Chem matters ch6_ionic_bond


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Chem matters ch6_ionic_bond

  1. 1. Chemistry Matters – Chapter 6 : Ionic Bonding
  2. 2. Are all atoms reactive?Most of them are!But …Atoms of Noble Gases are different …Atoms of noble gases are unreactive or stable.This means that they do not combine with otheratoms to form compounds.They exist as individual atoms.
  3. 3. What are Noble Gases?Noble gases are elements that are foundin Group 8 (also called Group 0) of thePeriodic Table.Examples:helium, neon, argon, krypton, xenon,radon.
  4. 4. Why are Noble Gases unreactive?The outer shells of noble gases are shown here.What are the electrons in the outer shells alsocalled? Valence electronsWhat do they have in common?Each noble gas has a full valence shell.
  5. 5. What are valence electrons? The shell that is furthest from the nucleus which contains electrons is called the outer shell or the valence shell.The electrons in this shell are calledvalence electrons (or valency electrons).
  6. 6. Helium atoms are unreactive because …Helium has two valence electrons; this is themaximum number that can occupy the 1st (K-) shell. We say that it as a duplet configuration. This is a stable configuration (structure).
  7. 7. Atoms of the other noble gases have eight valenceelectrons.This is called an octet configuration; thisstructure is stable.
  8. 8. How do we know if an atom is stable or unstable? An atom is stable if it has a duplet or octet configuration. A duplet or octet configuration is also known as a noble gas structure or a noble gas configuration.
  9. 9. So why are other atoms reactive?Atoms react in order to have thenoble gas structure (duplet oroctet) (in order to become stable!!)
  10. 10. How do atoms achieve the noble gas structure? Atoms of elements (besides the noble gases) react to achieve the noble gas structures. They do so by losing, gaining or sharing valence electrons.When atoms lose or gain electrons, they form ions.
  11. 11. What type of ions do metals form?Metals form positively charged ions (cations).
  12. 12. How do atoms of metals become positive ions (cations)?Atoms of metals lose valence electrons toform positive ions (cations).Why don’t they gain electrons instead?Hint: Do metal atoms have few or many valenceelectrons? Few; between 1-3 valence electrons.It takes less energy to lose fewer electrons.
  13. 13. Example 1: Formation of a Sodium Ion A sodium atom has 11 protons and 11 11+ electrons. It is neutral (has a net charge of zero). Its electronic configuration is (2, 8, 1).11+ The sodium ion that is formed has one positive charge because it has11- 11 protons but 10 electrons. 0
  14. 14. Formation of a Sodium Ion To attain an octet configuration, a sodium atom (Na) loses 1 valence electron. + It forms a sodium ion (Na+).
  15. 15. Example 2: Formation of a Calcium Ion 2+ To attain an octet configuration, the atom loses 2 valence electrons.A calcium atom (Ca) It forms ahas an electronic calciumconfiguration ion (Ca2+).of (2, 8, 8, 2) (2, 8, 8)
  16. 16. What type of ions do non-metals form?Non-metals form negatively charged ions (anions).
  17. 17. How do atoms of non-metals become negative ions (anions)?Example 1: - A chlorine atom (Cl) gains an electron - to form a chloride ion (Cl ). The chloride ion has an octet configuration.
  18. 18. Example 2: Formation of an Oxide Ion 2- The oxygen atom has an electronic configuration of (2, 6). It gains two electrons to form an oxide ion (O2–).
  19. 19. Forming Ionic BondsWhen metals react with non-metals, anionic compound is formed.Example:Sodium reacts with chlorine to form anionic compound called sodium chloride.
  20. 20. When SODIUM meets CHLORINE…Na (2,8,1) Cl (2,8,7) Na+ (2, 8) Cl- (2,8, 8) Sodium ionSodium atom Chlorine atom Chloride ion
  21. 21. How do we show ionic bonding?The diagram here shows the formation of an ionic bond insodium chloride. It is called a ‘dot-and-cross’ diagram. Positive ions and negative ionsA valence electron is are attracted to each other andtransferred to the outermost move closer – an ionic bond isshell of a chlorine atom formed. Electrostatic attractionNa (2,8,1) Cl (2,8,7) Na+ (2, 8) Cl- (2,8, 8)Sodium atom Chlorine atom Sodium ion Chloride ion
  22. 22. Steps involved in the formation of anionic compound1. Formation of positive ions Example: Each sodium atom (Na) loses its single valence electron to form a positively charged sodium ion (Na+). Na Na+ + e
  23. 23. Steps involved in the formation of anionic compound2. Formation of negative ions Example: Each chlorine atom gains an electron from a sodium atom to form a negatively charged chloride ion. Cl + e Cl -
  24. 24. Steps involved in the formation of an ioniccompound3. Formation of ionic bondsPositive sodium ions and negative chloride ionsare attracted to one another by electrostaticattraction to form sodium chloride. - NaCl Na + Cl +
  25. 25. Dot-and-Cross diagram of an ionic compound, e.g. sodium chlorideThe dots represent the electrons of one atom,while crosses represent the electrons of anotheratom. This is the electron transferred from sodium to chlorine.
  26. 26. Formation of Ionic Compounds: Example 2: Magnesium Chloride.Each magnesium atom losestwo electrons to form amagnesium ion. Each chlorine atom gains an electron to become a chloride ion. Electrostatic attraction arises between magnesium and chloride ions. Magnesium chloride is formed.
  27. 27. How to write Chemical Formulae of Ionic CompoundsThe formula of an ionic compound is constructed bybalancing the charges on the positive ionswith those on the negative ions. All the positive charges must equal all the negative charges in an ionic compound.
  28. 28. How to write Chemical Formulae of Ionic Compounds (Method 1)Example 1: Formula of Magnesium Oxide Mg2+ O2–Magnesium ion Oxide ion Since the charges balance, the formula is MgO.
  29. 29. How to write Chemical Formulae of Ionic Compounds: Method 1Example 2: Formula of Aluminium Oxide Al3+ O2–Aluminium ion Oxide ionTo balance the charges, there must be 2 Al3+and 3 O2– . So, the formula is Al2O3
  30. 30. How to write Chemical Formulae of Ionic Compounds: Method 21. write down the ions with the charges: X m+ Yn–2. Move the values m and n diagonally (butwithout the charges). X m+ Yn– The formula is XnYm.
  31. 31. How to write Chemical Formulae of Ionic Compounds (Method 2) Example 1: Formula of Magnesium Oxide Mg2+ O2–Magnesium Oxide ionion Mg2 O2Reduce to thesimplest ratio Mg1 O1 Write the formula as MgO.
  32. 32. How to write Chemical Formulae of Ionic Compounds: Method 2 Example 2: Formula of Aluminium OxideAluminium ion Al3+ O2– Oxide ion Al2 O3 So, the formula is Al2O3
  33. 33. Sodium ions (Na+) and Chloride ions (Cl-) arrange into a 3-D lattice structure (crystal). chloride ionsodium ionThe formula NaCl for sodium chloride shows that for everysodium ion present in a piece of salt, there is one chlorideatom present (ratio of Na+ : Cl- = 1: 1)
  34. 34. Structure of Ionic Compounds Ionic compounds form giant ionic structures / giant lattice structures/ crystal lattice structures In a lattice, millions of sodium and chloride ions are arranged in an orderly manner. These ions are held in place by strong forces of electrostatic attraction (ionic bonds) throughout the entire lattice.
  35. 35. Physical Properties of Ionic Compounds• Volatility (non-volatile) - high melting and boiling points2. Solubility - most are soluble in water but not in organic solvents (e.g. ethanol)3. Electrical conductivity - conducts electricity in molten and aqueous states, but not in the solid state.
  36. 36. Why do ionic compounds have high melting and boiling points (i.e. low volatility)?Millions of ions in the lattice are held together bystrong forces of electrostatic attraction betweenthe ions. A large amount of energy is needed to overcome these many strong bonds. As a result, ionic compounds: - are solids at room temperature and pressure. - Have very high melting points and boiling points.
  37. 37. SolubilityIonic compounds are usually soluble inwater.(Ionic compounds are insoluble in organicsolvents.Examples of organic solvents : ethanol, petrol andturpentine.)
  38. 38. Electrical Conductivity of ionic compounds Bulb does not light up. SOLID ionic compound, e.g. sodium chlorideIonic compounds do not conduct electricity inthe solid state because the ions are not free tomove about.
  39. 39. Electrical Conductivity of ionic compounds Bulb lights up. Molten or aqueous ionic compoundWhen an ionic compound is melted or dissolved in water,it can conduct electricity.This is because the ions are FREE to move in the moltenstate or in aqueous solution.