AQA GCSE Chemistry (8462), Higher tier · Atomic structure and the periodic table › The periodic table
Practise Development of the periodic table. 14 exam-style questions on this subtopic, at up to four difficulty levels, with full mark schemes and a progress tracker. Free, no account needed.
Cover the answers and test yourself. The app has these as flashcards that come back just before you'd forget them.
Before protons, neutrons and electrons were discovered, scientists arranged the elements in order of one property. Name this property.
atomic weight
Complete the sentence. Knowledge of .......... made it possible to explain why the order based on atomic weights was not always correct.
isotopes
Sample questions
Written for this site in the style of AQA exam questions. They are not taken from real past papers.
Question 1Easy4 marks
Scientists tried to classify the elements long before the modern periodic table was developed.
(a) Before protons, neutrons and electrons were discovered, scientists arranged the elements in order of one property. Name this property.[1]
(b) Some elements were placed in inappropriate groups in early periodic tables. Suggest why.[1]
(c) Mendeleev left gaps in his periodic table. Why?[1]
(d) Give one reason why other scientists came to accept Mendeleev's periodic table.[1]
Show the answer and mark scheme
(a)Answer: atomic weight
atomic weight / relative atomic mass
(b)Answer: The strict order of atomic weights was followed.
(because) the strict order of atomic weights was followed
(c)Answer: For elements that he thought had not yet been discovered.
for (undiscovered) elements / elements that had not been discovered (yet)
(d)Answer: Elements were discovered that fitted the gaps and had the properties he predicted.
elements were discovered that filled the gaps / had properties that matched his predictions
Question 2Medium2 marks
Mendeleev left a gap in his table for an element he called eka-aluminium, and predicted its properties. When gallium was discovered, its properties matched his predictions closely. A student says: 'Mendeleev was just lucky that gallium turned out to have the properties he predicted.'
Evaluate the student's statement.[2]
Show the answer and mark scheme
Answer: It was not luck: Mendeleev based his predictions on the patterns in the properties of the elements in the same group, and other elements he predicted were also discovered with the properties he predicted.
the predictions were based on patterns / trends in the properties of the elements in the same group, not guesses
other elements that Mendeleev predicted were also discovered with the properties he predicted, which is very unlikely to happen by chance
Question 3Hard6 marks
Mendeleev published his periodic table in 1869.
Describe how Mendeleev's periodic table improved on earlier attempts to classify the elements. Explain how later discoveries showed that Mendeleev's ideas were correct.[6]
Show the answer and mark scheme
Answer: Earlier tables followed atomic weight strictly and were incomplete. Mendeleev grouped elements by properties, swapped some pairs and left gaps with predictions. Discovered elements matched the predictions; protons and isotopes later explained the order.
early tables were in strict order of atomic weight
early tables were incomplete and some elements were placed in groups with elements that had different properties
Mendeleev arranged elements by atomic weight but placed elements with similar properties in the same group
he changed the order in some places, e.g. tellurium and iodine
he left gaps for elements that had not been discovered
he predicted the properties of undiscovered elements, e.g. eka-silicon / eka-aluminium
elements such as germanium and gallium were discovered with properties that matched his predictions and filled the gaps
the discovery of protons showed the elements are in order of atomic number
knowledge of isotopes explained why the order based on atomic weights was not always correct
Marked with levels of response: the full level descriptors are in the app.