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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Anomalous Electronic Configuration of Thorium

The electronic configuration of thorium ($Z=90$) is $5\mathrm f^0 6\mathrm d^2 7\mathrm s^2$. But, according to the aufbau principle, the electrons should first enter the $\mathrm f$ subshell and not ...
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26 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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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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33 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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18 views

Why is mercury in the copper group?

In various old inorganic chemistry manuals it seems to have been the practice to group mercury in with the "copper group". Why is this?
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228 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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1answer
52 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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26 views

Chemical mixing question [closed]

What happens when Hydrogen is mixed with every chemical individually? What kind of reaction occurs? What happens when Lithium is mixed with every chemical individually? What kind of reaction occurs? ...
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1answer
56 views

Why do the chalcogens (Y) form YX4, YX6 but not YH4, YH6? [duplicate]

What is it about hydrogen that makes it different from the halides? What makes it only form di- and not tetra- or hexa- hydrides of the chalcogens?
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22 views

What explains the very high density of osmium and iridium? [duplicate]

Iridium with a density of $22.56$ g cm-3 & osmium with $22.59$ g cm-3. Data from their respective Wikipedia pages. Only these two naturally occurring elements have such a high density. I wish to ...
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1answer
73 views

What are inner core electrons and how do they influence chemical and physical properties?

There are six groups of p–block elements in the periodic table numbering from 13 to 18. Boron, carbon, nitrogen, oxygen, fluorine and helium head the groups. Their valence shell electronic ...
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How do I know the valence number by looking at the groups? [duplicate]

Groups say the valence number. For example Hydrogen is on group 1, has 1 electron on it's last and only level. So we can know the valence number on that are on the groups 1-2 and 13-18. But how am I ...
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51 views

A doubt about something related to elements above Feynmanium

Here I saw that if an element above atomic no 137 has to exist, it must have electron speed greater than speed of light. My question is , has this calculation been done keeping in mind Einstein's ...
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41 views

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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0answers
82 views

How do I model atoms with Moebius strips?

This question came to me while I was trying to model the list of elements (Mendeleïev), especially their masses and number of electrons. It came to my mind that it might be easier to model each ...
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2answers
740 views

Is iron the most stable element in the periodic table?

According to the binding energy per nucleon vs mass number graph, it is observed that iron-56 has the maximum value of binding energy per nucleon (8.75 MeV).It means that Iron-56 is the most ...
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1answer
46 views

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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22 views

Families of some columns [closed]

From previous lessons, I know that column 1 are alkali metals, column 2 are alkaline earth metals, column 3 till column 12 are transition metals, column 17 are halogens and column 18 are inert gases. ...
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1answer
304 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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237 views

Periodic table group naming confusion - schools don't follow latest IUPAC?

In high school I am taught that Group 7 were halogens and Group 8 were noble gases, and Group 3 the boron group, Group 4 was carbon group, etc. Then when I looked up the groups, I found that noble ...
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17 views

Easy method to mug up periodic table? [duplicate]

Is there any way or shortcut to mug up periodic table elements in order. I always mix up the order and forget their atomic numbers, etc. I am now in class 12. So all elements are not required. Only ...
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0answers
103 views

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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1answer
192 views

Anomalous configuration for Palladium?

The p block elements generally have the general valence she'll configuration as $$n\mathrm{p}^{1-6}\,n\mathrm{s}^{1-2}.$$ Expected electronic configuration for palladium is $$\ce{^46Pd} = ...
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92 views

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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1answer
435 views

Confusion with the Periodic Table

The periodic table has 7 periods and they have 2,8,8,18,18... elements respectively from 1 to 7. But from what I understand, the periods each state the number of electron shells that the elements in ...
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1answer
751 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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3k views

Is aluminium a metal or metalloid?

Aluminium is along the dark line of the Periodic Table and it is $p$-block metal. Is it metal or a metalloid? Why?
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499 views

Are the elements lanthanum and actinium considered to be in the d block or the f block of the periodic table?

Many periodic tables place lanthanum and actinium in the f-block of elements, for example, this periodic table from Los Alamos National Laboratory. However, this table from the Royal Society of ...
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9k views

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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1answer
102 views

Periodic table groups - which grouping is “right”? [closed]

In searching online, I've noticed there are a lot of different ways to group the elements of the periodic table. Take mercury in the two tables linked below, for example: ...
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3answers
608 views

Is there an abundance threshold of a 'synthetic' element for it to be considered natural?

I always (possible naively) thought that elements are either natural or synthetic, either one or the other. But, according to the Wikipedia page about Synthetic Elements, it states that: All ...
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1answer
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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1answer
2k views

How come uranium's relative atomic mass is 238.03 when it only contains isotopes with a mass number of 238 or less?

I have always been led to understand that the mass of an element on the periodic table is the weighted average atomic mass over all naturally occurring isotopes. This seems to make sense with all the ...
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2answers
66 views

Why isn't helium always He 1s?

Part 1: According to what I've learned so far, helium is in the first row of the periodic table, so its $n$ should always equal $1$. However, a question in my text asks about helium 2s. What is helium ...
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2answers
685 views

What do the numerals on the top right corner of the cells in the periodic table represent?

On the table published here (link) each cell has one to five numerals arranged vertically in its top right corner. The sum of those numbers is always the relative atomic mass of the element. I suspect ...
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1answer
116 views

Reading number of outer shell electrons and other properties from periodic table?

How can one read from the periodic table the number of outer shell electrons that an atom has, to predict how these atoms will make bonds with other atoms? For example to see that hydrogen ($\ce{H}$) ...
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1answer
84 views

What number should go underneath this fictitious element on the periodic table? [closed]

A new element (Wickium) was discovered on Mars. The isotopes of Wickium are Wickium-199, Wickium-200, and Wickium 201. The percent abundance of Wickium's isotopes are as follows: $$\ce{^199Wi} = ...
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1answer
56 views

Organisation in Periodic table [duplicate]

Why do we find big spaces in the periods of the Periodic Table between $\ce{H}$ and $\ce{He}$, $\ce{Be}$ and $\ce{B}$, and $\ce{Mg}$ and $\ce{Al}$? What is the logic of such organization of the ...
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1answer
4k views

How to find density of element metals

I was wondering, how do I determine what metal (element) has the highest density by using the periodic table? Is it possible?
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49 views

What exactly is Indium's ability to stabilize non-ferrous metals?

I was reading the History section about Indium on Wikipedia when I came across the following sentence: In 1924, indium was found to have a valued ability to stabilize non-ferrous metals, which ...
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1answer
97 views

Name for carbon and boron groups?

So group 17, 16, and 15, are called the halogens, chalcogens, and pnictogens respectively. Is there a name for the groups 14 and 13? (I really don't know if this is on topic here if it isn't tell me ...
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1answer
2k views

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

Most of the first electron affinities are positive, therefore the second ones are negative, and vice versa. but why? SPECIALLY WHEN THE FIRST ELECTRON AFFINITY IS NEGATIVE .. WHY THE SECOND ONE IS ...
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2answers
340 views

How adding one more electron increases the ionization energy?

Elements of group 6A, compared to 5A, require less ionization energy due to the paired electrons of 6A. But a question arises: why does group 7A, compared to group 6A, require more ionization energy ...
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55 views

degeneracy and Mendeleev table [closed]

A very basic question. When we construct Mendeleev table we can think of adding one electron at a time, filling one by one the electronic states, that are numbered by well known quantum numbers (using ...
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33 views

Why does the electron affinity increase in the 15th group

Why does the electron affinity increase by going down through the 15th group?
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1answer
60 views

Trying to figure out what these elements have in common [closed]

I have an old periodic table and I marked five metals from groups 1A and 2A with dots to indicate something about them. Only all this time later I can't figure out what exactly it was. I've been ...
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1answer
79 views

Why does the “gap” between atomic radii get smaller down the periodic table?

The question asks: why is the difference in atomic radii between $\ce{K}$ and $\ce{Na}$ larger than the difference in atomic radii between $\ce{Cs}$ and $\ce{Rb}$? I do have some kind of notion that ...
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1answer
52 views

Determine which is more electronegative based on ionization energy

One of the questions I got wrong in my assignment is this one: X, Y and Z are three unknown elements whose first 5 ionization energies are given above. The question is which of the 3 is the most ...
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162 views

Reaction between elements in a periodic table [closed]

Can we know the reaction between any two elements in the periodic table? If yes then can we know the reaction between any three or more elements in the periodic table?
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1answer
550 views

Why does potassium form peroxides but sodium does not?

As we go down the periodic table, Group 1 alkali metals hold their single outer valence electron more loosely, and so reactivity increases. Below potassium (Na, Li), we can store the metal in oil with ...