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Periodic Table Origins

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Periodic Table Origins

Read the short history, then use the clues and element grid to investigate how scientists built the periodic table. Answer in complete sentences where needed.

A pattern waiting to be found

In the 1800s, chemists had identified dozens of elements, but there was no agreed way to organise them. In 1864, English chemist John Newlands arranged known elements by increasing atomic mass and noticed that some properties seemed to repeat. His idea was not widely accepted at first. In 1869, Russian chemist Dmitri Mendeleev developed a table that grouped elements with similar properties. He mostly arranged them by increasing atomic mass, but he sometimes changed the order to keep similar elements together. He also left gaps where he thought undiscovered elements belonged. Mendeleev predicted some properties of those missing elements. Later discoveries matched several of his predictions, helping scientists take his table seriously. The table used today is ordered by atomic number: the number of protons in an atom. Henry Moseley’s work in the early 1900s helped establish this arrangement. The repeating patterns in the modern table are called periodic because they recur at regular intervals.

A tiny element grid

This simplified grid shows the two elements in Period 1 and the first three elements in Period 2. It is not the full periodic table. Atomic number tells you the number of protons.

Period 1 H Hydrogen Atomic number 1

Period 1 He Helium Atomic number 2

Period 1 — No third element in this period

Period 2 Li Lithium Atomic number 3

Period 2 Be Beryllium Atomic number 4

Period 2 B Boron Atomic number 5

History and evidence

Use the history passage and grid to solve the questions.

1.Who developed the influential 1869 table that included gaps for undiscovered elements?

John Newlands
Dmitri Mendeleev
Henry Moseley
Marie Curie

2.What pattern did John Newlands notice when he arranged elements by increasing atomic mass?

3.True or false: Mendeleev sometimes changed the order of elements so that elements with similar properties stayed together.

TrueFalse

4.Complete the sentence: The modern periodic table is arranged by increasing , which is the number of in an atom.

5.Match each scientist to the contribution described.

John Newlands
Dmitri Mendeleev
Henry Moseley

Made an influential table with gaps and predictions
Helped establish ordering by atomic number
Noticed repeating properties while ordering by atomic mass

6.In the element grid, which element has atomic number 4, and how many protons does one of its atoms have?

7.From the element grid, name the two elements in Period 1.

8.Why were the gaps in Mendeleev’s table useful rather than simply mistakes? Give two points.

9.A new element is found to have 6 protons. According to the modern table’s organising rule, what atomic number should it have, and where would it come after in the grid’s sequence?

10.Explain how Mendeleev acted like a scientific detective. Include one piece of evidence from the passage.