Exercises: Subatomic particles and isotopes

In the board game "Build an Atom", there are three types of counters: protons, neutrons, and electrons. State the electrical charge of each of the three particles: positive, negative, or no charge.

If the atom were a soccer stadium, the nucleus would be a marble in the center of the field. Which particles would be inside that "marble"? And which particles would be moving around the stands, surrounding the nucleus?

Complete the sentence with the missing words: "The proton has a $\dots$ charge, the electron has a $\dots$ charge, and the neutron has no $\dots$."

The atomic number $Z$ is like the identity card of an element. Explain what the number $Z$ counts and state its value for an atom with $6$ protons.

When you breathe, oxygen atoms reach your lungs, which have $8$ protons. If an oxygen atom is neutral, how many electrons does it have? Explain why.

The mass number $A$ counts the "heavy" particles of the atom. A carbon atom has $6$ protons and $6$ neutrons, as shown in the figure.

What is its mass number $A$? Which particles of the atom are not included in this count?

Carbon-12 and carbon-14 are like two siblings: they belong to the same element, but they do not "weigh" the same. Explain what the two atoms have in common and how they differ. What is the relationship between them called?

Table salt contains sodium atoms, with $11$ protons and $12$ neutrons in their nucleus, as shown in the figure.

Calculate the mass number $A$ of sodium.

Sparklers glow with an intense white light because they burn magnesium. A neutral magnesium atom has $Z = 12$ and $A = 24$. Calculate how many protons, neutrons, and electrons it has.

The chlorine used to disinfect swimming pools has $Z = 17$ and $A = 35$. Calculate how many neutrons its nucleus has and how many electrons a neutral chlorine atom has.

Aluminum foil used in the kitchen consists of atoms with $Z = 13$ and $A = 27$. Calculate the number of protons, neutrons, and electrons of a neutral aluminum atom.

The iron in lentils helps transport oxygen in the blood. A neutral iron atom has $Z = 26$ and $A = 56$. How many neutrons does it have in its nucleus? And how many electrons around it?

A neutral calcium atom, the mineral found in bones, has $20$ electrons and a mass number $A = 40$. Calculate its atomic number $Z$ and the number of neutrons in its nucleus.

Hydrogen has three known isotopes: protium ($A = 1$), deuterium ($A = 2$), present in so-called "heavy water", and tritium ($A = 3$). They all have $Z = 1$, as shown in the figure.

Calculate how many neutrons each isotope has and explain why all three are the same element.

Carbon-12 has $A = 12$ and carbon-14 has $A = 14$; both have $Z = 6$, as shown in the figure.

1. a) Calculate the number of neutrons each isotope has.
2. b) Explain what the two atoms share and what makes them the same element.

The smell of rotten eggs is due to a gas containing sulphur. A neutral sulphur atom has $16$ electrons and $16$ neutrons. Calculate its atomic number $Z$ and its mass number $A$.

Scientists study past climate by analysing glacier ice, where oxygen-16 ($Z = 8$, $A = 16$) and oxygen-18 ($Z = 8$, $A = 18$) are found.

1. a) Work out the number of protons, neutrons and electrons for each isotope, assuming neutral atoms.
2. b) Explain why both are the same element even though they have different masses.

Cell phone batteries use lithium. Its chemical symbol with its atomic numbers is written like this: ${}^{7}_{3}\text{Li}$. The top number is $A$ and the bottom number is $Z$.

1. a) How many protons, neutrons and electrons does a neutral lithium atom have?
2. b) Beryllium has $4$ protons and $5$ neutrons: write its symbol using the same format.

Potassium is a mineral abundant in bananas. A neutral potassium atom, with $Z = 19$, loses one of its electrons, as shown in the figure.

1. a) How many protons and how many electrons does the atom have left?
2. b) Is it still potassium? Justify your answer by considering what defines an element.
3. c) What net charge does the atom have now? Explain the result by comparing its positive and negative charges.

Archaeologists find a mammoth tusk and want to know its age. To calculate it, they use the carbon-14 remaining in the remains.

1. a) Carbon-14 is an isotope of carbon: explain what this means, referring to protons and neutrons.
2. b) All living things contain carbon and, when they die, their carbon-14 gradually decreases over the years. Explain why this allows us to estimate how long ago the animal died.

A neutral atom has a mass number $A = 31$ and $16$ neutrons in its nucleus.

1. a) Calculate its atomic number $Z$ and its number of electrons.
2. b) Using this list, find out which element it is: oxygen ($Z = 8$), sodium ($Z = 11$), silicon ($Z = 14$), phosphorus ($Z = 15$) or chlorine ($Z = 17$).
3. c) Match heads contain this element. Explain why it is the number $Z$, and not the number of neutrons, that determines which element an atom is.

A proton has almost the same mass as a neutron, and each of them has a mass about $2000$ times greater than that of an electron.

1. a) A carbon-12 atom has $6$ protons, $6$ neutrons and $6$ electrons: explain why virtually all its mass is concentrated in the nucleus.
2. b) Estimate how many times heavier the nucleus of that atom is than all its electrons combined.

Three atoms have these particles: atom X has $6$ protons and $6$ neutrons; atom Y has $6$ protons and $8$ neutrons; atom Z has $7$ protons and $7$ neutrons.

1. a) Which of them are the same element? Why?
2. b) Which pair represents a case of isotopes?
3. c) Calculate the mass number $A$ of each of the three atoms.

A puzzle in a magazine sets this challenge: build, using loose pieces of protons, neutrons and electrons, a neutral beryllium atom, which has $Z = 4$ and $A = 9$, as shown in the figure.

1. a) How many pieces of each type do you need?
2. b) If by mistake you add an extra electron, would the atom still be neutral? What net charge would it have? Justify your answer.
3. c) And if you removed a neutron, would the element change? Would anything about the atom change? Explain your answers.