BONDING AND GEOMETRY.ppt

1、BONDING AND GEOMETRY,Unit 10 Chemistry Langley,*Corresponds to Chapter 7 and 8 (pages 186-247) in the Prentice Hall Chemistry textbook,PERIODIC TABLE REVIEW,Location of Metals and Nonmetals on the periodic table: Metals are to the left of the “staircase” Nonmetals are to the right of the “staircase”

2、 For bonding, the 7 metalloids will treated as metals All though hydrogen is to the left of the “staircase”, it is not, nor has it ever been a metal. IT IS A NONMETAL!,ATOMS AND IONS REVIEW,Atoms are neutral They have the same number of protons and electrons Number of positives = number of negatives

3、 Example: Na 11 protons, 11 electrons 11 11 = 0 Ions have a charge They have a different number of protons and electrons Example: Na+111 protons, 10 electrons 11 10 = +1 If an atom GAINS an electron becomes negatively charged ANION If an atom LOSES an electron becomes positively charged CATION,TYPES

4、 OF BONDS,Bonding occurs because every element is either trying to get to 0 electrons in the valence or 8 electrons in the valence (zero and 8 are both stable) Valence is the outer electron shellplace where bonding occurs Ionic Bonding between a metal and a nonmetal Metallic Bonding between two meta

5、ls Covalent Bonding between two nonmetals,IONIC BONDING,Very stable and strong Strongest possible bond Requires a large amount of energy to break an ionic bond Forms compounds known as “ionic compounds” All ionic compounds will dissolve in water and carry a current (electrolyte) Generally have high

6、melting and boiling points Compounds are generally hard and brittle,IONIC BONDING,Draw the dot diagram for Na AND ClNa has 1 valence electron, wants to give that 1 away and get to zero and be stable Cl has 7 valence electrons, wants to get 1 electron so it can get to eight and be stable Na give an e

7、lectron to Cl and Cl takes that electron from Na,METALLIC BONDING,Metal atoms are pieces of metal that consist of closely packed cations (positively ions) Cations are surrounded by mobile valence electrons that are free to drift from one part of the metal to another Metal atoms are arranged in very

8、compact and orderly (crystalline) patterns Metallic bonding is the electrostatic attraction between conduction electrons, and the metallic ions within the metals, because it involves the sharing of free electrons among a lattice of positively-charged metal ions Occurs between 2 or more metals Result

9、 of the attraction of free floating valence electrons for the positive ion These bonds hold metals together,METALLIC BONDING,Properties of metallic bonds Good conductors of electricity Electrons are free flowing Malleablehammered into sheets Ductiledrawn into wires Alloy-two metals are bonded togeth

10、er to get the benefits of each 14 karat gold,COVALENT BONDING,Covalent: Prefix “co” means share, together “valent” means valence Covalent bonds are when atoms SHARE VALENCE electrons A covalent compound is called a molecule Covalent bond ALWAYS occurs between 2 nonmetals,TYPES OF COVALENT BONDS,Sing

11、le Bond Covalent bond where one pair of electrons (2 electrons total) are shared between 2 atoms Atoms share electrons so that each has a full octet (8 valence) Electrons that are shared count as valence electrons for both atoms Examples HCl Cl2,COVALENT BONDING,Double Bonds Bond in which two pairs

12、of electrons (4 electrons total) are shared between 2 atoms Examples O2 C2F2 Triple Bonds Bond in which 3 pairs of electrons (6 total electrons) are shared between atoms Examples N2 AsP,COVALENT BONDING,Covalent Bonds with more than 2 atoms Examples CH4 OF2 Electron Pairs Electron pairs involved in

13、the actual bond are called BONDING PAIR or SHARED PAIR electrons Electrons not involved in the actual bond, those surrounding the rest of each element are called LONE PAIR electrons,POLAR BONDS AND MOLECULES,Covalent bonds are formed by sharing electrons between two atoms The bonding pair of electro

14、ns is shared between both elements, but each atom is tugging on the bonding pair When atoms in a molecule are the same (diatomic) the bonding pair is shared equallythis bond is called non polar covalent When atoms in a molecule are different, the bonding pair of electrons are not shared equallythis

15、is called a polar covalent bond,POLAR BONDS AND MOLECULES,Why is the bonding pair not shared equally? The answer lies within electronegativity One of the elements is more electronegative than the other and therefore has a greater desire for the shared pair The MORE electronegative element tends to p

16、ull the electrons closer and thus has a slightly negative charge The LESS electronegative element has a slightly positive charge since the shared pair is being pulled away,POLAR BONDS AND MOLECULES,Drawing/Indicating Polarity,POLAR BONDS AND MOLECULES,Polar Molecules Molecule in which one end of the

17、 molecule is slightly negative and the other end is slightly positive Just because a molecule contains a polar bond DOES NOT mean the entire molecule is polar The effect of polar bonds on the polarity of an entire molecule depends on the shape of the molecule and the orientation of the polar bonds,P

18、OLAR BONDS AND MOLECULES,Example: CO2 O = C = O Carbon and Oxygen lie along the same axis. Bond polarities are going to cancel out because they are in opposite directions Carbon dioxide is a nonpolar molecule even though there are two polar bonds present Would cancel out if the polarities moved towa

19、rds each other as well When polarities cancel out, the molecule is non-polar,POLAR BONDS AND MOLECULES,Example: H2OExample: CH3Br,FORCES IN A MOLECULE,Dipole-Dipole Forces Dipoles are created when equal but opposite charges are separated by a short distance Have to have a positive and a negative end

20、 so that one of the elements is pulling on the electron Only happens in polar molecules Dipole forces are extremely strong and lead to high melting and boiling points,FORCES IN A MOLECULE,Hydrogen Bonding Very strong type of dipole force Only occurs when hydrogen is covalenty bonded to a highly elec

21、tronegative atom Always involves hydrogen Example: HF, HCl,FORCES IN A MOLECULE,London Dispersion Forces Electrons are in constant motion around a nucleus At any given time there might be more electrons on one side of an atom than on the other For a split second, the side with more electrons is nega

22、tive, and the side with less electrons is positive,FORCES IN A MOLECULE,London Dispersion Forces Recall that Noble Gases have a full outer shell and you have been told they are unreactive BUT due to London Dispersion Forces, they COULD bond for an instant Example: Ar2London Forces are very weak The

23、smaller the mass of the atom, the smaller the London Force,BOND DETAILS,Terminology Bond strength-energy required to break a bond Bond axis-imaginary line joining two bonded atoms (example: C-C) Bond length-the distance between two bonded atoms at their minimum potential enery; the average distance

24、between two bonded atoms Bond energy-energy required to break a chemical bond and form neutral isolated atoms Chemical compound tend to form so that each atom, by gaining, losing, or sharing electrons, has an octet of electrons in its highest occupied energy level,BOND DETAILS,Comparison of Bond Len

25、gth/Strength for Covalent Bond Types: Longer bond = less bond strength Rating 1-3 (with 3 as the largest and 1 as the smallest),BOND DETAILS,Coordinate Covalent Bonds Very rare Tend to form harmful molecules Occurs when both of the bonding pair of electrons in a covalent bond come from only ONE of t

26、he atoms Example: CO,BOND DETAILS,Resonance Occurs when there are more than one possible structures for a molecule Refers to bonding in molecules or ions that cannot be correctly represented by a single Lewis structure Example: CO2 To indicate resonance, a double-headed arrow is placed between a mol

27、ecules resonance structures Even though all of the structures are different, the number of bonding pair of electrons and lone pair of electrons stay the same in each structure,VSEPR THEORY,Valence Shell Electron Pair Repulsion Theory Allows us to picture molecules in 3 dimensions Centers around the

28、fact that electrons have negative charges and repel one another So electron pairs within a structure try to arrange themselves to be as far away from other pairs as possible,VSEPR THEORY,Tetrahedral Central atom bonds to 4 atoms and has zero lone pairs CH4,VSEPR THEORY,Pyramidal The central atom bon

29、ds to 3 atoms and has 1 lone pair of electons NH3,VSEPR THEORY,Trigonal Planar The central atom bonds to 3 atoms and has zero lone pairs CO3-2,VSEPR THEORY,Bent Triatomic The central atom bonds to 2 atoms and has 2 lone pair of electrons H2O,VSEPR THEORY,Linear Triatomic The central atom bonds to 2 atoms and has zero lone pair of electrons CO2,VSEPR THEORY,Linear One bond between 2 atoms HClN2,