The electronic configuration 2, 8, 6 indicates a total of 16 electrons, identifying the element as Sulfur. The number of valence electrons is 6. In the modern periodic table, elements with 6 valence electrons belong to Group 16 (the oxygen family), as the group number for p-block elements is calculated as 10 + valence electrons.

Periodic properties are those that repeat at regular intervals as atomic number increases. Atomic size, electronegativity, and ionization energy show clear periodic trends. The neutron-to-proton ratio is a nuclear property related to isotopic stability rather than a periodic trend of chemical behavior in the periodic table.

Non-metallic character increases as you move from left to right across a period in the periodic table. Sodium (Na) is an alkali metal, while Chlorine (Cl) is a halogen. As you move from Na to Cl across the third period, the atomic radius decreases and the effective nuclear charge increases, making it easier for the elements to gain electrons, thereby increasing their non-metallic properties.

Group 18 elements, known as noble gases, have a stable electronic configuration with a full valence shell (ns2 np6, except for Helium which is 1s2). This complete octet or duplet configuration makes them chemically inert under standard conditions, as they have little tendency to gain, lose, or share electrons.

The first period of the periodic table contains only Hydrogen and Helium. Hydrogen is a non-metal, and Helium is a noble gas (also a non-metal). Therefore, the first period is unique in that it lacks any metallic elements.

The electronic configuration 2, 8, 1 indicates that the element has three shells and one valence electron. Elements with one valence electron belong to Group 1 of the periodic table, which consists of the alkali metals. The number of shells (three) determines the period (Period 3), while the valence electron count determines the group.

Moving across a period from left to right, each successive element adds one proton and one electron to the same principal energy level. Consequently, the number of valence electrons increases by one for each step across the period.

Metallic character increases as you move from right to left across a period because the ionization energy decreases, making it easier for the atom to lose electrons. Sodium (atomic number 11) is an alkali metal in Group 1, whereas the others (13, 16, 17) are post-transition metals or non-metals. Therefore, sodium is the most metallic element in this set.

Silicon (Si) has an atomic number of 14 and is located in Period 3, Group 14. Aluminum (Al) has an atomic number of 13 and is located in Group 13, while Phosphorus (P) has an atomic number of 15 and is located in Group 15. Both are in the same period as Silicon.

In the modern periodic table, the horizontal rows are referred to as periods. There are seven periods in total, and elements within the same period have the same number of occupied electron shells. In contrast, vertical columns are known as groups.