Unit 4: Chemical Bonding

Outline Ionic Bonding (Ch.7) Covalent Bonding (Ch.8) Metallic Bonding Valence electrons Covalent bond Positive and negative ions and transition metal ions Lewis structure of a molecule Naming molecules Ionic bonding: Charge on compounds Structural formulas Ionic compounds characteristics Lewis structures for polyatomic ions, Resonance structures Writing ionic compound formulas Metallic Bonding Molecular shapes Bond polarity Metallic bond properties Properties of Covalent compounds Properties of metals explained by metallic bond 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 Recall that an electron dot structure is a diagram that shows the number of valence electrons. “Octet” is a stable arrangement of eight valence electrons in the outermost energy level. He: 1s2 Other noble gases: ns2np6 Elements tend to react to acquire the stable electron configuration of a noble gas.

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: Ion formation Metals: Metal atoms easily lose valence electrons. Eg. Group 1, 2, 13 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. Just have to know about it because we can’t predict it.

Ionic Bonding: Ion formation Metals: Although an octet is the most stable electron configuration, other electron configurations can also have some stability. “Pseudo-noble gas configuration”: Full s, p and d sublevels.

Ionic Bonding: Ion formation Examples: Write the electron configuration of the most likely ion and the charge of the ion. 1. Cs: [Xe]6s1 2. Ga: [Ar]4s23d104p1 3. Ag: [Kr]5s14d10 4. Sc: [Ar] 4s23d1

Ionic Bonding: Ion formation Nonmetals: Gain electrons Eg. Groups 15, 16, 17 Usually gain but can lose too. Name: non-metal element “–ide”

Ionic Bonding: Ion formation Examples: Textbook p.209 Q5 Name the following ions. 1. Ag+ 2. Li+ 3. Br- 4. Ca2+ 5. S2- 6. B3+ 7. As3- 8. H- 9. Cd2+ 10. Se2-

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: Ionic compounds https://www.youtube.com/watch?v=Qq jcCvzWwww

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 Name NH4+ Ammonium ClO- Hypochlorite NO2- Nitrite ClO2- Chlorite NO3- Nitrate ClO3- Chlorate OH- Hydroxide ClO4- Perchlorate CO32- Carbonate CrO42- Chromate HCO3- Hydrogen carbonate Cr2O72- Dichromate SO32- Sulfite S2O32- Thiosulfate SO42- Sulfate O22- Peroxide PO43- Phosphate MnO4- Permanganate HPO42- Hydrogen phosphate CN- Cyanide H2PO4- Dihydrogen phosphate BrO3- Bromate CH3COO- Acetate IO3- Iodate C2H3O2- IO4- Periodate

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”.