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Chemical Bonding

Chemical Bonding. Ionic, Covalent, and Metallic bonding. What does it mean to “bond”? Think about the types of “bonds” that you might be familiar with, for example:. Atoms & Bonding. I am bonded to the Houston TEXAN Football players by a sense of camaraderie, together we are one team.

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Chemical Bonding

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  1. Chemical Bonding Ionic, Covalent, and Metallic bonding

  2. What does it mean to “bond”? Think about the types of “bonds” that you might be familiar with, for example: Atoms & Bonding I am bonded to the Houston TEXAN Football players by a sense of camaraderie, together we are one team. When you use glue to hold two things together they are bonded. How does this idea relate to “Atoms & Bonding”?

  3. n +p You should remember the parts of an atom. A Little Review The proton The neutron The electron -e Of these three particles, which is the only one that has the ability to move from one place to another? The -e

  4. Chemical Bonds When atoms chemically combine, they create a chemical bond. A chemical bond is an attractive force that holds atoms or ions together to form a molecule. When chemical bonding occurs, electrons from one atom may be transferred to another atom or they may be shared by atoms.

  5. Why does transfer or sharing of –e occur? In order for an atom to be “satisfied” in nature, it always tries to achieve having 8 –e in its outer energy level. This is called “stability” YOU MUST ALWAYS REMEMBER THE NUMBER 8 In order to achieve “stability” atoms will gain, lose, or share the electrons in their outer energy level only.

  6. The three types of bonds: The chemical bond that forms between metal and non metal atoms when the electrons are transferred between atoms, is called an ionic bond. The formation of ionic bonds is always exothermic! 1. Ionic Bonds

  7. Let’s look at how an ionic bond is formed between Sodium (Na) and Chlorine (Cl) when NaCl (salt) is formed. Cl has 17 +p in its nucleus and 17 –e (neutral atom) 17+p 18-e 1 - ion 11+p 10-e 1 +ion Na has 11 +p in its nucleus and 11 – e (neutral atom) +- Sodium ionchlorine ion Electromagnetic force holds the Na and Cl together as NaCl molecule NaCl Na 1s22s22p63s1 Cl 1s22s22p63s23p5

  8. Ionic Bonding:The Formation of Sodium Chloride The resulting ions come together due to electrostatic attraction (opposites attract): The net charge on the compound must equal zero Na+ Cl- Ion a charged atom. Remember, if an atom loses –e It becomes a + ion (cation), it it gains –e it becomes a – ion (anion).

  9. More Gains and Losses • The element magnesium, Mg, in Group 2 has two electrons in its outer energy level. • Can elements lose or gain more than one electron? • Magnesium can lose these two electrons and achieve a completed energy level.

  10. Properties of Ionic Compounds

  11. Representation of Components in an Ionic Solid • form solids at ordinary temperatures. • organize in a characteristic crystal lattice of alternating positive and negative ions. • Lattice: A 3-dimensional system of points designating the centers of components (atoms, ions, or molecules) that make up the substance.

  12. 2. Covalent Bond In a covalent bond, electrons are SHARED between two atoms. • A molecule is the basic unit of a molecular compound.

  13. Diatomic Elements How does this work? H H O O H H 17+p 17+p Let’s look at the simplest covalent bond first. H2 Since hydrogen has only one energy level and since that level is satisfied with only 2 –e, if each H atom shares its 1 –e with the other then both are satisfied. Shared electrons Shared electrons Hydrogen forms only covalent bonds Cl has 7 valence electrons. It needs 8 to be stable, so each atom shares 1 –e with the other in a covalent bond.. Shared electrons ( ) Diatomic Chlorine

  14. 1. Have much lower boiling and melting points than ionic compounds. 2. Can exist as solids, liquids, or gases. 3. Are usually softer substances than ionic compounds. 4. Are usually poor conductors of heat and electricity. Properties of Covalent Bond

  15. Occurs when two atoms equally share a pair of electrons. • This occurs when two identical atoms form a bond with each other. • The diatomic elements (H2, N2, O2, F2, Cl2, Br2, and I2) are examples of molecules containing a nonpolar covalent bond. Nonpolar Covalent Bonds

  16. Occurs when two atoms do not equally share a pair of electrons. • This occurs when the two atoms forming the bond have significantly different electronegativities or are of significantly different sizes. • An example of a polar covalent bond is HCl. • As a result of the unequal sharing of an electron pair, the molecule has one end which is partially negative (δ-) and one end which is partially positive (δ+). • This is called a dipole (two poles) molecule. • The negative end of one polar molecule will be attracted to the positive end of another polar molecule. Polar Covalent Bonds

  17. Higher boiling point. • Lower vapor pressure. • Molecular alignment within a magnetic field. • Ability to dissolve many substances which nonpolar compounds cannot dissolve. Impact of Polar Bonds

  18. n n n n n n n n n n n n n n n n n How are the atoms held together in a piece of metal such as a copper wire? The Bond between Metal and Metal is called metallic Bond. 3. The Metallic Bond Metal atoms have a tendency to lose their valence electrons n -e -e -e -e -e -e -e -e -e - e -e -e -e -e -e -e -e -e -e -e -e -e -e -e -e -e -e -e -e -e -e -e -e -e -e -e -e -e -e -e -e -e -e -e -e -e -e -e -e - e -e -e -e -e -e -e When metals form a “metallic crystal” they simply dump their valence –e into a “sea of electrons”to be shared by all the nuclei of all the atoms in the metal

  19. Properties of Metals • Metals are good conductors of heat and electricity • Metals are malleable • Metals are ductile • Metals have high tensile strength • Metals have luster

  20. An alloy is a mixture (not a compound) of two or more elements, at least one of which is a metal. • The properties of alloys are different from the pure metals they are made from. Alloys

  21. Metal Alloys • Substitutional Alloy: some metal atoms replaced by others of similar size.

  22. Metal Alloys • Interstitial Alloy:Interstices (holes) in closest packed metal structure are occupied bysmallatoms.

  23. METALLIC BONDS The type of bond formed between atoms of different elements determine many of the properties of the compound formed. Bonds and Properties IONIC BONDSare the strongest bonds because of electromagnetic force. This bond accounts for: high melting point hardness brittleness shape (crystals) COVALENT BONDS are the weakest bonds. low melting points dull finish ductility malleability conductivity luster

  24. All of this is important By type of element: Metal + Nonmetal Ionic Bond Nonmetal + Nonmetal Covalent Bond Metal + Metal Metallic Bond Predicting Types of Bonds By location on PT Left + Right Ionic Bond Right + Right Covalent Bond Left + Left Metallic Bond By lose/gain –e Lose + Gain Ionic Bond Share + Share Covalent Bond Lose + Lose Metallic Bond

  25. Animation for Chemical bonding: http://www.teachersdomain.org/resource/lsps07.sci.phys.matter.chembonds/

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