The Periodic Table (AQA GCSE Combined Science: Trilogy: Chemistry): Flashcards

When ordered strictly by atomic weight, some elements had properties that didn’t match their column neighbours. Mendeleev switched their positions to keep elements with similar properties in the same group, prioritising chemical behaviour over atomic weight.

False.

Mendeleev used atomic weight, not atomic number. The modern periodic table uses atomic number — only possible after subatomic particles were discovered.

The discovery of subatomic particles revealed the atomic number (number of protons) for each element. This corrects ordering anomalies in Mendeleev’s table and accounts for isotopes, which have the same atomic number but different atomic weights.

Group 0 (the noble gases) had not been discovered when Mendeleev published his table in 1869. Their absence meant he left no gaps for them — their later discovery further confirmed the predictive success of his arrangement.

Metals react by losing electrons to form positive ions (cations). Non-metals react by gaining or sharing electrons — they do not form positive ions.

Metals are on the left side; non-metals are on the right. A small number of elements along the dividing line are called metalloids (or semi-metals) and display properties of both.

False.

Metal oxides are basic (alkaline). It is the oxides of non-metals that are acidic (e.g. SO₂, CO₂).

Outer-shell electrons move further from the nucleus as atomic size increases down the group. The attraction between the nucleus and outer electrons weakens, making electrons easier to lose — so the element behaves more like a metal.

Metallic character decreases. Left-side elements have few outer electrons and lose them readily (metals); right-side elements have more outer electrons and gain or share them instead (non-metals).

Noble gases have full outer shells of electrons, so they have no tendency to lose, gain, or share electrons. This makes them chemically inert.

Noble gases exist as single, separate atoms. This means they are described as monatomic rather than diatomic or polyatomic.

False.

Most noble gases have 8 outer-shell electrons, but helium is an exception — it has only 2 electrons, which completely fills its single shell.

Boiling points increase going down Group 0. As relative atomic mass increases, atoms become larger and intermolecular forces between them strengthen. More energy is needed to overcome these forces.

Although boiling points increase going down Group 0, all noble gases have boiling points below 0°C.

Argon is used to provide an inert atmosphere for welding (or to fill light bulbs). Its chemical inertness means it does not react with the hot metal or filament, preventing unwanted oxidation.

Neon’s electronic structure is 2,8. The outer shell contains 8 electrons and is completely full, so neon has no tendency to gain, lose, or share electrons — making it chemically inert.

They form alkaline solutions (pH > 7) when they react with water. For example, sodium reacts with water to produce sodium hydroxide solution and hydrogen gas.

False.

Melting points decrease going down Group 1. As atoms get larger, attractive forces between outer electrons and positive ions weaken, so less energy is needed to melt the metal.

Going down the group, the outer electron is in a shell further from the nucleus. The attraction between the nucleus and the outer electron weakens, so the electron is lost more easily — making the metal more reactive.

sodium + water → sodium hydroxide + hydrogen

Alkali metals react readily with both oxygen and water vapour in the air. Oil provides an airtight barrier that prevents the metal from reacting with either.

They form metal oxides (e.g. Na₂O, K₂O), which appear as a dull coating on the surface. The general equation is: 4M (s) + O₂ (g) → 2M₂O (s).

True.

Potassium reacts very vigorously with water. The hydrogen produced ignites immediately and burns with a characteristic lilac flame.

They form metal chlorides — ionic salts (e.g. 2Na (s) + Cl₂ (g) → 2NaCl (s)). The reaction becomes more vigorous going down the group.

False.

Each oxygen atom gains two electrons to form an oxide ion (O^2-). Two sodium atoms each lose one electron, and both electrons are gained by one oxygen atom. The product is the oxide ion — not the “oxygen ion.”

Group 7 elements (halogens) have 7 electrons in their outer shell and exist as diatomic molecules (e.g. F₂, Cl₂, Br₂, I₂). They are poisonous non-metals that form halide ions with a −1 charge when they react.

Fluorine: yellow gas.

Chlorine: pale yellow-green gas.

Bromine: red-brown liquid.

Iodine: grey solid.

Reactivity decreases going down Group 7 because the outer shell is further from the nucleus, giving a weaker attraction between the nucleus and the electron gained.

A more reactive halogen displaces a less reactive halogen from a solution of its salt. Reactivity order (most to least reactive): Cl > Br > I. For example, chlorine displaces both bromine and iodine from their salt solutions.

False.

All halogens exist as diatomic molecules. Chlorine is Cl₂, not individual Cl atoms.

When halogens react with metals, they form metal halides; when they react with non-metals (e.g. hydrogen), they form hydrogen halides.

Going down Group 7, halogen molecules get larger. Larger molecules have stronger intermolecular forces between them, so more energy is needed to separate the molecules, causing boiling points to increase.