Unit 3: Chemical Bonding Outline Ionic Bonding (Ch.7) Covalent Bonding (Ch.8) Valence electrons Covalent bond Positive and negative ions and transition metal ions Lewis structure of a molecule Ionic bonding: Charge on compounds Ionic compounds characteristics Writing ionic compound formulas Metallic Bonding Naming molecules Structural formulas Lewis structures for polyatomic ions, Resonance structures Molecular shapes Metallic bond properties Bond polarity Properties of metals explained by metallic bond Properties of Covalent compounds Metal alloys Ionic Bonding Whenever two atoms or ions are held strongly together, we say that there is a chemical bond between them. Chemical bond: A force that holds two atoms/ions together. Ionic Bonding Chemical bonds can form by the attraction between a positive ion and a negative ion, or they can form by the attraction between the positive nucleus and the negative electrons of another atom. Ionic Bonding: Ion formation Positive Ion formation: loses valence electrons Negative Ion formation: gains valence electrons (More information on unit 3 lecture slides) Losing electrons: Always from the highest energy level. Gaining electrons: Follows Aufbau principle. Recall: Atoms gain or lose electrons to acquire the electron configuration of the nearest noble gas. Ionic Bonding: Ionic compounds When a cation and an anion form and them come close to each other, they are attracted to each other by their opposite charges. An ionic bond is the electrostatic force that holds oppositely charged particles together in an ionic compound. Ionic compounds are compounds that contain ionic bonds between two different types of ions. Ionic Bonding: Ion formation Metals: Metal atoms easily lose valence electrons. Group 1, 2, 13 Naming: metal name + “ion” Transition metals have an outer energy level of ns2 and the d sublevel that is filled is in a lower energy level (n-1)d Transition metals commonly just lose the two s electrons from its valence shell and form the +2 ion. Transition metals also can lose their d electrons and form a +3 ion too. Naming: metal name + Roman numerals in brackets + “ion” Ionic Bonding: Ion formation Examples: Write the electron configuration of the most likely ion and the charge of the ion. 1. Cs: [Xe]6s1 3. Ag: [Kr]5s14d10 2. Ga: [Ar]4s23d104p1 4. Sc: [Ar] 4s23d1 Ionic Bonding: Ion formation Nonmetals: Gain electrons Groups 15 (-3 ion), 16 (-2 ion), 17 (-1 ion) Name: non-metal element “–ide” + “ion” Ionic Bonding: Ion formation Examples: Textbook p.209 Q5 Name the following ions. 1. Ag+ 2. Li+ 4. Ca2+ 5. S2- 7. As3- 8. H- 10. Se2- 3. Br6. B3+ 9. Cd2+ Ionic Bonding: Ionic compound properties Physical structure: (What it physically looks like) In an ionic compound, large numbers of positive and negative ions exist together in a regular repeating pattern that balances the forces of attraction and repulsion between the ions. Ionic Bonding: Ionic compound properties Physical structure: eg. NaCl Very organized arrangement Each sodium ion is surrounded by six chloride ions and vice versa Ionic Bonding: Ionic compound properties Physical structure: This 3D arrangement of particles in an ionic compound is called a crystal lattice. In a crystal lattice, each positive ion is surrounded by negative ions and each negative ion is surrounded by positive ions. Ionic Bonding: Ionic compound properties Physical properties: Melting point Boiling point Hardness Electrical conductivity Ionic Bonding: Ionic compound properties Physical properties: An ionic compound can’t conduct electricity as a solid, but when dissolved in water, it can conduct electricity. Electrolytes are substances that can conduct electricity in aqueous solution. Ionic Bonding: Ionic compound properties Physical properties: Lattice energy is the energy needed to separate 6.022 x 1023 ions from an ionic compound. Larger ions: smaller lattice energy Larger charges: larger lattice energy Ionic Bonding: Ionic compounds Many ionic compounds are binary. This means that they contain only two different elements. Binary ionic compounds: 1. Metal cation 2. Nonmetal anion. Ionic Bonding: Ionic compounds Compound formation: Look carefully at the charges on both the metal cation and the nonmetal anion. Ionic compounds have an overall charge of zero. Ionic Bonding: Ionic compounds Compound formation: Eg. Sodium and chlorine Eg. Calcium and fluorine Eg. Aluminium and oxygen Textbook p. 212 Q7-11 Ionic Bonding: Ionic compounds Another example: Formation of ionic compound from Boron and Selenium Ionic Bonding: Ionic compound formulas Writing Formulas: Since an ionic compound is made up of ions arranged in a repeating pattern, the chemical formula for an ionic compound represents the simplest ratio of the ions involved. Formula unit Ionic Bonding: Ionic compound formulas Writing Formulas: Eg. Magnesium and Chlorine 1. Cation is always written first. 2. Subscripts represent the number of ions of each element in the compound. Ionic Bonding: Ionic compound formulas Writing Formulas: Monoatomic ions A one-atom ion. Common metal and nonmetal ions. Eg. Groups 1,2,15,16,17 Ionic Bonding: Ionic compound formulas Writing Formulas: Monoatomic ions Textbook p.221 Q19-23 Ionic Bonding: Ionic compound formulas Writing Formulas: Polyatomic ions Ions that have more than one atom. A polyatomic ion acts as an individual ion in a compound and its charge applies to the entire group of atoms. Polyatomic ions exist as a unit, so do not change the subscripts within the ion. Ion NH4+ Name Ammonium Ion ClO- Name Hypochlorite NO2NO3- Nitrite Nitrate ClO2ClO3- Chlorite Chlorate OHCO32- Hydroxide Carbonate ClO4CrO42- Perchlorate Chromate HCO3SO32- Hydrogen carbonate Sulfite Cr2O72S2O32- Dichromate Thiosulfate SO42PO43- Sulfate Phosphate O22MnO4- Peroxide Permanganate HPO42H2PO4- Hydrogen phosphate Dihydrogen phosphate CNBrO3- Cyanide Bromate IO3IO4- Iodate Periodate CH3COO- Acetate C2H3O2- Ionic Bonding: Ionic compound formulas Writing Names: 1. Write the name of the cation first. For transition metals only: Write the “oxidation number” (=charge on the transition metal cation) in brackets next to the transition element’s name. 2. Write the name of the anion next to the name of the cation. Ionic Bonding: Ionic compound formulas Writing Names: Eg. Iron, Fe, can be both the Fe2+ and the Fe3+ ion in different compounds. So the ionic compound FeCO3 would be correctly named as “iron (II) carbonate” And the ionic compound Fe2(CO3)3 would be correctly named as “iron (III) carbonate”.