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Ionic Bonds

Ionic Bonds. Chapter 8 Chemistry Mr. Gilbertson. Chemical bond. May form by the attraction between the positive nucleus and the negative electrons Attraction between a positive ion and a negative ion (electrostatic force). Lewis Electron Dot Diagrams and Reactivity. Valence Electrons.

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Ionic Bonds

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  1. Ionic Bonds Chapter 8 Chemistry Mr. Gilbertson

  2. Chemical bond • May form by the attraction between the positive nucleus and the negative electrons • Attraction between a positive ion and a negative ion (electrostatic force)

  3. Lewis Electron Dot Diagrams and Reactivity

  4. Valence Electrons • Determine bonding properties of atoms. • Determine the bonding ratio

  5. Valence determines reactivity • Metals have low electron affinity and low ionization energies tend to lose electrons. • Nonmetals have high electron affinity and high ionization energies tend to gain electrons.

  6. Formation of positive ions (cations) • Metals lose electrons from their outermost energy level, exposing next energy level which is full • Results in the atom having a noble gas configuration. • Number of protons stays the same so….

  7. Reactivity of metals • Depends on the ease with which they lose electrons. • Group 1 elements must only lose one electron and form an ion with a 1+ charge (react very quickly) • As the number of energy levels increases the attraction for outer electron decreases, so it is easier to remove the electron (making them even more reactive)

  8. Reactivity of Alkali Earth Metals • Group 2 metals have to lose 2 electrons, so they will react but not as fast. • They involve both first and second ionization energies so the total amount of energy required increases,

  9. Reactivity of transition metals • Have the general configuration ns2 • From left to right elements fill d orbitals • Will tend to lose 2 s electrons in forming a bond (2+) • May also lose d electrons (3+ or more) • Difficult to predict the number of electrons lost by these elements. • Rule of thumb: they tend to form ions with 2+ and 3+ charge.

  10. Stability and Special Stability • Formation of an octet is the most stable electron configuration • Special stability • Not as stable as an octet • Pseudo-noble gas configurations - 1B through 4A (10-14) in periods 4-6 lose electrons to form an outer energy level containing full s, p, and d sublevels.

  11. Formation of negative ions (anion) • Nonmetals tend to gain electrons due to high electron affinity, and high ionization energy. • Form negative ions because of surplus electrons. • Anion name changes to end in “ide” flourine becomes flouride, chlorine becomes chloride, etc.

  12. The Formation and nature of ionic bonds

  13. Formation of an ionic bond The electrostatic force that holds oppositely charged particles together in an ionic compound

  14. Formation of an ionic bond • Metal Cation loses electrons to become positive ion • Nonmetal Anion gains electrons to become a negative ion. • Ions are attracted to each other due to opposite charge. • Bond is formed by electrostatic forces of attraction between opositly charged ions

  15. Comparison of ionic and covalent bonding

  16. What are Ionic compounds • Contain ionic bonds • If between a metal and oxygen known as oxides • All other ionic compounds are known as salts. • Biary compounds are made of a metal (cation) and a nonmetal (anion). • Sodium Chloride (NaCl), Potassium Oxide (K2O), Magnesium Phosphide (Mg3P2)

  17. Ionic compounds CaCl2 • The number of electrons lost by one element must equal the number gained by the other. • So the ratio of elements in a compound is determined by the number of electrons that must be transferred.

  18. Four different methods of demonstrating the formation of ionic bondsElectron configurationorbital notationelectron dot structure*atomic models*

  19. Electron Configurations The 3s1electon from Na moves to the 3p6 position of the Cl

  20. The 3s1electon from Na moves to the 3p6 position of the Cl. Because the product has less energy than the Reactants, energy is given off.

  21. The electron from Na moves to the Clgiving both an octet. Exothermic reaction Because the product has less energy than the reactants, energy is given off.

  22. The electon from Na moves to the Clgiving both an octet They are held together because of the opposite charges generated by the electron transfer. Exothermic reaction - Because the product has less energy than the reactants, energy is given off.

  23. Properties of Ionic Compounds Crystal • In the formation of a crystal the cations and anions are packed into a regular repeating pattern that balances the forces of attraction and repulsion between ions. • No single unit exists of one cation and one anion. (formula unit) • Large numbers form together in a ratio determined by the number of electrons transferred between the ions.

  24. Crystal lattice • Describes the 3-d geometric arrangement of particles • Each cation is surrounded by anions and each anion is surrounded by cations • Shape is determined by the size of ions and relative numbers of each.

  25. Properties of ionic compounds • Ionic bonds are relatively strong • High MP, BP, and hardness are common • Require large amounts of energy to break up the crystals • Color is related to structure. • Crystals are brittle solids. • Brittle because… • Strong attractive forces hold ions in place. • When a large external force is applied it overcomes forces of attraction. • This repositions like charged ions and weakens the crystal; then repulsive forces crack the crystal. • Ionic properties

  26. Conductivity • Nonconductors in the solid state due to fixed position of ions in crystal • Ions must be free to move, to carry a charge. • Conductors in a liquid state (molten). • Good conductors in solution. • Electrolytes • Ionic compounds whose aqueous solution conducts an electric current • electrolytes

  27. Energy and the ionic bond • In any chemical reaction energy must be absorbed or released. • If products have less energy than reacting ions then energy is released (exothermic) • If products have more energy than reacting ions then energy must be absorbed (endothermic) • Based on Law of conservation of energy. • Formation of an ionic bond is always exothermic because bonded ions are more stable (less energy) • If this energy is added back to the bonded ions, the bond is broken. • The energy required to separate one mole of ions of an ionic compound is called the lattice energy

  28. Lattice energy is related tosize of bonded ions(smaller is stronger)and to the charge of the ions involved

  29. Polyatomic Ions • When two or more atoms are covalently bonded and form a charged particle.

  30. The end of section 8.1 and 8.2

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