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Nuclear Physics - The nuclear atom

Grade 12IGCSEPhysics

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

🔑Concepts

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The Rutherford α\alpha-particle scattering experiment provided evidence for the nuclear atom. Observations showed that most α\alpha-particles passed straight through gold foil, while a few were deflected at large angles, concluding that the atom is mostly empty space with a tiny, dense, positively charged nucleus.

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The nucleus contains protons and neutrons, collectively known as nucleons. Protons have a relative charge of +1+1, while neutrons are neutral (00).

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Electrons orbit the nucleus in specific energy levels and have a relative charge of −1-1. In a neutral atom, the number of protons equals the number of electrons.

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Nuclide notation is written as ZAX{}^{A}_{Z}X, where XX is the chemical symbol, AA is the nucleon (mass) number, and ZZ is the proton (atomic) number.

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Isotopes are atoms of the same element that possess the same number of protons (ZZ) but different numbers of neutrons (NN). This means they have the same chemical properties but different physical properties.

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The mass of an atom is concentrated in the nucleus, as the mass of an electron is approximately 11840\frac{1}{1840} the mass of a proton.

📐Formulae

A=Z+NA = Z + N

Qnucleus=+ZeQ_{nucleus} = +Ze

e=1.6×10−19 Ce = 1.6 \times 10^{-19} \text{ C}

Number of Neutrons=A−Z\text{Number of Neutrons} = A - Z

💡Examples

Problem 1:

A neutral isotope of Uranium is represented as 92238U{}^{238}_{92}U. Calculate the number of protons, neutrons, and electrons present in the atom.

Solution:

Protons (ZZ) = 9292. Neutrons (N=A−ZN = A - Z) = 238−92=146238 - 92 = 146. Electrons (for a neutral atom) = 9292.

Explanation:

The bottom number (ZZ) represents the proton number. In a neutral atom, electrons equal protons. The top number (AA) is the total nucleons; subtracting ZZ from AA gives the neutron count.

Problem 2:

Calculate the total charge of the nucleus of a Nitrogen atom, given its notation is 714N{}^{14}_{7}N.

Solution:

Q=Z×e=7×(1.6×10−19 C)=1.12×10−18 CQ = Z \times e = 7 \times (1.6 \times 10^{-19} \text{ C}) = 1.12 \times 10^{-18} \text{ C}

Explanation:

The charge of the nucleus is determined by the number of protons (Z=7Z = 7) multiplied by the elementary charge (ee). Neutrons contribute no charge.

Problem 3:

Identify the relationship between 612C{}^{12}_{6}C and 614C{}^{14}_{6}C.

Solution:

They are isotopes of Carbon.

Explanation:

Both atoms have the same atomic number (Z=6Z = 6), which identifies them as Carbon, but different nucleon numbers (1212 and 1414), meaning they have different numbers of neutrons (66 and 88 respectively).

The nuclear atom - Revision Notes & Key Formulas | IGCSE Grade 12 Physics