C4 - History of the Atom & The Atom Flashcards
What are atoms?
Atoms are the tiny particles of matter which make up everything in the universe.
What did John Dalton describe atoms as?
John Dalton in the 19th Century described atoms as solid spheres and said that different spheres make up different elements.
What did J.J Thomson discover?
In 1897, J J Thomson concluded from his experiments that atoms weren’t solid spheres, His measurements of charge and mass showed that an atom must contain even smaller, negatively charged particles called electrons.
The Solid sphere idea of atomic structure had to be changed and the plum pudding model was what resulted from this.
What are electrons?
a stable subatomic particle with a charge of negative electricity, found in all atoms and acting as the primary carrier of electricity in solids.
What was the gold foil experiment?
In 1909, Ernest Rutherford and his students Hans Geiger and Ernest Marsden conducted the famous gold foil experiment.
They fired positively charged particles at an extremely thin sheet of gold.
What was expected of the gold foil experiment?
From the plum pudding model they were expecting most of the particles to be deflected by the positive pudding that made up most of the atom, in fact most of the particles passed through the gold atoms and a very small number were deflected backwards, They concluded that the plum pudding model couldn’t be right.
What idea did Rutherford come up and what was it called?
Rutherford came up with the nuclear atom theory, in this there is a tiny positively charged nucleus at the center surrounded by cloud of negative electrons, much of the atom is empty space.
What is the refined Bohr model?
Scientists realized that a cloud around the nucleus of an atom would be attracted to the nucleus causing the atom to collapse, Niels Bohr proposed a new model of the atom were all the electrons were contained in shells.
What did Bohr Suggest about the atom shells?
Bohr suggested that electrons can only exist in fixed orbits, or shells and not anywhere in between and thus each shell has a fixed energy.
Why did people accept Bohr’s ideas?
Bohr’s theory of atomic structure was supported by many experiments and it helped to explain lots of other scientist’s observations at the time.
Describe the Nucleus
- The nucleus is in the middle of the atom
- It contains protons and neutrons
- It has a positive charge because of the protons
- Almost the whole mass of the atom is concentrated in the nucleus
Where is the nucleus in the atom?
The Nucleus is in the middle of the atom
Why does a nucleus have a positive charge?
It has a positive charge because neutrons have no charge, but the protons have a charge, therefore the nucleus has a positive charge.
Where is the mass concentrated in an atom?
Almost the entire mass of an atom is concentrated in the nucleus.
Describe an Electron
Electrons move around the nucleus in electron shells
They are negatively charged
They are very tiny but cover a lot of space
The volume of their orbits determines the size of the atom.
electrons have virtually no mass
