1 / 19

Ions and Ionic Compounds

Ions and Ionic Compounds. Ionic Bonding and Salts. Key Terms: Salt Lattice Energy Crystal Lattice Unit Cell. Ionic Bonding. Opposites attract, so cations and anions should attract. This is exactly what happens when an ionic bond is formed.

kacy
Download Presentation

Ions and Ionic Compounds

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Ions and Ionic Compounds

  2. Ionic Bonding and Salts Key Terms: Salt Lattice Energy Crystal Lattice Unit Cell

  3. Ionic Bonding • Opposites attract, so cations and anions should attract. • This is exactly what happens when an ionic bond is formed. • Sodium ions (Na+) attract Chlorine ions (Cl-) to form NaCl (a salt) • Salt- An ionic compound that forms when a metal atom or a positive radical replaces the hydrogen of an acid • These attractions are what make Ionic Bonds • Bonding by attractions

  4. Ionic Bonding • In sodium chloride, there is one sodium and one chlorine to create a neutral compound (no longer an ion) • We write this out in lowest whole number ratios: NaCl, indicates 1 Na and 1 Cl • Depending on the magnitude of the charge, the anion or cation may attract several atoms: • In lithium phosphide, the P3- attracts three Li+ ions to be neutral • Sounds just like our nomenclature rules huhhhhh??

  5. Electrons and Energy • Transferring electrons involves energy changes • Recall that ionization energy is the energy that it takes to remove the outermost electron from an atom. In other words, moving a negatively charged electrons away from an atom that will become a positively charged ion requires an input of energy before it will take place. Na + energy  Na+ + e- Cl + e-  Cl- + energy

  6. Sodium Chloride: Endothermic Steps • Starting molecules are _____________ metal and _____________ gas. Energy must be supplied to make the solid sodium metal into a gas. Na(s) + energy  Na(g) • Recall that energy is also required to remove an electron from a gaseous sodium atom. Na(g) + energy  Na+(g) + e- • Chlorine is already a gas, but it is a _____________ gas, so we need energy to break it up. Cl—Cl(g) + energy  Cl(g) + Cl(g)

  7. Sodium Chloride: Exothermic Steps • When a cation and an anion come together to form an ionic bond, it is an exothermic process. Energy is released (exothermic process). Na+(g)+ Cl-(g) NaCl(s) + energy • The energy released when ionic bonds are formed is called the lattice energy. • The lattice energy is greater than the energy needed for the first three steps. • Without this energy, there would not be enough energy to make the overall process spontaneous. • Lattice energy is the key to salt formation.

  8. Lattice Energy • The value of the lattice energy is different if other cations and anions form the salt. • Magnesium cations, Mg2+, have much higher values than sodium because the ions have a much greater charge and are more strongly attracted to the oppositely charged ions in the crystal. • The lattice energy for magnesium oxide is almost five times greater than that for sodium chloride.

  9. Energy to break them apart • If energy is released when ionic bonds are formed, then energy must be supplied to break these bonds and separate the ions. • In the case of NaCl, the required energy can come from water. • In water, the Na+ ions and Cl- ions come apart and “dissolve” • This “dissolving” process is called ionization. Salts and strong acids/bases completely dissociate or ionize is water (aqueous) solutions.

  10. Ionic Compounds are not Molecules • Water is made up of billions of H2O “molecules” • But, sodium chloride is made up of billions of Na+ and Cl- ions held together by ionic bonds in a crystal lattice structure. • You can assume that a metal (cation) and a nonmetal (anion) will form an ionic compound and not a molecule. Similarily, you can think two nonmetals (____________) will be molecules and not ionic compounds. • BUT, this determination must be made in the laboratory and not simply by looking at your periodic tables.

  11. Ionic Bonds are Strong • There are both repulsive and attractive forces within a salt crystal. • There are repulsive forces between the Na+ and Na+as well as between the Cl- and Cl- • There ARE ALSO repulsive forces between valence electrons, even if they have opposite charges

  12. Ionic Bonds are Strong • The attractive forces include those between the positively charged nuclei of one ion and the electrons of other nearby ions. • In addition, attractive forces exist between oppositely charged ions. • Within the lattice, each Chlorine ion is surrounded by 6 Sodium ions. At the same time each Sodium ion is surrounded by 6 Chlorine ions. • As a result, the attractive forces are MUCH stronger in a lattice rather than if the sodium and chlorine ions existed as pairs.

  13. Ionic Properties • Ionic compounds have distinctive properties • The strong attractions create VERY high melting and boiling points (NaCl = 1413ºC) • Large amounts of energy are required to strip the ions away from all of their attracting neighbors. • As a result of the high BP’s, ionic compounds are rarely gaseous at room temperature, while many molecular compounds are.

  14. Conductors of Electric Current • Liquid and dissolved salts conduct electrical current. • To conduct electrical current the substance must: • Contain charged particles • Particles must be free to move • Solids are fixed in their positions, not free to move • When a salt melts or dissolves the ions are free to move. They are obviously charged, thus enabling them to carry the electric current.

  15. Salts Are Hard and Brittle • Hard – the crystal is able to resist a large force applied to it • Brittle – when the applied force becomes too strong to resist, the crystal develops a widespread fracture rather than a small dent. • As long as the layers stay in a fixed position relative to one another, the attractive forces between oppositely charge ions will resist motion (as in the lattice)

  16. Salt Crystals • Crystal Lattice • The regular pattern in which a crystal is arranged. • NaCl lattice involves interactions between more than just one sodium and one chlorine. They are SURROUNDED • Just as MgF2 involve more than one magnesium and two fluorine

  17. Ordered Packing Arrangements • Salts vary in the types of ions from which they are made. • Salts also vary in the ratio of ions that make up the crystal lattice. • Despite these differences, all salts are made up of simple repeating units. • Unit Cells– The smallest portion of a crystal lattice that shows the three-dimensional pattern of the entire lattice.

  18. 1. Explain the endothermic and exothermic steps in the creation of an ionic compound. You may use sodium chloride as an example. Be explicit and do not simply restate the notes. • 2. What is Lattice Energy? • 3. What is a unit cell? • 4. What are the properties for ionic compounds? • 5. Explain the stability of an ionic compound. What gives these structures these unique properties?

More Related