Subatomic particles and isotopes
If the atom were a football stadium, the nucleus would be the size of a marble placed right in the centre of the pitch. Inside that "marble" and around it live just three types of particle, and three are enough to explain almost all the chemistry you are going to study.
The three particles of the atom
If you rub a plastic ruler against a woollen jumper and bring it close to small pieces of paper, you will see them jump towards it as if by magic: the matter we touch contains electric charges that can be transferred, but what tiny charged particles is each atom actually made of?
Since the whole atom is neutral, a normal atom has the same number of protons as electrons: the positive and negative charges cancel out.
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:…
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 football stadium, the nucleus would be a marble in the centre of the pitch. Which particles would be inside that "marble"? And which particles would…
If the atom were a football stadium, the nucleus would be a marble in the centre of the pitch. 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 $\dots$."
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: the identity card
Iron is a hard, magnetic metal, helium is a gas that makes balloons float and sulphur is a yellow powder; yet all three are made up exclusively of protons, neutrons and electrons: what fixed internal property makes an atom iron rather than helium or sulphur?
Move the "Protons" slider in the interactive: notice that changing $Z$ also changes which element you are talking about.
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.
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.
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.
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…
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.
The mass number A: counting protons and neutrons
A proton and a neutron weigh almost the same, about $2000$ times more than an electron. That is why almost all the mass of an atom is in the nucleus.
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…
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?
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.
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…
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.
Ions: atoms with a charge
A neutral atom can gain or lose electrons. When that happens, its charges are no longer balanced and it becomes an ion.
Look at the interactive: if you lower the number of electrons below the number of protons, a net positive charge appears. That is exactly what happens to potassium when it loses an electron.
Potassium is a mineral abundant in bananas. A neutral potassium atom, with $Z = 19$, loses one of its electrons, as shown in the figure. a) How many protons and how many…
Potassium is a mineral abundant in bananas. A neutral potassium atom, with $Z = 19$, loses one of its electrons, as shown in the figure.
- a) How many protons and how many electrons does the atom have left?
- b) Is it still potassium? Justify your answer by considering what defines an element.
- c) What net charge does the atom have now? Explain the result by comparing its positive and negative charges.
Isotopes: same element, different mass
In 1912, when pure neon gas atoms were deflected with electric fields, scientists were surprised to discover that there were neon atoms with mass 20 and others with mass 22, even though their chemical behaviour was exactly the same: how can atoms of the same element have different masses?
Since $Z$ is the same, isotopes are still the same element and have very similar chemical properties. The mass changes and the nuclear stability may change: some isotopes are stable and others are radioactive.
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…
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?
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…
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.
Archaeologists find a mammoth tusk and want to know its age. To calculate it, they use the carbon-14 remaining in the remains. a) Carbon-14 is an isotope of carbon:…
Archaeologists find a mammoth tusk and want to know its age. To calculate it, they use the carbon-14 remaining in the remains.
- a) Carbon-14 is an isotope of carbon: explain what this means, referring to protons and neutrons.
- 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.