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The striking observation is that the groups of elements appear “periodically” in the ranking of the elements by atomic number. Looking at the list in [link] , in each case we find, in order, a halogen, a noble gas, an alkali metal, and an alkaline earth metal, and this pattern repeats itself over and over again. This observation is called the Periodic Law, and it is the reason that the usual table of the elements is called the “Periodic Table,” which is arranged with the elements in each group placed together in columns.

Periodic Law: The chemical and physical properties of the elements are periodic functions of the atomic number.

This observation is very surprising! To see this, consider an analogy. Imagine we looked for a pattern in the grades of students in a class by where they like to sit. We would not be surprised to find a pattern. Perhaps, for example, the most attentive students sit in a group near the front of the class and make the highest grades. However, we would be very surprised if we were to rank the students in order of decreasing grades and discover that every tenth student (1 st , 10 th , 21 st , 31 st ) in the list sat in the first row, every other tenth student (2 nd , 12 th , 22 nd , 32 nd ) sat in the second row, and so forth. That would be very unexpected and very hard to explain. But we would look for a reason for the pattern. In a similar way, we have seen a surprising pattern in the behavior of the elements with atomic number, and we must look for a reason for that pattern.

Observation 2: ionization energies of the atom

We are now ready to use Coulomb’s Law, as discussed in the Foundation, to understand the attraction of the electrons flying about the nucleus to the positive charge of the nucleus. Recall that the attraction of two charges together depends on the sizes of the charges and the distance between them. The size of the charge on an electron is often called –e . In the case of an atom with atomic number Z , there are Z protons so the nuclear charge is +Ze . The attraction of an electron at distance r away from this nucleus is given by the potential energy in Coulomb’s Law:

V ( r ) = ( + Ze ) ( e ) r size 12{V \( r \) = { { left (+ ital "Ze" \) \( - e right )} over {r} } } {}

This means that an electron close to the nucleus would be more strongly attracted to the nucleus, because its potential energy is much more negative. A large negative potential energy means that we would have to add a lot of energy to the electron to remove it from the atom so that r could become large. This also means that an electron in an atom with a large atomic number, Z, would be more strongly attracted to its nucleus than an electron in another atom with a smaller atomic number.

We can actually observe the attractions of the electrons to the nucleus by measuring the amount of energy required to remove the electron from the atom. This energy is called the “ionization energy” of the atom because it is the energy required to take a neutral atom and turn it into a charged ion:

A (g) → A + (g) + e - (g)

In this chemical process, A is an atom, the (g) means that this atom is in the gas phase, and A + (g) is the same atom with one electron removed, leaving behind a positive charge. We call A + an ion. Think about how the ionization energy is related to the potential energy in Coulomb’s Law. For an electron to be removed from the atom, r must become very large so that the potential energy becomes essentially zero. If an electron began with a negative potential energy V(r) , we would have added at least this must energy to bring the potential energy up to zero. Therefore, a large negative V(r) would require a large ionization energy. We often call the ionization energy, IE, and it is typically measured in kiloJoules (kJ) per mole of atoms. At this point, we don’t need to worry about how this experiment is actually done.

Questions & Answers

what does nano mean?
Anassong Reply
nano basically means 10^(-9). nanometer is a unit to measure length.
Bharti
do you think it's worthwhile in the long term to study the effects and possibilities of nanotechnology on viral treatment?
Damian Reply
absolutely yes
Daniel
how to know photocatalytic properties of tio2 nanoparticles...what to do now
Akash Reply
it is a goid question and i want to know the answer as well
Maciej
characteristics of micro business
Abigail
for teaching engĺish at school how nano technology help us
Anassong
Do somebody tell me a best nano engineering book for beginners?
s. Reply
what is fullerene does it is used to make bukky balls
Devang Reply
are you nano engineer ?
s.
fullerene is a bucky ball aka Carbon 60 molecule. It was name by the architect Fuller. He design the geodesic dome. it resembles a soccer ball.
Tarell
what is the actual application of fullerenes nowadays?
Damian
That is a great question Damian. best way to answer that question is to Google it. there are hundreds of applications for buck minister fullerenes, from medical to aerospace. you can also find plenty of research papers that will give you great detail on the potential applications of fullerenes.
Tarell
what is the Synthesis, properties,and applications of carbon nano chemistry
Abhijith Reply
Mostly, they use nano carbon for electronics and for materials to be strengthened.
Virgil
is Bucky paper clear?
CYNTHIA
so some one know about replacing silicon atom with phosphorous in semiconductors device?
s. Reply
Yeah, it is a pain to say the least. You basically have to heat the substarte up to around 1000 degrees celcius then pass phosphene gas over top of it, which is explosive and toxic by the way, under very low pressure.
Harper
Do you know which machine is used to that process?
s.
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
On having this app for quite a bit time, Haven't realised there's a chat room in it.
Cied
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
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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