Atomic structure
- Created by: holly6901
- Created on: 10-05-19 12:28
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- Atomic structure
- Atomic model
- An atom has a small, positively-charged nucleus surrounded by orbiting negatively-charged electrons.
- Atoms are very small and have a radius of about 1 × 10-10 metres.
- The electrons are arranged at different distances from the nucleus (different energy levels).
- The radius of a nucleus is less than 1/10 000 of the radius of an atom.
- Most of the mass of an atom is concentrated in the nucleus.
- Subatomic particles
- Protons have a relative charge of +1.They are found in the nucleus.
- An element’s atomic number is the number of protons it possesses.All atoms of the same element have the same number of protons.
- Electrons have a relative charge of -1.They are found in fixed orbits around the nucleus.
- In any atom, the total number of negative electrons equals the number of positive protons, meaning atoms have no overall electric charge.
- Neutrons have a relative charge of 0 - they are neutral.Like protons, they are found in the nucleus.
- Protons have a relative charge of +1.They are found in the nucleus.
- Rutherford's experiment
- Most alpha particles passed straight through the foil.This suggested that most of the atom is made up of empty space.
- However, some particles bounced back towards the source.
- The large deflections suggested that some positively charged mass in the atom was repelling the particles.
- This led to the model of the atom with negatively charged electrons orbiting a positively charged nucleus.
- Most alpha particles passed straight through the foil.This suggested that most of the atom is made up of empty space.
- Models of the atom
- In 1897, an English physicist called J. J. Thomson discovered electrons.
- He modelled the atom as a 'plum pudding' - a ball of positive charge (dough), with negatively charged electrons (currants) mixed in with the 'dough'.
- In 1909, Ernest Rutherford discovered that alpha particles could bounce back off atoms.
- He concluded that an atom's mass is concentrated in the atom's centre. This was called the "nucleus" and it contained positively charged particles called protons.
- Neils Bohr discovered that electrons orbit (fly around) the nucleus at fixed distances.
- In 1932, James Chadwick discovered that some particles in the nucleus have no charge at all. He called them neutrons.
- In 1897, an English physicist called J. J. Thomson discovered electrons.
- Electron arrangements
- When atoms absorb electromagnetic radiation, electrons move to a higher energy level further away from the nucleus.
- When atoms emit electromagnetic radiation, electrons can drop to a lower energy level, closer to the nucleus.
- Ions
- Atoms turn into positive ions if they lose one or more outer electrons.
- In an atom, the number of electrons is equal to the number of protons in the nucleus.Atoms have no overall electrical charge
- Atoms turn into negative ions if they gain one or more electrons.
- Isotopes
- Protium is a hydrogen atom with 1 proton and 0 neutrons.99.98% of hydrogen atoms are protium.
- It is used in hydrogen fuel cells and the production of plastics.
- Deuterium is a hydrogen atom with 1 proton and 1 neutron.Around 0.02% of hydrogen atoms are deuterium.
- It is used in nuclear fusion.
- Tritium is a hydrogen atom with 1 proton and 2 neutrons.It is very rare.
- It is used in thermonuclear fusion weapons.
- Isotopes are forms of an element that have the same number of protons, but a different number of neutrons.
- A nuclide is a type of isotope.A nuclide refers to a specific nucleus that contains a certain number of protons and neutrons.
- Protium is a hydrogen atom with 1 proton and 0 neutrons.99.98% of hydrogen atoms are protium.
- Atomic model
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