prep 1

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........................... discovered positive protons inside the nucleus

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............- block elements begin to appear in period 4 and they are called transition metals

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The energy level that filled with (18) electrons is ...........

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.................... are different forms of the same element's atoms that have the same atomic number but differ in mass number

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Number of ..................... = Mass number - Atomic number

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The symbol of copper atom is -------------

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In the potassium ( K ) mass number = 39 , atomic number 19 then :

No. of electrons = .............

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....................... imaginary places around the nucleus in which the electrons move according to their energy

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Negatively charged particles of negligible mass and revolve around the nucleus at a very high speed

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In this figure

Then atom ( ( Active or inactive ) ................