Ionic Bonding - MED-102 General Chemistry PDF

MED-102 General Chemistry Ionic Bonding  LOBs covered Describe the loss of electrons by metal atoms in forming positive ions Describe the gain of electrons by non-metal atoms in forming negative ions Explain the formation of ionic bonds between metals and nonmetals E...

MED-102 General Chemistry Ionic Bonding  LOBs covered Describe the loss of electrons by metal atoms in forming positive ions Describe the gain of electrons by non-metal atoms in forming negative ions Explain the formation of ionic bonds between metals and nonmetals Explain Coulomb’s Law as it pertains to chemical systems Use Coulomb’s Law to explain the strength of ionic bonding  Coulomb’s Law – Part 1 This Law is very important in understanding chemical bonding and in explaining aspects of chemical reactivity  Coulomb’s Law – Part 2 Describes mathematically the energy (of attraction or repulsion) between two charged particles Positive E means repulsion Negative E means attraction  Coulomb’s Law – Part 2 – Revision Slide WATCH: https://www.youtube.com/watch?v=rYjo774UpHI&t=125s R is the distance between the centres of the ions. k is a constant. We assume that it does not vary across different situations. If Q1 is positive and Q2 is negative, their product will be negative. We get a negative E, but this simply means that the interaction is attractive. If Q1 and Q2 are both positive or both negative, their product is positive. We get a positive E, which means that the interaction is repulsive.  Chemical Bonding Compounds are made up of atoms or ions joined together by chemical bonds Ionic bonding – involves ions joining together Covalent bonding – involves neutral atoms joining together In order to understand why and how bonds are formed, we need to revisit the topic of electronic configurations  Achieving Chemical Stability Which group of elements are chemically stable? Group 8A or 18 (Noble gases)  Noble gases Why are they chemically inert? s2p6 valence shell configurations – full outer shell – an octet (8) Neither give nor take electrons THEREFORE: Elements react by either giving or taking electrons until they have a full outer shell (or an octet) This is known at the Octet Rule  Formation of NaCl Sodium electron configuration Chlorine electron configuration  Formation of NaCl – Revision Slide Sodium Chlorine The sodium atom has one 3s electron in its The chlorine atom has an s2p5 valence shell. valence shell. If it gains one electron, it will have a full n = 3 If it loses that electron, it is left with a full n = shell. 2 shell. If it gains one electron, it will have an s2p6 Losing the 3s electron, will leave sodium with outer shell. an s2p6 electronic configuration. If it gains one electron, it will end up with a It will be left with 10 electrons and the same total of 18 electrons, the same as Argon. electronic configuration as Neon. Gaining one electron, it will have a total Losing one electron, it will end up with a total charge of -1, Cl- charge of +1, Na+ Therefore, the chlorine atom accepts the Therefore, sodium gives its extra electron to extra electron of sodium. They both gain the chlorine. They both gain stability. stability.  Ionic Bond - NaCl Force of attraction between positive and negative ions  Formation of NaCl – Revision Slide The Na atom gives its extra electron to the Cl atom. This produces Na+ and Cl- ions. Since the two ions are of opposite charge, the are attracted to each other. All ions join together to form a large crystal lattice, which is the NaCl compound (salt). The key words for ionic bonding are ‘transfer of electrons.’ WATCH: https://www.youtube.com/watch?v=j5M9_qoGKXY Ionic Bond - MgO  Ionic Bond – MgO – Revision Slide The Mg atom has two 3s outermost electrons. If it gives them up, it will have a full n = 2 shell. The O atom has 6 outermost electrons in the n = 2 shell. It needs 2 more electrons to fill its n = 2 shell. Therefore, the Mg atom gives 2 electrons to the O atom. This results in Mg2+ and O2- ions. Through Coulombic attraction of opposite charges, they join together to form the MgO crystal lattice.  Ionic Bond – MgCl2 The Mg atom needs to shed 2 electrons to have a full n = 2 shell. Each Cl atom needs one electron to have a full n = 3 shell. Therefore, the Mg atom gives one electron to each of the two Cl atoms. This gives Mg2+ and two Cl- ions. 5-Minute Break  Crystal Lattice Alternate arrangement of positive and negative ions. Ions arranged in all three dimensions. This forms a solid crystal (salt). Ionic bonds usually form from a metal and a nonmetal joining together.  Water solutions of ionic crystals conduct electricity  MCQ Quiz When Ca2+ and O2- ions join When Mg2+ and PO43- ions join together, what is the chemical together, the chemical formula of the compound? formula of the compound is: (a) CaO2 (a) MgPO4 (b) Ca2O (b) Mg2(PO4)3 (c) Ca2O2 (c) Mg3(PO4)2 (d) CaO (d) None of the above  MCQ Quiz When Ca2+ and O2- ions join When Mg2+ and PO43- ions join together, what is the chemical together, the chemical formula of the compound? formula of the compound is: (a) CaO2 (a) MgPO4 (b) Ca2O (b) Mg2(PO4)3 (c) Ca2O2 (c) Mg3(PO4)2 (d) CaO (d) None of the above  MCQ Quiz When Ca2+ and O2- ions join When Mg2+ and PO43- ions join together, what is the chemical together, the chemical formula of the compound? formula of the compound is: (a) CaO2 (a) MgPO4 (b) Ca2O (b) Mg2(PO4)3 (c) Ca2O2 (c) Mg3(PO4)2 (d) CaO (d) None of the above  MCQ Quiz When Ca2+ and O2- ions join When Mg2+ and PO43- ions join together, what is the chemical together, the chemical formula of the compound? formula of the compound is: (a) CaO2 (a) MgPO4 (b) Ca2O (b) Mg2(PO4)3 (c) Ca2O2 (c) Mg3(PO4)2 (d) CaO (d) None of the above  Coulomb’s Law Strength of ionic bonds depends on Coulomb’s Law Q1Q2 E=k d12  Lattice Energy and Coulomb’s Law Q1Q2 E=k d12  Lattice Energy and Coulomb’s Law – Revision Slide Q1Q2 E=k d12 Compare NaF, NaCl, NaBr, and NaI. We notice that the lattice energy decreases from NaF to NaI. The ionic charges are the same in all compounds, +1 for Na and -1 for the halogens. The only thing that varies is the distance between the ions. Halogens increase in size as we go from F to I. Therefore, as we go from NaF to NaI, d12 increases, and E decreases. In MgO, the charges are +2 and -2. Their product is -4. The product for NaF is (+1)(-1) = -1. Thus, we expect the lattice energy for MgO to be approximately 4 times as large as that of NaF. 910 versus 3795 is close to 4x. In ScN, the charges are +3 and -3. Their product is -9. Thus, we expect the lattice energy for ScN to be approximately 9 times as large as that of NaF. 910 versus 7547. This is close to 9x. WATCH: https://www.youtube.com/watch?v=kSWJPWMZ0-c  Summary for Revision Coulomb’s Law can be expressed qualitatively as: opposite charges attract, like charges repel. Coulomb’s Law can also be expressed mathematically. The energy of attraction/repulsion is directly proportional to the product of the two charges, and indirectly proportional to the distance between their centers. There are three main types of chemical bonds: ionic, covalent and metallic. In this section we consider ionic. Atoms can achieve chemical stability by either giving up or gaining electrons, until they achieve a full outer shell. Usually, this full outer shell corresponds to an octet (8) electrons in the valence shell. Atoms either give or take electrons to become isoelectronic with their nearest Noble Gas. Atoms then become charged ions through giving up of gaining electrons. Positive ions are called cations and negative ions are called anions. Cations and anions join together to form ionic bonds and ionic compounds. Cations are usually metallic, and anions are usually nonmetallic. Therefore, the most common ionic compounds are formed from a metal and a nonmetal. Ionic compounds form crystalline structures called lattices. Ionic compounds are always solid (crystals or powders) at room temperature. Lattice energy is the attractive energy between two ions. We can use Coulomb’s Law’s mathematical form to explain the magnitude of lattice energies.