Published on March 9, 2014
1.1 Periodic Table Learning Outcomes • History of the idea of elements, • The contributions of the Greeks, Boyle, Davy and Moseley.
Greek Periodic Table
Robert Boyle • Element cannot be split up into simpler substances by chemical means
Humphrey Davy • Used electrolysis to break down water into hydrogen and oxygen. Isolated potassium and sodium.
Henry Mosely • Measured No.of protons in the nuclei of atoms. Atomic number to arrange elements.
Dobereiner • Saw trends and similarities among several groups of elements in threes • Triads = groups of 3 elements • Chlorine = 35.5, Bromine = 80, Iodine = 127 (average of Cl and I = 81)
Newlands • Tried to find some mathematical relation between the atomic weights of elements which were chemically similar • Groups called octaves • Arranged the elements in rows of seven • Eighth element had properties similar to the first
“Law of Octaves” because of its similarity to musical octaves Li Be B C N O F Na Mg Al Si P S Cl K Ca ? ? As Se Br
Dimitri Mendeleev • He suggested that the properties of the elements were a function of their atomic masses • Left gaps for undiscovered elements • Gave a name and predicted the properties of these yet to be discovered elements.
Mendeleev’ s Table
Learning Outcomes • Elements. Symbols of elements 1–36. • The periodic table as a list of elements arranged to demonstrate trends in their physical and chemical properties. • Brief statement of the principal resemblances of elements within each main group, in particular alkali metals, alkaline earth metals, halogens and noble gases.
Modern periodic table • Elements in the periodic table are arranged in periods (rows) and groups(columns). Atomic number increases as you move across a row or period.
Modern periodic table
Periods • The period number of an element signifies the highest unexcited energy level for an electron in that element.
Groups • Elements within a group share several common properties. • Groups are elements have the same outer electron arrangement. • The outer electrons are called valence electrons. Because they have the same number of valence electrons, elements in a group share similar chemical properties. • The Roman numerals listed above each group are the usual number of valence electrons. For example, a group VA element will have 5 valence electrons.
Classifying Elements- Metals
Metals •Metals are lustrous (shiny), malleable (can be hammered) • are good conductors of heat and electricity.
Group 1: Alkali Metals Group 1: Alkali Metals The alkali metals are located in Group IA (Sodium and potassium are examples of these elements. Alkali metals form salts and many other compounds. These elements are less dense than other metals, form ions with a +1 charge, and have the largest atom sizes of elements in their periods. The alkali metals are highly reactive.
Alkaline Metals 1 Learning outcome Demonstration of the reaction with water of lithium, sodium and potassium.
Alkali metals • • • • • • Group 1 Very reactive Low density Soft-can be cut with a knife Burn in air to form oxides React with water to form hydroxides
Sodium • Sodium + Oxygen Sodium oxide • Sodium + Water Sodium Hydroxide + Hydrogen gas • Stored in oil to prevent them from reacting with air or water
Group 2: Alkaline Earth Metals The alkaline earths are located in Group IIA (second column) of the periodic table. Calcium and magnesium are examples of alkaline earths. These metals form many compounds. They have ions with a +2 charge. Their atoms are smaller than those of the alkali metals.
Alkaline Earths • • • • • Group 2 Reactive Harder than group one Burn in air to form oxide React with water to form hydroxides
Group 17: Halogens The halogens are located in Group VIIA of the periodic table. Examples of halogens are chlorine and iodine. You find these elements in bleaches, disinfectants, and salts. These nonmetals form ions with a -1 charge. The physical properties of the halogens vary. The halogens are highly reactive.
Halogens • • • • Group 7 Reactive Chlorine, Bromine, Iodine React with hydrogen to form acids
Chlorine • Green gas • Chlorine + Hydrogen Hydrogen Chloride gas • Hydrogen chloride gas dissolves in water to form Hydrochloric acid. • Chlorine reacts with sodium to form Sodium Chloride [Table Salt]
Group 18: Noble Gases The noble gases are located in Group VIII of the periodic table. Helium and neon are examples of noble gases. These elements are used to make lighted signs, refrigerants, and lasers. The noble gases are not reactive. This is because they have little tendency to gain or lose electrons.
Transition Metals •The transition elements are located in groups IB to VIIIB. •These elements are very hard, with high melting points and boiling points. The transition metals are good electrical conductors. •They form positively charged ions.
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