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block
A block of the periodic table of elements is a set of adjacent groups. The term appears to have been first used by Charles Janet. The respective highest-energy electrons in each element in a block belong to the same atomic orbital type. Each block is named after its characteristic orbital; thus, the blocks are:
s-block
p-block
d-block
f-block
g-block (hypothetical)
The block names (s, p, d, f and g) are derived from the spectroscopic notation for the associated atomic orbitals: sharp, principal, diffuse and fundamental, and then g which follows f in the alphabet.
The following is the order for filling the "subshell" orbitals, according to the Aufbau principle, which also gives the linear order of the "blocks" (as atomic number increases) in the periodic table:
1s, 2s, 2p, 3s, 3p, 4s, 3d, 4p, 5s, 4d, 5p, 6s, 4f, 5d, 6p, 7s, 5f, 6d, 7p, ...
For discussion of the nature of why the energies of the blocks naturally appear in this order in complex atoms, see atomic orbital and electron configuration.
The "periodic" nature of the filling of orbitals, as well as emergence of the s, p, d and f "blocks" is more obvious, if this order of filling is given in matrix form, with increasing principal quantum numbers starting the new rows ("periods") in the matrix. Then, each subshell (composed of the first two quantum numbers) is repeated as many times as required for each pair of electrons it may contain. The result is a compressed periodic table, with each entry representing two successive elements:
I got some leftover parts from my AR build
NE PDX. but I can always ship
A2 Mid-length with head shield, delta ring, and end cab (no barrel nut) $15
A2 birdcage with crush washer (1/2X28) $5
Anytime Trump issues a good Executive Order such as the Travel Ban, some liberal judge from California, Hawaii or wherever issues an injunction keeping it from going in to effect.
Now that Trump is starting to make bad gun laws "Bumpstocks, Ban them", "Age to purchase, raise it to 21" and...
Apex Polymer Armorer Block. It's never been used just knocking around my armorers kit. "The Apex Armorer's Block is designed for gunsmiths, law enforcement and military armorers and do-it-yourself home gunsmiths to work on Smith & Wesson M&P and Glock model pistols." I can meet anywhere in the...
SOLD
Like new take-off from a factory upper, unfired outside of factory testing. This is a DD 10.3 Mk18 barrel in the same setup with the dimpled and set screwed Mk12 gas block that the military contracts. Proper military spec gas port. All factory DD. Perfect barrel for your Mk18 clone...
Unmatched Quality Ar15 Rifles | Phoenix | Battle Tested Equipment
I have a BTE Adjustable Gas Block, it is rail/receiver height and .625 diameter... Magpul OD Green
Nice block... just ended up free floating the barrel.
Less than 100 rounds through it.
$30
Will consider trades for gun stuff...
I opened my S&W 610-3 to check out the internals. As the picture shows there is no hammer block. I am new to the S&W revolvers so I don't know if this model had one or if it was removed. Is it needed? Will any 610 hammer block work in a dash 3?
Hey all,
Selling an ALG EMR v3 15" rail
It's in what I'd describe as "very good" condition with only one small blemish on the right side. However, it has had a hole drilled on the right side to allow access to an adjustable gas block. I understand aftermarket modifications are not...
For sale or trade is my son's Chevy block. Small block 400 and I don't know much of anything about it although I do know it doesn't have a ring in the cylinders. It got hit with some overspray from my pressure washer so I will take a brass wheel and clean it up but other than that, a good...
I bought a new AR15 SAA pistol upper with a clamp on gas block that keeps coming loose because the two clamp bolts keep pulling out the aluminum threads (third time now) SSA fixed it under warranty but not so sure they want to fix it again, said they will call me back when they make up their...
Hi everyone,
I was wondering if anyone could recommend a local AR gunsmith to install a pinned Giessele Super Gas Block on a new barrel. Some drilling will definitely be required. I don't have the tools to do this myself and would like it to be done properly.
I haven't had a ton of luck...