Chapter 7 Chemical Bonds Chemical Bond An attractive

Chapter #7 Chemical Bonds.

Chemical Bond ► An attractive force that holds two atoms together in a complex unit. ► Electrons combine to form chemical bonds.

Ionic Bond ► Bond formed between ions ► Transfer of electrons from one atom to the other.

Covalent Bond ► Formed by sharing of one or more electrons between 2 atoms. ► Molecular compounds are formed.

Covalent/Ionic Bonds ► Only valence electrons participate in bonding. ► They try and follow the octet rule( eight electrons)

Valence electrons and Lewis Symbols ► Valence electrons-Electrons in the outermost electron shell of a representative element or a noble gas element. ► Found in s or p orbitals or both.

Valence Electrons ► How many valence electrons are in: ► Mg, Cl, Se, Ca , S , Br

Lewis Symbol ► Chemical symbol of an element surrounded by dots equal to the number of valence electrons. ► Also called as electron dot structures.

Draw Lewis symbols for: ► Li, Be, B, C, N, O, F, Ne

Lewis symbols prove ► Representative elements in same group have same number of valence electrons. ► Number of electrons in Lewis symbol= group number. ► Maximum number of valence electron is 8. ► He has 2 valence electrons.

The Octet rule ► Noble gases are stable. ► They are the most unreactive elements. ► They all are gases. ► Octet Rule: Atoms of an element lose, gain or share electrons to produce a noble gas configuration for each atoms involved.

The Ionic Bond Model ► Ion: Atom or group of atoms that is electrically charged by loss or gain of electrons. ► Cation: Positively charged ion. ► Anion: Negatively charged ion.

Ions ► What kind of ions are formed by Na, Mg, Al, P, S, Cl.

Ionic bond ►A chemical bond resulting from attraction of positive and negative ions for each other.

Sign and Magnitude of Ionic Charge ► Metal atoms containing 1, 2, or 3 valence electorns lose electrons to acquire a noble gas configuration. ► Noble gas involved is the one preceeding the metal ► Group 1= +1 ions ► Group 2 = + 2 ions ► Group 3 =+ 3 ions

Sign and Magnitude of Ionic Charge ► Nonmetal atoms containing 5, 6, or 7 valence electrons gain electrons to acquire a noble gas configuration. ► Noble gas involved is the one following the nonmetal in the periodic table. ► Group 7=-1 ions. ► Group 6=-2 ions. ► Group 5=-3 ions.

Sign and Magnitude of Ionic Charge ► Elements in group IV A form covalent bonds. ► They have +4 or -4 charges.

Isoelectronic Species ► Ions or an atom and ions having the same number and configuration of electrons.

Ionic Compound Formation ► Lewis structure: Grouping of Lewis symbols that show either the transfer or sharing of electrons in chemical bonds. ► Ionic compounds contain both metals and nonmetals. ► Ex: Na. Cl ► Covalent compounds contain only nonmetals. Ex: H 2 O

Formulas For Ionic Compounds ► Total charge on an ionic compound is zero. ► Symbol for positive ion is written first. ► Charges are not shown in the formula. ► Numbers in the formula (subscript) give combining ratio for the ions.

Formulas For Ionic Compounds Write formulas for: Na, P Al, P Ba, Cl Ba, Sr Ba, N

Ionic compounds ► Contain metal and nonmetal. ► Metal forms cation. ► Nonmetal forms anions. ► Compound is neutral. ► Metals in group 1=+1, group 2=+2 , group 3 =+ 3 ions. ► Metals in group 7=-1 , group 6=-2, group 5=-3.

Structure of Ionic Compounds ► Each ion is surrounded by opposite charges. ► Formula Unit: Smallest whole number repeating ratio of ions present in an ionic compound that results in charge neutrality. ► Repeated regular patterns. ► Ex: Crystalline solids.

Polyatomic Ions. ► Monoatomic ion- Ion formed from a single atom through loss or gain of electrons. ► Polyatomic ion- Ion formed by group of atoms through loss or gain of electrons. ► Do practice Ex: 7. 7 Page # 212.

The Covalent Bond Model ► Ionic bond is formed between metalsnonmetals. ► Ionic bond-transfer of electrons. ► Covalent bond = sharing of electrons. ► Covalent compounds are called molecular compounds. ► Ionic compound in water conducts electricity, but a covalent compund does not.

The Covalent Bond Model ► Covalent bond-Chemical bond resulting form two nuclei attracting same shared electrons. ► Ex: H-H

Lewis Structures for molecular compounds ► Formation of H-Cl ► Formation of Cl-Cl ► Formation of Br-Cl ► Bonding electrons: Pairs of valence electrons that are shared between atoms in a covalent bond. ► Nonbonding electrons: pairs of valence electrons about an atom not involved in electron sharing, also called as lone pairs.

Lewis Structures for molecular compounds ► Number of covalent bond an electron forms= number of electrons it needs to achieve noble gas configuration. ► Structures of water, ammonia, methane.

Lewis Structures for molecular compounds ► Write Lewis structures for : ► P and H ► O and Cl ► S and F ► N and F ► C and Cl ► S and Br

Single, Double, Triple covalent bonds ► Single= two atoms share 1 pair of valence electron Ex: H-H ► Double=two atoms share 2 pairs of valence electrons Ex: O= O ► Triple=two atoms share 3 pairs of valence electrons Ex: N-N bonds.

Valence electron count and number of covalent bonds formed. ►O bonds: Two single or 1 double bond. ► N bonds: 3 single, one single and one double, one triple bond. ► C bonds: 4 single, 2 single and 1 double, 2 double, 1 single and 1 triple bond.

Coordinate covalent bonds ► One atom supplies 2 electrons and other none. ► Both electrons of shared electron pair come from one of the two atoms involved in covalent bond. ► Ammonia + hydrogen ► HOCl ► CO

Resonance structures ► Bond strength: Measure of energy it takes to break a covalent bond. ► Bond length: Distance between nuclei of covalently bonded atoms. ► Resonance structures: Two or more Lewis structures for a molecule or polyatomic ion that have same structures but different arrangement of electrons. ► Ex: SO 2

Drawing Lewis Structures Determine total number of valence electrons 2. Write symbols of atoms arranged in a way they are bonded to each other. Place a single covalent bond. 3. Add nonbonding electron pairs to complete the octet. 4. Complete octet around central atom. 1.

Drawing Lewis Structures 5. If not enough electrons on central atom to complete octet, form multiple bonds. 6. Count total number of valence electrons and check if number =step 1 number.

Drawing Lewis Structures ► Draw Lewis structures for : ► H 2 SO 4 ► HCl. O 3 ► Na 2 SO 3 ► PO 33► O 3 ► SO 3

Molecular Geometry ►A description of three dimensional arrangement of atoms within a molecule. ► Determines physical and chemical properties. ► VSEPR: Valence shell electron pair Repulsion Theory: The electrons try and place themselves in such a way that they minimize the repulsion. ► Predicting geometry of a molecule from Lewis structure

Molecular Geometry ► 2 e pairs-linear-180 ► 3 e pairs- trigonal planar-120 ► 4 e pairs- tetrahedral- 109. 5 VSEPR Electron group: Group of valence electron present in a localized region about an atom in a molecule. Count double, triple bonds as single bonds. Do practice 7. 12, P. 234

Electronegativity ► Measure of the relative attraction that an atom has for the shared electrons in a bond. ► Higher the electronegativity of an element, greater is the electron attracting ability of an element.

Electronegativity ► For representative elements electronegativity value increases from left to right. ► For period 2 left to right increase by 0. 5 ► H=2. 1 ► For period 3 elements increase left to right by 0. 3 units, last two is 0. 4, 0. 5. ► Increase from bottom to top within a group.

Bond polarity ► Nonpolar covalent bond: equal sharing of electrons. ► Polar covalent bond: Unequal sharing of electrons. ► Unequal sharing causes partial + and _ charges. ► Ex: H-Cl

Bond polarity ► Bond polarity: Measure of degree of inequality in the sharing of electrons in a chemical bond. ► Percent ionic character of a bond: A measure of how actual charge separation in a bond due to electronegativity difference of the bonded atoms compares to the complete charge separation association with ions.

Bond polarity Similar eneg non polar bonds. 2. Eneg diff > 0. 5 but < 2. 0 -polar covalent bonds. 3. Eneg diff=or > 2. 0 -ionic bonds. Rank following in order of increasing polarity. C-Cl, Ca-F, C-O, B-H, P-Br N-S, H-H, Na-F, K-Cl, F-Cl 1.

Molecular polarity ► Measure of degree of inequality in the attraction of bonding electrons to various locations eithin a molecule. ► Polar molecule: unsymmetrical distribution of electronic charge. ► Nonpolar molecule: symmetrical distribution of electronic charge. ► Ex: CO 2, H 2 O, HCN. ► Practice Ex: 7. 14, page #242.