Answer :
Final answer:
The horizontal rows of the periodic table are known as periods, which indicate new principal energy levels. Atomic radii decrease across a period and increase down a group. Metals, nonmetals, and metalloids are distributed across the periodic table based on their properties.
Explanation:
Horizontal Rows of the Periodic Table: The horizontal rows of the periodic table are called periods. Each period marks a new principal energy level being used in the shells of the atoms that make up the elements within that row. There are seven periods in the periodic table, corresponding to the seven electron orbitals.
Trends in Atomic Radii: One of the trends observed concerning atomic radii is that as you move across a period from left to right, the atomic radius tends to decrease. This happens because, as you move across a period, each successive element has an additional proton and electron.
The increased nuclear charge due to extra protons pulls the electron cloud closer to the nucleus, reducing the size of the atom. As you move down a group, the atomic radius increases due to the addition of electron shells.
Metals, Nonmetals, and Metalloids: The metals are typically located on the left side of the periodic table and exhibit characteristics such as luster, good electrical conductivity, and malleability. Nonmetals are found on the upper right side and tend to be poor conductors of electricity and are not malleable. Metalloids, displaying properties of both metals and nonmetals, are situated between the metals and nonmetals along a diagonal line.
