Periodic Table. Larry Scheffler Lincoln High School. The Periodic Table-Key Questions. What is the periodic table ? What information is obtained from the table ? How can elemental properties be predicted based on the Periodic Table ?.
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Lincoln High School
The development of the periodic table brought a system of order to what was otherwise an collection of thousands of pieces of information
The periodic table is a milestone in the development of modern chemistry. It not only brought order to the elements but it also enabled scientists to predict the existence of yet undiscovered
Note: In each case, the numerical values for the atomic mass and density of the middle element are close to the averages of the other two elements
Dmitri Mendeleev is credited with creating the modern periodic table of the elements.
He gets the credit because he not only arranged the atoms, but he made predictions based on his arrangement which were shown to be quite accurate.
Mendeleev left some blank spaces in his periodic table. At the time the elements gallium and germanium were not known. He predicted their discovery and estimated their properties
The Periodic Table has undergone several modifications before it evolved in its present form. The current form is usually attributed to Glenn Seaborg in 1945
Vertical columns in the periodic table are known as groups or families The elements in a group have similar electron configurations
Horizontal Rows in the periodic table are known as Periods The Elements in a period undergo a gradual change in properties as one proceeds from left to right
Periodic properties include:
-- Ionization Energy
-- Electron Affinity
-- Atomic Radius
-- Ionic Radius
Ionization energy is the energy required to
Remove an electron from an atom
Electronegativity is a measure of the ability of an atom in a molecule to attract electrons to itself.
This concept was first proposed by Linus Pauling (1901-1994). He later won the Nobel Prize for his efforts
The radius decreases across a period owing to increase in the positive charge from the protons. Each added electron feels a greater and greater + charge because the protons are pulling in the same direction, where the electrons are scattered.
Radius in pm
Cations (positive ions) are smaller than their corresponding atoms
Does the size go up or down when gaining an electron to form an anion?
, 78 pm
2e and 3 p
Forming a cation.
3e and 3p
Positve ions or cations are smaller than the corresponding atoms.
Cations like atoms increase as one moves from top to bottom in a group.
Anions (negative ions) are larger than their corresponding atoms
F 64 pm
, 133 pm
9e- and 9p+
10 e- and 9 p+
Forming an anion.
Negative ions or anions are larger than the
Anions like atoms increase as one moves from top to bottom in a group.
Isoelectronic ions have the same number of electrons.
The more negative an ion is the larger it is and vice versa.
The periodic table is a classification system. Although we are most familiar with the periodic table that Seaborg proposed more than 60 years ago, several alternate designs have been proposed.