Module 1: The Dalton atomic model
Module 1: The Dalton atomic model
Today's presentation
In the following illustration you can see various elements and connections in a specific representation.
Task
Do you have any guesses as to which elements and compounds might be involved?
How did you recognise them?
Historical representation
The following two illustrations show tables by John Dalton from 1808. With the help of these illustrations, he introduced a model with which elements and compounds could be represented.
This is why the model on which the representation of the elements and compounds at the top of this page is based is also named after him: Dalton's atomic model.
Task
- Compare the representation of Dalton's elements and connections with those at the top of this page.
- Are there any similarities in the way they are presented?
- Can you recognise any differences between the illustrations?
- What differences can you recognise?
Dalton's hypotheses
At the beginning of the 19th century, Dalton hypothesised in his work "A New System of Chemical Philosophy", based on his investigations into the properties of various gases, that every substance consists of the smallest, indivisible particles, the atoms. Based on this, he made further assumptions:
- The atoms of an element are equal in size and mass; atoms of different elements differ in size and mass.
- Atoms cannot be divided, created or destroyed.
- In a chemical reaction, the atoms of the starting materials are rearranged and combined in certain ratios.
Various phenomena can be conclusively explained on the basis of Dalton's assumptions. He was also one of the first scientists to draw up a table of relative atomic masses based on experimental results (see additional material). He set the weight of a hydrogen atom equal to 1. Today's atomic mass unit unit(u) was therefore previously also referred to as Dalton (Da).
Tasks
With the help of Dalton's atomic model, we can explain and utilise some phenomena of chemical reactions.
Explain in your own words, with reference to Dalton's assumptions, the following observations and possibilities:
- In a chemical reaction, the total mass of the substances involved is conserved.
- If 2 or more elements combine to form a certain compound, this always happens in a certain, constant mass ratio.
- Example: 88.81 g of oxygen always reacts with 11.19 g of hydrogen to form 100 g of water.
- It is possible to calculate the mass of carbon dioxide produced when 24 g of carbon reacts completely with oxygen