# Describe how the atomic model has changed from the 'plum pudding' model to the nuclear model, and state one piece of experimental evidence that led to this change.

> Edexcel GCSE Chemistry (1CH0) — 1.3 Atomic structure · Describe · 4 marks

> Scientists in the early twentieth century carried out experiments that changed our understanding of atomic structure. The 'plum pudding' model described atoms as a ball of positive charge with electrons embedded throughout it.

## Mark scheme (4 marks)

1. In the plum pudding model, the positive charge is spread throughout the atom (accept: the atom is a ball/sphere of positive charge with electrons embedded in it)
2. In the nuclear model, the positive charge (and most of the mass) is concentrated in a small central nucleus
3. In the nuclear model, electrons orbit/surround the nucleus (and most of the atom is empty space)
4. Reference to the alpha particle scattering experiment as evidence (e.g. most alpha particles passed straight through but some were deflected/bounced back, showing the nucleus is small, dense and positively charged)

## Key terms

- [nuclear model](https://www.gradenine.co.uk/glossary/nuclear-model)

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Source: [GradeNine](https://www.gradenine.co.uk/q/describe-how-the-atomic-model-has-ee576bda) · Published by Druglandscape Ltd.