2 Types of Chemical Bonds 11.1 Bond – a force that holds groups of atoms of two or more atoms together and makes them function as a unitBond Energy – the amount of energy required to break the bond
3 Types of Bonds: 4 TYPES Cations packed in “a sea of electrons”Metals MetallicArtists rendering of a metallic bondCations packed in “a sea of electrons”MetalsMetals consist of closely packed cations floating in a “sea of electrons”.All of the atoms are able to share the electrons.The electrons are not bound to individual atoms.
4 Type 1: Metallic Properties of Metals Good conductorsDuctileMalleableElectrons act as a lubricant, allowing cations to move past each other
5 Metals have a Crystalline Structure Example: Body Centered Cubic (Chromium)Packed spheres of the same size and shape:Body Centered CubicFace Centered CubicHexagonal Close Packed
7 Last exampleHexagonal Close-Packed (zinc)picture
8 Type 2: IONIC IONIC picture Bond between closely packed, oppositely charged ionsBond between a metal and a nonmetalhard 22oChigh mp temperaturesnonconductors of electricity in solid phasegood conductors in liquid phase or dissolved in water (aq)
9 Covalent Bonding (2 types) Instead of gaining or losing electrons atoms can get stable by sharing electronsThis is always between two non-metals.Two fluorine atoms, for example, can form a stable F2 molecule in which each atom has 8 valence electrons by sharing a pair of electrons.In covalent bonds they can sharemore than two electrons
10 Type 3&4: COVALENT Electrons are shared pictureElectrons are sharedHave low melting, boiling pointsDo not conduct electricity when melted or dissolved in waterrelatively soft solids as compared to ionic compounds at room temp
11 Covalent bond –subtype #1 Non-polar CovalentpictureWhen two of the same elements bond they are called diatomic molecules, some examples of this are Hydrogen H2, Oxygen O2 and Nitrogen N2.The atoms in these bonds would have the same electronegativities. This means that both atoms attract the shared electrons to that same extent.
13 Dipole MomentA molecule that has a center of positive charge and a center of negative chargeDipole often represented by an arrowPoints towards negative charge center and its tail indicates the positive charge center
16 Lewis Dot Structures Show valence electrons Use group number to figure it out
17 The Octet RuleThe octet rule says that atoms tend to gain, lose or share electrons so they have eight electrons in their outer shell.There are some exceptions to the octet rule (imagine that)BF3BCl3PF5SF6
18 Follow the interactive website! Ionic Bonding: (this should be review)Covalent Bonding:
19 Drawing Lewis Structures Arrange the element symbols.Central atoms are generally those with the highest bonding capacity.Carbon atoms are always central atomsHydrogen atoms are always peripheral atomsAdd up the number of valence electrons from all atoms.For polyatomic ions, add one electron for each negative charge and subtract one for each positive charge.Draw a skeleton structure with atoms attached by single bonds.Complete the octets of peripheral atoms.Place extra electrons on the central atom.If the central atom doesn’t have an octet, try forming multiple bonds by moving lone pairs.
20 Simple Rules1. Figure out number of electrons by counting the TOTAL valence electrons in whole compound2. Place the central element in the middle and surround it with the other elements3. Place single bonds between elements4. Place lone pairs around each element until there are a total of eight (Hydrogen only wants 2)5. Count total electrons surrounding the compound (don’t forget the bonds count as 2 electrons)If electrons from #1 and #5 don’t match…. Erase electrons and put in double bond and recount
21 Single, Double and Triple Bonds With Covalent bonds the elements can share two or more electronsA Single Bond is when 2 electrons are shared they are represented by a single line in bond diagramsA Double bond is when 4 electrons are shared they are represented by two lines in bond diagramsA Triple bond is when 6 electrons are shared they are represented by three lines in bond diagrams
25 Electronegativity Values The electronegativity values can be found in the periodic tableThe higher the value the higher the electronegativityThe Pauling scale is used to measure electronegativity. It is a relative scale running from 0.7 to 4.0 (hydrogen = 2.2).The units for electronegativity are Pauling units.
26 ElectronegativityThe ability of an atom to attract electrons when bondedNonmetals have high electronegativityMetals have low electronegativityElectronegativity increases across a period and decreases down a group. WHY???
27 Electronegativity Chart Why would the metals have low electronegativity numbers?Why don’t the noble gases have electronegativity numbers?
28 Nonpolar Covalent Bond When electrons are shared between 2 atoms, a covalent bond is formed.If the atoms are identical, e.g. Cl2, the electrons are shared equally (nonpolar)Cl = therefore the ∆EN = = 0∆EN = electronegativity Difference0 = nonpolar
29 Polar Covalent BondIf the electrons are shared between 2 different atoms, e.g. HBr, the sharing is unequalThe bonding electrons spend more time near the more electronegative atomH = 2.1 and Br = 2.8 THEREFORE = 0.70.7 = a polar covalent bondHBr
30 Bond Type by Electronegativity Value Remember the higher the atom’s electronegativity value, the closer the shared electrons tend to be to that atom when it forms a bondTherefore, the polarity of a bond depends on the difference between the electronegativity values of the atoms forming the bondThe greater the difference, the more polar the bond.Electronegativity DifferenceType of Bond Formed0.0 to 0.2nonpolar covalent0.21 to 1.7polar covalent≥ 2.0ionic
31 Electronegativity Differences Why is there a gap between 1.7 and 2.0????If the two atoms are nonmetals =polar covalent bondIf nonmetal & metal = ionic bond0 to 0.2Nonpolar covalent0.21 to 1.7Polar covalent≥ 2.0IonicElectronegativity Difference
32 Sample Problems Choose the bond that will be more polar H-P or H-C O – F or O – IN – O or S – ON – H or Si - H
33 Sample Problems Choose the bond that will be more polar H-P or H-C O – F or O – IN – O or S – ON – H or Si - H
34 Polar Molecules (overall polarity of the molecule) Note: Not all molecules with polar bonds are polar moleculesThe dipoles in symmetrical molecules cancels out The bond is polar but the molecule is nonpolar
35 How to determine polar molecules There are two important factors1. The polarity of the individual bonds in the molecule;2. The shape or geometry of the molecule.Steps to takeDetermine if a given individual bond is polar, Look at the difference between electronegativity of the atoms in the perioidc table. If the difference is:0.2 < non polar0.2 - greater = polar
36 b) Determine the shape of molecule. For now I will give them to you b) Determine the shape of molecule. For now I will give them to you. Later you will figure out the shape yourself.i) if all bonds are non-polar, then the whole molecule is non- polar regardless of its shape.ii) If there is symmetry in the molecule so that the polarity of the bonds cancels out, then the molecule is non-polar. (symmetry arround the central atom)iii) If there are polar bonds but there is no symmetry the overall molecule is polar.