BOND FORMATION exothermic processEN ReactantsER EnergyG releasedY Products
BREAKING BONDS Endothermic reaction energy must be put into the bond in order to break it E N Products E R Energy G Absorbed Y Reactants
BOND STRENGTH Strong, STABLE bonds require lots of energy to be formed or broken weak bonds require little E
TWO MAJOR TYPES OF BONDINGIonic Bonding forms ionic compounds transfer of e-Covalent Bonding forms molecules sharing e-
ONE MINOR TYPE OF BONDING Metallic bonding Occurs between like atoms of a metal in the free state Valence e- are mobile (move freely among all metal atoms) Positive ions in a sea of electrons Metallic characteristics High mp temps, ductile, malleable, shiny Hard substances Good conductors of heat and electricity as (s) and (l)
It’s the mobileelectrons that enable me tals to conduct - electricity!!!!!!
IONIC BONDING electrons are transferred between valence shells of atoms ionic compounds are made of ions NOT MOLECULES • ionic compounds are called Salts or Crystals
IONIC BONDING Always formed between metals and non-metals + - [METALS ] [NON-METALS ] Lost e- Gained e-
IONIC BONDING Electronegativity difference > 2.0 Look up e-neg of the atoms in the bond and subtract NaCl CaCl2 Compounds with polyatomic ions NaNO3
PROPERTIES OF IONIC COMPOUNDS SALTS hard solid @ 22 C o Crystals high mp temperatures nonconductors of electricity in solid phase good conductors in liquid phase or dissolved in water (aq)
COVALENT BONDINGPairs of e- are shared molecules between non-metal atomselectronegativity difference < 2.0forms polyatomic ions
MOLECULARSUBSTANCES Covalent bondingLow m.p. temp and b.p. tempsrelatively soft solids as compared to ionic compoundsnonconductors of electricity in any phase
COVALENT, IONIC, METALLICBONDING?NO 2 NH + • COsodium 4 Aluminu hydride • CoHg m phosphateH S 2 KHsulfate Also study KCl your HF characteristics!
DRAWING IONIC COMPOUNDSUSING LEWIS DOT STRUCTURES• Symbol represents the KERNEL of the atom (nucleus and inner e-)• dots represent valence e-
NACL This is the finished Lewis Dot Structure - [Na] [ Cl ] How did we get here? +
Step 1 after checking that it is IONIC Determine which atom will be the +ion Determine which atom will be the - ion Step 2 Write the symbol for the + ion first. NO DOTS Draw the e- dot diagram for the – ion COMPLETE outer shell Step 3 Enclose both in brackets and show each charge
DRAW THE LEWIS DIAGRAMS LiF MgO CaCl 2 K S 2
DRAWING MOLECULES USINGLEWIS DOT STRUCTURES Symbol represents the KERNEL of the atom (nucleus and inner e-) dots represent valence e-
Always remember atoms are trying to complete their outer shell!The number of electrons the atoms needs is the total number of bonds they can make.Ex. … H? O? F? N? Cl? C? one two one three one four
METHANE CH4 This is the finished Lewis dot structure How did we get here?
Step 1 count total valence e- involved Step 2 connect the central atom (usually the first in the formula) to the others with single bonds Step 3 complete valence shells of outer atoms Step 4 add any extra e- to central atomIF the central atom has 8 valence e-
SOMETIMES . . . You only have two atoms, so there is no central atom, but follow the same rules. Check & Share to make sure all the atoms are “happy”. Cl2 Br2 H2 O2 N2 HCl
DOUBLE bond atoms that share two e- pairs (4 e-) O O TRIPLE bond atoms that share three e- pairs (6 e-) N N
DRAW LEWIS DOT STRUCTURESYou may represent valence electrons from different atoms with the following symbols x, , CO2 NH3
DIAGRAM FORPOLYATOMIC IONS Count all valence e- needed for covalent bonding Add or subtract other electrons based on the chargeREMEMBER! A positive charge means it LOST electrons!!!!!
TRIGONAL PYRAMID Ball and stick Space filling model model
TETRAHEDRAL Ball and stick Space filling model model
INTERMOLECULAR ATTRACTIONS Attractions between molecules van der Waals forces Weak attractive forces between non-polar molecules Hydrogen “bonding” Strong attraction between special
VAN DER WAALS Non-polar molecules can exist in liquid and solid phases because van der Waals forces keep the molecules attracted to each other Exist between CO2, CH4, CCl4, CF4, diatomics and monoatomics
VAN DER WAALS PERIODICITY increase with molecular mass. Greater van der Waals force? F2 Cl2 Br2 I2 increase with closer distance between molecules Decreases when particles are farther away
HYDROGEN “BONDING” Strong polar attraction Like magnets Occurs ONLY between H of one molecule and N, O, F of another H “bond”
WHY DOES H “BONDING” OCCUR? Nitrogen, Oxygen and Fluorine small atoms with strong nuclear charges powerful atoms very high electronegativities
INTERMOLECULAR FORCESDICTATE CHEMICAL PROPERTIES Strong intermolecular forces cause high b.p., m.p. and slow evaporation (low vapor pressure) of a substance.
WHICH SUBSTANCE HAS THEHIGHEST BOILING POINT? HF NH Fluorine has the highest e-neg, 3 H 2O SO HF will experience the WHY? strongest H bonding and ∴ needs the most energy to weaken the i.m.f. and boil
THE UNUSUAL PROPERTIES OF WATER Unusually high boiling point Compared to other compounds in Group 16
H2O(S) IS LESS DENSE THAN H2O(L) The hydrogen bonding in water(l) molecules is random. The molecules are closely packed. Thehydrogen bonding in water(s) molecules has a specific open lattice pattern. The molecules are farther apart.