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What is atomic number and mass number?

Answer Text:
What is atomic number and mass number?
Atomic number.
- Refers to the number of protons in the nucleus of an atom;
Examples.
-Sodium has 11 protons in the nucleus and thus said to have atomic number 11;
-Chlorine has 17 protons in the nucleus and thus said to have atomic number 17;
Mass number;
- Refers to the sum of the number of protons and neutrons in an atom of an element;
Examples:
-Sodium has 12 neutrons and 11 protons hence a mass number of 23;
-Chlorine has 18 neutrons and 17 protons hence a mass number of 35.
Notation of atomic number and mass number;
- Both atomic number and mass number of an element can be written along with the symbol of an element;
Mass number;
- Is conventionally represented as a superscript to the left of the symbol;
Examples:
Sodium; #\ ^23Na#;
Magnesium #\ ^24Mg#;
Atomic number;
- Is conventionally represented as a subscript to the left of the symbol;
Examples:
Sodium; #\ _11Na#;
Magnesium #\ _12Mg#;
Thus the elements can be conventionally represented as:
Sodium #\ _11^23Na#
Magnesium#\ _12^ 24Mg#