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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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
4k views
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
58 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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0answers
30 views
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
40 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^...
2
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0answers
49 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 ...
1
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1answer
58 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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0answers
110 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
314 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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0answers
23 views
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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0answers
71 views
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
41 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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2answers
183 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 ...
3
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0answers
539 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 ...
3
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2answers
218 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
1k 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
2k 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 ...
0
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0answers
27 views
Why doesn't the Atomic mass number(u) represent the exact mass of 1 mole of a given element? [duplicate]
From what i know, the Atomic mass number(u) of each element in the periodic table
is supposed to show the grams per mole of that atom.
but when i take the combined masses of every neutron, proton ...
0
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1answer
801 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 ...
0
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1answer
290 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 ...
6
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2answers
705 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
287 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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2answers
821 views
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 ...
3
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0answers
673 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
947 views
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
91 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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0answers
1k 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 ...
2
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0answers
72 views
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
361 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
637 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 ...
7
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1answer
404 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
197 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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0answers
110 views
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
55 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.
3
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0answers
805 views
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 (...
0
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2answers
8k 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
211 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 ...
0
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1answer
81 views
Do the spins of outer orbitals block measurement of spin of inner orbitals?
Do the outermost s1 and s2 electrons block an outside observer from measuring the larger inner group orbitals for elements heavier than Nitrogen (for instance, would Chromium's 4s1 electron or ...
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0answers
105 views
Halides in s-block elements [closed]
What is the reason behind the following statement:
The $Δ_fH^\circ$ for the fluorides become less negative as we go down the group while the reverse is true for chlorides, bromides and iodides.
3
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1answer
880 views
On the periodic table: Why are groups of elements organized by 'letter' [duplicate]
Why are the groups of elements on the periodic table organized into areas represented by the letters s,p,d,f,g, and h?
What does this mean?
3
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1answer
798 views
Mendeleev's predictions
While studying about Mendeleev's periodic table in my textbook( class 11 NCERT chemistry), I have studied that Mendeleev has predicted some elements like Eka-boron(scandium), Eka-Aluminium(Gallium),...
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2answers
2k views
Why are metalloids found in a zig-zag line on the periodic table
I am confused about the zig-zag pattern of metalloids in the periodic table. Why are metalloids arranged in a zig-zag line? Can anyone answer my question?
3
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0answers
79 views
What proof is there that the “Island of Stability” exists?
Often I see people talking about an "Island of Stability" existing for super-heavy elements on the periodic table, but I don't see any reason to thinks this exists? Surely the heavier you go the more ...
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0answers
274 views
Why group 13 elements don't show +2 as their major oxidation state?
These are the things I understand:
1) Group-13 elements show +1 and +3 as their major oxidation
states(OS).
2) The general configuration of G-13 elements is $ns^2$ $np^1$.
3) In the ...
5
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0answers
64 views
Trends in Slater's constant
I am aware of the various Slater rules to calculate the effective nuclear charge, $Z_\mathrm{eff}$
However, how can I decide the order in which the orbitals 2s, 3s, 3d, 3p, 4d, and 4f stand when ...
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1answer
626 views
Last electron of a transition element
The electronic configuration of nickel is
Ni: [Ar] $3d^84s^2$
Here, while writing the configuration, we fill the 3d after 4s.Hence the 28th electron enters the d orbital.
But
$\ce{Ni+}$: [Ar] $...
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2answers
320 views
What organizational methods pre-date the Periodic Table?
Dmitri Mendeleev noticed patterns in elements which allowed him to design the periodic table which ultimately led to the modern periodic table.
How were elements organized before this? Was there any ...
4
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1answer
112 views
Why don't elements having the same valency as Carbon bond so readily?
I haven't been in touch with Chemistry as a subject of study for several years now. Still- if I remember correctly, Si, Ge, Sn, Pb all have same number of electrons as Carbon in their outer orbits.
...
3
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1answer
238 views
Good collection of images showing periodicity of the Table?
Mendeleev's recognition of the periodicity of atomic trends was a milestone of human understanding, the detection of a pattern in what had appeared to be chaotic data. I think the significance and ...
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0answers
1k views
Comparing electronegativities of aluminium and gallium
If I were to compare the electronegativities of Al and Ga, shouldn't I be saying that the electronegativity of elements (in general) decreases down the group, I say this by thinking of the position of ...
