1) Why did Mendeleev leave gaps in the periodic table? a) He didn't have enough time to finish it b) Mendeleev left gaps to place elements not known at the time c) He couldn't think of any other elements to place in the gaps d) He was allowed to finish it e) He wanted to understand the elements that were already placed in the periodic table before he added the other elements  f) He had to finish it by a certain time so he didn't have enough time to finish it 2) How do you work out the mass number? a) Protons - Neutrons b) Neutrons + Electrons c) Neutrons + atomic number d) Protons + neutrons e) Protons - atomic number f) Electrons - Neutrons 3) How many groups are there in the perodic table? a) 0 b) 7 c) 4 d) 2 e) 9 f) 8 4) Atoms are ...... a) Charged b) Protons c) Metals d) Neutrons e) Uncharged f) Electrons

Periodic table

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