P4 - Atoms & Radiation Flashcards
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?
Dalton
Who theorised the plum pudding model?
Thomson
Whose discoveries led to the nuclear model of the atom?
Rutherford
Who calculated that electrons had fixed orbits?
Bohr
Who discovered neutrons?
Chadwick
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
10,000x
The radius of an atom is about ___m
1x10(^-10)m
Electron shells =
energy levels
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