AQA · Week 1 of the 13-week plan
Notes for every section, eight new exam-style questions with full worked solutions, and online recall cards for your review days. Nothing here is copied from the book.
What this chapter covers
- 1.1 Atoms, sub-atomic particles and isotopes
- 1.2 Relative masses
- 1.3 Time-of-flight (TOF) mass spectrometry
- 1.4 Reading a mass spectrum
- 1.5 Shells, sub-shells and orbitals
- 1.6 Electron configurations and blocks
- 1.7 Ionisation energies
- 1.8 Evidence for shells and sub-shells
Learn it
Read one section at a time, then answer its check question before you open the answer.
1.1 Atoms, sub-atomic particles and isotopes
Every atom has a tiny, dense nucleus containing protons and neutrons, surrounded by electrons in shells. Almost all the mass is in the nucleus; almost all the volume is empty space where the electrons are.
| Particle | Relative mass | Relative charge | Where |
|---|---|---|---|
| Proton | 1 | +1 | Nucleus |
| Neutron | 1 | 0 | Nucleus |
| Electron | 1/1836 (negligible) | −1 | Shells |
Atomic number, Z: the number of protons in the nucleus. It decides which element the atom is.
Mass number, A: the total number of protons and neutrons in the nucleus.
Neutrons = A − Z. In a neutral atom, electrons = Z.
A nuclide is written with the mass number at the top left and the atomic number at the bottom left, for example 2311Na: 11 protons, 12 neutrons, 11 electrons.
Ions. Only the number of electrons changes. A 2+ ion has lost two electrons; a 3− ion has gained three. So 24Mg2+ has 12 protons, 12 neutrons and 10 electrons.
Isotopes are atoms of the same element with the same number of protons but different numbers of neutrons.
Isotopes have the same chemical properties, because they have the same electron configuration and chemistry is about electrons. They have slightly different physical properties that depend on mass, such as density and rate of diffusion.
How ideas about the atom developed. Dalton pictured solid spheres; Thomson found the electron and proposed the "plum pudding" model; Rutherford's gold-foil experiment showed a small, dense, positive nucleus; Bohr put electrons in fixed energy levels. Each model was replaced when new evidence did not fit it.
Check yourself: How many protons, neutrons and electrons are in 37Cl−?
17 protons, 20 neutrons, 18 electrons
1.2 Relative masses
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1.3 Time-of-flight (TOF) mass spectrometry
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1.4 Reading a mass spectrum
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1.5 Shells, sub-shells and orbitals
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1.6 Electron configurations and blocks
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1.7 Ionisation energies
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1.8 Evidence for shells and sub-shells
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Extra worked questions
Cover the solution, answer on paper, then mark yourself against each step. Each step shows the mark it earns.
All 8 worked solutions are free for members. The first one is open to everyone.
Particles in ions
State the numbers of protons, neutrons and electrons in (a) the ion 56Fe3+ and (b) the ion 32S2−.
Try it first, then show the worked solution
| (a) Protons and neutrons | Fe has atomic number 26, so 26 protons. Neutrons = 56 − 26 = 30. | 1 |
|---|---|---|
| (a) Electrons | A 3+ ion has lost three electrons: 26 − 3 = 23 electrons. | 1 |
| (b) All three | S has atomic number 16: 16 protons, 32 − 16 = 16 neutrons, and 16 + 2 = 18 electrons. | 1 |
Answer: (a) 26 p, 30 n, 23 e (b) 16 p, 16 n, 18 e
Examiner tip: Only the electrons change when an atom becomes an ion. A positive charge means electrons lost; a negative charge means electrons gained.
Relative atomic mass of silicon
A sample of silicon contains 92.23% 28Si, 4.67% 29Si and 3.10% 30Si. Calculate the relative atomic mass of silicon in this sample, to one decimal place.
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Isotope abundances of antimony
A sample of antimony contains only 121Sb and 123Sb. Its relative atomic mass is 121.8. Calculate the percentage abundance of each isotope.
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Configurations of iron and copper
Give the full electronic configuration, in s, p, d notation, of (a) an iron atom, (b) an Fe2+ ion and (c) a copper atom.
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Which group? Successive ionisation energies
The first six ionisation energies of a Period 3 element Z, in kJ mol−1, are 1012, 1907, 2914, 4964, 6274 and 21 267. Deduce the group of Z, explain your answer and identify Z.
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Comparing sodium and potassium
The first ionisation energy of sodium is 496 kJ mol−1 and of potassium is 419 kJ mol−1. The second ionisation energy of sodium is 4562 kJ mol−1. (a) Explain why the first ionisation energy of potassium is lower than that of sodium. (b) Explain why the second ionisation energy of sodium is so much larger than the first.
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Identify an ion from its time of flight
In a time-of-flight mass spectrometer, every ion is accelerated to a kinetic energy of 3.00 × 10−16 J. A singly charged ion of a Period 3 noble gas takes 1.05 × 10−5 s to travel along a flight tube 1.00 m long. Calculate the mass of the ion and identify the isotope. Use KE = ½mv2 and the Avogadro constant, 6.02 × 1023 mol−1.
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The mass spectrum of chlorine gas
Chlorine has two isotopes, 35Cl (75%) and 37Cl (25%). In the mass spectrum of chlorine gas, Cl2, there are three peaks for Cl2+ ions. (a) Give the m/z value of each of these three peaks and the isotopes that make up each ion. (b) Calculate the ratio of the heights of the three peaks.
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Recall cards
Answer out loud or on paper before you turn the card. Only a complete answer counts as "Got it".
These are 3 of 18 recall cards. Premium members get the full deck for every chapter, ready for each review day in their plan.
Your review days
Count from your Day 0, the day you finish learning this chapter. Your plan schedules these for you.
- +1 Recall cards (these online cards, or the cards in the book)
- +3 Recall cards and Q1 to Q4
- +7 Recall cards and Q5 to Q8
- +14 Recall cards and Q9 to Q12
- +30 Full chapter test, timed
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