Protons, neutrons and electrons, electron shells for atoms 1–20, atomic and mass number, nuclide notation, relative atomic mass, isotopes and the uses of radioactive isotopes.
5 narrated scenes. Press play, listen and read along — the points appear as they are explained. Use ‹ Prev / Next › or the scene bar to jump to any scene.
Every substance you will ever meet is built from about a hundred kinds of atom. Knowing what is inside an atom tells you how the element will behave.
Narration uses your device’s built-in voice. No sound? Switch to “Captions only” — the captions advance on their own.
Pick an atom. Count the protons, neutrons and the electrons in each shell.
Copy these into your notebook in your own words — that is how they stick.
p: +1, mass 1; n: 0, mass 1; e: −1, mass 1/1 840.
Number of protons.
Protons + neutrons.
A − Z.
2, 8, 8, 2 for the first 20 elements.
Positive: electrons lost; negative: electrons gained.
Same protons (same element), different neutrons.
Average mass of an atom compared with 1/12 of carbon-12.
3 quick games on this lesson. Earn XP and badges as you play — your best score for each game is saved. Games are for practice and do not change your exam readiness. More games in the Chemistry Arcade.
8 items modelled on real CSEC Paper 1 questions. Choose one answer for each, then check. Aim for 80% or better. Work each item on paper first.
Write full answers, then reveal the mark scheme and tick the points you earned (14 marks in total). Show all your working — method marks count. Your answers are saved on this device.
Question 1 [14 marks]
The nuclide notation for an atom of sodium is ²³₁₁Na. A sample of magnesium contains the isotopes ²⁴Mg (80%) and ²⁶Mg (20%).
(a) (a) Define the term atomic number. [1]
(b) (b) State the number of protons, neutrons and electrons in a neutral atom of ²³₁₁Na. [3]
(c) (c) Draw the electron arrangement of a sodium atom. [2]
(d) (d) Explain the term isotope. [2]
(e) (e) Calculate the relative atomic mass of magnesium from the data. [3]
(f) (f) State two uses of radioactive isotopes. [2]
(g) (g) Write the number of electrons in the sodium ion, ²³₁₁Na⁺. [1]
Find these in your own past-paper booklets for extra timed practice. Items above are written in the style of these papers; any adapted from a specific question say so.