Chemical Bonds & Molecular Attractions Chapter 12 Image Credit: Khan Academy

Student Learning Objectives Describe and predict types of chemical bonds Determine the type of chemical bond Write the chemical formula Describe molecular attractions & provide examples Image Credit: Wikimedia Commons

Video by Kosasihiskansarsjah https://www.youtube.com/watch?v=QqjcCvzWwww Video by Kosasihiskansarsjah

What is a chemical bond? A chemical bond is an attraction between atoms. The chemical bond puts each atom in a lower energy state. Ibuprofen C13H18O2 Image Credit: NASA Image Credit: Wikimedia Commons

What is conserved in chemical reactions? Mass and charge are conserved in chemical reactions. The formula mass of the product is equal to the formula mass of the reactants. The relative mass of a substance is always the same. (law of definite proportions) H2O

Practice For each of the substances listed: CO2 HCl NH3 CH4 Calculate the formula mass. Set up the ratio and determine the relative mass. State the chemical and common name.

How does an electron dot structure compare to the shell model? The Lewis electron dot symbols represent the valence electrons of the main group elements. Unpaired e– The electron dot structure is based on the octet rule.

Practice Draw the electron dot structures. H C Ar Na How do the dot structures compare to the group number?

What is an ionic bond? Ionic bonds form between positive and negative ions. Electric force establishes bond Strongest chemical bond Ion charges must balance to a net charge of zero when atoms bond. Na + Cl Be + N

Practice 1) Ionic bonds are usually formed between metals from the left side of the periodic table and nonmetals from the far right side of the periodic table. Why? 2) Determine the chemical formula, and then name the compound. 1. Mg + S 2. Ca + Br 3. Rb + Se

What is a metallic bond? Metallic bonds form in metals as all electrons are shared among all the nuclei in the metal. e e e e e e e e e e e e e e e e Sharing of all electrons establishes bond Results in conductivity and malleability of metals Ions homogeneously distributed in alloys Weakest chemical bond Cu Cu Ni Ni

What is a covalent bond? Covalent bonds are formed between atoms that share pairs of electrons in the inter-nuclear region. Image Credit: Wikimedia Commons

Covalent Sharing of e— Sharing of electron pairs establishes the covalent bond. There can be 1, 2, or 3 pairs of electrons shared. H – H 2e single bond C  O 4e double bond N  N 6e triple bond

Polar Molecules In general, the farther apart (left↔right) two atoms are on the periodic table, the more polar the bond will be. Molecule is polar due to: Uneven sharing of electrons A-symmetric structure socratic.org

Practice Which are polar molecules? Which bond would be the most polar? CO CO2 H2O NH3 2) Polar molecules tend to have high boiling points. Why?

Molecular Attractions Molecular attractions occur as a result of polarity. Ion-Dipole Charged species as a rule dissolve readily in water Ionic substances are very hydrophilic (water-loving) Image Credit: Chemistry Libretexts

Dipole-Induced dipole Dipole-Dipole Water molecules are dipoles Intermolecular forces attract water molecules together Dipole-Induced dipole Soda Pop (Water-Carbon Dioxide) Images Credit: Openstax & ThomasNet News

Images Credit: ThomasNet News Induced Dipole-Induced Dipole Instantaneous uneven distribution of e− Molecules may vibrate Electrons may be unbalanced for a moment Images Credit: ThomasNet News

Practice Which of the molecular attractions is the strongest? Why? Which of the molecular attractions is the weakest? Why? What, specifically, causes the surface tension exhibited by water?

Hydrogen Bonding Hydrogen bonding is a special form of a dipole-dipole molecular attraction. This is not a chemical bond (no new substance produced) H is part of the bond pair Very uneven sharing of e−

A hydrogen bond is the attraction between the positively charged hydrogen and a negatively charged lone pair of electrons. Image Credit: Pinterest

Practice Why does it take a relatively long time for water to boil? Explain why the surface tension for water tends to be much greater than other fluids. Which of the following molecules would exhibit hydrogen bonding? NH3 CH4 HCl BF3