enthalpy than sulphur? [duplicate]

Oxygen has less negative electron gain enthalpy than sulphur. This statement is given in my book with a short reason: due to compact size of oxygen I'm unable to understand why. I would ...
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1answer
1k views

Why does hydride acidity increase across period and down group in periodic table?

Why exactly does hydride acidity increase across period and down group in periodic table? What is the explanation with respect to electrons? I can't figure this out because for 1st period etc H is an ...
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1answer
340 views

Why is the number of protons and neutrons equal to the atomic mass rounded?

The mass number is defined as the NUMBER of protons and neutrons. Electrons aside, why does the number of protons and neutrons equal the atomic mass rounded to the nearest whole number? That would ...
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2answers
886 views

Why do all atomic masses have decimals if there are some elements that don't have isotopes?

I understand that the way to calculate the atomic mass is to obtain a weighted average of the masses of all the isotopes of an element. I also understand that there are about 26 elements that are ...
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3answers
412 views

Why are there only less than 120 elements out there ? [duplicate]

Why stop at 118 , Why aren't any more stable elements possible ?
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Comparing ionic character of group 1 elements

According to Fajan's rule ionic character should increase down the group as the size of cation increase. So it must be $$\ce{LiH < NaH < KH < RbH < CsH}$$ However, the following two ...
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861 views

Comparison between Boron Nitride and Graphite: Interlayer distance

Boron-nitrogen chemistry has attracted significant attention, partly because a B–N unit is isoelectronic with C–C. Furthermore, the radius of carbon and its electronegativity are roughly the average ...
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1answer
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Trends in ionization energy in the second period [closed]

Question Which element among the following has the highest ionisation energy: fluorine, oxygen, neon. I know that all these elements belong to period 2 and ionisation energy increases from left ...
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1answer
161 views

How to calculate the position of an element from its atomic number? [closed]

How to calculate the place of of a element if know their atomic number in a periodic table?
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2k views

Abnormal ionisation energy trend: Group 13 and 14

I was going through some ionisation energy data, where I came across the following: Ionisation energy order for Group 13 and 14: B > Al ≈ Ga > In < Tl C > Si > Ge > Sn < Pb What could be the ...
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is there any evidence that there are ~75 extra elements on the periodic table? [duplicate]

there are 118 currently existing elements on the periodic table, and recently I've found like 77 elements that quote on quote "may exist" on our periodic table. Is this true?
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1answer
442 views

Elements in the lanthanide and Actinide series [duplicate]

How many elements are there in lanthanide and Actinide series? My big doubt is does the 57th element Lanthanum and 89th element Actinium include in it? In some periodic table the entire 57-71 is ...
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1answer
837 views

Why do the d suborbitals start at 3d instead of 4d?

Why do the suborbitals for d start at 3 instead of four? It is in the fourth row on the periodic table and all other suborbitals start according to the row on which they are located except for d. Why ...
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1answer
492 views

Why doesn't D block contraction affect the other P block groups 14 15 16 etc

Usually we come across anomalies in the trends of periodic properties for example the size [Atomic radius value from Raymond Chang Chemistry 9th Edition] of Gallium (135 pm) is smaller than Aluminium (...
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1answer
270 views

Should I provide a citation for atomic masses?

I am writing my first lab report ever, and the handbook I was given did not say anything in particular about this issue. I will use the atomic masses for my calculations and I am not sure if I should ...
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What do you chemists need from a periodic table? [closed]

I am developing a website and later on an app with the periodic table. The reason I started was that I thought almost all the other periodic tables was awfully ugly. I do not only want to make it a ...
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1answer
68 views

Quickly deduce block (s, p, d …) from atomic number [closed]

A question from previous year papers of IIT JEE. There's not enough time to write the electronic configuration in the exam. Please suggest a quick, objective approach.
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Non existence of B3+ in solution [closed]

I read that B3+ ions do not exist in aqueous solution, because hydration energy cannot compensate for the sum of first three ionisation energies. This leads me to the following questions: If boron (...
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2answers
9k views

Find atomic number given the group and period [closed]

I want to find the atomic number of an element in a short way, when I know the exact group and period of that element. For instance; there is a question in our textbook to find the atomic number of ...
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1answer
225 views

Are halogens a further classification of non-metals, or are they another group themselves? [closed]

I've searched many pages in the internet, and many just classify halogens (Grp 7A) as non-metals. However, my teacher classified them as another group in the periodic table, and when asked which ...