Chemical Bonds stable octet

Transcription

1 Chemical Bonds Elements form bonds to be in a lower energy state 1. Ionic Bonds transfer of electrons, between metal and nonmetal 2. Covalent Bonds sharing of electrons, between two nonmetals 3. Metallic Bonds- neighboring atoms in solid metals form bonds Octet rule: atoms tend to gain, lose, or share electrons until they are surrounded by eight valence electrons to achieve a stable octet (noble gas configuration)

2 Electron Dot Symbols Valence electrons: reside in the highest occupied energy level, reside in the outer s & p orbitals and are the electrons involved in chemical bonding. Electron-dot symbols are convenient way of showing the s & p electrons & tracking them in bond formation -They consist of the chemical symbol for the element plus a dot for each valence electron Consider sulfur whose electron configuration is [Ne]3s 2 3p 4, thus there are six valence electrons: S

3 Ch. 7 Ionic and Metallic Bonding I II III IV

4 B. Ionic Bonds Ionic Bonds atoms transfer electrons from a cation (positive ion) to an anion (negative ion) to achieve an octet. Ionic compounds are stable due to the electrostatic forces between unlike charges organizing the ions of ionic substances into a rigid, organized three-dimensional arrangement: The ions are drawn together Energy is released Ions form solid lattice structure

5 Lattice Energy Lattice energy: The energy required to completely separate a given quantity of a solid ionic compound into its gaseous ions. Thus, in reverse, the high energy is given off as heat and light when Na + and Cl - is incorporated into the NaCl salt lattice.

6 Steps in Ionic Bonding Process (1) Ionization Energy (IE) Step 1: The minimum energy required to remove an electron from the ground state of an isolated gaseous atom or ion. First ionization energy: Na(g) + IE 1 Na + (g) + e - ; + H (positive/ endothermic) Second Ionization Energy: Be(g) + IE 1 + IE 2 Be 2+ (g) + 2 e - ; + H (positive) The greater the IE, the more difficult it is to remove an e -.

7 Steps in Ionic Bonding Process (2) Electron Affinity (EA): Most atoms can attract e - to form negatively charged ions The energy change that occurs when an e - is added to a gaseous atom. For most atoms, the energy released when an e - is added. Cl(g) + e - Cl - (g) + electron affinity ; - H (negative/exothermic) The greater the attraction between a given atom and an added e -, the more negative the atom s EA. Halogens s 2 p 5 have the most negative EA.

8 Steps in Ionic Bonding Process (3) Lattice Energy (LE) The release of energy that occurs when ions of opposite charge are attracted to each other and form a stable ionic compound. Na + + Cl - NaCl + lattice energy ; - H (negative/exothermic) Ionic compounds have very large LE which makes up for endothermic ionization energy.

9 B. Properties of Ionic Compounds Most ionic compounds are crystalline solids at room temperature Arranged in repeating threedimensional patterns Ionic compounds generally have high melting points Large attractive forces result in very stable structures

10 B. Properties of Ionic Compounds Ionic compounds can conduct an electric current when melted or dissolved in water When ionic compounds are dissolved in water the crystalline structure breaks down so ions are able to move freely which results in conductivity

11 The positive Na ions move to the cathode and the negative Cl ions move to the anode

12 Ch. 7 Ionic and Metallic Bonding III. Bonding in Metals (p ) I II III IV

13 A. Metallic Bonding Metallic bonds: Consist entirely of metal atoms. Bonding is due to valence electrons which are delocalized throughout the entire solid The metal is held together by the strong forces of attraction between the positive nuclei and the delocalized electrons.

14 B. Metals Metals are good conductors of heat and electricity because the valence electrons are able to flow freely Valence electrons of metals can be thought of as a sea of electrons, very mobile

15 C. Metallic Bond Metallic Bonding - Electron Sea

16 D. Metallic Properties Have luster, are ductile and malleable Luster = shine Ductile = ability to be drawn into wires Malleable = ability to be shaped, pounded, etc

17 D. Metallic Properties Properties can be explained by the mobility of electrons in metals When subjected to pressure, the cations easily slide past each other like a ball bearing immersed in oil.

18 B. Types of Bonds Bond Formation Smallest Unit Physical RT Melting Point Solubility in Water Electrical Conductivity Other Properties METALLIC e - are delocalized among metal atoms electron sea solid very high no yes (any form) malleable, ductile, lustrous