1. Chemical Bonding An Introduction

2. Chemical Bonds A mutual electrical attraction between the nuclei and valence electrons of different atoms that bonds the atoms together to – A mutual electrical attraction between the nuclei and valence electrons of different atoms that bonds the atoms together to – Lower potential energy Lower potential energy Increase stability Increase stability

3. Octet Rule Atoms will gain, lose or share electrons to have eight valence electrons Atoms will gain, lose or share electrons to have eight valence electrons A full outer shell means the outermost s and p sublevels are full A full outer shell means the outermost s and p sublevels are full

4. Types of Bonds Three general types of bonds Three general types of bonds Ionic Ionic Covalent Covalent Metallic Metallic Type of bond is determined using the electronegativities of the atoms involved Type of bond is determined using the electronegativities of the atoms involved Most compounds have bonds that are partially ionic and partially covalent Most compounds have bonds that are partially ionic and partially covalent

5. Ionic Bonds Electrostatic attraction between ions with opposite electrical charges Electrostatic attraction between ions with opposite electrical charges No molecules are formed – huge numbers of cations are bonded to huge numbers of anions No molecules are formed – huge numbers of cations are bonded to huge numbers of anions Formulas are written as the lowest whole number ratio of ions Formulas are written as the lowest whole number ratio of ions

6. Covalent Bonds Two atoms share two or more electrons Two atoms share two or more electrons Two electrons (1 pair) = single bond Two electrons (1 pair) = single bond Four electrons (2 pairs) = double bond Four electrons (2 pairs) = double bond Six electrons (3 pairs) = triple bond Six electrons (3 pairs) = triple bond The electrons may not be shared evenly, which would result in a polar covalent bond The electrons may not be shared evenly, which would result in a polar covalent bond

7. Metallic Bonds Metals have delocalized electrons, which means the electrons are free to move around Metals have delocalized electrons, which means the electrons are free to move around Metallic bonds are the attraction between metal atoms and the surrounding sea of electrons Metallic bonds are the attraction between metal atoms and the surrounding sea of electrons Metallic bonds are formed when you have only metallic elements present Metallic bonds are formed when you have only metallic elements present

8. Electronegativity Tendency of an atom to attract electrons to itself Tendency of an atom to attract electrons to itself Values are on your formula chart Values are on your formula chart Fluorine is the highest Fluorine is the highest Francium is the lowest Francium is the lowest Use the difference in electronegativity to classify the bond by type Use the difference in electronegativity to classify the bond by type

9. Polar Covalent Bonds Some atoms don’t share the electrons evenly Some atoms don’t share the electrons evenly Polar bonds are formed when one atom “hogs” the electrons more than the other Polar bonds are formed when one atom “hogs” the electrons more than the other Non-polar: electrons are shared evenly Non-polar: electrons are shared evenly Mildly polar: electrons are pulled slightly to one side Mildly polar: electrons are pulled slightly to one side Very polar: electrons are pulled a lot to one side Very polar: electrons are pulled a lot to one side

10. Determining Bond Type Find the difference in electronegativity and match it to the values shown below Find the difference in electronegativity and match it to the values shown below Electronegativity Difference Type of Bond 0.0 – 0.3 Non-polar covalent 0.3 – 1.7 Polar covalent 1.7 or more Ionic

11. Determining Bond Type - Example What type of bond will be formed between aluminum and phosphorus? What type of bond will be formed between aluminum and phosphorus? Electronegativity of aluminum = 1.5 Electronegativity of aluminum = 1.5 Electronegativity of phosphorus = 2.1 Electronegativity of phosphorus = 2.1 Difference = 2.1 – 1.5 = 0.6 Difference = 2.1 – 1.5 = 0.6 Mildly polar covalent bond will be formed Mildly polar covalent bond will be formed

12. Wrap-Up 1 Predict the bond type that will form between the following elements: Predict the bond type that will form between the following elements: Oxygen and boron Oxygen and boron 3.5-1.5=2.0: Ionic 3.5-1.5=2.0: Ionic Lithium and silicon Lithium and silicon 1.8-1.0=0.8: mildly covalent 1.8-1.0=0.8: mildly covalent Platinum and gold Platinum and gold Two metals: metallic Two metals: metallic Fluorine and carbon Fluorine and carbon 4.0-2.5=1.5: very polar covalent 4.0-2.5=1.5: very polar covalent Hydrogen and boron Hydrogen and boron 2.1-2.0=0.1: non-polar covalent 2.1-2.0=0.1: non-polar covalent

13. Properties of Compounds Most properties are determined by the kind of bond holding the atoms together Most properties are determined by the kind of bond holding the atoms together We can generalize properties using the type of bond We can generalize properties using the type of bond

14. Properties of Ionic Bonds Very strong bond, which leads to: Very strong bond, which leads to: Crystalline solid at room temperature Crystalline solid at room temperature Brittle rather than malleable Brittle rather than malleable High boiling point High boiling point The ions are locked in place when a solid, so the ionic compounds don’t conduct electricity or heat The ions are locked in place when a solid, so the ionic compounds don’t conduct electricity or heat The ions separate when dissolved in water, so solutions of ionic compounds are good conductors The ions separate when dissolved in water, so solutions of ionic compounds are good conductors

15. Properties of Covalent Bonds Weak forces holding the molecules together (intermolecular forces), which leads to Weak forces holding the molecules together (intermolecular forces), which leads to Soft solids, liquids or gases at room temperature Soft solids, liquids or gases at room temperature Low boiling points Low boiling points Non-conductive (no ions and the electrons are locked into place) Non-conductive (no ions and the electrons are locked into place)

16. Properties of Metallic Bonds Sea of electrons leads to Sea of electrons leads to Good conductivity of electricity Good conductivity of electricity Good conductivity of heat Good conductivity of heat Malleable and ductile Malleable and ductile Shininess Shininess

17. Wrap-Up 2 A new compound has been discovered that is a brittle solid at room temperature. It is further found to allow a current to pass through a sample when it is dissolved into water. What are the most likely kind of bonds in this compound? A new compound has been discovered that is a brittle solid at room temperature. It is further found to allow a current to pass through a sample when it is dissolved into water. What are the most likely kind of bonds in this compound? Ionic bond Ionic bond

18. Intermolecular Forces Hydrogen bonds – attraction between hydrogen atoms and the negative side of very polar bonds (form in water) Hydrogen bonds – attraction between hydrogen atoms and the negative side of very polar bonds (form in water) Dipole-dipole forces – attractive forces between the partial charges on polar molecules Dipole-dipole forces – attractive forces between the partial charges on polar molecules London dispersion forces (aka van der Waals forces) – forces created by the motion of electrons making temporary polar molecules London dispersion forces (aka van der Waals forces) – forces created by the motion of electrons making temporary polar molecules

19. Ionic bonding Copy This metal atom transfers electrons to nonmetal atom They do to get stable octets of 8 valence electrons on outside The metal loses electrons to form positive ion The nonmetal gains these electrons and becomes a negative ion The newly formed positive and negative ions attract each other to form the ionic bond Na Cl Na Cl Na Cl + _ NaCl

20. Covalent bonding Non-metal atoms share electrons with non-metal atoms Non-metals don’t lose electrons easily – they are gainers They share electrons to form balanced valence energy levels Metallic bonding Metal atoms form a “sea of moving electrons” Metals give up electrons easily Electrons move from atom to atom Moving electrons form a common electron cloud F F F F Na