Flashcards in P4: Atomic structure Deck (109)
What was Dalton's model of the atom?
Atoms were solid, indivisible spheres. Each element was made of a different type of sphere.
What was Thomson's model of the atom?
Discovered electrons which could be removed from atoms- disproving Dalton's theory of indivisibility. Thomson suggested atoms were spheres of positive charge, with negative electrons scattered throughout (plum pudding model).
What was Rutherford's model of the atom?
Positively charged nucleus, surrounded by a cloud of negative electrons. This was the first nuclear model of the atom.
What discovery did Bohr make? How was he proven right?
Electrons orbit the nucleus in fixed positions, called energy levels. His theoretical calculations agreed with experimental data.
What discovery was made after electron orbits?
Experiments showed that the nucleus' positive charge was subdivided between a group of particles, called protons.
What discovery did Chadwick make? Why did this make sense?
He proved the existence of neutrons in the nucleus. This explained the imbalance between the atomic and mass numbers.
Who theorised that atoms were solid, indivisible spheres?
Who theorised the plum pudding model?
Whose discoveries led to the nuclear model of the atom?
Who calculated that electrons had fixed orbits?
Who discovered neutrons?
How was Rutherford's alpha scattering experiment conducted?
Scientists in Rutherford's lab fired a beam of alpha particles at a thin sheet of gold foil.
In Rutherford's alpha scattering experiment, what did the scientists expect to happen and why?
From the plum pudding model, they expected most particles to be slightly deflected, and a minority to pass straight through the foil.
What were the results of Rutherford's alpha scattering experiment? Why wasn't this as expected?
The majority of the alpha particles went straight through the gold sheet, and some were deflected more than expected and a few were deflected right back the way they came. The plum pudding model couldn't explain these results.
In Rutherford's alpha scattering experiment, a few alpha particles were deflected right back and some more than expected. What did the scientists deduce from this?
They realised that most of the atom's mass was concentrated in a central nucleus, which must also have a positive charge, since it repelled the positive alpha particles.
In Rutherford's alpha scattering experiment, most of the alpha particles passed straight through. What did the scientists deduce from this?
They realised that most of the atom is just empty space, rather than a solid sphere, and that the nucleus is very small relative to this space.
What was deduced from the results of Rutherford's alpha scattering experiment?
1. Because a few alpha particles were deflected back, they realised that most of the atom's mass was concentrated in a central nucleus, which must also have a positive charge, since it repelled the positive alpha particles.
2. Because most of the alpha particles passed straight through, they realised that most of the atom is just empty space, and that the nucleus is very small relative to this space.
The nucleus' radius is about ___x smaller than the radius of an atom.
The radius of an atom is about ___m.
Electron shells =
What happens when electrons gain energy by absorbing EM radiation?
They move to a higher energy level (further from the nucleus).
What happens when electrons lose energy by releasing EM radiation?
They move to a lower energy level (closer to the nucleus).
What are isotopes?
Isotopes of an element are atoms with the same number of protons, but different numbers of neutrons (so have different mass numbers).
All elements have isotopes, but...
...but there are usually only one or two stable ones.
What do unstable isotopes tend to do?
They decay into other elements, giving out radiation to become more stable. This process is called radioactive decay.
What is radioactive decay?
The process by which unstable nuclei emit radiation until they reach a stable state.
What types of radiation do unstable nuclei release?
Alpha, beta, gamma, neutron.
What makes a nucleus unstable?
A bigger nucleus would be less stable because it's harder to hold all the protons and neutrons together. The less energy holding them together, the less stable.
What is alpha radiation?
A particle: helium nucleus (2 protons, 2 neutrons).