Atomic Structure and the Periodic Table
What's covered
Key facts
Group 0 — Noble Gases
Argon is used in (incandescent) light bulbs as an inert filler that stops the hot tungsten filament burning.
Group 1 — Alkali Metals
Alkali metals are stored under oil to prevent them reacting with air and water.
Group 7 — Halogens
Down Group 7, boiling points increase as molecules get larger and intermolecular (London) forces strengthen.
Isotopes
Carbon has three natural isotopes: ¹²C (99%, stable), ¹³C (1%, stable), and ¹⁴C (trace, radioactive — used in radiocarbon dating).
Subatomic Particles
An atom has no overall charge because the number of protons (+1 each) equals the number of electrons (−1 each).
The Atomic Model
Niels Bohr placed electrons in fixed orbits at quantised energy levels around the nucleus.
The Periodic Table
Ordering by atomic number resolved anomalies that mass-order produced (e.g. tellurium/iodine).
Transition Metals
The transition metals are the block of elements found between Group 2 and Group 3 in the centre of the periodic table.
Group 0 — Noble Gases
Boiling points increase down Group 0: larger atoms with more electrons have stronger London (dispersion) forces between them.
Group 1 — Alkali Metals
Group 1 metals become more reactive down the group because there are more shells: the outer electron is further from the nucleus and shielded by inner electrons.
Sample questions
A taste of the 87 questions in this topic, answers marked. Sign up to practise the full set with spaced repetition.
Which is a correct use of a noble gas?
- ✓Argon in light bulbs (inert filler stops the filament burning)
- •Argon in scuba diving tanks (cheap inert filler)
- •Helium in tungsten light bulbs (cheap inert atmosphere)
- •Krypton in shop window signs (orange light)
What are the products when potassium reacts with cold water?
- •Potassium carbonate and carbon dioxide
- •Potassium chloride and oxygen
- ✓Potassium hydroxide solution and hydrogen gas
- •Potassium oxide and water
Why does reactivity decrease going down Group 7?
- •Atoms become larger and hold more electrons, so they need fewer extras
- •Higher melting/boiling points make the elements less likely to react with metals
- •More protons in the nucleus pull electrons inwards, making the atom too stable
- ✓Outer shell is further, more shielded — harder to attract an electron
What are isotopes?
- •Atoms of different elements with the same mass number
- ✓Atoms of the same element with different numbers of neutrons
- •Atoms of the same element with different numbers of protons
- •Ions of the same element with different numbers of electrons
Where are the three subatomic particles found in an atom?
- •Electrons in the nucleus; protons and neutrons in outer shells
- ✓Protons and neutrons in the nucleus; electrons in shells around it
- •Protons in the nucleus; neutrons and electrons in the shells
- •Protons, neutrons, and electrons all in the nucleus
What did Rutherford's gold foil experiment demonstrate about atomic structure?
- ✓Atom is mostly empty space with a tiny, dense, positively charged nucleus
- •Atoms contain equal numbers of protons and neutrons in the nucleus
- •Electrons orbit the nucleus in fixed shells (this was Bohr's contribution)
- •The nucleus contains both positive and negative particles that partly cancel
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