edexcel C2 topic 1

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Edexcel Additional Chemistry
Structure of Atom:
An atom is a particle that cannot be divided further by chemical
The nucleus is made up of protons and neutrons and it has an overall
positive charge due to the protons having a +ve charge and the
neutrons none.
The nucleus is surrounded by electrons which are negatively
The mass of the atom is concentrated in the nucleus.
In an atom there is the same number of protons and electrons therefore it has an overall neutral
Mass Charge
Protons 1 +1
Neutrons 1 0
Electrons 0.0005(almost zero) -1
The atomic number is the number of protons in an atom
The mass number is the total number of protons and neutrons in an atom.
The periodic table
Dmitri Mendeleev came up with the first periodic table and arranged the elements in order of
relative atomic mass. But he also took into account the physical and chemical properties of elements.
Mendeleev left gaps in his periodic table; this allowed him to work out the atomic masses of the
missing elements and so predict their properties.
Mendeleev turned out to be right for example when gallium was discovered in 1875, its properties
were found to be close to Mendeleev's prediction.
The modern periodic table
The columns are the groups and the rows are the periods.

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In periods the elements are arranged in order of increasing atomic number and the period number is
the same number as the number of electron shell.
Elements in the same group have the same number of electrons in their outer shell.
In the periodic table you have the metals on the left side and the non-metals on the right side.…read more


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