Chemical Bonds PDF

Bonds  Happy Atoms Why do atoms bond? Some atoms have too many electrons and like to give them up. Some atoms are really close to having a full shell and get electrons from other atoms. Valence electrons The electrons in the highest occupied energy level of an atom. Number of elect...

Bonds  Happy Atoms Why do atoms bond? Some atoms have too many electrons and like to give them up. Some atoms are really close to having a full shell and get electrons from other atoms. Valence electrons The electrons in the highest occupied energy level of an atom. Number of electrons that an element can lose, gain, or share in order to acquire the octet rule. Octet Rule The octet rule is the tendency for atoms to share or transfer electrons to obtain a stable configuration of 8 valence electrons. Lewis Dot Structures  Electron-Dot Symbols An electron-dot symbol indicates valence electrons as dots around the symbol of the element. Mg has 2 valence electrons and can be written in different Mgways Mg Mg Mg Mg Lewis dot structures The atom is represented with its symbol and the valence electrons with dots around it. 1. Write Electronic configuration. 2. Identify valence electrons. 3. Draw valence electrons around the element’s symbol as dots or crosses. In each of the sides (top, bottom, left, and right) there will be a maximum of 2 electrons. Dots or electrons are written singly first in each side, then they are paired Lewis structures Electronic configuration: 5 B=1s 2 2s 2 2p1 Last level Valence electrons * Occupy the B* most sides possible, before pairing electrons * Lewis structures Electronic configuration: 8 O=1s 2 2s2 2p4 O Bromine Electronic configuration Number of electrons Valence = 7 35 Br =1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p 5 Highest level Br  Valence Lewis e - that can Elemen Electron configuration t e- diagram be lost or gained 16 S 20 Ca 27 Co 35 Br Chemical Bonds Introduction Chemical Bonds The attractive forces that hold atoms together in molecules. Ionic Bonds Covalent Bonds Metallic Bonds Ionic Bonds Transfer of electrons (form ions) Metal with non-metal Difference in electronegativity is greater than 1.7 Solution conducts electricity  When ionic bonds are formed, metals lose valence electrons and Non-metals gain electrons to achieve having 8 valence electrons.  Anion Formation Non-metals gain electrons to have the noble gas configuration and form anions: This process is called reduction. :Cl. + 1e- :Cl:- chloride :O: + 2e- :O:2- oxide :N. + 3e- :N:3- nitride  Cation formation Main group metals lose all their valence electrons to form cations: This loss of electrons is called oxidation. Na. Na+ + e- Mg: Mg2+ + 2 e- :Al. Al 3+ + 3 e-  Ionic Compounds in Solution When ionic compounds are dissolved in water, they dissociate to form aqueous ions: NaCl(s) H2O Na+(aq) + Cl- (aq) The resulting solution conducts electricity and is called an electrolyte. Metallic Bonds Metal with metal Joined by electrons in movement (electron sea) Good conductors of heat and electricity Covalent Bonds Sharing electrons Non-metal with non-metal Do not conduct electricity Nonpolar bonds: Between equal atoms (electronegativity difference 0 to 0.4) Polar bonds: Between different atoms (electronegativity difference 0.4 to 1.7) Polar and Nonpolar bonds H-H is non-polar because H & H have the same electronegativity. Cl-Cl is non-polar because Cl & Cl have the same electronegativity. H-Cl is polar because H & Cl have different Electronegativities. ( H = 2.1, Cl = 3.0 )  Ionic Character Increases as the Difference in Electronegativity Increases 0.4 1.7 Electronegativity difference Type of bond Type or Electron Difference in Electricity elements behavior electronegativity conduction Ionic Covalent (polar) Covalent (non-polar) Metallic  http://www.youtube.com/watch?v=QXT4OVM4vXI http://www.youtube.com/watch?v=yjge1WdCFPs Lewis Structures for molecules 1. Draw the valence electrons for each element (Use dots for an element and crosses for the other one) 2. Place the atoms relative to each other in the most logical order F O F 3. Distribute the bonds in order to achieve the octet rule for all elements. Lewis Structures for molecules For ionic compounds the electron is written in the element where it has been transferred Na O Na For covalent compounds, for each pair of electrons shared, a line is written F F F─F