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Structure of Solids Chapter 7 7
Structure of Solids
Structure of Solids
Chapter 77
Chapter 77
contentscontents
You will learn about:
• Molecular structures
• Giant molecular structures
• Ionic structures
• Metallic structures
You will learn about:
• Molecular structures
• Giant molecular structures
• Ionic structures
• Metallic structures
molecular structuresmolecular structures
consist of small covalent molecules
have strong covalent bonds inside molecules; weak intermolecular forces between molecules
molecular compoundsmolecular compounds
have low boiling and melting points; weak intermolecular forces are easily broken
only the weak forces between the molecules break when water boils in a kettle
are insoluble in water; soluble in organic solvents
do not conduct electricity in any state; no moving electrons or ions
examples of covalent molecules: hydrogen, oxygen, nitrogen and Group VII elements
examples of covalent compounds: carbon dioxide, sulphur dioxide, methane and carbon tetrachloride
uses:
are insoluble in water; soluble in organic solvents
do not conduct electricity in any state; no moving electrons or ions
examples of covalent molecules: hydrogen, oxygen, nitrogen and Group VII elements
examples of covalent compounds: carbon dioxide, sulphur dioxide, methane and carbon tetrachloride
uses:
molecular structuresmolecular structuresmolecular compoundsmolecular compounds
sugar
water
fuels
fire extinguishers and aerosols
medical products
chemicals in foods
giant molecular structures
giant molecular structures
giant covalent (macromolecular) structures have atoms joined together by strong covalent bonds
giant covalent (macromolecular) structures have atoms joined together by strong covalent bonds
giant molecular compoundsgiant molecular compounds
diamond
each carbon atom is bonded to four others
at the corners
silicon
silicon dioxide
giant molecular structures
giant molecular structures
have high melting and boiling points
are quite hard
do not conduct electricity in any state
are insoluble in water
have high melting and boiling points
are quite hard
do not conduct electricity in any state
are insoluble in water
physical propertiesphysical properties
giant molecular structuresgiant molecular structures
each carbon atom is joined to four others in a tetrahedral arrangement
each carbon atom is joined to four others in a tetrahedral arrangement
diamonddiamond
diamond-tipped rock drill
strong covalent bonds between carbon atoms and rigid tetrahedral structure make diamond hard
used for cutting other hard solids
strong covalent bonds between carbon atoms and rigid tetrahedral structure make diamond hard
used for cutting other hard solids
giant molecular structuresgiant molecular structuresgraphitegraphite
weak forces between
layers, thus, layers can slide
over each other easily
arrangement of carbon atoms in one flat layer
layers of carbon atoms in graphite
carbon atoms are arranged in rings of six on flat layers carbon atoms are arranged in rings of six on flat layers
ionic structuresionic structures
consist of positive ions of metals and negative ions of non-metals
example: a crystal of sodium chloride consists of large numbers of Na+ and Cl- ions arranged in an orderly manner
consist of positive ions of metals and negative ions of non-metals
example: a crystal of sodium chloride consists of large numbers of Na+ and Cl- ions arranged in an orderly manner
ionic compoundsionic compounds
Cl- ion
Na+ ion
Na+ ion Cl- ion
ball-and-stick model of sodium chloride shows how ions are arranged inside the crystal
how ions are packed together
ionic structuresionic structures
have strong ionic bonds or electrostatic forces of attraction
have high melting and boiling points; large amount of energy needed to break strong ionic bonds
have strong ionic bonds or electrostatic forces of attraction
have high melting and boiling points; large amount of energy needed to break strong ionic bonds
physical propertiesphysical properties
molten NaCl
in molten state, ions are free to
move
soluble in water; insoluble in organic solvents
conduct electricity in molten state or in solution; moving ions carry electric current
example and use: MgO (high melting point); used as refractories (heat-resistant materials)
soluble in water; insoluble in organic solvents
conduct electricity in molten state or in solution; moving ions carry electric current
example and use: MgO (high melting point); used as refractories (heat-resistant materials)
Metallic Bonding
In a metal, the outer electrons are shared among all the atoms in the solid. Each atom gives up its outer electrons and becomes slightly positively charged. The negatively charged electrons hold the metal atoms together. Since the electrons are free to move, they lead to good thermal and electrical conductivity.
The phrase used is: “a lattice of positive ions in a sea of negative electrons”
metallic structuresmetallic structures
in metals, metal atoms are packed together very closely in an orderly arrangement
each metal atom gives up electrons to become positive metal ions; electrons go into the spaces between the ions
in metals, metal atoms are packed together very closely in an orderly arrangement
each metal atom gives up electrons to become positive metal ions; electrons go into the spaces between the ions
metalsmetals
metallic bonding is the force of attraction between the negative electrons and the positive metal ions
metallic bonding is the force of attraction between the negative electrons and the positive metal ions
metal atoms
arrangement of atoms in a metal
positive metal ions in a ‘sea of electrons’
positive metal ions
free electrons
metallic structuresmetallic structures
consist of positive metal ions in a ‘sea of electrons’
have strong metallic bonds
have high melting and boiling points; large amount of energy needed to break forces of attraction
insoluble in water
consist of positive metal ions in a ‘sea of electrons’
have strong metallic bonds
have high melting and boiling points; large amount of energy needed to break forces of attraction
insoluble in water
metalsmetals
metallic structuresmetallic structures
conduct electricity in solid and molten states; electrons can move freely to carry electric current
conduct electricity in solid and molten states; electrons can move freely to carry electric current
metalsmetals
conducting electricity through Cu wire
+ -
positive ions in fixed positions
electron flow
free electrons move towards + terminal
of battery
metallic structuresmetallic structures
summary of main structures of solids summary of main structures of solids
StructureStructureParticles Particles
in the in the SolidSolid
Bonds Bonds between between
the the ParticlesParticles
Boiling Boiling PointPoint
Solubility Solubility in Waterin Water
Electrical Electrical ConductivityConductivity ExamplesExamples
Molecularsmall
covalent molecules
very weak forces
low insolubledoes not
conduct in any state
methane, iodine, water
Giant molecular (macro-
molecular)
atomsstrong
covalent bonds
high insolubledoes not
conduct in any state
diamond, silicon dioxide
Ionicpositive and
negative ions
strong ionic
bondshigh soluble
conducts when molten, but not when
solid
sodium chloride,
magnesium oxide
Metallic
positive ions in a sea of
electrons
strong metallic bonds
high insoluble
conducts when solid and when
molten
magnesium, iron, copper,
sodium
elementselements
non-metalsnon-metals
molecular molecular structurestructure
metallic structuremetallic structure
atomsatoms
positive ionspositive ions
in small numbers in small numbers of atomsof atoms
in large numbers in large numbers of atomsof atoms
havehave
do not do not conduct conduct
electricityelectricity
formform
are joined are joined together bytogether by
covalent bondscovalent bonds
ionic structureionic structure
giant covalent giant covalent structurestructure
havehave
diamond, silicon diamond, silicon dioxide, graphitedioxide, graphite
havehaveHH22, , CCll22, I, I22, H, H22O, O,
COCO22, CH, CH44
conduct conduct electricityelectricity
metalsmetals
are joined are joined together bytogether by
metallic metallic bondsbonds
in large numbers in large numbers of atomsof atoms
Na, Cu, Fe, Na, Cu, Fe, AAll, Mg, Mg
consist ofconsist of
cons
ist of
cons
ist of
negative ionsnegative ionsformform
NaCNaCll, MgC, MgCll22, , MgOMgO
havehave
loss of loss of electronselectrons
gain of gain of electronselectrons
ionic ionic bondsbonds
in large in large numbers of numbers of
ionsions
are joined are joined together bytogether by
consist of
consist of
containscontains
