Unit 1
Atoms and elements.
Protons, neutrons and electrons, isotopes, electron shells, and how they lay out the periodic table and its families.
Before this unit
- Ratio and scale Mathematics
The unit, lesson by lesson
Lessons
7 lessons · 37 practice questions · about 3 hours
Inside an atom
Three particles build every atom: protons and neutrons in a tiny nucleus, electrons around it. The atomic number decides the element, and the mass number counts everything in the nucleus.
Isotopes
Atoms of the same element with different numbers of neutrons: what they are called, why their chemistry is the same, and how the mixture found in nature sets the relative atomic mass in the periodic table.
Electron shells
How electrons settle into shells, how to write the arrangement, why the outer shell decides the chemistry, and how the shells build the rows and columns of the periodic table.
Trends in the periodic table
Reading the periodic table: row and group, metals and non-metals, and the two key trends, atom size and ionisation energy, along a row and down a group, and why they run in opposite directions.
Metalloids
The elements on the table's staircase: silicon shines like a metal yet shatters like glass, and conducts better the warmer it gets. What the band gap explains, and why arsenic and antimony behave like metals.
Non-metals
A cabinet of sixteen non-metals: why most are gases at room temperature, what stays whole when they melt and boil, how boiling points climb down the halogens, and why carbon is the exception.
Transition metals
The ten columns in the middle of the table: d electrons, ions of more than one charge, and why copper solutions are blue while zinc's are colourless. Ligand-field splitting, the colour left when white light loses one colour, and what ammonia changes.