212.1 Ionic, covalent and polar covalent bonds. A bond is a force that holds atoms together.Ionic Bondinga. When a metal reacts with a nonmetal, electrons are transferred from a metal to a nonmetal and an ionic compound is made.
3Ionic Bondingb. In ionic bonding, electrostatic attraction holds atoms together.
4Covalent Bondinga. Atoms make covalent bonds by sharing electrons.b. Electrons are attracted to the nucleus of both atoms in the bond.c. Nonmetals make covalent bonds.Let’s share!HH
5ElectronegativityElectronegativity is a measure of how strongly an atom attracts electrons. Look at the electronegativity chart on p403.Fluorine has an electronegativity value of 4.0.Hydrogen has an electronegativity value of 2.1.Difference in electronegativity =4.0 – 2.1 = ________
6Bond TypesDetermined by difference in electronegativity values—absolute value of DENPauling Electronegativity Values
7Electronegativityd. At left is a picture of hydrofluoric acid (HF). At right is a picture of “The Blob.”e. F has a higher electronegativity than H, so electrons are closer to F.
8In a covalent bond, atoms have a difference of electronegativity of Electrons are shared equally.In a polar covalent bond, atoms have a difference in electronegativity of Electrons are not shared equally.
9Electronegativity Exampe: Si—C Electronegativity of Si is ________. Electronegativity of C is _______.Difference in electronegativity is ____________.Si – C bond is ( covalent /polar covalent ) [circle one].Which attracts more electrons? ( Si / C )188.8.131.52
10Covalent Polar covalent Ionic In the picture below, Label each molecule or compound as ionic bonding, covalent bonding or polar covalent bonding.For polar and ionic bonds, label the more electronegative atom.CovalentPolar covalentIonic
11Identify each of the following bonds as ionic, covalent or polar covalent.BondIs there a metal and nonmetal?Electronegativity differenceBond TypeH – HNo2.1 – 2.1 = 0CovalentS – H2.5 – 2.1 = 0.4Polar covalentNa – IYes ionicionicRb – NB – PH – P
12DipolesIn a polar molecule, one side has a partial positive charge, and the other has a partial negative charge.A dipole moment is represented with an arrow pointing to the negative side and the Greek letter “delta” δ to show the partial positive and negative charges:
13DipolesWrite the partial charges and draw the dipole moment on Cl –I
1412.2 Ionic Bonding Ions Metals ( lose / gain ) electrons. Nonmetals ( lose / gain ) electrons.Group 1 elements form ions with a charge of ____.Group 2 elements form ions with a charge of ____.Group 6 elements form ions with a charge of ____.Group 7elements form ions with a charge of ____.
15Ions That’s interesting…but WHY??? Atoms gain or lose electrons to get the electron configuration of a noble gas.Noble gases have completely filled energy levels, so they are very stable.He has a completely filled 2s sublevel.Other noble gases have filled s and p sublevels.
16Ions Example: Li The electron configuration of Li is ______ Li loses one 2s electron and becomes Li+.The electron configuration of Li+ is _____Li + has the same electron configuration as He.
17Ions The electron configuration of F- The electron configuration of F isF gains one 2p electron and becomes F-The electron configuration of F- isF- has the same electron configuration as ______
18Ions What would happen if Li reacted with F? Li gives an electron to FLi + F Li+ + F-And they form _______ (write the formula of the compound)Ionic bonding and structuresLiF is packed together in a group in order to maximize attractions of the cations and anions.It makes a hard, tight crystal.
19The size of ions Which is larger, Na or Na+? Why? Na. Na loses a 3s electron, and then only has electrons in the n=2 level. n=2 orbitals are smaller than n=3 orbitals.NaNa+F-F
20The size of ions Which is larger, F or F-? Why? F- because it gains electrons.Which is larger F- or Na+? Why?F-. They both have the electron configuration of Ne, but Na+ has more protons (a stronger + charge), which pulls electrons closer.Which is larger, Ca or Ca2+? Why?
2212.3 Lewis StructuresThe octet rule: Sharing of electrons usually occurs so that atoms acquire the electron configurations of noble gases (1s2 or ns2np6)
23Lewis dot structures The element symbol represents the core electrons. Dots to show thevalence electrons.
24Lewis dot structures 1. First, write the symbol for the element. 2. Imagine the molecule has four sides (but don’t draw the “x”)3. Draw one dot at a time in each empty section.4. You should only have pairs of e- if there are no empty sections.Cl
25Lewis dot structures The “paired” electrons cannot usually make bonds. The three “unpaired” electrons can make bonds.
26ArsenicDot Diagram?In order to get the configuration of a noble gas, how many bonds will arsenic form?Dot Diagram for Hydrogen?In order to get the configuration of a noble gas, how many bonds will H form?3H1
27Arsenic Trihydride, AsH3 Lewis dot structureStructural formulaAsHHHAsHHHAs
28Drawing Lewis Dot Structures Use the molecular formula to find the total number of valence electrons= 8H H H As
29Drawing Lewis Dot Structures 2. Draw the symbols of each element. Draw the backbone/skeleton structureTerminal atoms go aroundthe central atoms.Least Electronegative is usually centralHydrogen is always terminal.Carbon is usually centralOxygen and Halogens are usually terminal
30Drawing Lewis Dot Structures 3. Draw the valence electrons4. Make single bonds with pairs
31Drawing Lewis Dot Structures 5. Each pair represents a bond.6. Count electrons again and make sure you get the same number (8).Single bond
32Structural FormulaThe structural formula is drawn with a “–“ line to represent the bond.Double and triple bondsDouble bonds can be formed by sharing two pairs of electronsTriple bonds involve sharing three pairs of electrons.ON
33Try the Dot Diagrams for each of the following: O2 H2O BCl3 SiI4SiIBClOHOEach pair of shared electrons can be represented by a line.SiIBClOHO
34Structural formulas for polyatomic ions Example: NO3-The negative charge means there is one more electronHow many total electrons are there?5 + 3(6) + 1 = 24 electrons.NO3-Draw:
35Resonance Resonance Example: ozone Ozone’s structure can be drawn like this:The actual bonding in ozone is not like either of these structures. The actual structure lies somewhere in between these two.These drawings are resonance structures of ozoneO