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Ch.7 - Periodic Properties of the Elements
Brown - Chemistry: The Central Science 14th Edition
Brown14th EditionChemistry: The Central ScienceISBN: 9780134414232당신이 사용하는 게 아니라요?교과서 변경
모든 교과서Brown 14th EditionCh.7 - Periodic Properties of the Elements문제 106
7장, 문제 106

A historian discovers a nineteenth-century notebook in which some observations, dated 1822, were recorded on a substance thought to be a new element. Here are some of the data recorded in the notebook: 'Ductile, silver-white, metallic looking. Softer than lead. Unaffected by water. Stable in air. Melting point: 153 °C. Density: 7.3 g>cm3. Electrical conductivity: 20% that of copper. Hardness: About 1% as hard as iron. When 4.20 g of the unknown is heated in an excess of oxygen, 5.08 g of a white solid is formed. The solid could be sublimed by heating to over 800 °C.' (a) Using information in the text and the CRC Handbook of Chemistry and Physics, and making allowances for possible variations in numbers from current values, identify the element reported.

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Identify the physical properties of the unknown element: ductile, silver-white, metallic, softer than lead, unaffected by water, stable in air, melting point of 153 °C, density of 7.3 g/cm³, electrical conductivity 20% of copper, hardness 1% of iron.
Compare these properties with known elements from the CRC Handbook of Chemistry and Physics, focusing on elements with similar melting points, densities, and conductivity.
Consider the chemical reaction: 4.20 g of the unknown element reacts with oxygen to form 5.08 g of a white solid. Calculate the mass of oxygen that reacted by subtracting the mass of the unknown from the mass of the product.
Determine the molar mass of the unknown element by using the mass of the unknown and the mass of oxygen to find the empirical formula of the oxide formed.
Cross-reference the calculated molar mass and empirical formula with known elements to identify the element that matches the properties and reaction data.

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주요 개념

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Physical Properties of Metals

The observations recorded in the notebook describe several physical properties of the unknown element, such as ductility, density, and melting point. Metals typically exhibit high electrical conductivity, malleability, and a shiny appearance. Understanding these properties helps in identifying the element, as they can be compared to known metals to narrow down possibilities.
추천 영상:
가이드 코스
02:54
Physical Properties

Chemical Reactivity and Oxidation

The reaction of the unknown element with oxygen, resulting in a white solid, indicates its chemical reactivity. The formation of a solid product upon heating in excess oxygen suggests that the element may form an oxide. Analyzing the mass change during the reaction can provide insights into the element's identity and its oxidation state.
추천 영상:
가이드 코스
00:58
Oxide Reactions

Density and Element Identification

Density is a critical physical property used to identify elements. The recorded density of 7.3 g/cm³ can be compared to known densities of metals to help pinpoint the unknown element. Since density is a characteristic property, it can significantly narrow down the list of potential candidates when combined with other observed properties.
추천 영상:
가이드 코스
00:50
Main Group Elements: Density Example
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교과서 질문

We will see in Chapter 12 that semiconductors are materials that conduct electricity better than nonmetals but not as well as metals. The only two elements in the periodic table that are technologically useful semiconductors are silicon and germanium. Integrated circuits in computer chips today are based on silicon. Compound semiconductors are also used in the electronics industry. Examples are gallium arsenide, GaAs; gallium phosphide, GaP; cadmium sulfide, CdS; and cadmium selenide, CdSe. (b) Workers in the semiconductor industry refer to 'II–VI' and 'III–V' materials, using Roman numerals. Can you identify which compound semiconductors are II–VI and which are III–V? (c) Suggest other compositions of compound semiconductors based on the positions of their elements in the periodic table.

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교과서 질문

We will see in Chapter 12 that semiconductors are materials that conduct electricity better than nonmetals but not as well as metals. The only two elements in the periodic table that are technologically useful semiconductors are silicon and germanium. Integrated circuits in computer chips today are based on silicon. Compound semiconductors are also used in the electronics industry. Examples are gallium arsenide, GaAs; gallium phosphide, GaP; cadmium sulfide, CdS; and cadmium selenide, CdSe. (a) What is the relationship between the compound semiconductors' compositions and the positions of their elements on the periodic table relative to Si and Ge?

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