Dmitri Mendeleev is credited with grouping the elements by atomic mass and observing that similar properties emerge periodically.  Henry Moseley then determined that a fundamental property, which Ernest Rutherford later called the atomic number, is more important than atomic mass for ordering the elements.As the periodic table took shape, scientists noted certain properties and trends.  For example, Rayleigh and Ramsay observed that some elements are unreactive and gave them the name noble gases.  But it was not until Niels Bohr described his model of the atom that scientists understood why noble gases are stable.Another important trend was discovered by Linus Pauling.  He was the first to identify electronegativity as a way to describe bonds that are neither completely ionic nor completely covalent.  Pauling assigned fluorine the highest electronegativity value of 4.0 because of its strong tendency to attract electrons when bonded to other atoms.  All other atoms were assigned values relative to fluorine.  This became known as the Pauling electronegativity scale.Scientists identified other trends based on x-ray crystallography and reactivity studies.  Figure 1 shows the first ionization energy of the elements, and Figure 2 shows electron affinity.Figure 1  First ionization energy of elementsFigure 2  Electron affinity of several elements (larger negative values indicate greater electron affinity) Question 35According to the information in the passage, in general, adding electrons to nonmetals is:A.not possible for most nonmetals.B.energetically similar to adding electrons to metals.C.easier than adding electrons to metals.D.more difficult than adding electrons to metals.

How did Henry Moseley affect the development of the periodic table?A.He discovered that each element has its own atomic number.B.He discovered that the number of valence electrons increases to a full octet.C.He discovered that neutrons affect an element's atomic mass.D.He discovered that groups of elements have similar properties.

ue with Mendeleev's 1871 Periodic Table:First Issue:Noble gases were not included because they hadn't been discovered yet.Second Issue:Pairs of elements (e.g., Co and Ni) didn't fit into groups as expected based on their properties when arranged by atomic masses.Reason for Discrepancy:Later discovery of isotopes, different forms of an element with varying neutron numbers.Understanding Isotopes:Atomic mass of an element is an average of its isotopes' masses, considering their relative abundances.Impact on Mendeleev's Arrangement:

What breakthrough did Mendeleev make in devising a periodic table that was accepted by the scientific community?He arranged the elements in order of atomic weightHe left gaps in the table for unknown elementsHe devised the ‘law of octaves’He published the first full list of all the elements2Which of the following statements about the modern periodic table is not true?The number of shells decreases down a groupElements in the same group have the same number of electrons in the outer shellElements are arranged in atomic number orderElements in the same period have the same number of shells3Where are the non-metal elements found in the periodic table?On the rightAt the topAt the bottomOn the left4Which of the following elements, shown by its electronic structure, is found in group 2 of the periodic table?2, 8, 22, 72, 8, 12, 8, 45Why do fluorine, chlorine and iodine all have similar chemical properties?They are all metalsThey all have 7 electrons in their outer shellThey are all in the same periodThey all have odd numbers of electrons

Mendeleev left gaps in his periodic table for elements that hadn't been discovered yet.Identify which features of these elements he made predictions about.Their atomic weights onlyTheir atomic weights and propertiesTheir properties only

Describe how Mendeleev convinced the scientific community that his way of organising the elements into a periodic table was correct.