S2.4- from models to materials
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ionic bonding
electrostatic attraction between oppositely charged ions.
covalent bonding
electrostatic attraction between a shared pair of electrons and positively charged nuclei.
metallic bonding
electrostatic attraction between positive metal ions=cations in a lattice and delocalised electrons.
how is bonding best described
as a continuum between the ionic, covalent and metallic models rather than discrete categories.
what determines the physical properties of materials we use
the structure and bonding of the elements
describe structure of metallic bonding
lattice structure
describe structure of covalent bonding
small or large molecules, covalent netwrok structures
describe structure of ionic bonding
lattice structure
why are Covalent bonding is usually the most difficult to assign specific physical properties
because these properties depend on intermolecular interactions and whether or not the substance is a small molecule, large molecule or covalent network solid.
how do we classify materials
based on structure and bonding of elements which make up materials some use physical properties
polar covalent bonds are
bond type between ionic and covalent
electronegativity shows
the degree to which an individual atom will attract an additional electron from another atom.
metals have low or high electronegativity
Metals have a high tendency to lose electrons, low tendency to attract additional electrons, therefore low electronegativity values.
non metals have low or high electronegativity
have a high tendency to gain electrons, therefore high electronegativity values.
zero- very low electronegativity difference means
bonds are non polar because material is an element or a compound with atoms with very similar electronegativity, the material has no polar or ionic character; can either be: low average electronegativity= metal or medium to high average electronegativity= covalent
medium electronegativity difference indicates
increasing ionic character or molecules are polar can either be ; low average electronegativity= ionic or medium to high average electronegativity= polar covalent
high electronegativity difference indicates
substance is ionic
what should you expect for materials which fall along bonding line
show intermediate bonding and properties
what are alloys
mixtures of metals with other elements such as metals or non metals.
what are alloys of iron refered to as
steel
whats most commonly used steel and its composition
mild steel made of carbon mixed into iron
why are alloys more useful than pure metals
the ïmpurity metal” can inhance properties of pure metal. Eg an llow may have greater corrosion resistance, different color, greater strength and hardness
why are alloys harder
metal atoms and impurity atoms have different sized atoms, preventing layers from sliding past eah other so easily making the alloy harder
describe structure of alloys
non directional bonding, can decrease depending on what is the impurity and concentration of it different sized cations/ positive ions sea of delocolised electrons