Question

how to find how many neutrons there are in an isotope

Answer 1

Atomic mass A is measured by using laboratory experiments like diffusion speed etc.

The atomic number Z is known from number of electrons, charge, protons and chemical properties.

N = number of neutrons = A - Z.
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ISOTOPES -  A Seminar

1. Definition: Elements having the same number Z of protons but different number N of Neutrons .

  Meaning of word: iso-tope: same location (in periodic table) .

2. Examples:  U, Pu (plutonium) ,C, H, KL, Sin, Ra. .... H-1 = Protium. H-2 Deuterium. H-3: Tritium. .

Draw a diagram..of atom nucleus.

3. Notation for writing isotopes,  Meaning . Examples.

4. 80 chemical elements have 253 stable isotopes (naturally found). Also there are around 80 unstable isotopes.  Around 3000 stable/ unstable artificial isotopes are created in nuclear reactors. They are radioactive.

Tin has the maximum number (10) of stable isotopes.  Xenon has 8.

5. A Nuclide is same as an isotope. . But only used in nucleus related contexts.

6. Chemical properties
    In general all isotopes have same properties. Reason is (reaction) properties mainly  depend on electrons in an atom.
But isotopes of Hydrogen and some very large elements behave differently.

7. Stability
   In isotopes number N of neutrons is more than that Z of protons. If the ratio N/Z is greater than 1.3 or 1.4 then it is unstable. 

The repulsions between too many nucleons results in decay of nucleus.  They decay by Beta decay or positron decay.  They get converted into another isotope. Also when they are collided by high speed protons/neutrons/ alpha particles,  nuclear fission happens.

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The instability is like the tensions in a house with some hosts and too many guests.
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8. Atomic mass of an element is calculated as the weighted average of masses of its isotopes multiplied by its proportion in the world.

Majority of natural isotopes have even N and even Z.

9. Uses Applications.

**) Detection of adulteration in food products.
**) Identification of source of meteorites by composition of isotopes.  Eg. Meteorites from mars identified this way.

**) Study of some complicated chemical reaction mechanisms: by Kinetic Isotopic Effect.

**) Identification of elements by (radio) spectroscopy. By identifying frequencies of radiations emitted.

**) To determine concentrations of elements or compounds in a substance/ mixture, by Isotope Dilution Method.

**) Radiocarbon dating of fossils etc.

**) Generating power by Nuclear fusion/ fission.

**) Nuclear bombs

**) To treat cancer by radiation therapy.