How To Find Out The Mass Number
Atomic structure
Atoms consist of a nucleus containing protons and neutrons, surrounded by electrons in shells. The number of subatomic particles in an cantlet can be calculated from the atom's atomic number and mass number.
Atomic number and mass number
Diminutive number
The number of protons in an atom of an chemical element is its atomic number . Remember that:
- all atoms of a given chemical element take the same number of protons
- atoms of different elements have different numbers of protons
An atom contains equal numbers of protons and electrons . Since protons and electrons have equal and opposite charges, this means that atoms are have no overall electric charge.
For case, the diminutive number of sodium is 11. Every sodium atom has 11 protons and eleven electrons. It has xi positive charges and 11 negative charges.
Mass number
Atoms of different elements normally have different mass numbers , merely they can exist the same. For example, the mass number of argon atoms and calcium atoms can both be twoscore.
Calculating numbers of subatomic particles
The symbol for an atom can be written to show its mass number at the peak, and its diminutive number at the lesser.
To calculate the numbers of subatomic particles in an cantlet, utilise its atomic number and mass number:
- number of protons = atomic number
- number of electrons = atomic number
- number of neutrons = mass number - atomic number
- Question
-
The diminutive number of a sodium atom is eleven and its mass number is 23. Calculate the number of protons, neutrons and electrons it contains.
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Number of protons = 11
Number of electrons = 11
Number of neutrons (mass number - atomic number) = 23 - 11 = 12
Source: https://www.bbc.co.uk/bitesize/guides/z3sg2nb/revision/4
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