Structures of solids and other types of bonding
- 1. Structure of Solids Chapter 7
- 2. contents You will learn about: Molecular structures Giant molecular structures Ionic structures Metallic structures
- 3. molecular structures consist of small covalent molecules have strong covalent bonds inside molecules; weak intermolecular forces between molecules molecular 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
- 4. 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 structures molecular compounds sugar water fuels fire extinguishers and aerosols medical products chemicals in foods
- 5. giant molecular structures giant covalent (macromolecular) structures have atoms joined together by strong covalent bonds giant molecular compounds diamond each carbon atom is bonded to four others at the corners silicon silicon dioxide
- 6. giant molecular structures have high melting and boiling points are quite hard do not conduct electricity in any state are insoluble in water physical properties
- 7. giant molecular structures each carbon atom is joined to four others in a tetrahedral arrangement diamond diamond-tipped rock drill strong covalent bonds between carbon atoms and rigid tetrahedral structure make diamond hard used for cutting other hard solids
- 8. giant molecular structures graphite 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
- 9. ionic 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 C l - ions arranged in an orderly manner ionic compounds C l - ion Na + ion Na + ion C l - ion ball-and-stick model of sodium chloride shows how ions are arranged inside the crystal how ions are packed together
- 10. ionic 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 physical properties molten NaC l 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)
- 11. 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”
- 12. metallic 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 metals 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
- 13. metallic 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 metals
- 14. metallic structures conduct electricity in solid and molten states; electrons can move freely to carry electric current metals conducting electricity through Cu wire + - positive ions in fixed positions electron flow free electrons move towards + terminal of battery
- 15. metallic structures summary of main structures of solids strong metallic bonds strong ionic bonds strong covalent bonds very weak forces Bonds between the Particles high high high low Boiling Point insoluble soluble insoluble insoluble Solubility in Water conducts when solid and when molten conducts when molten, but not when solid does not conduct in any state does not conduct in any state Electrical Conductivity diamond, silicon dioxide atoms Giant molecular (macro-molecular) sodium chloride, magnesium oxide positive and negative ions Ionic magnesium, iron, copper, sodium positive ions in a sea of electrons Metallic Examples Particles in the Solid methane, iodine, water small covalent molecules Molecular Structure
- 16. elements non-metals molecular structure metallic structure atoms positive ions in small numbers of atoms in large numbers of atoms have do not conduct electricity form are joined together by covalent bonds ionic structure giant covalent structure have diamond, silicon dioxide, graphite have H 2 , C l 2 , I 2 , H 2 O, CO 2 , CH 4 conduct electricity metals are joined together by metallic bonds in large numbers of atoms Na, Cu, Fe, A l , Mg consist of consist of negative ions form NaC l , MgC l 2 , MgO have loss of electrons gain of electrons ionic bonds in large numbers of ions are joined together by consist of contains