Introduction: The atom is the smallest part of an element , which still has the properties of that element . The atom is a unit of matter which has a dense nucleus in the centre . This nucleus is surrounded by electrons which are negatively charged . These electrons appear in outer shells around the nucleus and the first shell is able to hold two electrons and any shell after that is able to hold up to eight electrons . At the centre of an atom in the dense nucleus you will find protons and neutrons . Protons are positively charged and neutrons are negatively charged . Protons and neutrons have a mass of one atomic mass unit as oppose to an electron where the mass is so small its value has to be taken as 0 . In most atoms there are the same number of protons as there are neutrons however this is not always true and the way in which we can go about deciphering and atom is with the use of its mass number and atomic number . The atomic number of an atom is the number of protons in that element , this is also always going to be the number of electrons in that element and there will always be the same number of electrons as there are protons . The mass number on the other hand is the number of protons and neutrons combined in an atom of that element . The word atom comes from a Greek word meaning "cannot be split". As we know this is not the case but back in the 1800's scientists believed an atom was the smallest particle in an element . From the reading of my introduction on the atom I hope your knowledge of the atom has increased and you look forward to the rest of my project.
John Dalton was born in England in 1766 . Dalton was born into a Quaker family and suffered from colour blindness . The scientist is most famous for his atomic theory . This theory has five main points which are listed below :