4.1 Atoms and isotopes
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Give an approximation for the radius of an atom
1x10 to the power of -10 meters
What are the three subatomic constituents of an atom?
Proton, neutron, electron
Where is most of the mass of an atom concentrated?
In the nucleus
Approximately what proportion of the total radius of an atom is the radius of the nucleus?
1/10,000
Describe the arrangement of protons, neutrons and electrons in an atom
The protons and neutrons are found in the atom’s nucleus. The electrons are found in discrete energy levels around the nucleus.
What type of charge does the nucleus of an atom have? Why?
Positive charge - the nucleus contains protons and neutrons. Protons have a positive charge but neutrons have no charge.
Give two ways that an atom’s electron arrangement can be changed
● Absorbing electromagnetic radiation ● Emitting electromagnetic radiation
Explain how an atom’s electron arrangement changes when it absorbs electromagnetic radiation
Electrons move further away from the nucleus to a higher energy level.
Explain how an atom’s electron arrangement changes when it emits electromagnetic radiation.
Electrons move closer to the nucleus to a lower energy level.
How does the ratio of electrons to protons in an atom result in an atom having no overall charge?
The number of protons is equal to the number of electrons. Protons and electrons have equal and opposite charges so the charges cancel.
What do all forms of the same element have in common?
They all have the same number of protons
What is the name given to the number of protons in an atom?
Atomic number
What is an atom’s mass number?
The total number of protons and neutrons in the atom
What is an isotope of an atom?
An atom of an element that has a different number of neutrons, but the same number of protons.
How do atoms turn into positive ions?
They lose one or more of their outer electrons. Electrons are negatively charged, so the resulting charge of the atom is positive.
What may lead to a scientific model being changed or replaced?
The discovery of new experimental evidence which doesn’t agree with the existing theory.
How did the plum pudding model describe the atom?
A ball of positive charge, with negatively charged electrons distributed evenly throughout it.
Prior to the discovery of the electron, what was believed about the atom?
The atom was believed to be indivisible
Which experiment led to the plum pudding model being discarded?
Rutherford’s alpha scattering experiment
What is the name given to the currently accepted model of the atom?
The planetary model / Bohr nuclear model
State the conclusions of the alpha scattering experiment
Most of the massive in the atom is concentrated at the center in the nucleus. The nucleus is positively charged.
What reinforces a scientific theory?
When experimental results agree with the hypothesised theoretical calculations and theories.
What did James Chadwick’s experiments on the atom prove?
The existence of neutrons