Hi Everyone =)

If you truly want to understand your favorite molecules I encourage you to study other molecules and their interactions as well, as this will give you a knowledge base that you can be confident about. Wrote this for a class and progressively extending it for the Nexus. Please feel free to ask any questions or correct me on any errors =)

This thread was inspired by acolon_5's Basic Chemistry thread

CHEMISTRY AND THE PERIODIC TABLE OF ELEMENTS

Chemistry is the study of the properties and interactions of matter. There are differences between a chemical reaction and a physical reaction. In a chemical reaction, a substance is completely changed and can not be changed back into it's original state. For example, frying an egg is considered a chemical reaction because once it is cooked, it cannot returned to its former state. Heat energy is transferred to and from the surroundings, while bonds WITHIN the particles are broken, and the substance itself changes.

On the other hand, melting ice is considered a physical reaction because the substance remains the same, and it is essentially still H2O, just at a lower temperature and with higher kinetic energy (the particles have more activity due to increased energy that allows them to stray a little further away from the other water molecules they are attracted to).

To understand the properties and relationships of matter, one of the tools that scientists use is the Periodic Table of Elements




The Periodic Table of Elements is an essential tool in the study of Chemistry. Although many older models exist, the current Periodic Table is credited to Dmitri Mendeleev in 1869. He developed it to show the periodic trends of the elements known at the time. Due to this organization, the Mendeleev model was able to predict some properties of unknown elements at the time (represented by blank gaps in the table), which would later be confirmed when these elements were discovered to have properties similar to these predictions.




Since Mendeleev’s time, the model has been refined and extended to include elements that were once blank gaps in the old model. Currently, the periodic table allows chemists to analyze the properties of known elements and predict the interactions/relations between these elements. A notable feature of the periodic table is the way it is organized. Elements are displayed within a rectangular grid, ordered by increasing atomic number. Columns make up the Groups and the rows make up the Periods. Elements of the same group tend to behave the same and thus have similar properties, which is why they are grouped together in a family.

(Note the Periods and Groups)

The first half of the 20th century saw an explosion in the development of quantum mechanical theories, of which led to the discovery that each period in the table corresponds to the filling of a quantum shell of electrons. Elements in group one on the far left have only one electron in their valence shells filled, while elements in group eighteen on the far right have all eight valence shell electrons filled; a beautiful, un-reactive filled octet. The first group, known as the alkali metals, contains elements such as Sodium, Lithium, and Hydrogen. Elements within this family usually form ions with a positive charge of +1 because their valence electron is easily lost. These elements are isoelctronic with noble gases (i.e. they have the same electronic configuration). Elements such as Calcium and Magnesium come from the second group, the alkaline earths. These elements form ions with a +2 charge and are isoelectronic with noble gasses only under the conditions that two electrons are removed. As we move further down the groups to the right, we find the halogens group at group number seventeen. This group contains elements like Chlorine and Iodine. Halogens form ions with a -1 charge in order to easily form an octet using covalent bonding. On the other hand, noble gasses, such as Helium, have a complete octet and are neutral because all valence electron sublevels are full. The periods, on the other hand, are organized in a way that they can tell us things, such as what energy level an element has, when looking at its electronic configuration.

(The Octet Rule: Atoms tend to gain, lose, or share one or more of their valence electrons to achieve a filled outer electron shell)

The electronic configuration of an element provides information of an atom’s principle energy level, sublevel, orbital(s), and the number of electrons each orbital has. An orbital is a mathematical function, a probability, of where an electron could be. This is important in further understanding chemical bonds and molecular geometry. The sublevels of an atom are split up into four categories, each increasing in energy: s, p, d, and f. The first element in a period of the Periodic Table introduces a new principal energy level. As the period number increases from one to seven, the energy level of the principle outer shell increases as well. The first two groups make up the s sublevel, while groups thirteen through eighteen make up the p sublevel, and the transition metals make up the d sublevel. Orbitals get filled up across the periods, telling us the probability of where an electron could possibly be. The last important data about electronic configuration that can be found within the organization of the periodic table is the number of valance electrons present in the atom, which is increasing from left to right across the periods, excluding transition metals.

(Energy sublevels as categorized in the Periodic Table)

(Sublevels and their Orbital Geometry)

Since fundamental chemistry studies the relation and interaction between elements, it is necessary to study the principles and properties of these interactions. One of these fundamental principles is polarity. Polarity is defined by an uneven, asymmetrical distribution of electron concentration. Understanding the polarity of an element/compound allows chemists to predict and identify the different types of electron bonding. The ability for an element to attract bonding electrons to itself is defined as electronegativity, and is represented in the organization of the periodic table. Electronegativity increases as you move up a group and from left to right across a period. It plays an important role in covalent bonds because the relative polarity of a bond is the difference between the electronegativity values for the bonding atoms. On a similar note, electronegativity has an effect on ionization energy because the higher the electronegativity, the higher the ionization energy required for that element.

The periodic table of elements can be described as a chemist’s best friend. It allows chemists to analyze the behavior of elements and compounds while assisting them in the quantitative measurement of a compound using a known chemical equation. As a result, it is widely used in chemistry and other sciences to analyze and predict chemical behavior. If chemistry was a religion, the periodic table would be like its bible.

This is a work in progress so I will add more to this soon. Feel free to discuss expand on this thread! <3

Nice work! Thanks for posting this.