What is the mass number?

The number of protons plus neutrons in an atom's nucleus.

How many electrons does a neutral atom have?

The same number as its protons (its atomic number).

An atom of the same element with the same number of protons but a different number of neutrons.

Why do isotopes of an element have the same chemical properties?

They have the same number of electrons.

What does the atomic number tell you about an element?

Which element it is, because each element has a different number of protons.

What is relative atomic mass?

The weighted average mass of the isotopes of an element, taking account of their abundance.

How do you calculate relative atomic mass from isotope data?

Multiply each mass number by its percentage abundance, add them, then divide by 100.

Why is relative atomic mass often not a whole number?

It is an average of the masses of different isotopes.

Atomic number, mass number and isotopesIB MYP Chemistry: Flashcards

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What is the atomic number?

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What is the atomic number?: The number of protons in an atom's nucleus.
What is the mass number?: The number of protons plus neutrons in an atom's nucleus.
How do you calculate the number of neutrons?: Mass number - atomic number.
How many electrons does a neutral atom have?: The same number as its protons (its atomic number).
Which number is written at the top in nuclide notation?: The mass number.
What is an isotope?: An atom of the same element with the same number of protons but a different number of neutrons.
Why do isotopes of an element have the same chemical properties?: They have the same number of electrons.
How many neutrons are in carbon-14 (atomic number 6)?: 8 (14 - 6).
How many neutrons are in carbon-12 (atomic number 6)?: 6 (12 - 6).
What does the atomic number tell you about an element?: Which element it is, because each element has a different number of protons.
What is relative atomic mass?: The weighted average mass of the isotopes of an element, taking account of their abundance.
How do you calculate relative atomic mass from isotope data?: Multiply each mass number by its percentage abundance, add them, then divide by 100.
A sample is 75% chlorine-35 and 25% chlorine-37. What is the relative atomic mass?: 35.5.
Why is relative atomic mass often not a whole number?: It is an average of the masses of different isotopes.

Exam questions on Atomic number, mass number and isotopes

A student is studying sodium, which is written in notation as $^{23}_{11}\mathrm{Na}$ . She is learning what the two numbers in the notation tell her about the particles inside a sodium atom.
Explain why a neutral sodium atom has 11 electrons.2 marks
Chemists describe atoms by the numbers of particles they contain. Four atoms are described below. Atom W has 17 protons, 18 neutrons and 17 electrons. Atom X has 18 protons, 18 neutrons and 18 electrons. Atom Y has 17 protons, 20 neutrons and 17 electrons. Atom Z has 19 protons, 20 neutrons and 19 electrons.
Explain why atoms W and Y are the same element but have different masses.2 marks
Chlorine has atomic number 17. A typical sample of chlorine contains two isotopes, $^{35}\mathrm{Cl}$ and $^{37}\mathrm{Cl}$ . In the sample, 75% of the atoms are $^{35}\mathrm{Cl}$ and 25% of the atoms are $^{37}\mathrm{Cl}$ .
State the number of protons, neutrons and electrons in a neutral atom of $^{37}\mathrm{Cl}$ .3 marks

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Written by the Exaim team, led by Shaun Daswani (Head of Upper Secondary, Improve ME Institute; MSc Financial Mathematics, Imperial College London; BSc, UCL) and Jason Daswani (operational lead, Improve ME Institute; LSE).