Question

 

Why does the modern periodic table place helium in a family with neon instead of with beryllium?

Why are the elements no longer organized by atomic mass?

What pattern is there with regard to valence electrons, oxygen bonding ratio and electron configuration?

Answer 1

1. Noble gases are usually the elements found in the 8th family in the period table of elements. The unique criterion that these elements are that there outer most shell is full. They all contain 8 electrons in the outer most shell and do not tend to loose or gain electrons which means they don't react. Helium, a monatomic gas, is a typical noble gas since its valence shell is completely filled. Because outer shells are full, it is extremely stable, tending not to form chemical bonds and having a small tendency to gain or lose electrons similar to noble gas.
2. Atomic number is the number of protons, while atomic mass is the number of protons and neutrons. The chemical behavior of the element is determined by the number of protons, which are equal to the number of electrons. The electrons are arranged in orbitals or shells, and those in the outer shell are responsible for chemical reactivity.The number of neutrons in the atom has little effect on chemical behavior, because they do not influence the number of outer shell electrons. So atomic mass is not a natural way to order a periodic table, since periodic tables are principally aimed at capturing the chemical relationships between elements.

• The valence electrons are the electrons in the last shell or energy level of an atom. They do show a repeating or periodic pattern. The valence electrons increase in number as you go across a period. Within a group, the number of valence electrons stays the same ie, elements with same valence electrons are arranged in a group.
• Elements combines together with oxygen to form oxides. Elements on the extreme left of the periodic table react with oxygen to form basic oxides while elements on the extreme right form acidic oxides on reaction with oxygen. Oxides of the elements in the center of the periodic table are amphoteric. Amphoteric oxides are those which behave as acids as well as bases.
• The electron configurations of elements are related to their location in the periodic table. The periodic table is structured so that elements with the same pattern of outer-shell (valence) electron configuration are arranged in columns. For example, the electron configurations for the elements in groups 2A all have ns² outer configurations, while the 3A elements have ns²np¹ configurations.