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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28
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1answer
6k 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 ...
24
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5answers
14k views

Why does radium have a higher first ionisation energy than barium?

I'm wondering why radium appears to buck the general trend that first ionisation energies decrease as you move down a group in the periodic table: barium (the group 2 element preceding it) has a first ...
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2answers
2k 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 $m_\mathrm{a}$ ...
18
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5answers
12k views

Where can I find a downloadable spreadsheet of element properties?

Sorry for the FAQ, but I really don't know where to find a full spreadsheet for element properties. I mean a table that has one row for each element, and the columns are its properties, such as name, ...
17
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2answers
3k views

What are the alternatives to the Periodic Table of the Elements?

What are the different diagrams/tables used to organize the elements other than the Periodic Table? What are the advantages/disadvantages of each?
17
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1answer
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What are the g-block's predicted properties?

I have been researching for a Physics/Chemistry exam and thought; what will the future periods in the periodic table (periods 8 and above) would entail? Each block contains its own properties that ...
17
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2answers
80k 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 ...
14
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2answers
5k views

Do non-English speaking countries use the same element symbols?

The question does sound pretty absurd, but hear me out first. The Periodic Table of the Elements, as I know it, is supposed to be a common standard adopted by the global scientific community. However,...
13
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7answers
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Why lanthanides and actinides are shown separate from standard Periodic Table layout?

In the standard Periodic Table layout , all the elements up to 56 are in order i.e are in the same layout table. However, lanthanides and actinides are always shown separately from the layout like in ...
13
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3answers
996 views

Biological Consequences of Asteroid Mining—Death by Isotope?

It's been documented that NASA hope to capture an asteroid in 2025, and have subsequent aims to mine that asteroid. If if this is successful, we would expect other asteroids to be mined in the future. ...
12
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3answers
391 views

What is the usage of orbitals more complex than f orbitals?

Every high school learner, in each corner of the world, faces the lesson History of Atom during his courses, just as I did. We learned about s, p, d and f orbitals, though there were no signs of ...
11
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2answers
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To which block of the periodic table does helium belong?

According to quite a few books I have read, helium belongs to the p-block with reasoning along the lines of "it's an inert gas, so let's clump it together with other noble gases which are in the p-...
11
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3answers
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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 ...
10
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2answers
397 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 ...
9
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2answers
487 views

Did Mendeleev predict the existence of neutrinos?

According to this Wikipedia page, Mendeleev originally believed that the inert gases belonged in Group 0 (to the left of the alkali metals). Thus, helium would be placed in the second period to the ...
9
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1answer
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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 ...
9
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3answers
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Why is lanthanum a lanthanide and actinium an actinide?

I do know that the lanthanides start with the element lanthanum, but why? Lanthanum doesn't even have an $f$ orbital, so why isn't it considered a transition metal? It's the same way with actinium, ...
9
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0answers
119 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 ...
8
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2answers
40k 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?
8
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2answers
13k views

What is the formula for finding the average atomic mass of an element based on the abundance of its isotopes?

In my class my teacher showed us how to find the average atomic mass of an element with a method, but he didn't really state a formula one could use. I came up with a formula of my own, and from what ...
8
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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?
8
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1answer
606 views

How chemists find out the electronic properties of elements (atomic numbers)

How did chemists find how many electrons, neutrons, and protons each element had? I mean I can understand the Mendeleev's table but without really knowing how you make one...
8
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1answer
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Is there a common name to refer to the groups 13 and 14?

The group 15, 16, and 17 are called the pnictogens, chalcogens, and halogens respectively. Is there a name for the groups 13 and 14 as well?
8
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1answer
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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 ...
8
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2answers
951 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 ...
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 ...
7
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3answers
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Diagonal line going through groups IIIA-VIA on the periodic table

Why is there a diagonal line cutting through some of the nonmetals and metalloids on the periodic table in groups IIIA, IVA, VA, VIA, and VIIA? Is there any historical background about it?
7
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1answer
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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 ...
7
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1answer
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Where did the rest of the elements come from?

There were ninety original elements on the Periodic Table. Over time, new ones were founded and put on. However, they were all either the original elements experimented on. For example, Plutonium was ...
7
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1answer
6k views

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 ...
7
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1answer
4k views

Outermost electronic configuration of f block elements

Why is it $(n-2)\mathrm{f}^{1-14}(n-1)\mathrm{d}^{0-1}n\mathrm{s}^2$. The only exception I thought to this formula was Thorium $\ce{5f^{0} 6d^{2} 7s^{2}}$. So I feel it should be $(n-2)\mathrm{...
7
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1answer
609 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 (...
7
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1answer
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Why are there 3 columns in Group VIII of the Periodic Table?

I'm currently reading in-depth about the layout of the Periodic Table, and I wondered why the table has 3 columns in its Group VIII: As I understand, this is an old notation of the table, now ...
6
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3answers
4k views

Periodic table for printing

I there a Good Version of a printable Periodic table Which is minimalistic and gives necessary information only such as - At. Number Element Name At. weight Shell configuration color coding of ...
6
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1answer
7k views

How can scientists be certain that there are no undiscovered elements missing from the periodic table from hydrogen to lawrencium?

Scientists are certain that there are no undiscovered elements missing from the periodic table from hydrogen to lawrencium. How? and why?
6
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1answer
293 views

Why is UuX used as a symbol for unnamed elements on the periodic table?

Until recently, the last few elements on the periodic table had the chemical symbols (now they have formal chemical symbols!): Uub, Uut, Uuq, Uup, Uuh, Uus, and Uuo Why did they have these temporary ...
6
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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 ...
6
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1answer
9k views

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

Many first electron affinities are positive, indicating a favourable process, but the corresponding second electron affinities are negative. For example, the first and second electron affinities of ...
6
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1answer
353 views

How can we confirm the number of protons in an atom?

The periodic table tells us that there are 6 protons in a carbon atom. Is there a way to verify this first-hand? Or are we just expected to believe it unquestioned?
6
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2answers
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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 ...
5
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8answers
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Memorizing the periodic table

Several people have said that the key to understanding chemistry is through memorizing the periodic table. I want to ask if there is a simple technique to learn it, or if I just have to remember ...
5
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4answers
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Phase diagram for first 10 elements

I've been looking on the net for a reference which shows a phase diagram for elements at least from $\ce{H}$ up to $\ce{Ne}$. Specifically, I'm looking which of these elements can be solid or liquid ...
5
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2answers
13k views

Where hydrogen belongs in the Periodic Table

Why do some people say that hydrogen should be above lithium in the periodic table and others argue it should be above fluorine?
5
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1answer
666 views

What is the joke that is shown in this picture?

There is supposedly a joke shown in this picture relating to periodic trends. Does anyone know what it is? And could they also explain where the elements on the eye exam came from?
5
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1answer
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Is there a similar characteristic of the lanthanide contraction in the other transition metal groups?

Basically, does the lanthanide contraction also occur with the 4d, 6d groups as well? I am at a lack of understanding in this topic, I am just wondering what specific elements does this jump in a ...
5
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2answers
13k 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 ...
5
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1answer
854 views

Why don't Schools follow latest IUPAC for naming groups?

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 ...
5
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1answer
155 views

Deviation of Ytterbium from general trend

What is the reason for deviation of ytterbium from the general trend of lanthanides in terms of hardness, melting point, density etc.?
5
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0answers
71 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 ...
4
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1answer
4k views

What is the group number or name for elements between group 3 and 4 (F-block) on the periodic table?

What is the group number or name for elements between group 3 and 4 (F-block) on the periodic table? I noticed when I look at a periodic table of elements, the elements of the F-block between group 3 ...