Creating the Periodic Table (2.3.1) Flashcards
• Mendeleev organized the known elements into a table using atomic mass and chemical reactivity and predicted the existence of undiscovered elements.
• Mendeleev organized the known elements into a table using atomic mass and chemical reactivity and predicted the existence of undiscovered elements.
• The discovery of argon posed new issues that instigated further changes in the order of the table.
• The discovery of argon posed new issues that instigated further changes in the order of the table.
• Arranging the elements on the periodic table according to their atomic numbers resolved all remaining inconsistencies.
• Arranging the elements on the periodic table according to their atomic numbers resolved all remaining inconsistencies.
Mendeleev organized the 63 elements known in his
time in the order of their atomic masses and into
groups based on their chemical reactivities and
physical properties.
Mendeleev found a regular repeating pattern in the
table of elements he developed that contained a few
inconsistencies. For example, iodine and tellurium
did not group properly given their atomic masses.
He also noticed gaps in the sequence and used this
information to make predictions of the existence of
undiscovered elements that he called eka-aluminum
and eka-silicon. These elements were later
discovered and called gallium and germanium.
Mendeleev organized the 63 elements known in his
time in the order of their atomic masses and into
groups based on their chemical reactivities and
physical properties.
Mendeleev found a regular repeating pattern in the
table of elements he developed that contained a few
inconsistencies. For example, iodine and tellurium
did not group properly given their atomic masses.
He also noticed gaps in the sequence and used this
information to make predictions of the existence of
undiscovered elements that he called eka-aluminum
and eka-silicon. These elements were later
discovered and called gallium and germanium.
The discovery of argon posed new issues that
instigated further changes in the order of the table.
Ramsay discovered the element argon in 1894. It
had an atomic mass that placed it between
potassium and calcium on the periodic table.
Potassium combines with oxygen in a 2:1 ratio,
whereas calcium combines in a 1:1 ratio. It was
unclear what an element placed between them
should do, moreover argon showed little reactivity
with any substances.
The discovery of neon and krypton in 1898, two
non-reactive gases like argon, motivated the
creation of a whole new group of elements, called
the noble gases, that included argon. Neon and
krypton had atomic masses that suggested they
belonged to the right of the last column in the
periodic table. Argon was placed in this new
grouping despite the issue of its atomic mass.
The discovery of argon posed new issues that
instigated further changes in the order of the table.
Ramsay discovered the element argon in 1894. It
had an atomic mass that placed it between
potassium and calcium on the periodic table.
Potassium combines with oxygen in a 2:1 ratio,
whereas calcium combines in a 1:1 ratio. It was
unclear what an element placed between them
should do, moreover argon showed little reactivity
with any substances.
The discovery of neon and krypton in 1898, two
non-reactive gases like argon, motivated the
creation of a whole new group of elements, called
the noble gases, that included argon. Neon and
krypton had atomic masses that suggested they
belonged to the right of the last column in the
periodic table. Argon was placed in this new
grouping despite the issue of its atomic mass.
Arranging the elements on the periodic table
according to their atomic numbers resolved all
remaining inconsistencies.
In 1911, Rutherford’s work shed light on the
structure of the nucleus and the concept of atomic
number (the number of protons in a nucleus). In
1913, Moseley found that the frequencies of the xray
emissions of different elements were correlated
with atomic number but not atomic mass.
These discoveries lead to recognition of the
importance of atomic number in determining the
characteristics of an element. It was also seen that
when the elements of the periodic table were
organized by atomic number, rather than atomic
mass, the inconsistencies in the table (like argon,
tellurium and iodine) disappeared. Thus atomic
number was adopted as the ordering criterion for
the table.
The organization of the elements into the periodic
table pointed to the existence of undiscovered
elements and to important information about the
elements. This is a demonstration of the value, in
science, of looking for trends in new data.
Arranging the elements on the periodic table
according to their atomic numbers resolved all
remaining inconsistencies.
In 1911, Rutherford’s work shed light on the
structure of the nucleus and the concept of atomic
number (the number of protons in a nucleus). In
1913, Moseley found that the frequencies of the xray
emissions of different elements were correlated
with atomic number but not atomic mass.
These discoveries lead to recognition of the
importance of atomic number in determining the
characteristics of an element. It was also seen that
when the elements of the periodic table were
organized by atomic number, rather than atomic
mass, the inconsistencies in the table (like argon,
tellurium and iodine) disappeared. Thus atomic
number was adopted as the ordering criterion for
the table.
The organization of the elements into the periodic
table pointed to the existence of undiscovered
elements and to important information about the
elements. This is a demonstration of the value, in
science, of looking for trends in new data.
Atomic Mass
The isotopically weighted average mass of an element in atomic mass units (grams per mole).
