atoms & radiation (p1) Flashcards
How much smaller is the atomic nucleus, compared to the whole atom?
10 000 times smaller
What is the basic structure of an atom?
a positively charged nucleus composed of both protons and neutrons surrounded by negatively charged electrons
What happens when electrons gain energy by absorbing electromagnetic radiation?
They move to a higher energy level (further from the nucleus).
What happens when electrons lose energy by releasing electromagnetic radiation?
They move to a lower energy level (closer to the nucleus).
How are the number of protons and electrons related in an atom?
same number of protons and electrons
How do atoms turn into positive ions?
by losing one or more electrons
What is the atomic number of an atom?
the number of protons in an atom
What is the mass number of an atom?
the total number of protons and neutrons in an atom
What are isotopes?
atoms which have the same number of protons but a different number of neutrons
𝗕𝗲𝗳𝗼𝗿𝗲 the discovery of electrons, what was the model of the atom?
Atoms were tiny spheres that could not be divided. Each element was made of a different type of sphere.
𝗔𝗳𝘁𝗲𝗿 the discovery of electrons, what was the model of the atom?
Plum pudding model: atoms are balls of positive charge, with negative electrons embedded in it
What is the nuclear model of the atom?
The atom has a nucleus which contains most of the mass and is charged
What was Bohr’s contribution to the model of the atom?
Electrons orbit the nucleus at specific distances (called energy levels). His theoretical calculations agreed with experimental observations
What was Chadwick’s contribution to the model of the atom?
He provided the evidence to show the existence of neutrons in the nucleus. This was about 20 years after the nucleus became an accepted scientific idea
Who calculated that electrons had fixed orbits?
Bohr
Who provided the evidence to show neutrons existed?
Chadwick
After the scattering experiment, how did ideas about the nucleus develop?
Experiments showed that the nucleus’ positive charge was actually carried by more than one particle, which were named protons
How was the alpha scattering experiment conducted?
Scientists fired a beam of alpha particles at a thin sheet of gold foil and recorded where the alpha particles went
What were the results of the alpha scattering experiment?
The majority of the alpha particles went straight through the gold sheet, and some were deflected and a small number were deflected right back the way they came. The plum pudding model couldn’t explain these observations.
In the alpha scattering experiment, a few alpha particles were deflected right back and some were deflected more than expected. What did the scientists deduce from this?
This showed that most of the atom’s mass was concentrated in a central nucleus, and that the nucleus must be charged
In the alpha scattering experiment, most of the alpha particles passed straight through. What did the scientists deduce from this?
This showed that most of the atom is just empty space, rather than a solid sphere, and that the nucleus is very small relative to the size of the atom
What changes were made to the atomic model based on evidence from the alpha scattering experiment?
Most of the atom’s mass was in a central nucleus, which is charged
Most of the atom is just empty space, and that the nucleus is very small
What happens when new experimental evidence can’t be explained by an existing scientific model?
The scientific model may be changed or replaced
