Edexcel IGCSE Physics: Double Science 复习笔记:7.1.2 Isotopes

Edexcel IGCSE Physics: Double Science 复习笔记:7.1.2 Isotopes

Isotopes

 

  • Although the number of protons in a particular element is always the same, the number of neutrons can be different
  • Isotopes are atoms of the same element that have an equal number of protons but a different number of neutrons
  • In the diagram below are three isotopes of Hydrogen:

 

11.1.4-Isotopes-of-Hydrogen

 

Hydrogen has three isotopes, each with a different number of neutrons

 

 

 

  • Isotopes occur naturally, but some are more rare than others
  • For example, about 2 in every 10,000 Hydrogen atoms is Deuterium
    • Tritium is even more rare (about 1 in every billion billion hydrogen atoms)

     

 

 

 

Differences Between Isotopes

  • The number of neutrons in an atom does not affect the chemical properties of an atom, such as its charge, but only its mass
    • This is because neutrons have no charge but do have mass

     

  • The charge of the nucleus of a particular element is always the same
  • In the periodic table, the mass number of Chlorine is often given as 35.5

 

 

4.1.4-Chlorine-isotope

 

This section of a periodic table shows Chlorine as having a mass number of 35.5, but other elements have an integer mass number

 

 

 

  • The mass number of Chlorine is given as 35.5 because it has roughly equal numbers of isotopes with a mass number of 35, and of 36
  • The number of electrons and protons in different isotopes remains the same
  • Isotopes tend to be more unstable due to the imbalance of protons and neutrons

 

Worked Example

State the number of protons, neutrons and electrons in Chlorine-35 and Chlorine-36 atoms.

 

Step 1: Determine the number of protons

    • The atomic number is the number of protons
    • Both Chlorine-35 and Chlorine-36 have 17 protons

     

 

Step 2: Determine the number of neutrons

    • The mass number is the number of protons and neutrons
    • Chlorine-35 neutrons: 35 - 17 = 18 neutrons
    • Chlorine-36 neutrons: 36 - 17 = 19 neutrons

     

 

Step 3: Determine the number of electrons

 

    • The number of electrons is equal to the number of protons
    • Both Chlorine-35 and Chlorine-36 have 17 electrons

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