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Atoms, elements and compounds

each element is made from one type of atom

arranged in columns, called groups

atoms have a nucleus surrounded by electrons

when elements react, their atoms join with atoms of other elements. compounds are formed when two or more elements combine together

Atomic structure

nucleus contains two types of particle, protons and neutrons

protons= positivie charge

neutrons= no charge

electrons = negative charge 

electrons move around the nucleus

an atom has no overall charage because the number of protons is equal to the number of electrons and their charges are equal and opposite (proton +1 and electron -1)

all atoms of an element contain the same number of protons. this number is called the atomic number (or proton number) of the element. 

elements are arranged in order of their atomic number in the periodic table.

the atomic number is also the number of electrons in an atom of the element

the mass number is the total number of particles in the nucleus of an atom, so it is the number of protons plus the number of neutrons 

The arrangement of electrons


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