Review the key concepts, formulae, and examples before starting your quiz.
🔑Concepts
The atomic number of an element is defined as the total number of protons present in the nucleus of an atom. It is denoted by the symbol .
Since atoms are electrically neutral, the number of protons in an atom is equal to the number of electrons. Therefore, for a neutral atom, atomic number also equals the number of electrons.
Every element has a unique atomic number. No two different elements can have the same atomic number; hence, it identifies the element.
The mass number () is the sum of the total number of protons () and neutrons () present in the nucleus of an atom. These particles are collectively called nucleons.
An element is represented using the notation , where is the chemical symbol, is the mass number, and is the atomic number.
📐Formulae
💡Examples
Problem 1:
The atomic number of Carbon is . Find the number of protons and electrons in a neutral Carbon atom.
Solution:
and
Explanation:
Since the atomic number , and is equal to the number of protons, . In a neutral atom, the number of electrons is equal to the number of protons, so .
Problem 2:
An atom has an atomic number and a mass number . Calculate the number of neutrons present in the nucleus.
Solution:
Explanation:
The number of neutrons is calculated by subtracting the atomic number from the mass number: Substituting the values: Thus, there are neutrons.
Problem 3:
An isotope of Oxygen is represented as . Determine the number of protons, electrons, and neutrons.
Solution:
Explanation:
From the notation, and . Therefore, . For a neutral atom, . The number of neutrons .