atom Flashcards
(25 cards)
An atom has a small, positively-charged nucleus surrounded by orbiting negatively-charged electrons.
The electrons are arranged at different distances from the nucleus (different energy levels).
The 3 different sub-atomic particles (protons, neutrons and electrons) have different relative charges. Atoms have no overall charge (are neutral). In an atom, these charges all cancel each other out.
What is the overall charge of the nucleus of an atom?
positive
Rutherford’s experiment
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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.
Rutherford’s conclusions
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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
Thomson’s plum pudding model
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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’.
Rutherford’s nuclear model
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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.
The modern model
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Niels 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.
Absorb radiation
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When atoms absorb electromagnetic radiation, electrons move to a higher energy level further away from the nucleus.
Emit radiation
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When atoms emit electromagnetic radiation, electrons can drop to a lower energy level, closer to the nucleus.
Why would the alpha particles be deflected by a smaller angle if the thin metal foil was made of a lighter element?
The nuclei of lighter elements contain fewer protons. This means they have a lower charge. Each alpha particle will, therefore, experience a smaller electric force acting on it and so deflect by a smaller angle.
What happens when atoms absorb electromagnetic radiation?
electron move to a higher level further away from the nucleus.
Proton number (Z):
The number of protons in a nucleus tells us what element an atom is.
For example, hydrogen atoms always have 1 proton.
Mass Number (A):
The mass number is the total number of protons and neutrons in a nucleus.
Atoms of the same element can have different numbers of neutrons.
For example, hydrogen can have 0, 1 or 2 neutrons.
Atoms of the same element can have different numbers of neutrons. For example, hydrogen can have 0, 1 or 2 neutrons.
Atoms have no overall electrical charge. When an atom becomes charged by gaining or losing electrons it becomes an ion.
ions
Ions are charged particles that form when an atom either loses or gains electrons.
isotopes
Two atoms with the same number of protons but a different number of neutrons are said to be isotopes.
A nuclide is a type of isotope.
A nuclide refers to a specific nucleus that contains a certain number of protons and neutrons.
A carbon nuclide with 6 protons and 6 neutrons is different to a carbon nuclide with 6 protons and 7 neutrons. However, both are isotopes of carbon.
bottom, top
protium = 1,1
Deuterium =1,2
Tritium = 1,3
How does an electron move to a higher or a lower energy level?
An electron can move to a
higher energy level by absorbing
electromagnetic radiation.
An electron can move to a lower energy level by emitting electromagnetic radiation.
Explain FOUR differences between the nuclear model of the atom and the plum pudding model.
Nuclear model was mostly empty space while plum pudding has no empty space (1)
Nuclear model states the positive charge is all in the nucleus while the plum pudding model shows the atom is a ball of positive charge with embedded electrons (1)
Nuclear model states the mass is concentrated in the nucleus while the plum pudding has the mass spread out (1)
Nuclear model states the electrons and the nucleus are separate or in orbit while the plum pudding model shows the electrons are embedded (1)
what is the meaning of the atomic number of an element.
The number of protons in the nucleus of the atom.
