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Flashcards · 8462 · Topic 1

Atomic structure and the periodic table flashcards

29 cards on Topic 1, subtopics 4.1.1 to 4.1.3. Pick a subtopic or study them all.

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4.1.1 A simple model of the atom, symbols, relative atomic mass, electronic charge and isotopes

Atom
The smallest part of an element that can exist.
Compound
Two or more elements chemically combined in fixed proportions. It can be separated only by chemical reactions.
Mixture vs compound
Mixture: not chemically combined, any proportions, each part keeps its properties, separated by physical processes. Compound: chemically combined, fixed proportions, new properties, separated only by chemical reactions.
Plum pudding model vs nuclear model of the atom
Plum pudding: a ball of positive charge with electrons embedded in it, no nucleus. Nuclear: a tiny, dense, positive nucleus holding almost all the mass, with electrons outside it and mostly empty space.
Alpha scattering: the three observations and what each showed
Most passed straight through → the atom is mostly empty space. Some were deflected → the nucleus is positively charged. A very few bounced back → the nucleus is very small and holds most of the mass.
What did Bohr and Chadwick add to the model of the atom?
Bohr: electrons orbit the nucleus at specific distances (shells). Chadwick: neutrons exist in the nucleus.
Relative charge and relative mass of a proton, a neutron and an electron
Proton: +1, mass 1. Neutron: 0, mass 1. Electron: −1, very small mass.
Approximate radius of an atom and of its nucleus
Atom: about 0.1 nm (1 × 10⁻¹⁰ m). Nucleus: about 1 × 10⁻¹⁴ m, less than 1/10 000 of the atomic radius.
Isotopes
Atoms of the same element (same number of protons) with different numbers of neutrons. They have the same chemical properties.
Chlorine is 75% chlorine-35 and 25% chlorine-37. Calculate its relative atomic mass.
(35 × 75 + 37 × 25) ÷ 100 = (2625 + 925) ÷ 100 = 35.5
How do electrons fill the shells for the first 20 elements? Give potassium (atomic number 19).
Lowest energy levels first: 2 in the first shell, 8 in the second, 8 in the third, then the fourth. Potassium: 2,8,8,1.
Half equation for a sodium atom forming a sodium ion, and the rule for half equationsHigher
Na → Na⁺ + e⁻ Electrons lost are written on the right, electrons gained on the left. Atoms and charge must both balance.

4.1.2 The periodic table

How is the modern periodic table ordered, and what do groups and periods tell you?
In order of atomic (proton) number. Group number = number of outer-shell electrons (similar chemical properties). Period number = number of occupied shells.
What did Mendeleev do that earlier tables did not?
He left gaps for undiscovered elements and predicted their properties, and he changed the atomic-weight order where properties required it (tellurium before iodine). Gallium and germanium were later found to fit his predictions.
Why is argon placed before potassium although its relative atomic mass is higher?
Argon has the lower atomic number (18 vs 19). Its relative atomic mass is higher because nearly all argon is argon-40 while most potassium is potassium-39: Ar is an average over isotopes.
Metal vs non-metal, defined by ions
A metal is an element that reacts to form positive ions (left and bottom of the table). A non-metal does not form positive ions (right and top).
Why are the noble gases (Group 0) unreactive, and how do their boiling points change down the group?
They have a stable arrangement of electrons: a full outer shell (8, or 2 for helium), so they do not easily lose, gain or share electrons. Boiling points increase down the group.
Explain why reactivity increases down Group 1
The outer electron is further from the nucleus, with more shielding by inner shells, so the attraction is weaker and the electron is lost more easily.
Group 1 metal + water: word and balanced equation (M = Li, Na or K)
Metal + water → metal hydroxide + hydrogen 2M + 2H₂O → 2MOH + H₂ The solution is alkaline (universal indicator turns purple).
Group 7 trends down the group, with the reason for the reactivity trend
Melting and boiling points increase; reactivity decreases. The outer shell is further from the nucleus, so an incoming electron is attracted less strongly and gained less easily.
Bromine water is added to sodium iodide solution. Equation and observation
Br₂ + 2NaI → 2NaBr + I₂ The more reactive bromine displaces iodine; the solution turns from orange to brown.
Ionic equation for bromine displacing iodide ionsHigher
Br₂ + 2I⁻ → 2Br⁻ + I₂ (sodium ions are spectators).

4.1.3 Properties of transition metals (chemistry only)

The six transition metals the specification uses as examples
Chromium, manganese, iron, cobalt, nickel, copper (Cr, Mn, Fe, Co, Ni, Cu).
Transition elements
Metals in the central block of the periodic table, with similar properties to each other that are different from those of Group 1.
Physical properties of transition metals compared with Group 1 metals
Transition metals have higher melting points (all six above 1000 °C; Group 1 all below 200 °C), higher density, and are stronger and harder.
Reactivity of transition metals compared with Group 1
Much less reactive with oxygen, water and halogens. Copper does not react with water; Group 1 metals react with cold water. Transition metals are less reactive, not unreactive.
Three typical properties of many transition elements
Ions with different charges (Fe²⁺ and Fe³⁺), coloured compounds, and use as catalysts. The specification says "many", not "all".
Name two transition metal catalysts and their reactions
Iron: the Haber process, N₂ + 3H₂ ⇌ 2NH₃. Manganese(IV) oxide: decomposition of hydrogen peroxide, 2H₂O₂ → 2H₂O + O₂.
Formula of iron(III) sulfate
Fe³⁺ and SO₄²⁻: two Fe³⁺ (6+) balance three SO₄²⁻ (6−), so Fe₂(SO₄)₃. The Roman numeral gives the metal ion charge.

Revise Atomic structure and the periodic table further