Question: What result came of more chemically similar lanthanide elements being discovered?
About the article "Atomic number", section "The periodic table and a natural number for each element".

Candidate passages:
The lanthanide contraction is responsible for the great geochemical divide that splits the lanthanides into light and heavy-lanthanide enriched minerals, the latter being almost inevitably associated with and dominated by yttrium.
This divide is reflected in the first two "rare earths" that were discovered: yttria (1794) and ceria (1803).
The geochemical divide has put more of the light lanthanides in the Earth's crust, but more of the heavy members in the Earth's mantle.
The result is that although large rich ore-bodies are found that are enriched in the light lanthanides, correspondingly large ore-bodies for the heavy members are few.
The principal ores are monazite and bastnäsite.
Monazite sands usually contain all the lanthanide elements, but the heavier elements are lacking in bastnäsite.
The lanthanides obey the Oddo-Harkins rule – odd-numbered elements are less abundant than their even-numbered neighbors.
Three of the lanthanide elements have radioactive isotopes with long half-lives (138La, 147Sm and 176Lu) that can be used to date minerals and rocks from Earth, the Moon and meteorites. 
The lanthanide or lanthanoid series of chemical elements comprises the fifteen metallic chemical elements with atomic numbers 57 through 71, from lanthanum through lutetium.
These fifteen lanthanide elements, along with the chemically similar elements scandium and yttrium, are often collectively known as the rare earth elements.
The informal chemical symbol Ln is used in general discussions of lanthanide chemistry to refer to any lanthanide.
All but one of the lanthanides are f-block elements, corresponding to the filling of the 4f electron shell; lutetium, a d-block element, is also generally considered to be a lanthanide due to its chemical similarities with the other fourteen.
All lanthanide elements form trivalent cations, Ln3+, whose chemistry is largely determined by the ionic radius, which decreases steadily from lanthanum to lutetium.
The lanthanide elements are the group of elements with atomic number increasing from 57 (lanthanum) to 71 (lutetium).
They are termed lanthanide because the lighter elements in the series are chemically similar to lanthanum.
Strictly speaking, both lanthanum and lutetium have been labeled as group 3 elements, because they both have a single valence electron in the d shell.
However, both elements are often included in any general discussion of the chemistry of the lanthanide elements.
In presentations of the periodic table, the lanthanides and the actinides are customarily shown as two additional rows below the main body of the table, with placeholders or else a selected single element of each series (either lanthanum and actinium, or lutetium and lawrencium) shown in a single cell of the main table, between barium and hafnium, and radium and rutherfordium, respectively.
This convention is entirely a matter of aesthetics and formatting practicality; a rarely used wide-formatted periodic table inserts the lanthanide and actinide series in their proper places, as parts of the table's sixth and seventh rows (periods). 
The lanthanide or lanthanoid (IUPAC nomenclature) series comprises the fifteen metallic chemical elements with atomic numbers 57 through 71, from lanthanum through lutetium.
These fifteen elements, along with the chemically similar elements scandium and yttrium, are often collectively known as the rare earth elements.
The informal chemical symbol Ln is used in general discussions of lanthanide chemistry.
All but one of the lanthanides are f-block elements, corresponding to the filling of the 4f electron shell; lutetium, a d-block element, is also generally considered to be a lanthanide due to its chemical similarities with the other fourteen.
All lanthanide elements form trivalent cations, Ln3+, whose chemistry is largely determined by the ionic radius, which decreases steadily from lanthanum to lutetium.
Between initial and final 6s2 electronic shells The lanthanide elements are the group of elements with atomic number increasing from 57 (lanthanum) to 71 (lutetium).
They are termed lanthanide because the lighter elements in the series are chemically similar to lanthanum.
Strictly speaking, both lanthanum and lutetium have been labeled as group 3 elements, because they both have a single valence electron in the d shell.
However, both elements are often included in any general discussion of the chemistry of the lanthanide elements.
In presentations of the periodic table, the lanthanides and the actinides are customarily shown as two additional rows below the main body of the table, with placeholders or else a selected single element of each series (either lanthanum or lutetium, and either actinium or lawrencium, respectively) shown in a single cell of the main table, between barium and hafnium, and radium and rutherfordium, respectively.
This convention is entirely a matter of aesthetics and formatting practicality; a rarely used wide-formatted periodic table inserts the lanthanide and actinide series in their proper places, as parts of the table's sixth and seventh rows (periods). 
Together with scandium and yttrium, the trivial name "rare earths" is sometimes used to describe all the lanthanides.
This name arises from the minerals from which they were isolated, which were uncommon oxide-type minerals.
However, the use of the name is deprecated by IUPAC, as the elements are neither rare in abundance nor "earths" (an obsolete term for water-insoluble strongly basic oxides of electropositive metals incapable of being smelted into metal using late 18th century technology) .
Cerium is the 26th most abundant element in the Earth's crust, neodymium is more abundant than gold and even thulium (the least common naturally occurring lanthanide) is more abundant than iodine, which is itself common enough for biology to have evolve critical usages for.
Despite their abundance, even the technical term "lanthanides" could be interpreted to reflect a sense of elusiveness on the part of these elements, as it comes from the Greek λανθανειν ("lanthanein"), "to lie hidden".
However, if not referring to their natural abundance, but rather to their property of "hiding" behind each other in minerals, this interpretation is in fact appropriate.
The etymology of the term must be sought in the first discovery of lanthanum, at that time a so-called new rare earth element "lying hidden" in a cerium mineral, and it is an irony that lanthanum was later identified as the first in an entire series of chemically similar elements and could give name to the whole series.
The term "lanthanide" was introduced by Victor Goldschmidt in 1925. 
Experimenting with the energy of β-particles in 1912, Moseley showed that high potentials were attainable from a radioactive source of radium, thereby inventing the first atomic battery, though he was unable to produce the 1MeV necessary to stop the particles.
In 1913, Moseley observed and measured the X-ray spectra of various chemical elements (mostly metals) that were found by the method of diffraction through crystals.
This was a pioneering use of the method of X-ray spectroscopy in physics, using Bragg's diffraction law to determine the X-ray wavelengths.
Moseley discovered a systematic mathematical relationship between the wavelengths of the X-rays produced and the atomic numbers of the metals that were used as the targets in X-ray tubes.
This has become known as Moseley's law.
Before Moseley's discovery, the atomic numbers (or elemental number) of an element had been thought of as a semi-arbitrary sequential number, based on the sequence of atomic masses, but modified somewhat where chemists found this to be desirable, such as by the great Russian chemist, Dimitri Ivanovich Mendeleev.
In his invention of the Periodic Table of the Elements, Mendeleev had interchanged the orders of a few pairs of elements in order to put them in more appropriate places in this table of the elements.
For example, the metals cobalt and nickel had been assigned the atomic numbers 27 and 28, respectively, based on their known chemical and physical properties, even though they have nearly the same atomic masses.
In fact, the atomic mass of cobalt is slightly larger than that of nickel, which would have placed them in backwards order if they had been placed in the Periodic Table blindly according to atomic mass.
Moseley's experiments in X-ray spectroscopy showed directly from their physics that cobalt and nickel have the different atomic numbers, 27 and 28, and that they are placed in the Periodic Table correctly by Moseley's objective measurements of their atomic numbers.
Hence, Moseley's discovery demonstrated that the atomic numbers of elements are not just rather arbitrary numbers based on chemistry and the intuition of chemists, but rather, they have a firm experimental basis from the physics of their X-ray spectra.
In addition, Moseley showed that there were gaps in the atomic number sequence at numbers 43, 61, 72, and 75.
These spaces are now known, respectively, to be the places of the radioactive synthetic elements technetium and promethium, and also the last two quite rare naturally-occurring stable elements hafnium (discovered 1923) and rhenium (discovered 1925).
Nothing about these four elements was known of in Moseley's lifetime, not even their very existence.
Based on the intuition of a very experienced chemist, Dimitri Mendeleev had predicted the existence of a missing element in the Periodic Table, which was later found to be filled by technetium, and Bohuslav Brauner had predicted the existence of another missing element in this Table, which was later found to be filled by promethium.
Henry Moseley's experiments confirmed these predictions, by showing exactly what the missing atomic numbers were, 43 and 61.
In addition, Moseley predicted the two more undiscovered elements, those with the atomic numbers 72 and 75, and gave very strong evidence that there were no other gaps in the Periodic Table between the elements aluminium (atomic number 13) and gold (atomic number 79).
This latter question about the possibility of more undiscovered ("missing") elements had been a standing problem among the chemists of the world, particularly given the existence of the large family of the lanthanide series of rare earth elements.
Moseley was able to demonstrate that these lanthanide elements, i.e.
lanthanum through lutetium, must have exactly 15 members - no more and no less.
The number of elements in the lanthanides had been a question that was very far from being settled by the chemists of the early 20th Century.
They could not yet produce pure samples of all the rare-earth elements, even in the form of their salts, and in some cases they were unable to distinguish between mixtures of two very similar (adjacent) rare-earth elements from the nearby pure metals in the Periodic Table.
For example, there was a so-called "element" that was even given the chemical name of "didymium".
"Didymium" was found some years later to be simply a mixture of two genuine rare-earth elements, and these were given the names neodymium and praseodymium, meaning "new twin" and "green twin".
Also, the method of separating the rare-earth elements by the method of ion exchange had not been invented yet in Moseley's time.
Moseley's method in early X-ray spectroscopy was able to sort out the above chemical problems promptly, some of which had occupied chemists for a number of years.
Moseley also predicted the existence of element 61, a lanthanide whose existence was previously unsuspected.
Quite a few years later, this element 61 was created artificially in nuclear reactors and was named promethium.