Atomic Number Chemistry Example 2

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Example 2

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Two atoms both have a mass number of 40. Atom A has 20 protons and Atom B has 19 protons. Are they the same element? How many neutrons does each have?

Solution

  1. 1
    Atom A: Z=20Z = 20 (calcium), neutrons =40−20=20= 40 - 20 = 20.
  2. 2
    Atom B: Z=19Z = 19 (potassium), neutrons =40−19=21= 40 - 19 = 21.
  3. 3
    They are different elements because they have different atomic numbers, even though they share the same mass number (these are called isobars).

Answer

Atom A: Ca (20 neutrons), Atom B: K (21 neutrons) — different elements\text{Atom A: Ca (20 neutrons), Atom B: K (21 neutrons) — different elements}
The atomic number, not the mass number, determines the identity of an element. Atoms with the same mass number but different atomic numbers are called isobars.

About Atomic Number

The number of protons in an atom's nucleus, which uniquely identifies the element and determines its position in the periodic table.

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More Atomic Number Examples

Example 1 easy

Element X has 15 protons. Identify the element and determine the number of electrons in a neutral at

Example 3 easy

What is the atomic number of an element with 29 protons? Name the element.

Example 4 easy

An atom has atomic number 15. How many protons does it have? If the atom is neutral, how many electr

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