The structure of an atom… How did we get to where we are today?

Lesson Goals To be able to explain how models have to be reviewed and changed as further scientific knowledge is discovered. To understand and explain the differences in the plum pudding model and the nuclear model of the atom. To be able to explain how Rutherford’s scattering experiment led to the change in the atomic model. To have fun!

Who will you be today? There are 11 roles to play. In pairs (3 groups of 3) you will need to read your role and the discovery / theory you had about the structure of the atom. Choose one person to act as that person. I will interview them to find out what they think about the structure of the atom. Some of you have been given information about the character of the person you are playing (try to include that as you answer the questions) You will all complete the table to note who, when, experiments & models for your records. We can have a bit of fun, BUT we must focus on the science as that’s what will come up in the exam!

5 minutes to read your character notes and ensure you understand your part…

Aristotle (Greek Scientist 384BC – 322 BC)

Other Greek Scientists & Demokritos (460 – 370BCE)

John Dalton (1766 - 1844)

J. J. Thomson (1856 - 1940)

Ernest Rutherford (1871 - 1937) With Geiger and Marsden

Niels Bohr (1885 - 1962)

James Chadwick (1891 - 1974)

Aristotle (Greek Scientist 384BC – 322 BC) Proposed that all matter is made of five elements: Fire (hot and dry) Earth (cold and dry) Air (hot and wet) Water (cold and wet) Aether (divine substance that makes up the heavenly spheres and heavenly bodies (stars & planets)

Other Greek Scientists & Demokritos (460 – 370BCE) Matter composed of tiny undividable particles.

John Dalton (1766 - 1844) All matter is made of atoms, and atoms are indestructible and cannot be broken down into pieces All the atoms of a particular element are identical to each other and different from the atoms of other elements Atoms are rearranged in a chemical reaction Compounds are formed when two or more different kinds of atoms join together Atoms cannot be divided into smaller particles – they are indivisible. There are spaces between atoms.

J. J. Thomson (1856 - 1940) Development of the plum pudding model Electrons (like negative ‘plums’) embedded in a ‘pudding’ of positive matter, with the negative charge of the electrons balanced by the positive charge of the ‘pudding’

Ernest Rutherford (1871 - 1937) Gold foil alpha particle scattering experiment: Most particles undeflected (atom mostly empty space) Some deflected (nucleus has a positive charge) Few bounce back (nucleus is dense but VERY small 1/4000 size of atom Positive nucleus containing protons surrounded by a cloud of orbiting electrons. With Geiger and Marsden

Niels Bohr (1885 - 1962) Electrons circle the nucleus at high speed Electrons are kept in certain energy levels in a stable formation around the atomic nucleus.

James Chadwick (1891 - 1974) Discovered the neutron in the nucleus Neutron – subatomic particle. Same mass as a proton but zero charge.

Can you… Explain how models have to be reviewed and changed as further scientific knowledge is discovered. Explain the differences in the plum pudding model and the nuclear model of the atom. Explain how Rutherford’s scattering experiment led to the change in the atomic mode.

Homework Answer the questions from the History of Atomic structure sheet.