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The smallest particle into which an element can be divided and still have the properties of that element.
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- small particles inside the atom. Thus, atoms can be divided into even smaller parts
- negatively charged particles that Thomson discovered are now called electrons.
- a guess that the electrons were mixed throughout an atom, like plums in a pudding (plum-pudding model)
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- tiny particles went straight through the gold foil. A small number of them were deflected. The explanation for this must be that most matter in an atom is found in a very small part of the atom
- the center of the atom is a tiny, extremely dense, positively charged area called the nucleus
- atoms are mostly empty space with a tiny, massive nucleus at the center.
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- electrons move around the nucleus in definite paths
- electrons can jump from a path in one level to a path in another level
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Modern Atomic Theory
(Schrödinger & Heisenberg) |
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- electrons do not travel in definite paths as Bohr suggested
- exact path of an electron cannot be predicted
- there are regions inside the atom where electrons are likely to be found. These regions are called electron clouds
- Sometimes the regions are called orbitals
- he energy of each electron in an atom keeps it in motion around the positive nucleus to which it is attracted.
- electrons can move by gaining or losing energy, but they are never found between energy levels
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- particles that make-up an atom
- protons
- neutrons
- electrons
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- center of the atom
- very dense
- (+) charged
- contains protons and neutrons
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- (+) charged particles in the nucleus of an atom
- also have mass
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atomic mass unit
The SI unit that describes the mass of a particle of an atom |
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- particle in the nucleus of an atom
- does NOT have a charge
- does have mass
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- (-) charged particles of an atom
- found OUTSIDE the nucleus
- so small, they have almost NO mass
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the number of protons in an atom |
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Atoms that have the same number of protons but a different number of neutrons |
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forces that hold atoms together |
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- gravitational
- electromagnetic
- strong
- weak
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very small in atoms because the particles in atoms are very small |
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- protons and electrons are attracted to each other because they have opposite charges
- electromagnetic force holds the electrons around the nucleus
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- force between protons
- holds nucleus together
- stronger than electromagnetic force
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- in radioactive atoms
- a neutron can change into a proton and an electron
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