a) Name the Russian scientist pictured on the right who was the first person to successfully devise a periodic table of the elements - Leaving Cert Chemistry - Question 5 - 2016

Elements in the same group generally have the same number of electrons in their outer shell.

Element X is nitrogen (N), element Y is oxygen (O), and element Z is fluorine (F).

The mass number of an atom is the sum of protons and neutrons. For fluorine (Z), which has 9 protons, the mass number is 9 + 10 = 19.

The electron arrangement for neon (Ne) would be represented as:

     
       *
     *   *   *   *   *   *   *   *   *  (2nd shell)
     * *   *
     
       *

Neon has a total of 10 electrons, filling its first two shells with 2 and 8 electrons respectively.

Neon is chemically unreactive because it has a noble (inert) gas configuration, meaning its outer shell is completely filled with electrons, which fulfills the octet rule.

The atomic radius decreases from X to Z due to an increase in nuclear charge (more protons) across periods of the periodic table. As the positive charge of the nucleus increases, it pulls the electrons closer, resulting in a smaller atomic radius.

Electronegativity is defined as the relative ability of an atom in a molecule to attract shared electrons (or electrons in a covalent bond).

Given the electronegativity values: Na = 0.93 and Z (fluorine) = 3.05, the difference in electronegativity is 3.05 - 0.93 = 2.12, indicating an ionic bond due to the large difference.