Dmitri Mendeleev’s Periodic table is based on atomic weight, whereas, the modern periodic table keeps the atomic number as the base. An atomic table arranges elements from left to right in a row with the atomic number and properties gradually changing. The elements on the next row will actually exhibit similar properties as the ones above or below it. This provides an example of the periodicity nature of the elements. The columns of different elements in a period have the same or very similar properties. The properties of the elements change gradually as the columns move down through the periodic table.
Atoms in similar families, such as H2S and H2O, exhibit both similar properties and molecular structure. This shows periodicity in both the molecules and the individual atoms. Alkali metals contain a single electron in their outer shell rendering them highly reactive. This allows them to be ready to donate this single electron to form molecules with substances like water. Halogens are also extremely reactive containing seven electrons in their outer shell. Similar to alkali metals, halogens need only one electron in their outer shell to become stable.
The reactivity of an element increases the when the number of outer shell electrons is closer to one or seven. Elements that contain eight electrons in their outer shell exhibit little or no reactivity. Alkali metals are the elements found in group one of the periodic table. Mixing these metals with water creates a strong base used to neutralize acids. An example of an alkali metal is sodium (Na). Sodium contains one free electron to donate to form instant bonds like NaCl. Chlorine (Cl) is an example of a halogen. Chlorine requires one single electron to make eight electrons in its’ outer shell.
Ultimately the high reactivity of alkali metals and halogens are a result of their unstable electronic configuration in the outer shell. In contrast, noble gases tend to be non-reactive because these elements have stable electronic configurations in their outer shell. Helium, for example, has two electrons and neon has eight electrons in the outer shell. These elements do not normally react with other elements. Molecules from atoms in similar families, such as H2S and H2O, have the same type of molecular shape and structure.
Sulfur is less electronegative than oxygen making the hydrogen-sulfur bond less polar than the hydrogen-oxygen bond. Due to this difference in polarity, the molecules of H2S tend to remain in a gaseous state. In contrast, the polarity between hydrogen and oxygen keeps the molecules of H2O together in a liquid state. This phenomenon is known as electrostatic attraction which is stronger in H2O molecules and weaker in H2S molecules. The electronic structure of atoms refers to the way electrons are arranged around the nucleus.
Four quantum numbers describe this structure and define the position of an electron in the electronic structure of the atom. These numbers illustrate the structure and arrangement of electrons. This can also be defined as a wave function showing the probability of finding an electron in a point in space. Electronic configuration is important for chemists in understanding how and why certain elements react with other elements. This method is much simpler than the quantum model and allows chemists to predict how certain elements will react sometimes before the chemical reaction has taken place.
Chemists can then theorize a reaction based on this electronic structure. Chemists can also use knowledge of the electronic structure of atoms to predict how elements will bond. They can determine whether the bond will be an electrochemical bond, a covalent bond, or a coordinate bond, etc. This also helps in explaining how certain elements will behave. Diagrams illustrating the energy level of elements also aid chemists but electronic configuration is a more preferred and simpler method for chemists to use.