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Chemistry - Atomic Structure (Protons, Neutrons, Electrons)

Grade 8Cambridge (IGCSE)

Review the key concepts, formulae, and examples before starting your quiz.

🔑Concepts

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The atom consists of three subatomic particles: protons, neutrons, and electrons. Protons and neutrons are located in the nucleus, while electrons orbit in shells.

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The Atomic Number (ZZ) is the number of protons in an atom's nucleus. This defines the element's identity.

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The Mass Number (AA) is the total number of protons and neutrons in the nucleus.

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In a neutral atom, the number of protons equals the number of electrons. For example, a neutral Carbon atom (CC) has 66 protons and 66 electrons.

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Subatomic particles have relative charges and masses: Protons (+1+1 charge, mass 11), Neutrons (00 charge, mass 11), and Electrons (−1-1 charge, mass 11840\frac{1}{1840} or negligible).

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Isotopes are atoms of the same element with the same number of protons but different numbers of neutrons. For example, 12C^{12}C and 14C^{14}C.

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Electronic configuration for the first 20 elements follows the rule of 2,8,82, 8, 8 for the first three shells.

📐Formulae

Mass Number (A)=Number of Protons (Z)+Number of NeutronsMass\ Number\ (A) = Number\ of\ Protons\ (Z) + Number\ of\ Neutrons

Number of Neutrons=A−ZNumber\ of\ Neutrons = A - Z

Net Charge=Number of Protons−Number of ElectronsNet\ Charge = Number\ of\ Protons - Number\ of\ Electrons

Relative Atomic Mass (Ar)=∑(Isotope Mass×Isotope Abundance)100Relative\ Atomic\ Mass\ (A_r) = \frac{\sum (Isotope\ Mass \times Isotope\ Abundance)}{100}

💡Examples

Problem 1:

An atom of Sodium is represented as 1123Na^{23}_{11}Na. Determine the number of protons, neutrons, and electrons in this neutral atom.

Solution:

Protons = 1111, Electrons = 1111, Neutrons = 1212.

Explanation:

The atomic number (ZZ) is the subscript (1111), which gives the number of protons. Since it is a neutral atom, electrons = protons = 1111. The mass number (AA) is the superscript (2323). Neutrons = A−Z=23−11=12A - Z = 23 - 11 = 12.

Problem 2:

An ion has 1717 protons, 1818 neutrons, and 1818 electrons. Identify the element and its charge using nuclide notation.

Solution:

1735Cl−^{35}_{17}Cl^{-}

Explanation:

The number of protons (1717) identifies the element as Chlorine (ClCl). The mass number is 17+18=3517 + 18 = 35. The charge is calculated as protons−electrons=17−18=−1protons - electrons = 17 - 18 = -1. Therefore, the symbol is 1735Cl−^{35}_{17}Cl^{-}.

Problem 3:

Calculate the number of electrons and the electronic configuration for an Aluminum atom with atomic number 1313.

Solution:

Electrons = 1313; Configuration = 2,8,32, 8, 3.

Explanation:

A neutral Aluminum atom has 1313 protons and therefore 1313 electrons. Following the shell rules: the 1st shell takes 22, the 2nd shell takes 88, and the remaining 33 go into the 3rd shell.