Missy Sorhirun
Grade 10
/The Periodic
Table & Me
The First International Congress of Chemists took place in Germany, in September 1860. At the Congress, the Chemists settled the issue of atomic mass and other matters which made communication difficult. Stanislao Cannizzaro showed a method for accurately measuring the masses of atoms. His method was the first step of standard values for atomic mass and initated a search for relationships between atomic mass and other properties of the elements. Later on, Dmitri Mendeleev arraged cards (which included the atomic mass of the element and list of observed physical and chemical properties), and looked for trends or patterns. As resolution, the cards showed a repeating pattern, which is called PERIODIC. He then created a table, in 1869, where similar properties were grouped together- a periodic table of elements. Mendeleev vompleted his periodic table in 1886.
Purpose & History
The periodic table for the vertical columns is called a group. Elements in each group have the same number of valence electrons. As you count each columns, you'll know the amount of electrons in the outer shell. This is with the eception of transition elelments.
All of the rows, reading from left to right, is known as a period. The elements in a period have the same number of atomic orbitals. Every row adds an orbital, as you move down the table.
Arrangement
In a periodic table, periodic trends are specific patterns which illustrate different aspects of a certain element. The existence of the trends are based on the similar atomic structure of the elements (in group families or periods) and the periodic nature of the elements.
Some of the major periodic trends include: electronegativity, ionization energy, electron affinity, atomic radius, and ionic radii.
Electronegativity trend is a chemical property describing an atom's ability to attract and bind with elelctrons. The existence of this property is due to the electronic configuration of atoms. Electronegativity increases across the period because it requires less energy to lose an electron, than to gain one. It decreases down the group because the atomic number increases, meaning greater atomic radius. (This rule does not apply to noble gases, lanthanides, and actinides.)
The energy required to remove an electron from a neutral atom in its gaseous phase is called the ionization energy. As the ionization energy increases across the period, it decreases down the group. This is due to valence shell stability and electron shielding.
Electron affinity is the ability of an atom to accept an electron. It is the quantitative measurement of the energy change that occurs when an electron is added to a neutral gas atom. The increase of electron affinity within a period is caused by the decrease of atomic radius.On the other hand, it decreases within a group becuase the increase in atomic radius.
One-half the distance between the nuclei of two atoms is called the atomic radius. The increase of protons and electrons across the period causes the atomic radius within the period to decrease. Becuase of electron shielding, the atomic radius increases from top to bottom within a group.
Atomic radii are convalent molecules in which two like atoms are held together by a single convalent bond. It is the total distance from an atom's nucleus to the outermost orbital of electron. Atomic radii depends on the Zeff effect.