The Periodic Table
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Periodic table organisation (1b.1)
Elements arranged in order of atomic number. Rows are periods (number of electron shells), columns are groups (number of outer electrons).
Group number tells you outer electrons (for main groups). Period number tells you how many shells are occupied.
Periodic table organisation (1b.1) — Key Knowledge
- Period row — number of shells
- Group column — number of outer electrons
- Atomic number how elements are ordered
Mendeleev's periodic table (1b.1)
Mendeleev arranged elements by atomic weight, left gaps for undiscovered elements, and swapped the order of some elements where their properties didn't fit.
Predictions confirmed when gallium, germanium and scandium were discovered with the properties he'd predicted.
Mendeleev's periodic table (1b.1) — Key Knowledge
- Mendeleev 1869 periodic table
- Gaps predicted undiscovered elements
Metals and non-metals (1b.1)
Metals are on the left and centre of the periodic table. Non-metals are on the right. Metals form positive ions by losing electrons; non-metals form negative ions by gaining electrons.
The dividing line runs roughly diagonally. Most elements are metals.
Metals and non-metals (1b.1) — Key Knowledge
- Metals left/centre, lose electrons, form + ions
- Non-metals right, gain electrons, form − ions
Group 1 — properties (1b.2)
Group 1 metals have one electron in their outer shell. They are soft, have low melting points and low density compared to typical metals. Stored in oil because they react with air and water.
Lithium, sodium and potassium all float on water. Very different from "typical" metals like iron or copper.
Group 1 — properties (1b.2) — Key Knowledge
- Alkali metals Group 1: lithium, sodium, potassium…
- Soft, Low melting point, Low density
Group 1 — reaction with water (1b.2)
Group 1 metals react with water to produce hydrogen gas and a metal hydroxide (an alkaline solution). Reaction gets more vigorous down the group.
Lithium fizzes gently; sodium fizzes vigorously and melts into a ball; potassium reacts violently and the hydrogen ignites with a lilac flame.
Group 1 — reaction with water (1b.2) — Key Knowledge
- Metal + water → metal hydroxide + hydrogen e.g. sodium + water → sodium hydroxide + hydrogen
Group 1 — reactivity trend (1b.2)
Reactivity increases going down Group 1. The outer electron is further from the nucleus and more easily lost — weaker attraction between the nucleus and the outer electron.
Opposite trend to Group 7. In Group 1, further = easier to lose = more reactive.
Group 1 — reactivity trend (1b.2) — Key Knowledge
- Reactivity increases down Group 1 outer electron easier to lose
Group 7 — properties (1b.3)
Group 7 elements have seven electrons in their outer shell. They form diatomic molecules (F₂, Cl₂, Br₂, I₂).
At room temperature: chlorine is a green gas, bromine is an orange-brown liquid, iodine is a grey solid.
Group 7 — properties (1b.3) — Key Knowledge
- Halogens Group 7: fluorine, chlorine, bromine, iodine
- Diatomic molecules of two atoms
Group 7 — reactivity trend (1b.3)
Reactivity decreases going down Group 7. The outer shell is further from the nucleus, making it harder to attract and gain an extra electron.
Opposite to Group 1. In Group 7, further = harder to gain = less reactive.
Group 7 — reactivity trend (1b.3) — Key Knowledge
- Reactivity decreases down Group 7 harder to gain an electron
Group 7 — displacement reactions (1b.3)
A more reactive halogen can displace a less reactive halogen from a solution of its compound.
Chlorine displaces bromine and iodine. Bromine displaces iodine but not chlorine. Iodine cannot displace either.
Group 7 — displacement reactions (1b.3) — Key Knowledge
- Displacement reaction more reactive halogen pushes out a less reactive one
Group 0 — noble gases (1b.4)
Noble gases have full outer electron shells, making them very unreactive (stable). They exist as single atoms (monatomic) and don't normally form compounds. Boiling points increase going down the group.
No need to gain, lose or share electrons.
Group 0 — noble gases (1b.4) — Key Knowledge
- Noble gases Group 0: helium, neon, argon…
- Full outer shell stable, unreactive
- Monatomic single atoms
Transition metals — properties (1b.5)
Transition metals are harder, stronger, denser, and have much higher melting points than Group 1 metals. They are less reactive than Group 1 metals.
These are the "typical" metals people think of — hard, strong, high melting point.
Transition metals — properties (1b.5) — Key Knowledge
- Transition metals central block: iron, copper, nickel, gold…
Transition metals — special properties (1b.5)
Transition metals form coloured compounds, are useful as catalysts, and can form ions with different charges.
These three properties are what distinguish transition metals from other metals in exam answers.
Transition metals — special properties (1b.5) — Key Knowledge
- Coloured compounds e.g. CuSO₄ = blue
- Catalysts e.g. iron in Haber process
- Variable oxidation states e.g. Fe²⁺ and Fe³⁺
Why reactivity trends go opposite ways (context)
Group 1 metals want to lose their outer electron — further from nucleus = easier to lose = more reactive down the group. Group 7 non-metals want to gain an electron — further from nucleus = harder to attract = less reactive down the group.
This is the single most confused point in the topic.
Why reactivity trends go opposite ways (context) — Key Knowledge
- Group 1 lose electron, more reactive down
- Group 7 gain electron, less reactive down