Chemistry 11. Unit 8 Atoms and the Period Table Part III Periodic Table

Transcription

1 Chemistry 11 Unit 8 Atoms and the Period Table Part III Periodic Table

2 2 1. A short history of the periodic table Periodic table is an arrangement of chemical elements organized in terms of their atomic numbers, electron configurations and properties. Such a table (or list) did not appear at the beginning; it is instead a collective work of several generations of chemists. The development of the periodic table was in line with the development of chemical elements (or inorganic chemistry).

3 3 (1) Antoine Lavoisier ( ) He was called the father of modern chemistry. He published the first ever textbook in chemistry, Elementary Treatise of Chemistry in In his book, he classified hydrogen, nitrogen, oxygen, phosphorus, sulfur, zinc and mercury as either metal or non-metal. The classification was trivial and lacked completeness.

4 4 (2) Johann Wolfgang Döbereiner ( ) He proposed one of the earliest ways of classifying elements in He grouped elements into groups of three called triads. These elements possess analogous chemical properties. For example: chlorine / bromine / iodine calcium / strontium / barium sulfur / selenium / tellurium lithium / sodium / potassium

5 5 (3) Alexandre-Emile Béguyer de Chancourtois ( ) He arranged all known elements at that time in order of atomic weights in He created a spiral table, telluric helix, in which species with similar properties are lined up vertically. Not well recognized as it was given in terms of geology.

6 6 (4) John Newlands ( ) He was the first to assign atomic numbers to elements in He proposed the law of octaves: in many cases elements different by multiple of 8 in mass number show similar properties. He introduced the concept of periodicity in chemistry. His model could not make any prediction, and needed modification whenever new element was discovered.

7 7 (5) William Odling ( ) He published his table in He put elements into 7 groups in order of atomic weights. He left vacancies for elements yet to be discovered. He solved the tellurium-iodine problem, and was able to place thallium, lead, mercury and platinum in correct groups.

8 8 (6) Lothar Meyer ( ) He was the first to group elements according to their valence rather than atomic weights. Two versions of periodic tables were published: horizontal form (1862, 1864) and vertical form (1870)

9 9 (7) Dmitri Ivanovich Mendeleev ( ) He arranged all the known elements in orders of both atomic weights and valence in Elements show periodic patterns of properties. He predicted the existence of undiscovered elements at that moment such as germanium and gallium. He suggested that certain properties of elements can be foretold by their atomic masses.

10 10 The periodic tables published by Mendeleev: (In 1869) (In 1871)

11 11 After Mendeleev had proposed his periodic table, many scientists continued to contribute to its further modifications. Most notably: (1) Henry Moseley ( ) He discovered the physical meaning of atomic number as the number of protons in the nucleus of an atom. He therefore re-sequenced the periodic table in order of nuclear charges. (We have studied his story before)

12 12 (2) William Ramsay ( ), William Strutt ( ) and Friedrich Ernst Dorn ( ) They discovered and isolated a series of gases from minerals and air which showed extremely low level of reactivity during Mendeleev added these elements into group 0 in the periodic table in 1902.

13 13 (3) Charles Janet ( ) He proposed an innovative left-step periodic table in His table agrees perfectly with quantum theory. But his table was only up to element 120.

14 14 (4) Glenn T. Seaborg ( ) He discovered 10 trans-uranium elements (atomic number: , 106) plus many isotopes by means of nuclear chemistry and physics. In order to incorporate these elements into the periodic table, he developed the actinide concept and introduced the actinide series. Element 106 (seaborgium) was named after him in 1997.

15 15 The most up-to-date periodic table (2016 version):

16 16 2. Features of modern periodic table Chemical elements in the periodic table can be grouped into several ways. (1) Groups / Families A group or family is the set of elements in a given column going up and down the table. Elements in one group have the same electron configurations in their valence shell, hence showing more significant periodic trends than periods and blocks. Groups are numbered from 1 to 18, left to right.

17 17 (2) Periods A horizontal row of elements in a periodic table forms a period. Elements in a period do not usually show trends and similarities in properties. For transition and rare earth elements, however, trends across periods become much more significant. For example, lanthanide elements have similar chemical and physical properties, making them very difficult to be isolated and purified.

18 18 (3) Blocks A block of the periodic table refers to a set of elements in adjacent groups. Elements within a block have the highest-energy electrons in the same type of orbitals. The elements in the periodic table are divided into 4 blocks: (1) s-block: group 1 and group 2 (2) p-block: groups 13 to 18 (3) d-block: transition metals (4) f-block: lanthanide and actinide series

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20 20 (4) Metals / Metalloids / Non-metals According to their physical and chemical properties, elements can be classified into metals, metalloids and non-metals.

21 21 (i) Metals Metals share the following properties: Lustrous Opaque Good electrical and heat conductors Malleable and ductile Solid at room temperature Reactive to acids

22 22 (ii) Non-metals Non-metals share the following properties: Mainly gases or solids at room temperature Solid non-metals are brittle Poor heat and electrical conductors Various appearance (dull, opaque, translucent, etc)

23 23 (iii) Metalloids Metalloids possess properties from both metals and non-metals (e.g. lustrous but brittle) Seven metalloids: boron, silicon, germanium, arsenic, antimony, tellurium, polonium Some of them are semiconductors, whose electrical conductivity increases with temperature. This is opposite to metals whose conductivity decreases with temperature.

24 24 The variation of the metallic behaviors of elements can be summarized into two trends: (1) Left to right: decreasing metallic character (2) top to bottom: increasing metallic character

25 25 The periodic table contains 18 columns categorized into 4 groups: main group elements, transition elements, rare earth elements, and synthetic elements. (1) Main group elements consist of the two columns on the left and six columns on the right of the table. Group # Trivial name IUPAC name (old) IUPAC name (new) 1 Alkali metals IA 1 2 Alkaline earth metals IIA 2 13 Icosagens IIIA Crystallogens IVA Pnictogens VA Chalcogens VIA Halogens VIIA Noble gases VIIIA 18

26 26 Alkali metals All silvery metals Low melting points Very soft Extremely reactive in air and water They are reducing in nature In reactions they form +1 ions. Metal M.P. Metals M.P. Lithium 181 C Rubidium 39 C Sodium 98 C Cesium 29 C Potassium 64 C Francium 27 C

27 27 Alkaline earth metals Shiny, silvery-white, and soft They are reactive in water, forming strongly basic hydroxides They form +2 ions in reactions.

28 28 Crystallogens This group shows a big variation of physical and chemical properties from carbon to lead. They are able to exist in +2 or +4 oxidation states. All members except lead have allotropes (e.g. graph/diamonds for C, grey/white tin) Catenation: element can make chains with itself. Element Length of catenation Carbon Silicon Germanium 9-10 Tin 2 Lead 2

29 29 Pnictogens These elements can either gain three electrons or lose five electrons to form mainly covalent compounds. They are in general less reactive than group 16 neighbors. These elements are quite distinctive, and demonstrate not much connection.

30 30 Chalcogens These elements are relatively reactive, forming ions with 2 charges. They form volatile compounds with hydrogen. Their oxides are mainly acidic; they hydrolyze to form acids. The chemistry of polonium is not very well known, because of its high radioactivity, but similar to tellurium.

31 31 Halogens The only group that contains elements in 3 states. They are extremely reactive, and form a variety of salts when reacting with metals. Fluorine is the most reactive element; it even reacts with glass and noble gases.

32 32 Noble gases Also called inert gases, as they virtually do not react with any elements in the periodic table. They are all gases with low boiling points. They show different colors under electric discharge. Indeed they do react; first compound was made by Neil Bartlett at UBC in 1962.

33 33 (2) Transition elements refer to the groups (3 to 12) sandwiched by the s- and p-block elements. They are so named because their physical and chemical properties are somewhat between those exhibited by s-block and p-block elements. Their chemistry is very abundant: (i) versatile oxidation states and charges (ii) amphoteric when reacting with acids and bases (iii) forming both ionic and covalent bonds (iv) very colorful solutions containing transition metal ions

34 34 (3) Rare earth elements is made of a set of 17 chemical elements (15 lanthanides plus scandium and yttrium). The first rare earth, yttrium, was found from a mineral Ytterbite by Carl Axel Arrhenius in They are actually not rare (e.g. cerium has a similar abundance as copper), but they are geologically dispersed and not concentrated enough to be economically or technologically exploitable. They usually co-exist in nature, and are very difficult to separate from one another due in part to their similar chemical properties (related to their f-subshell electron configurations).

35 35 They all form +3 ions preferentially in solutions and compounds. These elements are widely used as: (1) catalytic converters (2) refining catalysts (3) superconductors (4) ultra-strong magnets (5) lasers (6) medical fluorophores

36 36 (4) Synthetic elements are the elements that do not occur naturally on Earth. They are created artificially using nuclear techniques. Usually, this term is used for trans-uranium elements having the atomic numbers of 95 or higher. The following elements are often obtained by synthesis although they exist in nature in trace amounts: Tc, Pm, Po, At, Fr, Ac, Pa, Np, Pu They are all radioactive and undergo decays to transform into lighter elements.

37 37 Applications of synthetic elements: cancer therapy, atomic bombs, atomic energy. Americium Curium Berkelium Californium Einsteinium Mendelevium Fermium Lawrencium

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