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.
195
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1answer
100 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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0answers
53 views
How many inner transition elements are there?
Why is caesium not considered an inner transition element. From how far I have read, the inner transition elements are the elements who have ultimate, penultimate and antipenultimate shells ...
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2answers
52 views
How to determine the chemical state of a reactant or product in a chemical equation?
I am asked this question:
Write a balanced equation, including state symbols, for this reaction:
$\ce{calcium + hydrochloric acid -> calcium chloride + hydrogen}$
I answered this:
$\ce{...
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0answers
52 views
Why are group 7 to 9 elements good hydrogenation catalyst?
In my exam question came: statement 1- activity of hydrogenation catalyst increase from group 5 to 11 with maximum activity shown by group 7 to 9 group elements.
Statement 2- reactants are very ...
1
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1answer
52 views
The number of transition elements
I searched in the internet but most of them said that there are 38 transition metals. But our text book says that group 12 or the group of zinc CAN'T BE COUNTED as transition metals. Which already ...
3
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1answer
61 views
Structure of the periodic table
The periodic table I understand is arranged by order of increasing atomic number after Henry Moseley's X-ray experiment.
But I also learned that the periodic table also has its shape due to the ...
0
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1answer
86 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 ...
3
votes
1answer
86 views
The boiling points of Alkali metal group
As I know, the melting points of Alkali metals decrease down to the group due to decreasing of the energy of the metallic bond.
But according to my understanding, after it has become to liquid the ...
4
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1answer
87 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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0answers
27 views
Electrons and Atomic Mass
Is the mass of electrons covered when talking about atomic mass. For example, the mass of Carbon is $12.011\space\text{amu}$. If this is including the mass of electrons (assuming the atom is neutral) ...
3
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1answer
68 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 ...
0
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1answer
172 views
Comparison between van der Waals radius and metallic radius
I was reading about different types of atomic radius. It was written that if any atom can possess all the three types of radius, then van der Waals radius will be greater than metallic radius. However ...
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0answers
16 views
What trend exists in the enthalpy change of reaction of group 2 carbonates with HCl
I am currently investigating the trends in enthalpy change of the reaction of group 2 carbonates with HCl. As per ion polarization theory there should be an upward trend in stability and thus a ...
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2answers
182 views
Why is atomic number unique? [closed]
We all know that atomic number of an atom is "unique" just like fingerprint. And no two elements can have same atomic number. But how can we be So sure that no two elements can have same atomic number?...
0
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2answers
113 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
52 views
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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0answers
320 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, ...
0
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1answer
201 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 ...
0
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1answer
93 views
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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0answers
103 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 ...
0
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0answers
19 views
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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0answers
62 views
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 ...
0
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0answers
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?
...
3
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1answer
150 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 ...
0
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1answer
2k 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
251 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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0answers
522 views
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
131 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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0answers
28 views
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 ...
7
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3answers
5k 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 ...
-2
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2answers
749 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
45 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 ...
3
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1answer
2k 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
82 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 ...
2
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1answer
236 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 ...
5
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2answers
813 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 ...
1
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1answer
2k 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
27 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
83 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 ...
0
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1answer
54 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
1k 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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0answers
1k views
How to quickly predict the group of elements with atomic numbers 117 and 120? [closed]
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 ...
4
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2answers
556 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 ...
0
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1answer
4k 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 ...
0
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1answer
6k 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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1answer
2k 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
393 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
1k 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
594 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
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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 ...
