The Atomic Number and Atomic Mass of ¹⁷O are 8 and 17 respectively.
Atomic Number: Atomic Number of Element is the Number of Protons contained by the Element. So, there are 8 Protons in ¹⁷O.
Atomic Mass: Atomic Mass of Element is the total number of Protons and Neutrons present in the Nucleus of that element. So, Atomic Mass = # of Protons + # of Neutrons
As the Atomic mass of ¹⁷O is 17 and it has 8 protons, So # of Neutrons are calculated as,
# of Neutrons = Atomic Mass - # of Protons
# of Neutrons = 17 - 8
# of Neutrons = 9 And, As there is no charge on ¹⁷O, so the number of Electrons and Protons are equal. i.e. # of Electrons = 8
Result: In ¹⁷O Number of Neutrons are 9, Number of Protons are 8 and Number of Electrons are 8.
Electrons determine the chemical properties. Protons and neutrons are in the nucleus the number of protons determines the number of electrons of an atom
The reason for covering the container is to make sure that the atmosphere in the beaker is saturated with solvent vapour. Saturating the atmosphere in the beaker with vapour stops the solvent from evaporating as it rises up the paper.