CHEMICAL BONDS TOPIC 6 –REVIEW BOOK Chemical bonds are forces that hold atoms together in a compound. Potential energy is stored in chemical bonds.

CHEMICAL BONDSTOPIC 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 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 BONDbond 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

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 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+

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

*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, CuSO4

Conductivity apparatus

Conductivity for ionic substances

• Ionic substance conduct electricity in the liquid state (fused) or dissolved in water.

• They are called ELECTROLYTES

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

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 BONDINGSHARING OF ELECTRONS

• NON POLAR

• POLAR

COVALENT BONDbond formed by the sharing of electrons

Covalent Bond

• Between nonmetallic elements of similar electronegativity.

• Formed by sharing electrons

• Examples; O2, CO2, C2H6, H2O, 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

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

electronegativity

POLAR COVALENT BONDS

H2O

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 NH3 , H2O, CHCl3

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

PYRAMIDAL (NH3)

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

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 H2, O2 H2O CO2 C6H12O6 C12H22O11 C25H52

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 BONDbond 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.

Ionic Bond, A 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

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

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