Atomic structure and the periodic table

A sealed jar contains only argon atoms. State whether its contents are an element, a compound or a mixture, and give one reason.

Magnesium burns in oxygen to form magnesium oxide. Write the word equation, then complete and balance the symbol equation Mg + O₂ → MgO.

Molecule E has formula $\mathrm{C}_2\mathrm{H}_6\mathrm{O}$. It reacts fully with oxygen to produce carbon dioxide and water. Balance $\mathrm{C}_2\mathrm{H}_6\mathrm{O}+\mathrm{O}_2\rightarrow\mathrm{CO}_2+\mathrm{H}_2\mathrm{O}$, then explain why chemical products are not merely the starting materials mixed together.

A beaker contains chalk powder suspended in water. Name the physical process that collects the chalk and identify what passes through the paper.

A student needs dry copper sulfate crystals from a copper sulfate solution. Describe a suitable sequence after the solution has been placed in an evaporating basin.

A liquid mixture contains propanone, which boils at 56 °C, water, which boils at 100 °C, and a dissolved non-volatile blue solid. Design a separation that obtains all three components.

Place these developments in chronological order: Chadwick's neutron evidence, the plum pudding model, Bohr's shells, the nuclear model.

In an alpha-scattering trial, nearly every alpha particle crossed a thin metal sheet without changing direction, but a tiny proportion returned towards the source. Explain the conclusions about atomic structure.

Compare the plum pudding and nuclear models, then explain how scattering evidence and later discoveries produced the modern GCSE model of the atom.

State the relative charge of a proton, a neutron and an electron.

A particle contains 13 protons, 14 neutrons and 10 electrons. Determine its overall charge and explain whether it is an atom or an ion.

Species X has 26 protons, 30 neutrons and 23 electrons. Give its atomic number, mass number and ionic charge, then identify X using a periodic table.

Convert an atomic radius of $0.12\,\text{nm}$ into metres and write the result in standard form.

An oxygen-18 atom has atomic number 8. Calculate its numbers of protons, neutrons and electrons, and state where almost all its mass is located.

An atom has radius $9.0\times10^{-11}\,\text{m}$ and its nucleus has radius $7.5\times10^{-15}\,\text{m}$. Calculate how many times larger the atomic radius is. A related ion has 26 protons, 30 neutrons and 24 electrons; write its nuclide symbol and charge.

A sample of copper contains 69% copper-63 and 31% copper-65. Calculate its relative atomic mass.

Element Z has isotopes Z-24, Z-25 and Z-26. Their abundances are 79%, 10% and 11% respectively. Determine the relative atomic mass of Z.

An element has only isotopes of mass 79 and 81. Its relative atomic mass is 79.90. Calculate the percentage abundance of the mass-79 isotope.

Give the electronic structure of an aluminium atom, which has atomic number 13.

Calcium has atomic number 20. State the electronic structure of a calcium atom and of a Ca²⁺ ion.

Neutral atom X is one of the first 20 elements. It has three occupied shells and seven electrons in its outer shell. Identify X, give its atomic number and electronic structure, and state the structure after it gains one electron.

An atom has electronic structure 2,8,2. Give its atomic number, period and group.

Elements P and Q have electronic structures 2,1 and 2,8,1. Explain why they have similar chemical properties and identify which one has the larger atomic number.

Element R has atomic number 16 and element S has atomic number 19. Write both electronic structures, locate each by period and group, and predict which is more likely to form a positive ion.

Give two decisions Mendeleev made that improved the arrangement of the elements known in his time.

Mendeleev predicted that an empty position would be filled by an element forming an oxide X₂O₃. Years later, a new element was found and its oxide had that formula. Explain why this strengthened his periodic table.

Two elements have relative atomic masses 39.1 and 40.0. Their chemical properties place the 40.0 element before the 39.1 element in the modern table. Explain why this ordering troubled early tables, how Mendeleev could respond, and how later atomic theory resolved the issue.

Element T reacts by losing two electrons from each atom. Classify T as a metal or non-metal and state the charge on the ion formed.

Magnesium has electronic structure 2,8,2, while sulfur has 2,8,6. Use these structures and periodic-table positions to explain why magnesium is a metal but sulfur is a non-metal.

Unknown A is shiny, bends without snapping, conducts electricity and forms A³⁺. Unknown B is dull, breaks when hammered and does not conduct as a solid. Compare the evidence and predict where each lies in the periodic table.

Explain why neon is unreactive using its electronic structure 2,8.

The boiling points of neon, argon and krypton are −246 °C, −186 °C and −153 °C. Choose the most plausible boiling point for xenon from −260 °C, −170 °C and −108 °C, and justify your choice.

An unknown gas is monatomic, has electronic structure 2,8,8 and boils at a higher temperature than neon. Identify the gas and explain all three observations.

Name the two products when sodium reacts with water, and state one visible observation.

Complete and balance the equation Na + Cl₂ → NaCl. Explain why sodium and potassium both form compounds with one metal atom for each chlorine atom.

A teacher compares lithium, sodium and potassium in water using equal-sized pieces. Predict the order from least to most vigorous, explain the trend using atomic structure, and predict how rubidium would behave.

State two features shared by chlorine, bromine and iodine atoms or molecules that explain their placement in Group 7.

Chlorine water is added to aqueous potassium bromide. Predict the products, write a balanced equation and explain why the reaction occurs.

Bromine water is tested separately with sodium chloride and sodium iodide solutions. Predict each result, write any equation that occurs, and explain the different outcomes using the Group 7 reactivity trend.

Give three ways in which iron typically differs from sodium in its physical or chemical properties.

A manufacturer needs a metal component that remains solid above 900 °C, resists deformation and does not react rapidly with water. Explain why nickel is a better choice than potassium.

Metal U melts at 98 °C, has low density, cuts easily and reacts violently with water. Metal V melts at 1495 °C, is dense and hard, and reacts slowly with oxygen when heated. Classify U and V, justify each classification, and name one specified transition element in V's class.

State three typical chemical properties of transition elements or their compounds.

Iron forms pale-green FeCl₂ and yellow-brown FeCl₃. Chloride ions have charge 1−. Determine the charge on iron in each compound and explain what the colours demonstrate.

Equal samples react under identical conditions. Without a catalyst the reaction takes 240 s; with an iron compound it takes 80 s; with a copper compound it takes 60 s. Select the more effective catalyst, calculate how many times faster its trial is than the uncatalysed trial using reciprocal time as rate, and explain two catalyst features.