Dmitri Ivanovich Mendeleev, a Russian chemist and inventor, is best known for his revolutionary contribution to the periodic table of elements. His work laid the foundation for modern chemistry and significantly influenced how scientists understand the relationships between elements. Mendeleev’s periodic table not only provided a systematic arrangement of known elements but also predicted the existence of undiscovered ones.
Early Life and Education
Born on February 8, 1834, in Tobolsk, Siberia, Dmitri Mendeleev was the youngest of 14 siblings. His father, a teacher, passed away when Mendeleev was young, leaving his mother to support the family. She recognized her son’s potential and took him to St. Petersburg, where he enrolled in the Main Pedagogical Institute. After graduating in 1855, Mendeleev continued his education, earning a master’s degree in chemistry and later a doctoral degree. His passion for scientific inquiry led him to various teaching and research positions, eventually resulting in his groundbreaking work on the periodic table.
The Development of the Periodic Table
During the mid-19th century, chemists faced challenges in organizing the growing number of discovered elements. Scientists recognized certain patterns among elements but lacked a comprehensive system. Mendeleev, who was working on a chemistry textbook, sought to create a logical arrangement of elements based on their properties.
In 1869, Mendeleev devised his periodic table by arranging elements in order of increasing atomic weight while grouping them according to similar chemical properties.
Mendeleev observed that when elements are arranged in order of increasing atomic number, those with similar chemical properties appear at regular intervals, or periodically. Based on this pattern, he organized the elements so that those with similar properties were aligned in the same vertical column, which he called a “group.”
Mendeleev’s observation can be illustrated using the first twenty elements of the periodic table. When arranged horizontally in order of increasing atomic number, the list appears as follows:
H He Li* Be B C N O F Ne Na* Mg Al Si P S Cl Ar K* Ca
The three starred elements—lithium, sodium, and potassium—share similar properties; they are highly reactive metals that react vigorously with water, producing hydrogen gas. By temporarily omitting hydrogen and helium and reorganizing the list so that these three elements align in the same vertical column, the periodic pattern becomes more evident:
| Li | Be | B | C | N | O | F | Ne |
| Na | Mg | Al | Si | P | S | Cl | Ar |
| K | Ca |
All the elements in each vertical column share similar, though not identical, properties. Mendeleev described each column as a group, containing a family of elements with similar characteristics. This arrangement clearly demonstrates the periodic repetition of properties when elements are listed in order of increasing atomic number.
So, unlike previous attempts by other scientists, Mendeleev’s table had a predictive nature, setting it apart from earlier classifications.
Predicting Undiscovered Elements
One of Mendeleev’s greatest contributions was his ability to predict the properties of elements that had not yet been discovered.
While arranging the elements as discussed above, Mendeleev left gaps where he reasoned that unknown elements would fit. By analyzing the properties of known elements in a group, he was able to predict, with remarkable accuracy, the properties of these undiscovered elements.
For instance, he correctly predicted the melting point, boiling point, and atomic mass of gallium—six years before it was discovered.
Long story short, some of his most notable predictions included:
- Gallium (Eka-Aluminium) – Discovered in 1875 by French chemist Paul Émile Lecoq de Boisbaudran, gallium closely matched Mendeleev’s predicted properties.
- Scandium (Eka-Boron) – Lars Fredrik Nilson discovered scandium in 1879, confirming Mendeleev’s predictions.
- Germanium (Eka-Silicon) – Clemens Winkler discovered germanium in 1886, further validating Mendeleev’s periodic table.
The accuracy of these predictions established Mendeleev’s credibility and solidified the periodic table as a fundamental tool in chemistry.
Mendeleev’s Periodic Law
Mendeleev formulated the Periodic Law, stating that “the properties of elements are a periodic function of their atomic weights.” This principle explained the recurring trends in element properties, such as atomic size, electronegativity, and valency. His periodic law was later refined by Henry Moseley in 1913, who arranged elements by atomic number instead of atomic weight, resolving inconsistencies in Mendeleev’s original table.
Challenges and Recognition
Despite his groundbreaking work, Mendeleev initially faced skepticism from the scientific community. Some chemists doubted his predictions and the logic behind his arrangement of elements. However, the discoveries of gallium, scandium, and germanium validated his predictions, earning him widespread recognition.
Mendeleev’s contributions extended beyond the periodic table. He conducted research in various fields, including physics, meteorology, and engineering. His work on petroleum and the development of a new state of matter, known as the “Mendeleev-Clapeyron equation,” further demonstrated his scientific versatility.
Legacy and Impact
Mendeleev’s periodic table revolutionized chemistry by providing a systematic way to organize elements. His work influenced the development of atomic theory, quantum mechanics, and materials science. Today, the periodic table remains an essential tool for scientists, guiding research in chemistry, physics, and biology.
In honor of his contributions, the element Mendelevium (Md), atomic number 101, was named after him in 1955. This tribute reflects his lasting impact on the scientific community.
