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Date: 26-1-2017
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Date: 13-4-2019
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Date: 30-3-2019
1539
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A crystalline solid, like those listed in Table 1.1 has a precise melting temperature because each atom or molecule of the same type is held in place with the same forces or energy. Thus, the attractions between the units that make up the crystal all have the same strength and all require the same amount of energy to be broken. The gradual softening of an amorphous material differs dramatically from the distinct melting of a crystalline solid. This results from the structural nonequivalence of the molecules in the amorphous solid. Some forces are weaker than others, and when an amorphous material is heated, the weakest intermolecular attractions break first. As the temperature is increased further, the stronger attractions are broken. Thus amorphous materials soften over a range of temperatures.
Type of Solid | Type of Particles | Type of Attractions | Properties | Examples |
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ionic | ions | ionic bonds | hard, brittle, conducts electricity as a liquid but not as a solid, high to very high melting points | NaCl, Al2O3 |
metallic | atoms of electropositive elements | metallic bonds | shiny, malleable, ductile, conducts heat and electricity well, variable hardness and melting temperature | Cu, Fe, Ti, Pb, U |
covalent network | atoms of electronegative elements | covalent bonds | very hard, not conductive, very high melting points | C (diamond), SiO2, SiC |
molecular | molecules (or atoms) | IMFs | variable hardness, variable brittleness, not conductive, low melting points | H2O, CO2, I2, C12H22O11 |
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دراسة يابانية لتقليل مخاطر أمراض المواليد منخفضي الوزن
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اكتشاف أكبر مرجان في العالم قبالة سواحل جزر سليمان
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اتحاد كليات الطب الملكية البريطانية يشيد بالمستوى العلمي لطلبة جامعة العميد وبيئتها التعليمية
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