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Radioactivity - Atomic Structure
An atom which has lost an electron is called an ion.

Radioactivity - Atomic Structure

This GCSE Physics quiz is about radioactivity, specifically atomic structure. The scientific method involves developing a hypothesis and then carrying out experiments to gather evidence to support it, however, that hasn't always been the case. The ancient Greeks, for example, did not carry out anything other than thought experiments, in other words, they imagined what would happen if they had been able to do an experiment. One of these was the beginning of the theory of atomic structure. A philosopher (thinker) called Democritus did a thought experiment about what would happen if you hit a piece of rock with a hammer and broke it again and again. He reasoned that eventually you would end up with a piece that was so small that you could not break it into anything smaller. The Greek word for 'indivisible' is 'atomos' and that is how we get our modern word - atom. Similar ideas were developed in other civilisations, completely independently of the Greeks.

With the fall of the Greek civilisation, many scientific ideas were lost, at least to the western European countries. This started to change in the seventeenth century and some very clever and well-educated people had the time and money to think about science. One of these, a man called John Dalton, revived the idea of atoms. He came up with a model that suggested that atoms were the building blocks of all chemicals and were small, hard spheres that joined together in specific proportions. As with the Greeks, there was no way of testing this or proving this at the time. But this model of atoms seemed to work quite well, especially when Italian scientist, Amedeo Avogadro, modified it slightly to apply to gases, which was the main flaw.

During most of the 19th century, scientists believed that atoms of different elements were made up from different numbers of hydrogen atoms. We now know that it wasn't far off being the truth as a hydrogen atom is one proton with one electron. Then, at the end of the nineteenth century, a scientist called J. J. Thompson discovered the electron which was clearly a lot smaller than an atom. This showed that atoms were not the smallest particles of matter. He suggested that rather than being solid spheres, atoms were spheres of positive charge with the negatively-charged electrons spread through it. This model was replaced about a decade later when Ernest Rutherford discovered that most of the mass of an atom is contained in a small nucleus at the very centre. It is still a bit strange to think of atoms being mainly empty space. Eight years later, Rutherford carried out experiments with radioactive materials that proved that the hydrogen atom was indeed present in other elements and this is regarded as being the discovery of the proton. Rutherford also suggested the idea of neutrons but it wasn't until 1932 that the neutron was finally discovered.

What is an atom?
An atom is made up of an electron
An atom is a particle consisting of a small central nucleus containing protons and neutrons surrounded by electrons
An atom is made up of molecules such as H2O
An atom is a particle consisting of a small central nucleus containing neutrons and electrons surrounded by protons
The numbers of the protons and electrons are exactly equal in an atom
What is the relative charge of a proton?
One way of remembering this is to think about the first letter of proton - p for positive
What is the relative charge of a neutron?
Neutrons are neutral particles
What is the relative mass of a proton?
Whilst the mass of a proton is not actually +1, it is helpful for calculating relative masses when dealing with atomic physics
What is the relative mass of an electron?
OK, that's not strictly true but you would need nearly 2,000 electrons to equal the mass of one proton or one neutron. The element with the highest number of electrons is element 118. Its atoms contain only 118 electrons which contribute so little to the mass of an atom, their mass can be ignored
A neutral atom has five protons. How many electrons does it contain if it is not an ion?
An atom will always have the same number of electrons as it does protons
What is an atom called which has lost an electron?
Ions can be formed when atoms gain electrons as well
What does an atom's atomic number represent?
The number of particles within an atom in its nucleus
The number of protons in an atom in its nucleus
The number of neutrons in an atom in its nucleus
The number of electrons in an atom in its nucleus
Make sure that you know how to work out the number of particles in an atom from its atomic number and mass number, it is an easy way to gain marks
Atoms of an element always have the same number of protons but can have a different number of what?
Atomic numbers
Electron masses
Proton masses
An element is recognised for having a specific fixed number of protons in every atom, the number of neutrons is variable. Atoms of a particular element which contain different numbers of neutrons are described as isotopes
If an atom has 3 electrons, how many protons does it contain?
Remember, in an atom, the number of electrons is equal to the number of protons
You can find more about this topic by visiting BBC Bitesize - The structure of the atom

Author:  Martin Moore

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