Tuesday, Jan. 14 th : “A” Day Wednesday, Jan. 15 th : “B” Day Agenda Homework Questions?/Collect Sec. 5.1 Quiz: “Simple Ions” Begin Section 5.2: “Ionic Bonding and Salts” Salt, lattice energy ACT Practice We will finish section 5.2 next time…
Quiz 5.1: “Simple Ions” You may use your notes, your book, and your periodic table to complete the quiz on your own. Quiz Corrections: #3: 3s 6 should be 3p 6 #8 and #9: The term “ionize” means to lose or gain electrons to form an ion. Take your time, this quiz is a little tricky… Good Luck!
Section 5.2: “Ionic Bonding and Salts” Because opposite charges attract, cations and anions should attract one another. This is exactly what happens when an ionic bond forms.
Ionic Bonds Form Between Ions of Opposite Charge Remember, An alkali metal, such as sodium, will LOSE 1 electron to form a 1 + ion (cation) Na + A halogen, such as chlorine, will GAIN 1 electron to form a 1 - ion (anion) Cl -
Ionic Bonds Form Between Ions of Opposite Charge The force of attraction between the 1 + charge on the sodium cation and the 1 charge on the chloride anion creates the ionic bond in sodium chloride. Sodium chloride is a salt.
Ionic Bonds Form Between Ions of Opposite Charge Salt: an ionic compound that forms when a metal atom or a positive radical replaces the hydrogen of an acid. Plain English: the scientific name given to thousands of different ionic compounds. Examples of salts: KCl: Potassium chloride AlCl 3 : Aluminum chloride
Ionic Bonds Form Between Ions of Opposite Charge All salts are electrically neutral ionic compounds that are made up of cations and anions held together by ionic bonds in a simple, whole- number ratio. However, the attractions between the ions in a salt do not stop with a single cation and a single anion. One cation attracts several anions, and one anion attracts several cations. They are all pulled together into a tightly packed crystal structure.
Transferring Electrons Involves Energy Changes Remember, ionization energy is the energy required to remove the outermost electron from an atom. The equation below shows this process for sodium. Na + energy Na + + e (Energy added = ENDOTHERMIC process)
Transferring Electrons Involves Energy Changes Remember, electron affinity is the energy change that occurs when a neutral atom gains an electron. Some elements, such as chlorine, easily accept electrons and energy is released when an electron is added. Cl + e Cl + energy (Energy released = EXOTHERMIC process)
Transferring Electrons Involves Energy Changes The energy released when chlorine accepts an electron is less than the energy required to remove an electron from a sodium atom. Adding and removing electrons is only part of forming an ionic bond. The rest of the process of forming a salt supplies enough energy to make up the difference so that the overall process releases energy.
Salt Formation The process of forming the salt sodium chloride can be broken down into five steps: 1. Energy is added to make solid sodium metal into a gas. Na(solid) + energy Na(gas) 2. Energy is added to remove an electron from the gaseous sodium atom to make an ion. Na(gas) + energy Na + (gas) + e
Salt Formation 3.Chlorine gas exists as 2 chlorine atoms bonded together, so energy must be added to separate the chlorine atoms so that they can react with sodium. Cl–Cl(gas) + energy Cl(gas) + Cl(gas) The first three steps have all been endothermic (energy added) and have produced sodium cations and chlorine atoms. Cl Na +
Salt Formation The last 2 steps will be exothermic (energy released) and will produce chloride anions and the salt NaCl. Cl - NaCl 4. An electron is added to a chlorine atom to form an anion. This step releases energy. Cl(gas) + e Cl (gas) + energy
Salt Formation 5. When a cation and anion form an ionic bond, it is an exothermic process and energy is released. Na + (gas) + Cl (gas) NaCl(solid) + energy The last step is the driving force for salt formation because of the energy released.
Lattice Energy Lattice Energy: the energy associated with constructing a crystal lattice relative to the energy of all constituent atoms separated by infinite distances. Plain English: the energy released during salt formation when ionic bonds are formed.
Lattice Energy With the release of the lattice energy, the crystal lattice structure has lower potential energy than the neutral atoms that form the salt. Without this energy, there would not be enough energy to make the overall process spontaneous.
ACT Practice During the 2 nd semester, we will practice ACT- type problems to help foster critical thinking and problem solving skills. Please read the passage “The Modern Periodic Table” and completed the associated questions. We will go over them once everyone is finished, so hold on to them. Yes, this is for a grade!