Periodic TablePeriodic Table

Done by: John Tan Wen YuDone by: John Tan Wen Yu

History of the Periodic TableHistory of the Periodic Table

• In 1789, Antoine Lavoisier published a list of 33 chemical elements. Although Lavoisier grouped the elements into gases, metals, non-metals, and earths, chemists spent the following century searching for a more precise classification scheme.

• In 1829, Johann Wolfgang Döbereiner observed that many of the elements could be grouped into triads (groups of three) based on their chemical properties. – Lithium, sodium, and potassium, for example, were

grouped together as being soft, reactive metals – Döbereiner also observed that, when arranged by

atomic weight, the second member of each triad was roughly the average of the first and the third. This became known as the Law of triads.

• German chemist Leopold Gmelin worked with this system, and by 1843 he had identified ten triads, three groups of four, and one group of five.

• Jean Baptiste Dumas published work in 1857 describing relationships between various groups of metals.

• Although various chemists were able to identify relationships between small groups of elements, they had yet to build one scheme that encompassed them all

• German chemist August Kekulé had observed in 1858 that carbon has a tendency to bond with other elements in a ratio of one to four.

– Methane, for example, has one carbon atom and four hydrogen atoms. This concept eventually became known as valency

• In 1864, fellow German chemist Julius Lothar Meyer published a table of the 49 known elements arranged by valency – The table revealed that elements with similar

properties often shared the same valency

• English chemist John Newlands published a series of papers in 1864 and 1865 that described his attempt at classifying the elements

• Russian chemistry professor Dmitri Ivanovich Mendeleev and Julius Lothar Meyer independently published their periodic tables in 1869 and 1870, respectively.

– They both constructed their tables in a similar manner: by listing the elements in a row or column in order of atomic weight and starting a new row or column when the characteristics of the elements began to repeat.

– The success of Mendeleev's table came from two decisions he made: The first was to leave gaps in the table when it seemed that the corresponding element had not yet been discovered

• With the development of modern quantum mechanical theories of electron configurations within atoms, it became apparent that each row (or period) in the table corresponded to the filling of a quantum shell of electrons.

• In the years that followed after Mendeleev published his periodic table, the gaps he left were filled as chemists discovered more chemical elements.

• The first transuranic element to be discovered was neptunium, which was formed by bombarding uranium with neutrons in a cyclotron in 1939

What is the Periodic Table?What is the Periodic Table?

• It is a tabular display of the chemical elements

• Its layout has been refined and extended over time, as new elements have been discovered, and new theoretical models have been developed to explain chemical behaviour

• It is now ubiquitous within the academic discipline of chemistry, providing a useful framework to classify, systematize, and compare all of the many different forms of chemical behaviour

• The table has found many applications in chemistry, physics, biology, and engineering, especially chemical engineering

• The current standard table contains 118 elements to date. (elements 1–118).

Description of the Periodic TableDescription of the Periodic Table

• The layout of the periodic table demonstrates recurring ("periodic") chemical properties.

• Elements are listed in order of increasing atomic number (i.e., the number of protons in the atomic nucleus).

• Rows are arranged so that elements with similar properties fall into the same columns (groups or families).

• In printed tables, each element is usually listed with its element symbol and atomic number; many versions of the table also list the element's atomic mass and other information, such as its abbreviated electron configuration, electronegativity and most common valence numbers.

• As of 2010, the table contains 118 chemical elements whose discoveries have been confirmed. Ninety-four are found naturally on Earth, and the rest are synthetic elements that have been produced artificially in particle accelerators.

• The primary determinant of an element's chemical properties is its electron configuration, particularly the valence shell electrons.

• Note that as atomic number (i.e., charge on the atomic nucleus) increases, this leads to greater spin-orbit coupling between the nucleus and the electrons, reducing the validity of the quantum mechanical orbital approximation model, which considers each atomic orbital as a separate entity.

ClassificationClassification

• Groups– A group or family is a vertical column in the

periodic table. – Groups are considered the 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.

– e.g., the alkali metals, alkaline earth metals, halogens, pnictogens, chalcogens, and noble gases.

• Periods– A period is a horizontal row in the periodic

table. – Although groups are the most common way of

classifying elements, there are some regions of the periodic table where the horizontal trends and similarities in properties are more significant than vertical group trends.

• Blocks– Because of the importance of the outermost

shell, the different regions of the periodic table are sometimes referred to as periodic table blocks, named according to the subshell in which the "last" electron resides.

• Other– The chemical elements are also grouped

together in other ways – Some of these groupings are often illustrated

on the periodic table, such as transition metals, poor metals, and metalloids

– Other informal groupings exist, such as the platinum group and the noble metals

A simpler description of its A simpler description of its characteristicscharacteristics

• Period– When you look at a periodic table, each of the

rows is considered to be a different period– In the periodic table, elements have

something in common if they are in the same row

• Groups– When a column goes from top to bottom, it's

called a group. – The elements in a group have the same

number of electrons in their outer orbital.

• Two at the top– Hydrogen (H) and helium (He) are special

elements – Hydrogen can have the talents and electrons

of two groups, one and seven – To scientists, hydrogen is sometimes missing

an electron, and sometimes it has an extra– Helium is different from all of the other

elements

– It can only have two electrons in its outer shell– Even though it only has two, it is still grouped

with elements that have eight (inert gases).

• The elements in the center section are called transition elements. They have special electron rules

Periodicity of chemical propertiesPeriodicity of chemical properties

• The main value of the periodic table is the ability to predict the chemical properties of an element based on its location on the table.

• It should be noted that the properties vary differently when moving vertically along the columns of the table than when moving horizontally along the rows.

• Trends of groups– Modern quantum mechanical theories of

atomic structure explain group trends by proposing that 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.

– With 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

• Trends of periods– Elements in the same period show trends in

atomic radius, ionization energy, electron affinity, and 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. 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

– 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.

Some uses of the periodic tableSome uses of the periodic table

• The noble gases are used in industry in arc welding, to dilute the oxygen in deep-sea divers' gas tanks, and to fill light bulbs.

• Argon is used in arc welding and in common light bulbs, as it does not react with the metal at high temperatures.

• Helium is used for diluting the pure oxygen in deep-sea diving tanks because the helium has a low solubility in human blood

• Helium is also used to inflate the tires of large aircraft, weather balloons, and blimps because it is nonflammable.

• Neon is used in sign tubing because it glows bright red when electricity is passed through it.

• Krypton and xenon are used in photographic flash units and in lighthouses, as running an electric current through either element generates a very bright light.

ReferencesReferences

• http://en.wikipedia.org/wiki/Periodic_table

• http://www.learner.org/interactives/periodic/groups4.html

• http://www.chem4kids.com/files/elem_pertable.html