The Periodic Table.
Origins.
Explanations.
Terminologies.
Origins.
Explanations.
Terminologies.
Chemistry Ace:The Periodic Table
Hi everyone, this
is a blog done by Timothy and Sam about the periodic table. Here we have facts about the periodic table and
how to read and interpret it, enjoy ;)
Origins of the periodic table
In the past, Aristotle (a Greek philosopher) proposed that there were
only four main elements: air, fire, water and earth. These elements were said to be able
to combine with one another to form new elements.However, this theory was dismissed when the real chemical elements started being discovered.
Scientists needed an easily accessible, well organized database with which information about the elements could be recorded and accessed. This was to be known as the periodic table.
The original table was created before the discovery of subatomic particles or the formulation of current quantum mechanical theories of atomic structure. In 1829 Döbereiner proposed the Law of Triads: The middle element in the triad had atomic weight that was the average of the other two members. The densities of some triads followed a similar pattern.
Soon other scientists found chemical relationships extended beyond triads. This was followed by the English chemist John Newlands, who noticed in 1865 that when placed in order of increasing atomic weight, elements of similar physical and chemical properties recurred at intervals of eight, which he likened to the octaves of music
Finally, in 1869 the Russian chemistry professor Dmitri Ivanovich Mendeleev and four months later the German Julius Lothar Meyer independently developed the first periodic table, arranging the elements by mass.
Scientists needed an easily accessible, well organized database with which information about the elements could be recorded and accessed. This was to be known as the periodic table.
The original table was created before the discovery of subatomic particles or the formulation of current quantum mechanical theories of atomic structure. In 1829 Döbereiner proposed the Law of Triads: The middle element in the triad had atomic weight that was the average of the other two members. The densities of some triads followed a similar pattern.
Soon other scientists found chemical relationships extended beyond triads. This was followed by the English chemist John Newlands, who noticed in 1865 that when placed in order of increasing atomic weight, elements of similar physical and chemical properties recurred at intervals of eight, which he likened to the octaves of music
Finally, in 1869 the Russian chemistry professor Dmitri Ivanovich Mendeleev and four months later the German Julius Lothar Meyer independently developed the first periodic table, arranging the elements by mass.
The Periodic Table: a brief introduction
The periodiс table of the chemical elements is a tabular method of displaying the chemical elements.
Although precursors to this table exist, its invention is generally credited to Russian chemist Dmitri Mendeleev in 1869. Mendeleev
intended the table to illustrate recurring ("periodic") trends in the properties of the elements.
The layout of the table has been refined and extended over time, as new elements have been discovered, and new theoretical models have been developed to explain chemical behavior.
The periodic table is now an important tool within the academic discipline of chemistry, providing an extremely useful framework to classify, systematize and compare all of the many different forms of chemical behavior. The table has found wide application in chemistry, physics, biology, and engineering, especially chemical engineering. The current standard table contains 117 elements as of March 10, 2009
The layout of the table has been refined and extended over time, as new elements have been discovered, and new theoretical models have been developed to explain chemical behavior.
The periodic table is now an important tool within the academic discipline of chemistry, providing an extremely useful framework to classify, systematize and compare all of the many different forms of chemical behavior. The table has found wide application in chemistry, physics, biology, and engineering, especially chemical engineering. The current standard table contains 117 elements as of March 10, 2009
why is it like that?
The layout of the periodic table
• demonstrates recurring chemical properties.
• Elements are listed in order of increasing atomic number.
• Rows
o arranged so that elements with similar properties fall into the same columns.
o According to quantum mechanical theories of electron configuration within atoms, each row (A.K.A. period) in the table corresponded to the filling of a quantum shell of electrons.
o There are progressively longer periods further down the table, grouping the elements into s-, p-, d- and f-blocks to reflect their electron configuration.
As of 2009, the table contains 117 chemical elements whose discoveries have been confirmed.
• Ninety-four are found naturally on Earth
• Rest are synthetic elements that have been produced artificially in particle accelerators.
o Elements 43 (technetium), 61 (promethium), 93 (neptunium) and 94 (plutonium) have no stable isotopes and were first discovered synthetically; however, they were later discovered in trace amounts on earth as products of natural radioactive decay processes.
• demonstrates recurring chemical properties.
• Elements are listed in order of increasing atomic number.
• Rows
o arranged so that elements with similar properties fall into the same columns.
o According to quantum mechanical theories of electron configuration within atoms, each row (A.K.A. period) in the table corresponded to the filling of a quantum shell of electrons.
o There are progressively longer periods further down the table, grouping the elements into s-, p-, d- and f-blocks to reflect their electron configuration.
As of 2009, the table contains 117 chemical elements whose discoveries have been confirmed.
• Ninety-four are found naturally on Earth
• Rest are synthetic elements that have been produced artificially in particle accelerators.
o Elements 43 (technetium), 61 (promethium), 93 (neptunium) and 94 (plutonium) have no stable isotopes and were first discovered synthetically; however, they were later discovered in trace amounts on earth as products of natural radioactive decay processes.
what are these terms?
• A group or family is a vertical column in the periodic table of the elements.
- most important method of classifying the elements
- In some groups, the elements have very similar properties and exhibit a clear trend in properties down the group.
- These groups tend to be given trivial (unsystematic) names e.g., the alkali metals, alkaline earth metals, halogens and noble gases.
- Some other groups in the periodic table display fewer similarities and/or vertical trends (for example Groups 14 and 15), and these have no trivial names and are referred to simply by their group numbers.
-> A period is a horizontal row in the periodic table of the elements.
- some regions of the periodic table where the horizontal trends and similarities in properties are more significant than vertical group trends.
-> This can be true in the transition metals
-> The f-block, where the lanthanoids and actinoids form two substantial horizontal series of elements.
Periodic trends of groups
• Elements within the same group have the same electron configurations in their valence shell, which is the most important factor in accounting for their similar properties.
• Elements in the same group also show patterns in their atomic radius, ionization energy, and electronegativity.
-From top to bottom in a group, the atomic radii of the elements increase.
-Since there are more filled energy levels, valence electrons are found farther from the nucleus. From the top, each successive element has a lower ionization energy because it is easier to remove an electron since the atoms are less tightly bound. Similarly, a group will also see a top to bottom decrease in electronegativity due to an increasing distance between valence electrons and the nucleus.
Periodic trends of periods
Periodic trend for ionization energy.
• Each period begins at a minimum for the alkali metals, and ends at a maximum for the noble gases.
Elements in the same period show trends in:
• atomic radius
• ionization energy
• electron affinity
• electronegativity
Moving left to right across a period, atomic radius usually decreases. This occurs because each successive element has an added proton and electron which causes the electron to be drawn closer to the nucleus. This decrease in atomic radius also causes the ionization energy to increase when moving from left to right across a period. The more tightly bound an element is, the more energy is required to remove an electron.
Similarly, electronegativity will increase in the same manner as ionization energy because of the amount of pull that is exerted on the electrons by the nucleus. Electron affinity also shows a slight trend across a period. Metals (left side of a period) generally have a lower electron affinity than nonmetals (right side of a period) with the exception of the noble gases.
So how exactly does the periodic table classify the elements into periods and groups?
In reality, this is very simple.
.the group of an element is determined by the number of valence electrons in its outermost subshell.
-> so for example you take two elements with the electronic configuration 1s2 2s2 2s6 3s1(sodium) and 1s2 2s2 2p6 3s2 3p6 4s1 (potassium)
- these elements belong to the same group as they only have one valence electron in the outermost subshell
.As for the period, elements are divided into periods based on the total number of electron shells that it has.
-> therfore elements with the electronic configuration 1s2 2s2 (berillium) and 1s2 2s2 2p6 (neon) belong in the same period as they have the same number of subshells.
- most important method of classifying the elements
- In some groups, the elements have very similar properties and exhibit a clear trend in properties down the group.
- These groups tend to be given trivial (unsystematic) names e.g., the alkali metals, alkaline earth metals, halogens and noble gases.
- Some other groups in the periodic table display fewer similarities and/or vertical trends (for example Groups 14 and 15), and these have no trivial names and are referred to simply by their group numbers.
-> A period is a horizontal row in the periodic table of the elements.
- some regions of the periodic table where the horizontal trends and similarities in properties are more significant than vertical group trends.
-> This can be true in the transition metals
-> The f-block, where the lanthanoids and actinoids form two substantial horizontal series of elements.
Periodic trends of groups
• Elements within the same group have the same electron configurations in their valence shell, which is the most important factor in accounting for their similar properties.
• Elements in the same group also show patterns in their atomic radius, ionization energy, and electronegativity.
-From top to bottom in a group, the atomic radii of the elements increase.
-Since there are more filled energy levels, valence electrons are found farther from the nucleus. From the top, each successive element has a lower ionization energy because it is easier to remove an electron since the atoms are less tightly bound. Similarly, a group will also see a top to bottom decrease in electronegativity due to an increasing distance between valence electrons and the nucleus.
Periodic trends of periods
Periodic trend for ionization energy.
• Each period begins at a minimum for the alkali metals, and ends at a maximum for the noble gases.
Elements in the same period show trends in:
• atomic radius
• ionization energy
• electron affinity
• electronegativity
Moving left to right across a period, atomic radius usually decreases. This occurs because each successive element has an added proton and electron which causes the electron to be drawn closer to the nucleus. This decrease in atomic radius also causes the ionization energy to increase when moving from left to right across a period. The more tightly bound an element is, the more energy is required to remove an electron.
Similarly, electronegativity will increase in the same manner as ionization energy because of the amount of pull that is exerted on the electrons by the nucleus. Electron affinity also shows a slight trend across a period. Metals (left side of a period) generally have a lower electron affinity than nonmetals (right side of a period) with the exception of the noble gases.
So how exactly does the periodic table classify the elements into periods and groups?
In reality, this is very simple.
.the group of an element is determined by the number of valence electrons in its outermost subshell.
-> so for example you take two elements with the electronic configuration 1s2 2s2 2s6 3s1(sodium) and 1s2 2s2 2p6 3s2 3p6 4s1 (potassium)
- these elements belong to the same group as they only have one valence electron in the outermost subshell
.As for the period, elements are divided into periods based on the total number of electron shells that it has.
-> therfore elements with the electronic configuration 1s2 2s2 (berillium) and 1s2 2s2 2p6 (neon) belong in the same period as they have the same number of subshells.
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