solids states of matter.notebook 1 November 04, 2013 There are four types of solids: (1) molecular solids [formed from molecules] (2) covalent network solids [formed from atoms] (3) ionic solids [formed form ions] (4) metallic solids [formed from metal atoms]. Their physical properties relate closely to the intermolecular and intramolecular forces between the particles. Solids
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solids states of matter.notebook · Amorphous solids have a random orientation of particles. •Examples of amorphous solids are glass and plastic. •They are considered supercooled
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solids states of matter.notebook
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There are four types of solids: (1) molecular solids [formed from molecules] (2) covalent network solids [formed from atoms] (3) ionic solids [formed form ions] (4) metallic solids [formed from metal atoms].
Their physical properties relate closely to the intermolecular and intramolecular forces between the particles.
Solids
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Crystalline solids are arranged in fixed geometric patterns or lattices.
Examples of crystalline solids– Ice and sodium chloride. – They have an ordered arrangement of units
maximizing the space they occupy, and are practically incompressible.
Ionic and atomic crystals:hard brittle high melting points.
Molecular crystals: soft low melting points.
Metallic crystals are composed of positively charged ions in a field of freely moving electrons.
Amorphous solids have a random orientation of particles. • Examples of amorphous solids are glass
and plastic. • They are considered supercooled liquids in
which the molecules are arranged in a random manner similar to the liquid state.
More than 90% of naturally occurring and artificially prepared solids are crystalline. Minerals, sand, clay, limestone, metals, alloys, carbon (diamond and graphite), salts ( NaCl, KCl etc.) , all have crystalline structures.
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Crystalline structure is formed by repeating a three dimensional pattern of atoms, ions or molecules.
Repetition of the structural units of the substance over long atomic distances is referred to as long range order.
Liquids and amorphous solids (e. g. glass) do not have longrange order, but have a limited, localized order proximate to their structural units.The physical properties of liquids and amorphous solids are identical in all directions alongany axis. These are referred to as isotropic properties.
3 Basic Types of Unit Cells
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Another difference between solids in a crystalline versus amorphous state is their behavior when they are heated.
Crystals become liquids at a specific temperature, Tm (the melting point). At this temperature physical properties of the crystalline solids change sharply.
Amorphous solids soften gradually when they are heated. There tends to be a relatively wide temperature range for the melting point, a zone between the solid and the liquid state where physical properties of the substance change gradually.
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Crystalline Solids
Crystalline solid: is a wellordered, definite arrangements of molecules, atoms or ions.• Crystals have an ordered structure, which repeats itself.
• The smallest repeating unit in a crystal is a unit cell.
• The unit cell is the smallest unit. It has the same symmetry as the entire crystal.
• Threedimensional packing of unit cells produces the crystal lattice.
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There are seven different crystal systems:
• Cubic: All three axes have same length and intercept at right angles. Typical crystal shapes are the cube, octahedron,rhombic dodecahedron, icositetrahedron, and hexacisochedron.
• Tetragonal: The three axes intercept at right angles, but one axis is longer or shorter than the other two equal axes.Typical crystal shapes are foursided prisms and pyramids, trapezohedrons and eightsided pyramids, and doublepyramids.
• Hexagonal: Three of the four axes are in one plane, intercept at 120°, and are of the same length. The main axis is longer or shorter and is normal to the plane of the other three. Typical crystal shapes are hexagonal prisms andpyramids and twelvesided pyramids and double pyramids.
• Trigonal ﴾rhombohedral﴿: Same axes as hexagonal, but having a cross section showing threesided symmetry insteadof sixsided.Typical crystal shapes are threesided prisms and pyramids, rhombohedra , and scalenohedra.
• Orthorhombic: The three axes are of different lengths and are at right angles to each other. Typical crystal shapes arebasal pinacoids, rhombic prisms and pyramids, and rhombic double pyramids.
• Monoclinic: The three axes are of different lengths and two are at right angles to each other. The third axis isinclided. Typical crystal shapes are basal pinacoids and prisms with inclided end faces.
• Triclinic: All three axes are of different lengths and form oblique angles. Typical crystal shapes are paired faces.
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Allotropes
Allotrope, two or more distinct physical forms of a chemical element in the same physical state. The term allotropy comes from the Greek allos tropos meaning “another shape.” Allotropes arise because of differing arrangements of an element’s atoms within its molecules or crystals. Allotropes are in the same phase but have vastly different chemical and physical properties.
One of the bestknown examples of allotropy is carbon , which has multiple distinct allotropes including graphite , diamond , and buckminsterfullerene (buckeyball).
Carbon atoms in diamond form a rigid, threedimensional structure, with each carbon atom bonded to four other carbon atoms.
In graphite the carbon atoms form stacks of flat honeycomb layers with only weak intermolecular forces between layers.
Buckminsterfullerene forms balls and tubes with structures reminiscent of the geodesic domes designed by the architect Richard Buckminster Fuller.
Elements exhibiting allotropy include arsenic, antimony, iron, oxygen, phosphorus, selenium, sulfur, and tin.
C(s) 3 formsO(g) 2 forms
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Because of their different internal structures, allotropic forms of an element may exhibit greatly differing values for such physical properties as color, luster, density , hardness, odor, and electrical and thermal conductivity.
For example, diamond is extremely hard and does not conduct electricity, while graphite is much softer and does conduct electricity.
Allotropes may also differ in chemical reactivity.
Oxygen, another allotropic element, normally exists as an odorless gas necessary for life, each of whose molecules contains two atoms of oxygen.
Sometimes, however, it exists as ozone, a highly reactive, poisonous gas with a sharp, pungent odor, each of whose molecules contains three atoms of oxygen.
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Some Allotropes of Carbon
Diamond
Graphite
Graphite Buckminsterfullerene
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Hydrated Crystal
Hygroscopic Crystal
A hydrated crystal is a crystal that contains water as part of its chemical formula and structure. It may or may not absorb water vapor from the atmosphere.
A crystal that is hygroscopic is one that absorbs water vapor from the atmosphere.
CaCl2 and P2O5 are examples
CuSO4 . 5H2O . Means wated is added. Indicates that they are waters of
hydration, not really part of the compound (you can remove them by heating the crystals).
If the water of crystallization is removed from blue crystals of copper (II) sulfate, a white powder (anhydrous copper (II) sulfate) is formed.
The formula for anhydration of pentahydrate copper (II) sulfate (CuSO4·5H2O) is as follows:
CuSO4·5H2O + heat → CuSO4 + 5H2O
Anhydrous Crystal
To dissolve and become liquid by absorbing moisture from the air.
Deliquescence
The absorption of atmospheric water vapor by a crystalline solid until the crystal eventually dissolves into a saturated solution.
This behavior is well known for certain salts such as hydrated calcium chloride, CaCl2 · 6H2O, and zinc chloride , ZnCl2, but it is a property of all soluble salts in air of sufficiently high humidity.
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Polycrystalline solid
A solid composed of many individual crystals or grains arranged in a more or less random order.