Chemical Bonds

HW review book Page 99 question 1 to 5

CHEMICAL BONDS Chemical bonds are forces that hold atoms together in a compound. Potential energy is stored in chemical bonds. A chemical bond forms because atoms become more stable when they are bonded.

ENERGY AND CHEMICAL BONDS STABILITY = LOW ENERGY When a bond forms ENERGY IS RELEASED. Bond forming is an EXOTHERMIC process. The more energy released during bond formation the more stable the bond.

Electron Dot Structures LEWIS DOT DIAGRAMS Symbols of atoms with dots to represent the valence-shell electrons 1 2 13 14 15 16 17 18 H He:            Li Be  B   C   N   O  : F  :Ne :                    Na Mg  Al  Si  P S :Cl  :Ar :        

Learning Check A. X would be the electron dot formula for  A. X would be the electron dot formula for 1) Na 2) K 3) Al   B.  X  would be the electron dot formula 1) B 2) N 3) P

IONIC BOND bond formed between two ions by the transfer of electrons

TRANSFER OF ELECTRONS FROM THE METAL TO THE NON METAL Ionic bonds Between metals and non metals TRANSFER OF ELECTRONS FROM THE METAL TO THE NON METAL The difference in electronegativity is greater than 1.7 D en >1.7

Ionic Bonds: One Big Greedy Thief Dog!

Formation of Sodium Ion Sodium atom Sodium ion Na  – e  Na + 2-8-1 2-8 ( = Ne) 11 p+ 11 p+ 11 e- 10 e- 0 1+

Formation of Magnesium Ion Magnesium atom Magnesium ion  Mg  – 2e  Mg2+ 2-8-2 2-8 (=Ne) 12 p+ 12 p+ 12 e- 10 e- 0 2+

Learning Check A. Number of valence electrons in aluminum 1) 1 e- 2) 2 e- 3) 3 e- B. Change in electrons for octet 1) lose 3e- 2) gain 3 e- 3) gain 5 e- C. Ionic charge of aluminum 1) 3- 2) 5- 3) 3+

Solution A. Number of valence electrons in aluminum 3) 3 e- B. Change in electrons for octet 1) lose 3e- C. Ionic charge of aluminum 3) 3+

Learning 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+ 2) 3- 3) 5-

IONIC BOND A BOND IS IONIC IONIC BOND A BOND IS IONIC *When the difference in electronegativity between the atoms is greater than 1.7 D en > 1.7 *Between a metal and a non metal

Ide Binary compounds They are made up of 2 elements The name of a binary compound ends in Ide Write the metal first. The name will be the name of the metal and the non metal change the end to ide Example the compound between Lithium and Fluorine will be Lithium Fluoride Li F

The non-metal changes the ending F - fluoride Cl - chloride Br- bromide I- iodide O-2 oxide S-2 sulfide N-3 nitride

Formation of Ions from Metals Ionic compounds result when metals react with nonmetals Metals lose electrons to match the number of valence electrons of their nearest noble gas Positive ions form when the number of electrons are less than the number of protons Group 1 metals  ion 1+ Group 2 metals  ion 2+ Group 13 metals  ion 3+

Some Typical Ions with Positive Charges (Cations) Group 1 Group 2 Group 13 H+ Mg2+ Al3+ Li+ Ca2+ Na+ Sr2+ K+ Ba2+

Ions from Nonmetal Ions In ionic compounds, nonmetals in 15, 16, and 17 gain electrons from metals Nonmetal add electrons to achieve the octet arrangement Nonmetal ionic charge: 3-, 2-, or 1-

Fluoride Ion     1 - : F  + e : F :     2-7 2-8 (= Ne) unpaired electron octet     1 - : F  + e : F :     2-7 2-8 (= Ne) 9 p+ 9 p+ 9 e- 10 e- 0 1 - ionic charge

Ionic Bond Between atoms of metals and nonmetals with very different electronegativity Bond formed by transfer of electrons Produce charged ions . The attraction between the ions is electrostatic force .

IONIC SOLIDS The substances that contain ionic bonding * Are all solids (crystalline structure) and brittle. * Have high melting points. * Are generally soluble in water. * Do not conduct electricity in the solid state but they do conduct in the liquid state (fused). * Are electrolytes ( conduct electricity when they are dissolved in water). Examples: compounds containing metals and non metals NaCl , MgO, LiBr

Conductivity apparatus

Conductivity for ionic substances Ionic substance conduct electricity in the liquid state (fused) or dissolved in water. They are ELECTROLYTES Electrolytes: substances that conduct electricity in solution because they produced IONS

1). Ionic bond – electron from Na is transferred to Cl, this causes a charge imbalance in each atom. The Na becomes (Na+) and the Cl becomes (Cl-), charged particles or ions.

Octet Rule = atoms tend to gain, lose or share electrons so as to have 8 electrons C would like to N would like to O would like to Gain 4 electrons Gain 3 electrons Gain 2 electrons

COVALENT BONDING SHARING OF ELECTRONS NON POLAR POLAR

COVALENT BOND bond formed by the sharing of electrons

Between Non-metals Formed by sharing electrons Examples; O2, CO2, C2H6, H2O, SiC

Covalent Bonds

Multiple covalent bonds Single bond – one pair of electrons shared Double bond- 2 pair of electrons shared Triple bond – 3 pair of electrons shared

MOLECULE A group of atoms joined by covalent bonds

when electrons are shared equally NONPOLAR COVALENT BONDS when electrons are shared equally H2 O2 F2 Br2 I2 N2 Cl2 (all diatomic molecules)

2. Covalent bonds- Two atoms share one or more pairs of outer-shell electrons. Oxygen Atom Oxygen Atom Oxygen Molecule (O2)

POLAR COVALENT BONDS H2O when electrons are shared unequally Happens when the atoms have different electronegativity H2O

Polar Covalent Bonds: Unevenly matched, but willing to share.

February 3 How to classify molecules based on their bond type and their shape? Do now : draw the dot diagram for the molecule of NH3

POLAR MOLECULES Have unequal distribution of charges. A part of the molecule is positive, the other is negative, like a magnet or a battery. IF THE BONDS ARE POLAR AND THE MOLECULE IS ASYMMETRICAL THEN THE MOLECULE IS POLAR.

ASYMMETRICAL MOLECULES LACK IDENTICAL PARTS ON EACH SIDE OF AN AXIS

ASYMMETRICAL SHAPES LINEAR WITH POLAR BONDS BENT OR ANGULAR PYRAMIDAL TETRAHEDRAL (WITH DIFFERENT ATOMS AROUND CARBON If the bond is polar the molecule will be polar. Examples to remember NH3 , H2O, CHCl3

- water is a polar molecule because oxygen is more electronegative than hydrogen, and therefore electrons are pulled closer to oxygen. SHAPE BENT OR ANGULAR

PYRAMIDAL (NH3)

Tetrahedral: for compounds that contain Carbon with 4 atoms around CH4 CBr4 CF4 CH3Cl

SYMMETRICAL MOLECULES HAVE IDENTICAL PARTS ON EACH SIDE OF AN AXIS

NON POLAR MOLECULES SYMMETRICAL MOLECULES IF THE MOLECULE HAS POLAR BONDS BUT IT HAS A SYMMETRICAL SHAPE THEN IS NON POLAR. Examples to know CO2 , CH4, CF4 , CCl4 (compounds of carbons that have 4 equal atoms around Carbon)

FEBRUARY 4 Objective: How to classify compounds based on their chemical bonds? Do now : draw the dot diagram for the molecule of NH3 What is the geometry/shape of the molecule? Is the bond between N and H polar or non polar? Justify your answer Is the molecule polar or non polar?

Homework from review book page 105 and 107 Questions 13 to 25

Difference between ionic and covalent bonds In the ionic bond electrons are TRANSFERRED . In the covalent bond electrons are SHARED. Ionic bond occur between metals and non metals. Covalent occurs between non metals.

Comparing ionic and covalent bonds IONIC BONDS COVALENT BONDS Between metals and non metals Transfer of electrons Difference in electronegativity D en > 1.7 Between non metals Sharing of electrons Difference in electronegativity 0 < D en < 1.7

Difference between polar and non polar covalent bond POLAR BONDS NON POLAR BONDS Electrons shared unequally. Atoms have different electronegativity. Electrons are shared EQUALLY. Atoms have same electronegativity

Difference between polar and non polar Molecules UNEVEN distribution of charges. The molecules have no symmetry. EVEN distribution of charges. If the bonds are polar the molecules must be symmetric to be non polar.

February 5 Objective: What are the properties of substances based on the type of bond they have? Hw page 111 q 38 to 44

Worksheet answer page 105 page 108 2 3 1 4 3 1 2

Answer to questions in Appendix 2 Page A 18 3 4 1 2 3 2 1 a) 5610.3 g b) 0.029g 28) a) 2070g/cm3 b)10. g 29) 3

MOLECULAR SUBSTANCES *Solids are soft and have low melting points. (remember molecules are a group of atoms joined by covalent bonds) Substances containing covalent bonds. *Could be solid, liquid or gas. *Solids are soft and have low melting points. *Are not conductors of heat or electricity. Examples H2, O2 H2O CO2 C6H12O6 (glucose) C12H22O11 (sugar) C25H52 (wax)

NETWORK SOLIDS OR MACROMOLECULES They are a special type of substances that contain covalent bonds but the atoms form huge networks in which the molecule has as many atoms as are there in the sample. They have very different properties than regular molecular substances. Diamonds, *Graphite , Asbestos, Silicon Carbide (SiC) Silicon Dioxide (SiO )

PROPERTIES OF MACROMOLECULES 1) Very Hard 2)Poor conductors of electricity and heat. 3)High melting points *Graphite is an exception because is soft and is a good conductor of electricity.

February 6 What is the metallic bond and what are the properties of metals? Hw page 113 1 to 10, 12 to 30

METALLIC BOND bond found in metals; holds metal atoms together very strongly

METALLIC BOND Mobile electrons. Positive ions immersed in a sea of mobile electrons. The ions are arranged in the fixed position of a crystalline lattice. The valence electrons move freely throughout the crystal and do not belong to any atom.

Metallic Bond - Sea of Electrons

Metallic Bonds: Mellow dogs with plenty of bones to go around.

Metals 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.

PROPERTIES OF METALS * Are all solids (have a crystalline structure) except Hg *Malleable, ductile, and have metallic luster. *Are good conductors of heat and electricity. HW P 110 Q 38 TO 44

Review Book answers page 111 4 1 3 2

Ternary Ionic compounds Contain ionic and covalent bonds. A polyatomic ion is a group of atoms joined by covalent bonds that have a charge. USE YOUR TABLE E!!! In order to form a compound a positive ion (usually a metallic ion) will cancel out the charge of the negative polyatomic ion.

February 9 Objective: attraction between molecules Attraction between atoms form BONDS and result in types of material. Attraction between molecules result in different boiling point, and several physical properties of matter like vapor pressure and surface tension.

INTERMOLECULAR FORCES OF ATTRACTION Forces of attraction between atoms form BONDS. When the atoms are joined together forming molecules the forces of attraction that exist between the MOLECULES are called INTERMOLECULAR FORCES of ATTRACTION . The forces of attraction are electrostatic and some of them are strong but never as strong as a chemical bond.

If the attractions between molecules are strong the substances will boil, and melt at high temperatures. If the INTERMOLECULAR FORCES are WEAK then the melting point and boiling points will be low. Also intermolecular forces affect the vapor pressure of a liquid. We mentioned intermolecular forces when we discuss table H.

TYPES OF INTERMOLECULAR ATTRACTION Dipole – Dipole Hydrogen bonding London dispersion forces Molecule – ion attractions

DIPOLE-DIPOLE Between polar molecules. Polar molecules have dipoles in them, that means that they have uneven distribution of charges. In a polar molecule, one end of the molecule is positive and the other end is negative, therefore they will attract each other. Polar molecules have polar bonds between the atoms, and no symmetry. Remember bent and pyramidal molecules are always polar if the bond between them is polar

LIKE DISSOLVES LIKE Polar substances will dissolve in polar substances. If there is no dipole the substance is non polar and it will dissolve in a non-polar substance. Chemist use this say : LIKE DISSOLVES LIKE That means that if a substance dissolves in a polar solvent then we know that the substance is polar. Water (H2O) and ammonia (NH3) are examples of polar solvents.

HYDROGEN BONDING IS NOT A TYPE OF BOND BUT KIND OF INTERMOLECULAR ATRACTION. It occur in molecules that contain Hydrogen atoms bonded directly to Nitrogen, Fluorine or Oxygen. These molecules have a very high boiling point. It is a strong INTERMOLECULAR attraction

HYDROGEN BONDING

HYDROGEN BONDS

LONDON DISPERSION FORCES Are the only forces of attraction that exist between non polar molecules. They are very weak. This forces of attraction increase with the number of electrons in a molecule and with the decrease in the distance between them. The closer the molecules are together the more important they become. They are responsible for the physical state of the Halogen group, and are the forces of attractions that allow the condensation of gases.

MOLECULE-ION ATTRACTIONS Are attractions between POLAR MOLECULES and IONS. When ionic substances dissolve in water the ions are attracted to the polar water molecules.

MOLECULE ION ATTRACTIONS

P 112 1 2 4