6electron shells Atomic number = number of Electrons Electrons vary in the amount of energy they possess, and they occur at certain energy levels or electron shells.Electron shells determine how an atom behaves when it encounters other atoms
7Electrons are placed in shells according to rules: The 1st shell can hold up to two electrons, and each shell thereafter can hold up to 8 electrons.
8Octet Rule = atoms tend to gain, lose or share electrons so as to have 8 electrons C would like toN would like toO would like toGain 4 electronsGain 3 electronsGain 2 electrons
9Why are electrons important? Elements have different electron configurationsdifferent electron configurations mean different levels of bonding
12Electron Dot Structures Symbols of atoms with dots to represent the valence-shell electronsH He: Li Be B C N O : F :Ne : Na Mg Al Si P S :Cl :Ar :
13Electron Dot Structure or Lewis Dot Diagram A notation showing the valence electrons surrounding the atomic symbol.
14Chemical bonds: an attempt to fill electron shells Ionic bonds –Covalent bonds –Metallic bonds
15Learning Check A. X would be the electron dot formula for A. X would be the electron dot formula for1) Na 2) K 3) Al B X would be the electron dot formula1) B 2) N 3) P
16IONIC BOND bond formed between two ions by the transfer of electrons
17Formation of Ions from Metals Ionic compounds result when metals react with nonmetalsMetals lose electrons to match the number of valence electrons of their nearest noble gasPositive ions form when the number of electrons are less than the number of protonsGroup 1 metals ion 1+Group 2 metals ion 2+Group 13 metals ion 3+
18Check your NeighborWhen Na, (Z= 11) loses its valence electron, what element does its configuration look like ?NeonPotassiumBerylliumSodiumC. discover the property called inertia.
19A Stable OctetWhen the valence shell is full, the atom is stable, less likely to react.Example: Noble (Inert Gases)Kr
20Formation of Sodium Ion Sodium atom Sodium ionNa – e Na +( = Ne)11 p p+11 e e-
21Formation of Magnesium Ion Magnesium atom Magnesium ionMg – 2e Mg2+(=Ne)12 p p+12 e e-
22Equations for the Formation of Cations H H e-Li Li e-Mg: Mg e-
23Equations for the Formation of Anions : F : + e- : F - :
24Some Typical Ions with Positive Charges (Cations) Group 1 Group 2 Group 13H+ Mg2+ Al3+Li+ Ca2+Na+ Sr2+K+ Ba2+
25Learning Check A. Number of valence electrons in aluminum 1) 1 e ) 2 e- 3) 3 e-B. Change in electrons for octet1) lose 3e ) gain 3 e ) gain 5 e-C. Ionic charge of aluminum1) ) ) 3+
26Solution A. Number of valence electrons in aluminum 3) 3 e- B. Change in electrons for octet1) lose 3e-C. Ionic charge of aluminum3) 3+
27Learning Check Give the ionic charge for each of the following: A. 12 p+ and 10 e-1) 0 2) 2+ 3) 2-B. 50p+ and 46 e-1) 2+ 2) 4+ 3) 4-C. 15 p+ and 18e-2) ) 3- 3) 5-
28Ionic Compounds Are made up of: a metal and a nonmetal ion. polyatomic ions.
29Ions from Nonmetal Ions In ionic compounds, nonmetals in 15, 16, and 17 gain electrons from metalsNonmetal add electrons to achieve the octet arrangementNonmetal ionic charge:3-, 2-, or 1-
30Fluoride Ion 1 - : F + e : F : 2-7 2-8 (= Ne) unpaired electron octet : F e : F : (= Ne)9 p p+9 e e-ionic charge
31Ionic BondBetween atoms of metals and nonmetals with very different electronegativityBond formed by transfer of electronsProduce charged ions all states. Conductors and have high melting point.Examples; NaCl, CaCl2, K2O
38COVALENT BOND bond formed by the sharing of electrons
39Covalent BondBetween nonmetallic elements of similar electronegativity.Formed by sharing electron pairsStable non-ionizing particles, they are not conductors at any stateExamples; O2, CO2, C2H6, H2O, SiC
52Metals Form Alloys Metals do not combine with metals. They form Alloys which is a solution of a metal in a metal.Examples are steel, brass, bronze and pewter.
53Chemical FormulaA representation of the kinds and number of atoms in a substance.
54Formula UnitA chemical formula that shows the lowest whole number ratio of the atoms (ions) in an ionic compound.Example: KCl, Mg Cl2
55The formula unit is used because ionic compounds have a lattice arrangement of ions. Ex: NaCl Which ball represents the Na?
56NUMBER OF BONDS BETWEEN ATOMS Single bonds – one pair of electrons; longest bond length; weakest bondCl – Be – ClDouble bonds – two pairs of electronsO=C=OTriple bonds – three pairs of electrons; shortest bond length; strongest bondN N
57INTERMOLECULAR FORCES London Dispersion Forces (Van der Waals Forces)1. weakest of all intermolecular forces2. the attractive or repulsive force between molecules (or between parts of the same molecule)Dipole-Dipole Interactions1. between polar moleculesHydrogen Bonds1. strongest of all intermolecular forces2. hydrogen bonded to a very electronegative atom (O,N,F)H FN N
58Electronegativity & Bond Type ExampleNonpolar covalentH-H (0.0)Polar covalentH-Cl (0.9)>1.7IonicNa-Cl (2.1)
59VSEPR Valence Shell Electron-Pair Repulsion A. predicts the shape of individual molecules based upon the extent of electron-pair electrostatic repulsionB. Double bonds count as one pair of electrons
60Linear 180° 3 2 BeCl2 CO2 Bent 104.5 4 H2O Trigonal Pyrimidal 107° 1 Bond Angle# atoms# e- pairs# unshared e- pairsExampleLinear180°32BeCl2CO2Bent104.54H2OTrigonal Pyrimidal107°1NH3Tetrahedral109.55CH4Trigonal Planar120°BF3