Element of the Day Tungsten, also known as wolfram (wuul­frәm), is a chemical element with the chemical W symbol W and atomic number 74. The word tungsten comes from the Swedish language tung sten directly translatable to heavy stone. A hard, rare metal under standard conditions when uncombined, tungsten is found naturally on Earth only in chemical compounds. It was identified as a new element in 1781, and first isolated as a metal in 1783. The free element is remarkable for its robustness, especially the fact that it has the highest melting point of all the non­alloyed metals. Also remarkable is its high density of 19.3 times that of water. The unalloyed elemental form is used mainly in electrical applications. Tungsten's many alloys have numerous applications, most notably in incandescent light bulb filaments, X­ ray tubes (as both the filament and target), and superalloys. Tungsten compounds are most often used industrially as catalysts. Question: If tungsten is used as the cathode of a galvanic cell, then is it being oxidized or reduced? 1 Chemistry 1. Element of the Day ­ W 2. Review Notes 2. Continue POGIL Activity Announcements Due Tuesday: POGIL Activity through question 10. 2 Lecture Notes Oxidation States: Electronegativity Rules for Assigning Oxidation States 1. The oxidation state of an atom in an uncombined element is 0. 2. The oxidation state of a monoatomic ion is the same as its charge. 3. Oxygen is assigned an oxidation state of ­2 in most of its covalent compounds. 4. In its covaent compounds with nonmentals, hydrogen is assigned an oxidation state of +1. 5. In binary compounds, the element with the greater electrogeativeity is assigned a negative oxidation state equal to its charge as an anion in its ionic compounds. 6. For an electrically neutral compound, the sum of the oxidation states must be zero. 7. For an ionic species, the sum of the oxidation states must equal the overall charge. 3 Lecture Notes Electrochemistry Electrochemistry: the study of the interchange of chemical and electrical energy. Involves 2 Processes 1. The production of an electric current from a chemical (oxidation ­ reduction) reaction. 2. The use of an electric current to produce a chemical change. To do useful work, we must separate the redox reaction into two parts. Simple diagram without salt bridge. Charge build up. More complex diagram with salt bridge, to connect solutions together without letting them mix. 4 Lecture Notes Electrochemical batteries can be called galvanic cells or voltaic cells: The oxidizing reagent is separated from the reducing reagent, thereby forcing electrons to travel through a wire. As electrons travel through the wire, they do work. In an electrochemical battery 1. Oxidation occurs at the anode 2. Reduction occurs at the cathode 5 POGIL Activity 6 Exit Question At the anode of a galvanic cell _____________ occurs as electrons are transferred. Reminders Due Tuesday: POGIL Activity through question 10. 7.