The Development of the Periodic Table

In this worksheet, students will explore the structure of the Periodic Table and learn how it was developed.

Key stage:  KS 4

GCSE Boards:   AQA, AQA Trilogy, OCR 21st Century, OCR Gateway, Pearson Edexcel, AQA Synergy

Difficulty level:

QUESTION 1 of 10

Everything (even us) is made of atoms. By about 1800, scientists had discovered about 40 elements (or different types of atom), and knew some of their properties. Then scientists started looking for patterns, because that's what scientists do.

The first scientist to get anywhere with this problem was Johann Wolfgang Döbernier. He noticed that the known elements mostly fitted into groups of three. The groups of three had similar properties, and each group of three had a light element, a heavy element and one with middle weight. Döbernier called his groups of three Triads (tri means three- like in triangle). For example, lithium, sodium and potassium were a triad of metals which reacted violently with water.

The next scientist in this story was John Newlands. He wrote about a Law of Octaves (oct means eight- like in octopus). He took the elements known at the time, and ordered them from lightest to heaviest. Some of the time, similar elements appeared every eighth position. This picture shows how that worked; the elements are sorted into order from light to heavy, and similar elements have been highlighted in bright colours.

Then came the key person in this story- Russian scientist Dimitri Mendeleev. He had two ideas which might seem obvious now, but were revolutionary at the time.

First, there might be elements which exist, but haven't been discovered yet. So leave gaps if it helps make the patterns work better.

Second, if the patterns (like the octaves) work better if pairs of elements are swapped round, then swap them.

The really impressive thing about Mendeleev's idea for the Periodic Table was that the gaps in the table were predictions of new elements to discover. The patterns in the table helped Mendeleev to predict what these elements would be like. After the Periodic Table was published, scientists looked for the missing elements. They all appeared, and had the properties which Mendeleev had predicted.

A few decades later, a British chemist, Henry Moseley, realised that it would be better to use atomic number rather than mass, so he put the final touch on the Periodic Table. This resolved some issues that surfaced from Mendeleev's work.

The Periodic Table, as we know it today, is shown below. The different colours show elements with similar characteristics. They sit in columns; these are the triads of Döbernier (except the groups have more than three in them now), and repeat as Newland's octaves (for the first few rows, anyway). The crucial ideas to make the Periodic Table work came from Mendeleev.

What idea did Dimitri Mendeleev develop?

Atoms

The Periodic Table

Nitrogen

How was Mendeleev's table different to earlier ideas?

He sorted elements by weight

He sorted elements by name

He left gaps in his table

Column B

Döbereiner sorted elements into
groups of three
elements with a low, middle and high mass
similar properties

One of the triads was lithium, sodium and potassium. The mass of lithium is 7, and the mass of potassium is 39. What's the average of 7 and 39?

11

23

26.5

46

Look at the diagram of Newland's octaves.

Mg is an octave after Be, which is why they are both coloured yellow. Which element is an octave after N?

P

S

H

N

What did Mendeleev think the gaps in his table meant?

His table was wrong.

There were elements which hadn't been discovered yet.

He wasn't sure.

Sort these ideas about organising elements into order, from the oldest to the most recent.

Column B

First (oldest)
Newlands's Octaves
Second
Third (most recent)
Mendeleev's Periodic Table

Look at a modern periodic table- either the one in the introduction, or another copy.

Which of these elements are in the same column (or group) as fluorine (F)? Tick all the right answers.

boron (B)

nitrogen (N)

chlorine (Cl)

iodine (I)

neon (Ne)

hydrogen (H)

Fill in the gaps to summarise how the Periodic Table was developed. Use these words:

discovered

elements

gaps

patterns

right

boron (B)

nitrogen (N)

chlorine (Cl)

iodine (I)

neon (Ne)

hydrogen (H)

Lithium (Li), sodium (Na), potassium (K) and rubidium (Rb) all have similar properties. How does the periodic table show this?

All these elements are in the same row

All these elements are in the same column

• Question 1

What idea did Dimitri Mendeleev develop?

The Periodic Table
EDDIE SAYS
Dmitri Mendeleev created the first edition of the Periodic Table. He now has an element named after him (Mendelevium).
• Question 2

How was Mendeleev's table different to earlier ideas?

He left gaps in his table
EDDIE SAYS
In Mendeleev's time, new elements were being discovered every few years. It seems a bit obvious now, but nobody before Mendeleev had thought about how to fit new elements into the table.
• Question 3

Column B

Döbereiner sorted elements into
groups of three
similar properties
elements with a low, middle and h...
EDDIE SAYS
Check the introduction again if you're not sure. Döbereiner's discovery was a good start, but he didn't have enough information to build a complete ordering of the elements.
• Question 4

One of the triads was lithium, sodium and potassium. The mass of lithium is 7, and the mass of potassium is 39. What's the average of 7 and 39?

23
EDDIE SAYS
To get the average of two numbers, add them together (7 + 39 = 46), and divide the total by 2 (46 ÷ 2 = 23). If you got 26.5, it's because you only halved the 39, not the total. The neat thing about the answer 23 is that it's also the atomic mass of sodium, the middle member of the triad.
• Question 5

Look at the diagram of Newland's octaves.

Mg is an octave after Be, which is why they are both coloured yellow. Which element is an octave after N?

P
EDDIE SAYS
The octave includes the first and last element in the group, so you only count on seven elements to get the next element in the octave. Try counting from Li to Na.
• Question 6

What did Mendeleev think the gaps in his table meant?

There were elements which hadn't been discovered yet.
EDDIE SAYS
This is a really important thing to remember about Mendeleev's Periodic Table. At the time, it had gaps, and Mendeleev was confident that those gaps would be filled if people looked for the missing elements. Now we know that he was right- there aren't any gaps in the modern Periodic Table.
• Question 7

Sort these ideas about organising elements into order, from the oldest to the most recent.

Column B

First (oldest)
Second
Newlands's Octaves
Third (most recent)
Mendeleev's Periodic Table
EDDIE SAYS
Have a look back at the introduction if you're not sure about the order of these. As time passed, the model got more complicated, but was able to explain more, which made it better.
• Question 8

Look at a modern periodic table- either the one in the introduction, or another copy.

Which of these elements are in the same column (or group) as fluorine (F)? Tick all the right answers.

chlorine (Cl)
iodine (I)
EDDIE SAYS
The columns in the periodic table are really important, they group elements with similar properties and behaviours. The clever thing Mendeleev did was to take that idea more seriously than anyone had before, changing other parts of his table to make it work.
• Question 9

Fill in the gaps to summarise how the Periodic Table was developed. Use these words:

discovered

elements

gaps

patterns

right

EDDIE SAYS
All the gaps Mendeleev left have been filled, so Mendeleev's idea was right.
• Question 10

Lithium (Li), sodium (Na), potassium (K) and rubidium (Rb) all have similar properties. How does the periodic table show this?

All these elements are in the same column
EDDIE SAYS
All these elements are in the leftmost column of the periodic table. Chemists call these columns "groups", and they are very important for sorting similar elements together.
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