CHEMICAL BONDS TOPIC 6 –REVIEW BOOK 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. HW P 99 REVIEW BOOK Q 1 TO 5
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 1) Na2) K3) Al B. X would be the electron dot formula 1) B2) N3) P
IONIC BOND bond formed between two ions by the transfer of electrons
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 en >1.7
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 Mg 2+ 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) 02) 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 *When the difference in electronegativity between the atoms is greater than 1.7 en > 1.7 *Between a metal and a non metal
Binary compounds They are made up of 2 elements The name of a binary compound ends in 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 1Group 2Group 13 H + Mg 2+ Al 3+ Li + Ca 2+ Na + Sr 2+ K + Ba 2+
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 unpaired electronoctet 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, CuSO 4
Hw from review book – Page 110 questions 26 to 37 When atoms lose or gain electrons and form ions they achieve the electron configuration of a noble gas. The formulas of ionic compounds are empirical (it means that the ratio between the atoms is the simplest ratio possible)
COVALENT BONDING SHARING OF ELECTRONS NON POLAR POLAR
COVALENT BOND bond formed by the sharing of electrons
Covalent Bond Between nonmetallic elements of similar electronegativity. Formed by sharing electrons Examples; O 2, CO 2, C 2 H 6, H 2 O, SiC
Multiple covalent bonds Single bond – one pair of electrons shared Double bond- 2 pair of electrons shared Triple bond – 3 pair of electrons shared
Bonds in all the polyatomic ions and diatomics are all covalent bonds
when electrons are shared equally NONPOLAR COVALENT BONDS H 2 O 2 F 2 Br 2 I 2 N 2 Cl 2 (all diatomic molecules)
2. Covalent bonds- Two atoms share one or more pairs of outer-shell electrons. Oxygen Atom Oxygen Molecule (O 2 ) Oxygen Molecule (O 2 )
when electrons are shared unequally Happens when the atoms have different electronegativity POLAR COVALENT BONDS H2OH2O
Polar Covalent Bonds: Unevenly matched, but willing to share.
Objective To distinguish between polar and non polar molecules To draw Lewis structures of molecules To describe the properties of materials containing covalent bonds (molecular substances and macromolecules) HOMEWORK REVIEW BOOK P 105 QUESTIONS 13 TO 17 AND PAGE 107 QUESTIONS 18 TO 25
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. Bent and pyramidal shapes are ALWAYS asymmetrical. If the bond is polar the molecule will be polar. Examples to remember NH 3, H 2 O, CHCl 3
ASSYMETRICAL SHAPES LINEAR WITH POLAR BONDS BENT OR ANGULAR PYRAMIDAL TETRAHEDRAL (WITH DIFFERENT ATOMS AROUND CARBON)
- water is a polar molecule because oxygen is more electronegative than hydrogen, and therefore electrons are pulled closer to oxygen. SHAPE BENT OR ANGULAR
NON POLAR MOLECULES SYMMETRICAL MOLECULES IF THE MOLECULE HAS POLAR BONDS BUT IT HAS A SYMMETRICAL SHAPE THEN IS NON POLAR. Examples to know CO 2, CH 4, CF 4, CCl 4
HW REVIEW BOOK P 105 QUESTIONS 13 TO 17 AND PAGE 107 QUESTIONS 18 TO 25
MOLECULAR SUBSTANCES (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 electricity. Examples H 2, O 2 H 2 O CO 2 C 6 H 12 O 6 C 12 H 22 O 11 C 25 H 52
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.
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 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
INTERMOLECULAR FORCES OF ATTRACTION Forces of attraction between atoms form BONDS. When the atoms are joined together forming molecules there are forces of attraction that exist between them and are called MOLECULAR ATTRACTIONS OR INTERMOLECULAR FORCES. 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 Chorine, Fluorine or Oxygen. These molecules have a very high boiling point. It is a strong INTERMOLECULAR attraction
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.