C1.2 Flashcards
Describe the difference between an atom and a molecule
- An atom is the smaller particle of an element that still has its chemical properties. Different elements are made from different atoms.
- A molecule is made from two or more atoms join together. They are joined by attractive forces called chemical bonds.
Describe what is inside of an atom
- Atoms contain mainly empty space, but they do have three even smaller subatomic particles.
- protons and neutrons are joined together as the nucleus at the centre.
- electrons are surrounding the nucleus in shells.
How do you find the number of protons neutrons and electrons.
Protons = atomic number
Electrons = Protons
Neutrons = Atomic mass - atomic number
What is an isotope?
Isotopes are forms of the same element with the same number of protons and electrons, but different number of neutrons.
What are ions?
Ions are charged particles. They are formed when atoms, or groups of atoms, lose or gain electrons.
What did Dalton do?
- In 1803, John Dalton suggested that all matter is made from atoms.
- he believed that all atoms of an element are identical, and that different elements contain different types of atoms.
- he imagined atoms as tiny solid balls.
What did Thomson do?
- Joseph John Thomson discovered the first subatomic particle, the electron is 1897.
- Thomsons model of the atom had to make sense of two observations: atoms contain electrons, and atoms are neutral overall.
- In his plum pudding model, he suggested that atoms are spheres of positive charge with electrons spread out randomly inside
What did Rutherford do?
In 1909, Ernest Rutherford, hans Geiger and Ernest Marsden conducted an experiment which pointed beams of positively charged alpha particles at thin gold foil.
- Some atoms changed direction slightly, and some even came straight back. Rutherford explained the results by suggesting that an atom has a positively charges nucleus containing most of its mass. He also said that outside the nucleus, electrons orbit like planets in a solar system.
What did Bohr do?
- Niels Bohr realised that orbiting electrons would attracted to the oppositely charged nucleus and would rapidly spiral inwards.
- In 1913 he used mathematical models to improve Rutherfords model.
- He showed that electrons occupy fixed energy levels, or shells, around the nucleus.