Unit 1: Structure and Properties of Matter 4.8 Structure and Properties of Solids

Types of Solids Ionic Solids : metal and nonmetal Metallic Solid: two metals Molecular Solid: two nonmetals Covalent Network: metalloids/carbon

Ionic Crystals anions and cations are attracted together in CRYSTAL LATTICE each anion surrounded by cations and vice versa Ex: NaCl (salt), MgO (used in antacid tablets)

Crystal Lattice exists in three dimension ionic substance held together by STRONG electrostatic attractions in all three dimensions bonds are directional lattice is composed of ions no molecules in ionic compounds, referred to as formula units

Physical Properties of Ionic Compounds Hard, brittle crystalline solids Relatively high melting and boiling points Do not conduct electricity when solid Conduct electricity when molten or in aqueous solution Soluble in water

Metallic Crystals atoms are packed closely together in 3 dimensions (CLOSE-PACKED LATTICE) metals have low ionization energies so the valence electrons become DELOCALIZED amongst (shared by) all the atoms no electrons belong to a particular atom, free to move throughout metal

Metallic Bonding atoms have lost valence electrons, are positively charged (CATIONS) attraction of positive ions for mobile electrons provides force that holds structure together a lattice of positive ions filled by a mobile ‘sea’ of valence electrons

Physical Properties of Metals attraction is between ions and mobile electrons, not between ions themselves this means that layers of ions can slide past each other without breaking any bonds means that metals are MALLEABLE and DUCTILE if atoms are different sizes (in ALLOYS), it is harder for layers to slide alloys are usually harder than pure metals

Physical Properties of Metals delocalized electrons are free to move from one side of lattice to the other and can carry an electric current metals are good CONDUCTORS of both electricity and heat strength of bond between metals depends on how many electrons each atom shares MP of Potassium is 337 K MP of Calcium is 1123 K MP of Scandium is 1703 K strength also depends on how far from the nucleus the sea of electrons are going down a group, the melting points will decrease

Molecular Crystals covalent bonds result in molecules the covalent bonds holding molecules together (intramolecular) are strong, the forces between molecules (intermolecular) are much weaker these weaker intermolecular forces lead to properties generally soft in solid state, do not conduct electricity, more soluble in non-polar solvent than in water, have low melting and boiling points Examples: iodine, sulfur, ice

Covalent Network Solids giant, three dimensional covalent structure look at the allotropes of carbon and silicon dioxide ALLOTROPES : different forms of an element that exist in the same physical state

Allotropes of Carbon diamond (a) graphite (b) C60 Fullerene (Buckyball) (d) Londaleite (c) C540 (e) C70 (f) amorphous carbon (g) carbon nanotube (h)

Diamond each carbon is joined to 4 other carbons in the tetrahedral shape extremely strong structure! all intramolecular bonds explains high MP, BP and exceptionally hard structure

Graphite comprises a giant covalent network in 2 dimensions each layer has C atoms bonded to 3 other C atoms each layer is very strong between the layers, only weak van der Waals forces hold the layers together

Graphite distance between the sheets is quite large and the forces between very weak so layers can slide over each other easily often used as lubricant layers are easily rubbed off on paper - why it is used in ‘lead’ pencils can conduct electricity due to delocalized electrons

Fullerene approximately spherical molecule made up of five- and six-membered C ring C60 resembles a soccer ball there is a small amount of delocalized electrons but not enough to strongly conduct electricity

Fullerene behaves as an electron deficient molecule and readily accepts electrons is a molecular molecule and can dissolve in some non-polar solvents lower MPs than diamond or graphite

Silicon forms 4 covalent bonds almost identical structure to diamond found in crystalline quartz Shares the same chemical formula as glass but doesn’t form crystalline structure

Lab Review Purpose Hypothesis Materials Procedure Observation Tables

Homework Pg.254#1-9 Reminder: Solids Design Lab tomorrow