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A = N + Z , size 12{A=N+Z} {}

where A size 12{A} {} is also called the mass number    . This name for A size 12{A} {} is logical; the mass of an atom is nearly equal to the mass of its nucleus, since electrons have so little mass. The mass of the nucleus turns out to be nearly equal to the sum of the masses of the protons and neutrons in it, which is proportional to A size 12{A} {} . In this context, it is particularly convenient to express masses in units of u. Both protons and neutrons have masses close to 1 u, and so the mass of an atom is close to A size 12{A} {} u. For example, in an oxygen nucleus with eight protons and eight neutrons, A = 16 size 12{A="16"} {} , and its mass is 16 u. As noticed, the unified atomic mass unit is defined so that a neutral carbon atom (actually a 12 C size 12{"" lSup { size 8{"12"} } C} {} atom) has a mass of exactly 12 u size 12{u} {} . Carbon was chosen as the standard, partly because of its importance in organic chemistry.

Masses of the proton, neutron, and electron
Particle Symbol kg u MeV c 2
Proton p 1 . 67262 × 10 27 size 12{1 "." "67262" times "10" rSup { size 8{ - "27"} } } {} 1.007276 938.27
Neutron n 1 . 67493 × 10 27 size 12{1 "." "67493"´"10" rSup { size 8{-"27"} } } {} 1.008665 939.57
Electron e 9 . 1094 × 10 31 size 12{9 "." "1094"´"10" rSup { size 8{-"31"} } } {} 0.00054858 0.511

Let us look at a few examples of nuclides expressed in the Z A X N notation. The nucleus of the simplest atom, hydrogen, is a single proton, or 1 1 H (the zero for no neutrons is often omitted). To check this symbol, refer to the periodic table—you see that the atomic number Z of hydrogen is 1. Since you are given that there are no neutrons, the mass number A is also 1. Suppose you are told that the helium nucleus or α particle has two protons and two neutrons. You can then see that it is written 2 4 He 2 . There is a scarce form of hydrogen found in nature called deuterium; its nucleus has one proton and one neutron and, hence, twice the mass of common hydrogen. The symbol for deuterium is, thus, 1 2 H 1 (sometimes D is used, as for deuterated water D 2 O ). An even rarer—and radioactive—form of hydrogen is called tritium, since it has a single proton and two neutrons, and it is written 1 3 H 2 . These three varieties of hydrogen have nearly identical chemistries, but the nuclei differ greatly in mass, stability, and other characteristics. Nuclei (such as those of hydrogen) having the same Z size 12{Z} {} and different N size 12{N} {} s are defined to be isotopes    of the same element.

There is some redundancy in the symbols A size 12{A} {} , X size 12{X} {} , Z size 12{Z} {} , and N size 12{N} {} . If the element X size 12{X} {} is known, then Z size 12{Z} {} can be found in a periodic table and is always the same for a given element. If both A size 12{A} {} and X size 12{X} {} are known, then N size 12{N} {} can also be determined (first find Z size 12{Z} {} ; then, N = A Z size 12{N=A-Z} {} ). Thus the simpler notation for nuclides is

A X , size 12{"" lSup { size 8{A} } X} {}

which is sufficient and is most commonly used. For example, in this simpler notation, the three isotopes of hydrogen are 1 H, 2 H, and 3 H, while the α particle is 4 He . We read this backward, saying helium-4 for 4 He , or uranium-238 for 238 U . So for 238 U , should we need to know, we can determine that Z = 92 for uranium from the periodic table, and, thus, N = 238 92 = 146 size 12{N="238"-"92"="146"} {} .

A variety of experiments indicate that a nucleus behaves something like a tightly packed ball of nucleons, as illustrated in [link] . These nucleons have large kinetic energies and, thus, move rapidly in very close contact. Nucleons can be separated by a large force, such as in a collision with another nucleus, but resist strongly being pushed closer together. The most compelling evidence that nucleons are closely packed in a nucleus is that the radius of a nucleus    , r size 12{r} {} , is found to be given approximately by

Questions & Answers

where we get a research paper on Nano chemistry....?
Maira Reply
what are the products of Nano chemistry?
Maira Reply
There are lots of products of nano chemistry... Like nano coatings.....carbon fiber.. And lots of others..
Even nanotechnology is pretty much all about chemistry... Its the chemistry on quantum or atomic level
no nanotechnology is also a part of physics and maths it requires angle formulas and some pressure regarding concepts
Preparation and Applications of Nanomaterial for Drug Delivery
Hafiz Reply
Application of nanotechnology in medicine
what is variations in raman spectra for nanomaterials
Jyoti Reply
I only see partial conversation and what's the question here!
Crow Reply
what about nanotechnology for water purification
RAW Reply
please someone correct me if I'm wrong but I think one can use nanoparticles, specially silver nanoparticles for water treatment.
yes that's correct
I think
Nasa has use it in the 60's, copper as water purification in the moon travel.
nanocopper obvius
what is the stm
Brian Reply
is there industrial application of fullrenes. What is the method to prepare fullrene on large scale.?
industrial application...? mmm I think on the medical side as drug carrier, but you should go deeper on your research, I may be wrong
How we are making nano material?
what is a peer
What is meant by 'nano scale'?
What is STMs full form?
scanning tunneling microscope
how nano science is used for hydrophobicity
Do u think that Graphene and Fullrene fiber can be used to make Air Plane body structure the lightest and strongest. Rafiq
what is differents between GO and RGO?
what is simplest way to understand the applications of nano robots used to detect the cancer affected cell of human body.? How this robot is carried to required site of body cell.? what will be the carrier material and how can be detected that correct delivery of drug is done Rafiq
analytical skills graphene is prepared to kill any type viruses .
Any one who tell me about Preparation and application of Nanomaterial for drug Delivery
what is Nano technology ?
Bob Reply
write examples of Nano molecule?
The nanotechnology is as new science, to scale nanometric
nanotechnology is the study, desing, synthesis, manipulation and application of materials and functional systems through control of matter at nanoscale
Is there any normative that regulates the use of silver nanoparticles?
Damian Reply
what king of growth are you checking .?
What fields keep nano created devices from performing or assimulating ? Magnetic fields ? Are do they assimilate ?
Stoney Reply
why we need to study biomolecules, molecular biology in nanotechnology?
Adin Reply
yes I'm doing my masters in nanotechnology, we are being studying all these domains as well..
what school?
biomolecules are e building blocks of every organics and inorganic materials.
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Source:  OpenStax, Concepts of physics with linear momentum. OpenStax CNX. Aug 11, 2016 Download for free at http://legacy.cnx.org/content/col11960/1.9
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