Constituents of the atom Flashcards – AQA A-level Physics (7408)

What is the basic structure of an atom?

A small, positively charged nucleus contains protons and neutrons; electrons occupy the space around it.

Which particles are called nucleons?

Protons and neutrons.

How do the numbers of protons and electrons compare in a neutral atom?

They are equal.

Where is almost all of an atom’s mass concentrated?

In the nucleus.

What are the charges in coulombs of a proton, a neutron and an electron?

• Proton: $+1.602 \times 10^{-19}\,\mathrm{C}$
• Neutron: $0\,\mathrm{C}$
• Electron: $-1.602 \times 10^{-19}\,\mathrm{C}$

What is the approximate mass of a proton in kilograms?

$1.673 \times 10^{-27}\,\mathrm{kg}$

What is the approximate mass of a neutron in kilograms?

$1.675 \times 10^{-27}\,\mathrm{kg}$

What is the approximate mass of an electron in kilograms?

$9.11 \times 10^{-31}\,\mathrm{kg}$

What are the relative charges of a proton, a neutron and an electron?

Proton: $+1$; neutron: $0$; electron: $-1$.

What are the approximate relative masses of a proton, a neutron and an electron?

Proton: $1$; neutron: $1$; electron: $1/1836$.

How is the atomic mass unit (u or amu) defined?

One twelfth of the mass of a carbon-12 atom.

What is the approximate value of one atomic mass unit in kilograms?

$1.661 \times 10^{-27}\,\mathrm{kg}$

What is the proton number $Z$ of a nucleus?

The number of protons in the nucleus.

What does the proton number determine about a nuclide?

Its chemical element.

What is the nucleon number $A$ of a nucleus?

The total number of protons and neutrons in the nucleus.

How is the number of neutrons calculated from nucleon number $A$ and proton number $Z$?

$A-Z$

In nuclide notation, where are the nucleon number and proton number written relative to the element symbol?

The nucleon number is at the upper left and the proton number at the lower left.

What composition does nuclide notation specify, and what particle count does it not specify?

It specifies nuclear composition, not the number of electrons.

What are isotopes of an element?

Atoms with the same proton number but different neutron numbers, and therefore different nucleon numbers.

How is the mean atomic mass of an isotopic mixture calculated from isotopic masses and fractional abundances?

$\bar{m}=\sum_i f_i m_i$ where $f_i$ is the fractional abundance and $m_i$ the mass of isotope $i$.

What must the fractional abundances of all isotopes in a sample sum to?

$1$

How is a percentage isotopic abundance converted to a fractional abundance?

Divide the percentage by $100$.