# 0.2 The atom  (Page 7/14)

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## Interesting fact

In Greek, “same place” reads as $\stackrel{}{\iota }\sigma o\varsigma$ $\tau \stackrel{}{o}\pi o\varsigma$ (isos topos). This is why atoms which have the same number of protons, but different numbers of neutrons, are called isotopes . They are in the same place on the Periodic Table!

The following worked examples will help you to understand the concept of an isotope better.

For the element ${}_{92}^{234}\mathrm{U}$ (uranium), use standard notation to describe:

1. the isotope with 2 fewer neutrons
2. the isotope with 4 more neutrons
1. We know that isotopes of any element have the same number of protons (same atomic number)in each atom, which means that they have the same chemical symbol. However, they have a different number of neutrons, and therefore a different mass number.

2. Therefore, any isotope of uranium will have the symbol:

$\mathrm{U}$

Also, since the number of protons in uranium isotopes is always the same, we can write down the atomic number:

${}_{92}\mathrm{U}$

Now, if the isotope we want has 2 fewer neutrons than ${}_{92}^{234}\mathrm{U}$ , then we take the original mass number and subtract 2, which gives:

${}_{92}^{232}\mathrm{U}$

Following the steps above, we can write the isotope with 4 more neutrons as:

${}_{92}^{238}\mathrm{U}$

Which of the following are isotopes of ${}_{20}^{40}\mathrm{Ca}$ ?

• ${}_{19}^{40}\mathrm{K}$
• ${}_{20}^{42}\mathrm{Ca}$
• ${}_{18}^{40}\mathrm{Ar}$
1. We know that isotopes have the same atomic number but different mass numbers.

2. You need to look for the element that has the same atomic number but a different atomic mass number. The only element is ${}_{20}^{42}\mathrm{Ca}$ . What is different is that there are 2 more neutrons than in the original element.

For the sulphur isotope ${}_{16}^{33}\mathrm{S}$ , give the number of...

1. protons
2. nucleons
3. electrons
4. neutrons
1. $Z=16$ , therefore the number of protons is 16 (answer to (a)).

2. $A=33$ , therefore the number of nucleons is 33 (answer to (b)).

3. The atom is neutral, and therefore the number of electrons is the same as the number of protons. The number of electrons is 16 (answer to (c)).

4. $\begin{array}{c}\hfill N=A-Z=33-16=17\end{array}$

The number of neutrons is 17 (answer to (d)).

## Isotopes

1. Atom A has 5 protons and 5 neutrons, and atom B has 6 protons and 5 neutrons. These atoms are...
1. allotropes
2. isotopes
3. isomers
4. atoms of different elements
2. For the sulphur isotopes, ${}_{16}^{32}\mathrm{S}$ and ${}_{16}^{34}\mathrm{S}$ , give the number of...
1. protons
2. nucleons
3. electrons
4. neutrons
3. Which of the following are isotopes of ${}_{17}^{35}\mathrm{Cl}$ ?
1. ${}_{35}^{17}\mathrm{Cl}$
2. ${}_{17}^{35}\mathrm{Cl}$
3. ${}_{17}^{37}\mathrm{Cl}$
4. Which of the following are isotopes of $\mathrm{U-}235$ ? (X represents an element symbol)
1. ${}_{92}^{238}\mathrm{X}$
2. ${}_{90}^{238}\mathrm{X}$
3. ${}_{92}^{235}\mathrm{X}$

## Relative atomic mass

It is important to realise that the atomic mass of isotopes of the same element will be different because they have a different number of nucleons. Chlorine, for example, has two common isotopes which are chlorine-35 and chlorine-37. Chlorine-35 has an atomic mass of 35 u, while chlorine-37 has an atomic mass of 37 u. In the world around us, both of these isotopes occur naturally. It doesn't make sense to say that the element chlorine has an atomic mass of 35 u, or that it has an atomic mass of 37 u. Neither of these are absolutely true since the mass varies depending on the form in which the element occurs. We need to look at how much more common one is than the other in order to calculate the relative atomic mass for the element chlorine. This is the number that you find on the Periodic Table.

#### Questions & Answers

how can chip be made from sand
Eke Reply
is this allso about nanoscale material
Almas
are nano particles real
Missy Reply
yeah
Joseph
Hello, if I study Physics teacher in bachelor, can I study Nanotechnology in master?
Lale Reply
no can't
Lohitha
where is the latest information on a no technology how can I find it
William
currently
William
where we get a research paper on Nano chemistry....?
Maira Reply
nanopartical of organic/inorganic / physical chemistry , pdf / thesis / review
Ali
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..
learn
Even nanotechnology is pretty much all about chemistry... Its the chemistry on quantum or atomic level
learn
Google
da
no nanotechnology is also a part of physics and maths it requires angle formulas and some pressure regarding concepts
Bhagvanji
hey
Giriraj
Preparation and Applications of Nanomaterial for Drug Delivery
Hafiz Reply
revolt
da
Application of nanotechnology in medicine
has a lot of application modern world
Kamaluddeen
yes
narayan
what is variations in raman spectra for nanomaterials
Jyoti Reply
ya I also want to know the raman spectra
Bhagvanji
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.
Damian
yes that's correct
Professor
I think
Professor
Nasa has use it in the 60's, copper as water purification in the moon travel.
Alexandre
nanocopper obvius
Alexandre
what is the stm
Brian Reply
is there industrial application of fullrenes. What is the method to prepare fullrene on large scale.?
Rafiq
industrial application...? mmm I think on the medical side as drug carrier, but you should go deeper on your research, I may be wrong
Damian
How we are making nano material?
LITNING Reply
what is a peer
LITNING Reply
What is meant by 'nano scale'?
LITNING Reply
What is STMs full form?
LITNING
scanning tunneling microscope
Sahil
how nano science is used for hydrophobicity
Santosh
Do u think that Graphene and Fullrene fiber can be used to make Air Plane body structure the lightest and strongest. Rafiq
Rafiq
what is differents between GO and RGO?
Mahi
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
Rafiq
if virus is killing to make ARTIFICIAL DNA OF GRAPHENE FOR KILLED THE VIRUS .THIS IS OUR ASSUMPTION
Anam
analytical skills graphene is prepared to kill any type viruses .
Anam
Any one who tell me about Preparation and application of Nanomaterial for drug Delivery
Hafiz
what is Nano technology ?
Bob Reply
write examples of Nano molecule?
Bob
The nanotechnology is as new science, to scale nanometric
brayan
nanotechnology is the study, desing, synthesis, manipulation and application of materials and functional systems through control of matter at nanoscale
Damian
What makes metals better to use as wires than non-metals? (please link to bonding type)??? HELP
Yash Reply

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Source:  OpenStax, Chemistry grade 10 [caps]. OpenStax CNX. Jun 13, 2011 Download for free at http://cnx.org/content/col11303/1.4
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