THE FORMATION OF COMPOUNDS: IONIC & MOLECULAR

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1 TE FORMATION OF COMPOUNDS: IONIC & MOLECULAR As previously discussed, only one group of atoms are stable in nature, the. Atomically speaking, this means that they have a. Most other atoms cannot be found in nature in their elemental form. These atoms need to employ a strategy to become more stable. One of the ways this is achieved is to or electrons. Atoms which gain electrons to become are called. Atoms which lose electrons to become are called. Cations are found on the hand side of the periodic table from: Anions are found on the hand side of the periodic table from: As a quick review, indicate the charge of common ions formed for by MOST of the first 20 elements. In truth, these ions are not completely stable because they are charged particles and from the law of electric charges, we know that opposite charges. To fully become stable, cations will be attracted to anions to form. Examples of ionic compounds include: Not all of these atoms form ions either. Other than the Noble Gases, these two elements do not have any charges listed:,. These elements employ another strategy to form stable compounds. Instead of gaining or losing electrons, they share their valence electrons. These molecules are called Molecular Compounds and the bonds are referred to as. Silicon and carbon readily use this strategy, along with other non metals. 1

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3 SCEMATIC DRAWINGS OF IONIC COMPOUNDS Lewis Diagrams are the best place to start when showing the formation of an ionic compound. One of the easiest examples of an ionic compound is the most common form of table salt. Recall Atomic Notation 3 Li Bohr Rutherford Diagram 3p Lewis Diagrams It is important to note that most elements want to become more stable and the way they do this is to become an ion. Because of an electrostatic attraction, a cation will form an ionic compound with an anion. The formation of the ionic compound NaCl would be as follows: Na Cl loses its valence electron to become a stable cation. picks up any electron to become a stable anion. [Na] + Cl Now these oppositely charged ions are attracted to each other. We now have a model of the ionic compound NaCl. [Na] + Cl Na + Cl What happens when the charges are not equal such as Magnesium and Chlorine? loses its valence electrons to become stable cations. picks up any electron to become a stable anion. NOW... in what combination would these ions come together to form a stable ionic compound (how many of each ion are needed )? Now all three charged ions are attracted to each other. We now have a model of the ionic compound MgCl 2. OMEWORK 1. Complete the 3 step schematic diagram for NaF, CaCl 2, BeO, Mg 3 N Write the chemical formulas for magnesium fluoride, sodium phosphide. Complete the schematic drawings if you are having difficulty. 3

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5 C04 Formation of Compounds SCEMATIC DIAGRAMS OF MOLECULAR COMPOUNDS Lewis diagrams can also be used to show the formation of Molecular Compounds (where the electrons are ). The atoms that form molecular compounds have valence electrons that allow them to combine in some fashion to share electrons with each other to fill their valence shells. The schematic drawings of molecular compounds are slighlty different because the electrons are instead of transferred. A line connecting two atoms represents the shared pair of electrons between two atoms. EXAMPLE #1 ydrogen Gas ( 2 ) Start with the Lewis diagram (unstable) of all atoms. As the atoms come close together, the electrons can be shared. This is called a Lewis Structure. We now replace the shared pair of electrons with a covalent bond. EXAMPLE #1 Water ( 2 O) Start with the Lewis diagram (unstable) of all atoms. The difficult part is trying to decide what the structure will look like. int: SYMMETRY O We now replace the shared pair of electrons with a covalent bond. O Aside water molecules actually look slightly different. The unpaired electrons are closer together so the molecule looks more like Mickey Mouse (shapes of molecules will be studied more in grade 11 and 12). Just thought you'd like to know. O 5

6 Most molecular compounds are combinations of different types of elements. Examples include There are a few special cases where atoms of the same element pair up with another atom of the same element. Because the compound contains two atoms of the same atom it is called a molecule (di meaning 2). The list of these atoms can be remembered with the following expression: OFBrINCl EXAMPLE #3 Oxygen Gas (O 2 ) EXAMPLE #4 Methane (C 4 ) OMEWORK 1. Draw the schematic diagrams for the remaining diatomic molecules. 2. Draw the schematic diagrams for CF 4, PBr 3, N 3.. 6

7 SNC 2D NAME: Complete the following tables for both Ionic and Molecular Compounds. IONIC COMPOUNDS ELEMENTS INVOLVED LEWIS DIAGRAMS IONS FORMED LEWIS STRUCTURE CEMICAL FORMULA potassium & oxygen lithium & chlorine aluminum & oxygen calcium & fluorine magnesium & nitrogen 7

8 MOLECULAR COMPOUNDS CEMICAL FORMULA LEWIS DIAGRAMS LEWIS STRUCTURE BOND STRUCTURE SiF 4 Cl 2 CO 2 2 S N 2 4 8