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This concept also applies to elements just below carbon, nitrogen, oxygen, and fluorine. Silicon will form SiH 4 , so an Si atom has a valence of 4. Phosphorous forms PH 3 , so P has a valence of 3, and Sulfur forms H 2 S, so S has a valence of 2. Each halogen atom (Cl, Br, I) prefers to form molecules by combining with a single hydrogen atom (e.g. HCl, HBr, HI), so each halogen has a valence of 1.

We can make further progress using the valence of the halogens. Lithium, sodium, potassium, and rubidium each bind with a single Cl atom to form LiCl, NaCl, KCl, and RbCl. Therefore, they also have a valence of 1. Because we also find that, for example, the combination of two potassium atoms with a single oxygen atom forms a stable molecule, our assignments are all still consistent, since oxygen’s valence of 2 can be satisfied by the two K atoms, each with a valence of 1. We can proceed in this manner to assign a valence to each element by simply determining the number of atoms to which this element’s atoms prefer to bind.

If we arrange the valences according to Periodic Table as in [link] , we discover that there is a pattern. Just as we would expect from the Periodic Law, elements in the same group all share a common valence.

Most common valence of each element in periods 2 and 3
Li Be B C N O F Ne
1 2 3 4 3 2 1 0
Na Mg Al Si P S Cl Ar
1 2 3 4 3 2 1 0

The inert gases with a valence of 0 sit to one side of the table. Each inert gas is immediately preceded in the table by one of the halogens: fluorine precedes neon, chlorine precedes argon. And each halogen has a valence of one. This “one step away, valence of one” pattern can be extended. The elements just prior to the halogens (oxygen, sulfur, selenium, tellurium) are each two steps away from the inert gases in the table, and each of these elements has a valence of two (e.g. H 2 O, H 2 S). The elements just preceding these (nitrogen, phosphorus, antimony, arsenic) have valences of three (e.g. NH 3 , PH 3 ), and the elements before that (carbon and silicon most notably) have valences of four (CH 4 , SiH 4 ). The two groups of elements immediately after the inert gases, the alkali metals and the alkaline earths, have valences of one and two, respectively. Hence, for many elements in the periodic table, the valence of its atoms can be predicted from the number of steps the element is away from the nearest inert gas in the table. This systemization is quite remarkable and is very useful for remembering what molecules may be easily formed by a particular element.

Next we discover that there is an additional very interesting aspect to the pattern of the valences: for elements in Groups 4 through 8 (e.g. carbon through neon), the valence of each atom plus the number of electrons in the valence shell in that atom always equals eight . For instance, carbon has a valence of 4 and has 4 valence electrons; nitrogen has a valence of 3 and has 5 valence electrons; oxygen has a valence of 2 and has 6 valence electrons. We have made one of the most important observations in Chemistry, the “Octet Rule”:

Questions & Answers

so some one know about replacing silicon atom with phosphorous in semiconductors device?
s. Reply
how to fabricate graphene ink ?
SUYASH Reply
for screen printed electrodes ?
SUYASH
What is lattice structure?
s. Reply
of graphene you mean?
Ebrahim
or in general
Ebrahim
in general
s.
Graphene has a hexagonal structure
tahir
what is biological synthesis of nanoparticles
Sanket Reply
what's the easiest and fastest way to the synthesize AgNP?
Damian Reply
China
Cied
types of nano material
abeetha Reply
I start with an easy one. carbon nanotubes woven into a long filament like a string
Porter
many many of nanotubes
Porter
what is the k.e before it land
Yasmin
what is the function of carbon nanotubes?
Cesar
I'm interested in nanotube
Uday
what is nanomaterials​ and their applications of sensors.
Ramkumar Reply
what is nano technology
Sravani Reply
what is system testing?
AMJAD
preparation of nanomaterial
Victor Reply
Yes, Nanotechnology has a very fast field of applications and their is always something new to do with it...
Himanshu Reply
good afternoon madam
AMJAD
what is system testing
AMJAD
what is the application of nanotechnology?
Stotaw
In this morden time nanotechnology used in many field . 1-Electronics-manufacturad IC ,RAM,MRAM,solar panel etc 2-Helth and Medical-Nanomedicine,Drug Dilivery for cancer treatment etc 3- Atomobile -MEMS, Coating on car etc. and may other field for details you can check at Google
Azam
anybody can imagine what will be happen after 100 years from now in nano tech world
Prasenjit
after 100 year this will be not nanotechnology maybe this technology name will be change . maybe aftet 100 year . we work on electron lable practically about its properties and behaviour by the different instruments
Azam
name doesn't matter , whatever it will be change... I'm taking about effect on circumstances of the microscopic world
Prasenjit
how hard could it be to apply nanotechnology against viral infections such HIV or Ebola?
Damian
silver nanoparticles could handle the job?
Damian
not now but maybe in future only AgNP maybe any other nanomaterials
Azam
Hello
Uday
I'm interested in Nanotube
Uday
this technology will not going on for the long time , so I'm thinking about femtotechnology 10^-15
Prasenjit
can nanotechnology change the direction of the face of the world
Prasenjit Reply
At high concentrations (>0.01 M), the relation between absorptivity coefficient and absorbance is no longer linear. This is due to the electrostatic interactions between the quantum dots in close proximity. If the concentration of the solution is high, another effect that is seen is the scattering of light from the large number of quantum dots. This assumption only works at low concentrations of the analyte. Presence of stray light.
Ali Reply
the Beer law works very well for dilute solutions but fails for very high concentrations. why?
bamidele Reply
how did you get the value of 2000N.What calculations are needed to arrive at it
Smarajit Reply
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Source:  OpenStax, Concept development studies in chemistry 2013. OpenStax CNX. Oct 07, 2013 Download for free at http://legacy.cnx.org/content/col11579/1.1
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