States of matter: Why do metals have the properties that they have?
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Solid / Liquid / Gas
Metal is a type of solid
Metal is usually an imperfect crystal
At any temperature above absolute zero, atoms vibrate, so even in solids the atoms are always somewhat in motion
Iron atoms, like many other metals, take on this shape
Body-Centered Cubic (BCC) Structure: there are 8 atoms at the 8 corners, and one atom in the centre of the unit cell. This structure is then repeated over and over.
“The structure of iron atoms isn’t continuous throughout the entire paper clip. When a metal cools and is transitioning from liquid to solid, its atoms come together to form tiny grains, or crystals. Even though the crystalline structure does not continue from crystal to crystal, the crystals are bound to one another. In this diagram, each square represents an individual atom.”
atoms held together with metallic bonds
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Defects break the bonds
“When a metal crystal forms, the atoms try to assemble themselves into a regular pattern. But sometimes there isn’t an atom available to fill in a space, and sometimes a growing layer is halted by other growing layers. There are many imperfections within each crystal, and these flaws produce weak points in the bonds between atoms. It is at these points, called slip planes, that layers of atoms are prone to move relative to adjacent layers if an outside force is applied. Adding other elements to a metal can counteract the effects of the imperfections and make the metal harder and stronger. Carbon, for example, is added to iron to make steel, and tin is added to copper to make bronze.”
Atoms can slip into a new position
Metal atoms can bend
Heat can loosen the fixed positions of metal atoms
Massachusetts Science and Technology/Engineering Curriculum Framework
High School Chemistry
HS-PS2-6. Communicate scientific and technical information about the molecular-level structures of polymers, ionic compounds, acids and bases, and metals to justify why these are useful in the functioning of designed materials.*
PS1.A Structure of matter. That matter is composed of atoms and molecules can be used to explain the properties of substances, diversity of materials, how mixtures will interact,
states of matter, phase changes, and conservation of matter. States of matter can be modeled in terms of spatial arrangement, movement, and strength of interactions between particles.
PS2.B Types of interactions. Electrical forces between electrons and the nucleus of
atoms explain chemical patterns. Intermolecular forces determine atomic composition, molecular geometry and polarity, and, therefore, structure and properties of substances.