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Interesting fact

In Greek, “same place” reads as ι ` σ o ς τ o ` π o ς (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 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:

    U

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

    92 U

    Now, if the isotope we want has 2 fewer neutrons than 92 234 U , then we take the original mass number and subtract 2, which gives:

    92 232 U

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

    92 238 U

Which of the following are isotopes of 20 40 Ca ?

  • 19 40 K
  • 20 42 Ca
  • 18 40 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 Ca . What is different is that there are 2 more neutrons than in the original element.

For the sulphur isotope 16 33 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. N = A - Z = 33 - 16 = 17

    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 S and 16 34 S , give the number of...
    1. protons
    2. nucleons
    3. electrons
    4. neutrons
  3. Which of the following are isotopes of 17 35 Cl ?
    1. 35 17 Cl
    2. 17 35 Cl
    3. 17 37 Cl
  4. Which of the following are isotopes of U- 235 ? (X represents an element symbol)
    1. 92 238 X
    2. 90 238 X
    3. 92 235 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 does Neisseria cause meningitis
Nyibol Reply
what is microbiologist
Muhammad Reply
what is errata
Muhammad
is the branch of biology that deals with the study of microorganisms.
Ntefuni Reply
What is microbiology
Mercy Reply
studies of microbes
Louisiaste
when we takee the specimen which lumbar,spin,
Ziyad Reply
How bacteria create energy to survive?
Muhamad Reply
Bacteria doesn't produce energy they are dependent upon their substrate in case of lack of nutrients they are able to make spores which helps them to sustain in harsh environments
_Adnan
But not all bacteria make spores, l mean Eukaryotic cells have Mitochondria which acts as powerhouse for them, since bacteria don't have it, what is the substitution for it?
Muhamad
they make spores
Louisiaste
what is sporadic nd endemic, epidemic
Aminu Reply
the significance of food webs for disease transmission
Abreham
food webs brings about an infection as an individual depends on number of diseased foods or carriers dully.
Mark
explain assimilatory nitrate reduction
Esinniobiwa Reply
Assimilatory nitrate reduction is a process that occurs in some microorganisms, such as bacteria and archaea, in which nitrate (NO3-) is reduced to nitrite (NO2-), and then further reduced to ammonia (NH3).
Elkana
This process is called assimilatory nitrate reduction because the nitrogen that is produced is incorporated in the cells of microorganisms where it can be used in the synthesis of amino acids and other nitrogen products
Elkana
Examples of thermophilic organisms
Shu Reply
Give Examples of thermophilic organisms
Shu
advantages of normal Flora to the host
Micheal Reply
Prevent foreign microbes to the host
Abubakar
they provide healthier benefits to their hosts
ayesha
They are friends to host only when Host immune system is strong and become enemies when the host immune system is weakened . very bad relationship!
Mark
what is cell
faisal Reply
cell is the smallest unit of life
Fauziya
cell is the smallest unit of life
Akanni
ok
Innocent
cell is the structural and functional unit of life
Hasan
is the fundamental units of Life
Musa
what are emergency diseases
Micheal Reply
There are nothing like emergency disease but there are some common medical emergency which can occur simultaneously like Bleeding,heart attack,Breathing difficulties,severe pain heart stock.Hope you will get my point .Have a nice day ❣️
_Adnan
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Innocent
I think infection prevention and control is the avoidance of all things we do that gives out break of infections and promotion of health practices that promote life
Lubega
Heyy Lubega hussein where are u from?
_Adnan
en français
Adama
which site have a normal flora
ESTHER Reply
Many sites of the body have it Skin Nasal cavity Oral cavity Gastro intestinal tract
Safaa
skin
Asiina
skin,Oral,Nasal,GIt
Sadik
How can Commensal can Bacteria change into pathogen?
Sadik
How can Commensal Bacteria change into pathogen?
Sadik
all
Tesfaye
by fussion
Asiina
what are the advantages of normal Flora to the host
Micheal
what are the ways of control and prevention of nosocomial infection in the hospital
Micheal
what is inflammation
Shelly Reply
part of a tissue or an organ being wounded or bruised.
Wilfred
what term is used to name and classify microorganisms?
Micheal Reply
Binomial nomenclature
adeolu
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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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