Chemical Bonds Power Point 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: Wikimedia Commons

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

A chemical bond is an attraction between atoms. 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 Images: NASA & 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 for a molecule follows the law of definite proportions. Set ratios of atoms H2O

Practice Apply the conservation of mass and law of definite proportions to these molecules. Calculate the formula mass. Set up the ratio and determine the relative mass. State the chemical and common name. CO2 HCl NH3 CH4

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

Dot Structures & Group Numbers Image: texas.gateway.org

Na + Cl Be + N 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 Mg + S Ca + Br Rb + Se 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? Determine the chemical formula, and then name the compound. Mg + S Ca + Br 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: 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 more left/right separation on the periodic table, the more polar the bond will be. Molecules may be polar due to electron sharing or structure. 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 Polar molecules tend to have high boiling points. Explain why the structure of an atom would cause high boiling point (high energy to phase change). https://demonstrations.wolfram.com/FormulasAndStructuresForSomeSimpleMolecules/

Molecular Attractions Molecular attractions occur as a result of polarity. Ion-Dipole Ionic bonds dissolve easily in water – ions Ionic substances are very hydrophilic (water-loving) Potassium Chloride solute Water solvent Image Credit: Chemistry Libretexts

Dipole-Induced dipole Dipole-Dipole Water molecules are dipoles Intermolecular forces attract water molecules together Dipole-Induced dipole CO2 vibrates and becomes polar CO2 attracts to water dipoles Soda Pop (Water-Carbon Dioxide) Images: Openstax & ThomasNet News

Images: ThomasNet News Induced Dipole-Induced Dipole Instantaneous uneven distribution of e− Vibration of molecules One temporary dipole induces dipole behavior in neighbor molecule Images: ThomasNet News

Practice Which of the molecular attractions is the strongest? Explain what makes these attractions strong. Which of the molecular attractions is the weakest? Explain what makes these attractions weak.

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− results in stronger molecular attractions.

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

Hydrogen bonding does not just occur in water. Hydrogen bonding occurs whenever H is part of an asymmetric structure or uneven proton distribution

Practice 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