Question

How do metallic character and valency of elements change in a period moving left to right in the modern periodic table?

Answer 1

The modern periodic table is based on Mendeleev’s table, except the modern table arranges the elements by increasing atomic number instead of their atomic mass. The atomic number is the number of protons in an atom, and this is unique for each element. The modern periodic table has more elements than Mendeleev’s table because many elements have been discovered since Mendeleev’s time.

Complete step by step solution:
First, we have to understand the modern periodic table and what moving from left to right or moving from top to bottom means.
Rows in the modern periodic table are called periods, as in Mendeleev’s table. From left to right across a period, each element has an extra proton than the element before it. Some periods in the modern table are longer than others.
Columns in the modern table are called groups, as in Mendeleev’s table. However, the modern table has many more groups—18 compared with the number of columns in Mendeleev’s table. Elements in the same group have similar properties.
Metallic character decreases as you move left to right across a period in the periodic table. This is because the atoms more readily accept electrons to fill a valence shell than lose them to remove the unfilled shell to reach it’s nearest noble gas configuration.
The combining capacity of an atom is called its valency. The number of bonds that an atom can form as part of a compound is expressed by the valency of that element. It has a typical trend of moving from left to right in a modern periodic table. Valency of elements on moving left to right first increases from group 1A (Hydrogen family) to 4A (Carbon family) up to 4 and then decreases to 1 on group 7A.

Note: Remember that as we move down the group, this trend will no longer work if we move from left to right in the modern periodic table because of some other factors like atomic radius, electron gain enthalpy etc.