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Periodic Table
Johann Dobereiner German
Found that Ca, Ba and Sr were very similar.
He noted that the atomic mass of strontium was about midway between the other two.
John Newlands 1863 English Chemist
He arranged the elements in order of their increasing atomic masses. He noted that there
appeared to be a repetition of similar properties every eighth element. He placed seven
elements in each group. He arranged the 49 elements known at that time into seven
groups of seven each
Law of Octaves
1869 Dmitri Mendeleev---Russian Chemist
Properties of the elements were a function of their atomic masses but that the similar
properties occurred after periods that could vary in length.
He placed seven elements in each of the first two periods and seventeen elements in the
next two.
Mendeleev
Mendeleev had to leave some blank spots in order to group all the elements in the same
column
To explain these blanks spots he suggested that there must be other elements to be
discovered.
He predicted what properties and atomic masses that these would have and he was very
close
Mendeleev’s Periodic Table
He arranged the elements by atomic mass
1913 Henry Moseley
Something was wrong with Mendeleev’s table
Te and I are in the wrong column if they are to be arranged by atomic mass
X-ray experiments showed that the nucleus of each element has an integral positive
charge, the atomic number
Modern Periodic Table
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The modern periodic table is now based on atomic number instead of atomic mass
Periodic Trends
Ionization Energy
Electron Affinity
Electronegativity
o The Relative ability to attract electrons in a chemical bond
Relative Atomic Sizes Can Be Predicted by the Periodic Table
Down a Group, Atomic Size Increases
o Higher Primary Shells
Across a Period (lr), Atomic Size Decreases
o Same Primary Shell
o More Protons, More Electrons
o The + Charge from p
+
Pulls All e
-
In
Relative Ionization Energy Can Be Predicted from Periodic Table
Ionization Energy is the Energy Required to Remove One Electron from an Atom in the
Gaseous State
X(g) X
+
(g) + e
-
(g)
First Ionization Energy
X
+
(g) X
2+
(g) + e
-
(g)
Second Ionization Energy...
Ionization Energy Increases Across a Period
Ionization Energy Decreases Down a Group
o The attractive forces between the nucleus and electrons are tempered by distance.
o Valence electrons are shielded from nucleus by all the core electrons.
Octet Rule
Atoms tend to gain, lose or share electrons to acquire 8 valence electrons
Radius changes in the formation of ions
Cation--- Positively charged ion
Lose electrons, the radius gets smaller
Anion-- Negatively charged ion
Gain electrons, the radius gets larger

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Periodic Table Johann Dobereiner– German • Found that Ca, Ba and Sr were very similar. • He noted that the atomic mass of strontium was about midway between the other two. He grouped these elements--- triads John Newlands– 1863 English Chemist • He arranged the elements in order of their increasing atomic masses. He noted that there appeared to be a repetition of similar properties every eighth element. He placed seven elements in each group. He arranged the 49 elements known at that time into seven groups of seven each • Law of Octaves 1869– Dmitri Mendeleev---Russian Chemist • Properties of the elements were a function of their atomic masses but that the similar properties occurred after periods that could vary in length. • He placed seven elements in each of the first two periods and seventeen elements in the next two. Mendeleev • Mendeleev had to leave some blank spots in order to group all the elements in the same column • To explain these blanks spots he suggested that there must be other elements to be discovered. • He predicted what properties and atomic masses that these would have and he was very close Mendeleev’s Periodic Table • He arranged the elements by atomic mass 1913 Henry Moseley • Something was wrong with Mendeleev’s table • Te and I are in the wrong column if they are to be arranged by atomic mass • X-ray experiments showed that the nucleus of each element has an integral positive charge, the atomic number Modern Periodic Table • The modern periodic table is now based on atomic number instead of atomic mass Periodic Trends • Radius • Ionization Energy • Electron Affinity • Electronegativity o The Relative ability to attract electrons in a chemical bond Relative Atomic Sizes Can Be Predicted by the Periodic Table • Atomic Size = Atomic Radius • Down a Group, Atomic Size Increases o Higher Primary Shells • Across a Period (l→r), Atomic Size Decreases o Same Primary Shell o More Protons, More Electrons o The + Charge from p+ Pulls All e- In Relative Ionization Energy Can Be Predicted from Periodic Table • Ionization Energy is the Energy Required to Remove One Electron from an Atom in the Gaseous State • X(g) → X+(g) + e-(g) • X+(g) → X2+(g) + e-(g) • Ionization Energy Increases Across a Period • Ionization Energy Decreases Down a Group First Ionization Energy Second Ionization Energy... o The attractive forces between the nucleus and electrons are tempered by distance. o Valence electrons are shielded from nucleus by all the core electrons. Octet Rule • Atoms tend to gain, lose or share electrons to acquire 8 valence electrons Radius changes in the formation of ions • Cation--- Positively charged ion • • Lose electrons, the radius gets smaller Anion-- Negatively charged ion • Gain electrons, the radius gets larger Name: Description: ...
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