Topic 4 - Atomic Structure Flashcards
Which group of historic people were the first to think about atoms?
The greeks
What did Democritus think about matter? When? (2)
- Thought all matter was made up of identical lumps called ‘atomos’.
- 5th century BC
What did John Dalton think/do regarding the understanding of atoms? When? (3)
- He agreed with Democritus that matter is made up of tiny spheres that couldn’t be broken up.
- But thought each element was made up of different types of atoms.
- 1804
What did JJ Thomson discover? When? (2)
- Discovered particles called electrons that could be removed from atoms.
- Around 1905
What did JJ Thomson’s discovery mean for John Dalton’s theory? What did Thompson suggest instead? (2)
- Dalton’s theory was now proved incorrect.
- Thomson suggested that atoms were spheres of positive charge with tiny negative electrons stuck in them - ‘plum pudding model’.
What was Rutherford’s experiment? How did it work? (3)
- Alpha Particles Scattering Experiment.
- Fired beam of alpha particles at thin gold foil.
- A circular detector screen surrounds the gold foil and the alpha source, and is used to detect alpha particles deflected by an angle.
What was the expected outcome of the alpha particles scattering experiment?
Expected that the positively charged alpha particles would go straight through or be slightly deflected by electrons if plum pudding model was true.
What was the actual outcome of the alpha particle scattering experiment? (3)
- Most particles went straight through foil.
- Some deflected back more than expected and some came completely out.
- Showed that atoms must have small, positively charged nuclei at centre.
Why did the alpha particle scattering experiment show that atoms must have small, positively charged nuclei at their centre? (3)
- Most of atom = empty space as most alpha particles passed straight through the foil.
- Nucleus must have large positive charge as some positively charged alpha particles were repelled and deflected by a big angle.
- Nucleus must be small as very few alpha particles were deflected back.
How did Niels Bohr adapt the initial nuclear model, which had been derived from the alpha particle scattering experiment? Was it accepted? Why? (3)
- He concluded that electrons orbiting the nucleus can only do so at certain distances.
- These distances are called energy levels.
- Bohr’s theoretical calculations were found to agree with experimental data, so the model was accepted.
How did evidence from further experiments change Niels Bohr’s nuclear model?
Evidence changed the model to think of the positively charged nucleus as a group of particles (protons) which all had the same positive charge that added up to the overall charge of the nucleus.
What did James Chadwick do after the idea of the nucleus was accepted? When? (2)
- He proved the existence of the neutron, which explained the imbalance between atomic and mass numbers.
- 1932 - about 20 years after the idea of the nucleus was accepted.
What 3 types of particle does the atom contain, according to the nuclear model?
- Electrons => negatively charged
- Protons => positively charged
- Neutrons => neutral/no charge
Where is the nucleus? What is the mass of the nucleus? What does it contain? The size? (4)
- At centre of atom.
- Tiny but makes up most of the mass of the atom.
- Contains protons and neutrons - giving it an overall positive charge.
- Radius of nucleus is about 10,000 times smaller than the radius of the atom.
What gives the atom its overall size?
The negative electrons which move round the outside of the nucleus really fast.
What is the radius of an atom?
About 1 x 10(-10) m
What is the relative mass and charge of the proton?
- 1
- +1
What is the relative mass and charge of the neutron?
- 1
- 0
What is the relative mass and charge of the electron?
- 1/2000
- -1
Do atoms have an overall charge? Why? (2)
- No overall charge.
- The charge of an electron is equal and opposite to the charge of a proton meaning the number of protons always equals the number of electrons in a neutral atom.
Can electrons move within or leave energy levels of an atom? How?
- Electrons can move within or sometimes leave the energy levels of an atom.
- If they gain energy by absorbing EM radiation they move to a higher energy level, further from the nucleus.
- If they release EM radiation, they move to a lower energy level that is closer to the nucleus.
What is the atomic number?
The number of protons in the nucleus of an atom.
What is the mass number?
The number of protons plus the number of neutrons in the nucleus of an atom.
What is an ion? (2)
- Atoms are neutral, but if some electrons are added or removed, the atom becomes a charged particle called an ion.
- The ions still have the same number of protons and neutrons as usual, but a different number of electrons.