chemical bonds chemical bonds are forces that hold atoms together in a compound. potential energy is...
TRANSCRIPT
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 StructuresLEWIS 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) Na 2) K 3) Al
B. X would be the electron dot formula
1) B 2) N 3) P
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 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 aluminum1) 1 e- 2) 2 e- 3) 3 e-
B. Change in electrons for octet1) 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 aluminum3) 3 e-
B. Change in electrons for octet1) lose 3e-
C. Ionic charge of aluminum 3) 3+
Group work
• For each pair of elements
• A) Calculate the difference in electronegativity
• B) Draw the dot diagram of the elements
• C) Draw the dot diagram of the compounds
• D) Formula of the compound
• E) Name of the compound
• Each group will present their compound to the class
Do Now
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
*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 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
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 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 toO would like to
Gain 4 electronsGain 3 electronsGain 2 electrons
Multiple covalent bonds
• Single bond – one pair of electrons shared
• Double bond- 2 pair of electrons shared
• Triple bond – 3 pair of electrons shared
when electrons are shared equally
NONPOLAR COVALENT BONDS
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 AtomOxygen Atom Oxygen AtomOxygen Atom
Oxygen Molecule (O2)
when electrons are shared unequally
Happens when the atoms have different
electronegativities
POLAR COVALENT BONDS
H2O
February 6
• How to classify molecules based on their bond type and their shape?
• Do now : draw the dot diagram for the
molecule of CO2
• HW P 107 q 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.
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
NON POLAR MOLECULESSYMMETRICAL MOLECULES
• IF THE MOLECULE HAS POLAR BONDS BUT IT HAS A SYMMETRICAL SHAPE THEN IS NON POLAR. Examples to know CO2 , CH4, CF4 , CCl4
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.
Difference between polar and non polar covalent bond
• POLAR BOND: Electrons shared unequally. Atoms have different electronegativity.
• NON POLAR BOND: Electrons are shared EQUALLY. Atoms have same electronegativity.
Difference between polar and non polar Molecules
• Polar molecules have UNEVEN distribution of charges. The molecules have no symmetry.
• Non Polar molecules: have EVEN distribution of charges. If the bonds are polar the molecules must be symmetric to be non polar.
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 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.
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.
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 111 Q 38 TO 44
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.
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.
February 25
• 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.
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
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.