The first period of the periodic table contains only two elements: hydrogen and helium. Helium is a noble gas (inert gas) with a full valence shell (1s²), making it the only inert gas found in the first period.
3672
Which scientist proposed the 'Law of Octaves', observing that the properties of every eighth element repeat those of the first?
John Newlands proposed the Law of Octaves in 1864. He noted that when elements are arranged by increasing atomic mass, every eighth element exhibits properties similar to the first, analogous to musical octaves. This was an early attempt to identify periodicity in chemical properties.
3673
Which set of atomic numbers corresponds to the group of alkali metals?
Alkali metals are found in Group 1 of the periodic table. The atomic numbers 3 (Lithium), 19 (Potassium), 37 (Rubidium), and 55 (Cesium) all belong to Group 1, characterized by having a single valence electron in their outermost s-orbital.
3674
Which scientist demonstrated that the atomic number of an element is a more fundamental property than its atomic mass for periodic classification?
Henry Moseley (often misspelled as Mojle) used X-ray spectroscopy to show that the frequency of X-rays emitted by elements is related to their atomic number (Z) rather than their atomic mass. This discovery corrected the anomalies in Mendeleev's periodic table and established the modern periodic law, which states that properties are a periodic function of atomic number.
J.W. Döbereiner was a German chemist who, in 1817, identified the existence of triads of elements with similar properties. He observed that the atomic weight of the middle element was roughly the average of the other two. This work laid the groundwork for later developments in periodic classification, although it was limited to a small number of elements and did not account for all known elements at the time.
3676
Which of the following elements does not belong to the group of noble gases?
Neon, Krypton, and Argon are all members of Group 18 in the periodic table, known as noble gases, characterized by their full valence electron shells and chemical inertness. Platinum, however, is a transition metal located in Group 10, which exhibits different chemical and physical properties compared to the noble gases.
3677
An element has an electronic configuration of 2, 8, 8, 2. In which period of the modern periodic table is this element located?
The period number of an element is determined by the number of occupied electron shells. Since the configuration 2, 8, 8, 2 shows four occupied shells (K, L, M, and N), the element is located in the fourth period.
3678
In which period of the periodic table is the element with atomic number 16 located?
The element with atomic number 16 is Sulfur (S). Its electron configuration is 1s2 2s2 2p6 3s2 3p4. The highest principal quantum number (n) in the ground state configuration is 3, which corresponds to the third period of the periodic table. Elements in the third period have their valence electrons in the third energy shell, and Sulfur is located in Group 16 of this period.
3679
Which scientist demonstrated that atomic number is a more fundamental property than atomic mass, leading to the modern periodic law?
Henry Moseley conducted X-ray spectroscopy experiments that established a direct relationship between the frequency of X-rays emitted by elements and their atomic numbers. This discovery proved that atomic number is the true basis for periodic trends, correcting Mendeleev's mass-based arrangement.
3680
In which year was Mendeleev's Periodic Table published in a German scientific journal?
Dmitri Mendeleev published his comprehensive periodic table in the journal 'Annalen der Chemie' in 1872, which helped solidify his periodic law and predictions for undiscovered elements.
