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5.1-Organizing the elements:. To find a way to organize the elements, scientist studied the elements and their properties. Dmitri Mendeleev was the first Russian chemist to design a way to organize the elements.
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5.1-Organizing the elements: • To find a way to organize the elements, scientist studied the elements and their properties. • Dmitri Mendeleev was the first Russian chemist to design a way to organize the elements. • In 1869, Mendeleev published the first periodic table of the elements. He arranged the elements in his P.T. in rows by increasing atomic mass.
Characteristics of Mendeleev’s P.T. • Elements are arranged in rows by increasing atomic masses. Each time, a new row is started when chemical properties of the elements repeated. Therefore elements in the same column had similar properties. • Mendeleev left gaps in the list, and predicted that new elements would be discovered that would fill these gaps. He used each new element’s position in the P.T. to predict some of the properties of the elements. • Mendeleev is often considered father of the P.T. The element “mendelevium” was named in his honor.
Achievement & drawback • Drawback of mendeleev’s P.T.- It was difficult to find out accurate values of atomic masses of the elements, therefore some elements did not quite fit the pattern in Mendeleev’s P.T. according to increasing atomic masses. • Achievement of mendeleev’s P.T.- In 1886, a new element germanium was discovered that is very similar to those predicted by Mendeleev. Then other two elements, gallium and scandium also discovered that closely matched Mendeleev’s prediction.
Periodic law and modern P.T. • As mendeleev’ P.T. was found defective & as scientists learned more about the structure of atom, they improved Mendeleev’s table. • The modern periodic table organizes elements by increasing atomic number. This new arrangement fixed the discrepancies with elements such as tellurium and Iodine in Mendeleev’s periodic table. • Modern Periodic Law: The law that states that the repeating chemical and physical properties of elements change periodically with the atomic numbers of the elements.
Characteristics of modern P.T. • Elements are arranged with increasing atomic number from left to right in horizontal rows. • Horizontal rows are known as periods. • Elements become less metallic across each period. • Each vertical column in the P.T. is called a group. Elements in a same group have similar properties. • Atomic number of the elements in the groups increase with definite interval of 2, 8, 8, 18, 18 and 32.
Properties of elements in modern P.T. • There are total 18 groups and 7 periods. • Group-1 is known as Alkali metals Group-2 is known as Alkaline earth metals Group-3 to12 are called Transition metals Group-13→boron gr. elements (are nonmetal) Group-14→carbon gr. elements, are nonmetal Group-15→nitrogen gr. elements, nonmetals Group-16→oxygen gr. elements are nonmetal Group-17→Halogen gr. elements nonmetals. • Group-18→are Noble gases, Inert gases, orZero group elements, and also nonmetals. • Elements along zigzag line are called semi metals or metalloids. (B, Si, As, Te, Ge, & Sb)
Properties of elements in modern P.T. • Period-1 is shortest period with only two elements, Periods-2 and 3 are shorter periods with 8-elements. • Periods - 4 and 5 are longer period with 18-elements and period-6 is longest period with total 32 elements. Period-7 is incomplete. • Below the transition metals, there are two rows known as actinide series and lanthanide series elements. • The properties of elements are periodic with increase in atomic number of the elements in groups and periods.
The role of electrons in formation of positive and negative ions • The periodic trends in the periodic table are the result of electron arrangement. • Valence electron: Electrons in outer most energy level or outer most shell in an atom are called valance electrons. • Valence electrons account for similar properties of elements in the same group. • If number of valence electrons are 1, 2, or 3, then atom shows tendency to lose these electrons and form positive ions losing electrons. Metal atoms form positive ions only
Li(+1) and Na(+1) ions These elements (Li and Na) in group-1 each have one valence electron. One valence electron is lost easily with lowest ionization energy to form mono positive(+1) ions. Ion: An atom, radical, or molecule that has gained or lost one or more electrons and has a negative or positive charge. Formation of ions: continued…..
In lithium neutral atom, one valence electron is lost since one proton is greater than total electrons. So that Lithium atom achieves 1-positive charge. On other hand, Chlorine atom gains one electron, so one electron is greater than proton, Cl-atom achieves 1-negative charge. Formation of ions:
Classification of elements: • Elements in each category have similar properties.
Classification of elements in P.T. • Generally all metals form positive ions by losing electrons but nonmetals form negative ions by gaining electrons. • All elements in periodic table are classified into three different categories: 1) metals, 2)nonmetals, or 3) semi conductors • Groups 1 to 12 are different types of metal elements. • Group 13 to 18 are nonmetal elements. • Properties of actinides and lanthanides resemble to properties of transition elements.
Families of elements & their properties • Elements in the same column or group is known as elements of same family. • The elements in a same family have the same number of valence electrons since have similar properties. • Gr. # # of valence electron Name of family Gr. 1 1 alkali metals Gr. 2 2 alkaline earth metals Gr. 3 3 transition metals Gr. 17 varied halogens Gr. 18 8 noble gases • Only in noble gas Helium, it has only 2-valence electrons instead of 8-electrons exceptionally.
Properties of family-alkali metals • Alkali metals are very reactive because of only one valence electron. • Soft, shiny and react violently with water. • Alkali metals are stored in kerosene oil to prevent from reaching with moisture in the air. • Alkali metals form positive ions with +1 charge, and found in combined with other elements in the form of compounds like NaCl. • Many alkali metals have similar melting point, boiling point, and densities.
Properties of alkaline-earth metals: • Alkaline-earth metals form compounds that are found in limestone and in the human body • Alkaline-earth metals are harder, denser, stronger, and have higher melting points than alkali metals. • They have two valence electrons since their ions have +2 charge. • Bones and teeth get strength from calcium compounds. • Magnesium is used to build airplanes, activates enzymes, and in medicine like milk of magnesia and Epsom salt.
Properties of transition metals: • Located in the middle of the periodic table and show variable oxidation states from +1 to +7 • With the exception of mercury (Hg is liquid), transition metals are harder, more dense, and have higher melting points than alkali, alkaline-earth metals. • Gold, silver, and platinum are noble metals and often shaped to make jewelry. • Copper is used in electrical wire, Tungsten is used in light bulb-filament, mercury is used in thermometer, iron ,cobalt and manganese play important roles body chemistry.
Properties of synthetic elements: • Some elements are made in laboratory known as synthetic elements. Ex. Technetium, and promethium are synthetic and radioactive. • The most stable isotope technetium-99, is used by doctors to create brain scan to detect cancer. Also medical problems that occur in soft tissue of body can be detected. • Promethium-147 is used as an ingredient in some glow-in-the-dark paints. • All elements have atomic number greater than 92 are also synthetic. Americium-241 are found in most household detectors.
Properties of nonmetals Carbon gr. • Nonmetals and their compounds are plentiful on earth. Examples: oxygen, nitrogen, sulfur • Carbon is also nonmetal and can form many compounds. Diamonds, and graphite are pure form of carbon. The “fullerenes” is third form of carbon was confirmed in 1990. The most famous fullerene, a cluster of 60 carbon atoms, is called a buckministerfullerene invested by R. Buckminister Fuller. • Carbon can also combine with other elements to form millions of carbon containing compounds. Sugar, glucose, all organic compounds are carbon compounds.
Properties of nonmetals-halogens • Gr. 17 most reactive nonmetals are known as halogens. They have 7 valence electrons, adding 1-electron, they complete stable system of 8-electrons forming -1negative ions. • Chlorine has strong smell and used to kill bacteria in pool water, drinking water too. • Cl combine with sodium metal to form compound common salt or table salt-NaCl. • Fluorine, bromine, and iodine are other halogens. Fluorine is used in tooth paste to prevent tooth decay. • Iodine used in iodized salt responsible for proper thyroid gland function in human body.
Properties of nonmetal- elements: • Except hydrogen all nonmetals are found on the right side of P.T. Nonmetals include some elements from gr. 13-16 and all elements of gr. 17 (halogens) and 18 (noble gases). • Outer most shell in noble gases is completely filled, so they are chemically inert with other elements, exist as single atom. They neither lose, nor gain electron since their oxidation state is zero. • Helium is used to give lift to blimps & balloons Argon is used to fill light bulb since it is inert. Neon gives bright reddish-orange light.
Properties of semiconductors: • The six elements: B, Si, As, Te, Ge, and Sb along zigzag line in P.T. are referred as semiconductors or metalloids. • Metalloids have half of the properties like metals and remaining half like a nonmetal. • Metalloids are able to conduct heat and they are known as semiconductors. • Silicon, 28 % mass of earth’s crust. The common compound is silicon dioxide-SiO2. • Boron is extremely hard used to make heat resistance glass. • Arsenic is a shiny solid and tarnishes when exposed to air. Antimony is a bluish, white and shines like metal. Tellurium silvery white solid.