chemical bonding.....aim 1

what are the different forms of  bonding?

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HW From textbook “CHEMISTRY a Contemporary Approach”

 

Chemical bonding happens for different reasons;

·         Electrostatic forces between anions and cations. Ionic bonding

·         Sharing of valence electrons between atoms. Covalent bonding

·         Cohesive force of moving electrons. Metallic bonding

 

The result of bonding is a lower energy state and the attainment of a stable valence electron configuration (Noble gases) for the bonded species.

 

Ionic bonds are formed when valence electrons are transferred from metals to nonmetals forming ionic compounds. 

·         Metals (elements under the staircase division of the periodic table) lose electrons and become cations.

·         Nonmetals (elements above the staircase division of the periodic table, including hydrogen) gain electrons and become anions

Example 1: KCl

                    

Example 2: CaBr2

           

Problems

Draw the following ionic compounds: SrF2, LiI, BaCl2, Na2O, AlCl3, and Al2O3 as the examples above

 

Covalent bonds are formed when valence electrons are shared between nonmetal atoms forming molecular (covalent) compounds.

 

A single covalent bond is formed when 2 electrons (1 pair) are shared.

Example 1: HCl         

           

           

Example 2: Cl2

 

       

 

A double covalent bond is formed when 4 electrons (2 pairs) are shared.

Example: O2

           

A triple bond is formed when 6 electrons (3 pairs) are shared.

Example: N2

 

           

 

Ionic compounds containing polyatomic ions (see table E) have both ionic and covalent bonding.

Example 1: KNO3

            

Notice that NO3- is composed of 2 nonmetals therefore the bonding is covalent between N and O but the bonding between K+ and NO3-  is ionic.

 

Example 2: (NH4)3PO4

        

Note: The bonding is covalent between N and H and P and O but ionic between the two polyatomic ions.

 

Problem 

Draw the Lewis structure of the following ionic compounds NaOH, H3PO4, Mg(NO3)2 and (NH4)2CO3

 

The table below illustrates all  the possible combinations for ionic compounds.

Key:

M  = metals

NM  = non-metals

P  =  polyatomic ions

Formula

 

(+)

(-)

Examples

M

NM

NaCl, KI, and CaF2

M

P

LiNO3, Sr(CN)2, and RbSCN

P

NM

NH4Br, Hg2S,and (H3O)2Se

P

P

NH4NO3, H3OMnO4, and (Hg2)3(PO4)2

 

Problem 

In table I and L, find all ionic compounds and write their Lewis structures.

 

Writing Lewis structure for molecules and polyatomic ions

1. Count the number of valence electrons. Add  one electron for every minus charge and remove one for every  positive charge.

2. Draw a skeleton  structure. In  general, the first element in a formula with 3 or more elements is the center of the molecule and the other fit  around  it.  

3. Add the  remaining electrons to satisfy the octet rule.

Example:

1. H2O has   2(1) + 6 =  8 valence electrons

2. The skeleton structure  uses 4 valence electrons therefore 4  remains.

3. The  4  remaining  valence electrons go  around  the  oxygen  atom.

Problems: Write the Lewis structure for  NH3, CO2, NO3-,  NH4+,  H3O+, CH4, CCl4, and HCN

 

Electronegativity indicates how strongly an atom of an element attracts electrons in a covalent bond. See table S

 

The electronegativity difference between two covalently bonded atoms is used to assess the degree of polarity.

·        When the difference is 0 the bond is nonpolar.

·        When there is a difference the bond is polar. The greater the difference the more polar the bond is.

Example:  HF, NO and N2

 

Note:

The bonded electrons in HF are closer to F than H

 he bonded electrons in NO are closer to O than N

The bonded electrons in N2are right between the two N

 

Problem 

Calculate the degree of polarity in the following molecules CO, HI, O2, HCl, and HBr 

 

Metallic bonds are formed when valence electrons of a metal are shared by every cations.  Therefore, valence electrons are mobile and the cohesive force of the electrons holds the metal together.

Example:  Al(s)

 

                       

TEST YOUR UNDERSTANDING

1/07

6 An atom of argon rarely bonds to an atom of another element because an argon atom has

        (1) 8 valence electrons         (2) 2 electrons in the first shell         (3) 3 electron shells         (4) 22 neutrons

12 Which two substances are covalent compounds?

        (1) C6H12O6(s) and KI(s)     (2) C6H12O6(s) and HCl(g)   (3) KI(s) and NaCl(s)   (4) NaCl(s) and HCl(g)

28 Given the structural formula:

What is the total number of electrons shared in the bond between the two carbon atoms?    (1) 6     (2) 2     (3) 3     (4) 4

37 Which Lewis electron-dot diagram correctly represents a hydroxide ion?

    

6/07

11 An oxygen molecule contains a double bond because the two atoms of oxygen share a total of         (1) 1 electron         (2) 2 electrons         (3) 3 electrons         (4) 4 electrons

62 Explain, in terms of electronegativity, why a P–Cl bond in a molecule of PCl5 is more polar than a P–S bond in a molecule of P2S5.

8/07

7 Atoms of which element have the greatest tendency to gain electrons?    (1) bromine     (2) chlorine     (3) fluorine    (4) iodine

13 Which formula represents an ionic compound?

1/06

12 Which type of bond is found in sodium bromide?  (1) covalent (2) hydrogen (3) ionic (4) metallic

26 Which Lewis electron-dot diagram is correct for CO2?

  

53 Draw a Lewis electron-dot diagram of a selenium atom in the ground state.

54 Explain, in terms of atomic structure, why liquid mercury is a good electrical conductor.

63 Explain, in terms of electronegativity difference, why the bond in H–Cl is more polar than the bond in H–I.

64 Explain, in terms of intermolecular forces, why hydrogen has a lower boiling point than hydrogen bromide.

65 Explain, in terms of molecular polarity, why hydrogen chloride is more soluble than hydrogen in water under the same conditions of temperature and pressure.

6/06

3 Which element is malleable and can conduct electricity in the solid phase?  (1) iodine (2) phosphorus (3) sulfur (4) tin

9 Which type of bond results when one or more valence electrons are transferred from one atom to another?

        (1) a hydrogen bond (2) an ionic bond (3) a nonpolar covalent bond (4) a polar covalent bond

10 What is the total number of electrons shared in the bonds between the two carbon atoms in a molecule of ?  (1) 6 (2) 2 (3) 3 (4) 8

13 Which element has atoms with the greatest attraction for electrons in a chemical bond?    (1) beryllium     (2) fluorine     (3) lithium     (4) oxygen

36 A metal, M, forms an oxide compound with the general formula M2O. In which group on the Periodic Table could metal M be found?

        (1) Group 1 (2) Group 2 (3) Group 16 (4) Group 17

8/06

9 What is the total number of pairs of electrons shared in a molecule of N2?        (1) one pair (2) two pairs (3) three pairs (4) four pairs

34 Based on electronegativity values, which type of elements tends to have the greatest attraction for electrons in a bond?

        (1) metals         (2) metalloids         (3) nonmetals         (4) noble gases

51  Draw a Lewis electron-dot diagram for a sulfur atom in the ground state.

1/05

11 Which compound contains both ionic and covalent bonds?  (1) CaCO3     (2) PCl3     (3) MgF2     (4) CH2O

14 Which Lewis electron-dot diagram represents a boron atom in the ground state?

53 Explain, in terms of electronegativity, why a C–O bond in CO2 is more polar than the F–F bond in F2.

12 Based on Reference Table S, the atoms of which of these elements have the strongest attraction for electrons in a chemical bond?     (1) N     (2) Na     (3) P     (4) Pt

6/05

40 Which molecule contains a nonpolar covalent bond?

Base your answers to questions 55 and 56 on the balanced equation 2Na(s) + Cl2(g) ---> 2NaCl(s)

55 In the box in your answer booklet, draw a Lewis electron-dot diagram for a molecule of chlorine, Cl2.

56 Explain, in terms of electrons, why the bonding in NaCl is ionic.

1/04

7 The bond between Br atoms in a Br2 molecule is
    (1) ionic and is formed by the sharing of two valence electrons (3) covalent and is formed by the sharing of two valence electrons
    (2) ionic and is formed by the transfer of two valence electrons (4) covalent and is formed by the transfer of two valence electrons

9 What occurs when an atom of chlorine and an atom of hydrogen become a molecule of hydrogen
chloride?
        (1) A chemical bond is broken and energy is released. (3) A chemical bond is formed and energy is released.
        (2) A chemical bond is broken and energy is absorbed. (4) A chemical bond is formed and energy is absorbed.

31 When an atom of phosphorus becomes a phosphide ion (P3-), the radius (1) decreases (2) increases (3) remains the same

37 What is the correct Lewis electron-dot structure for the compound magnesium fluoride?

Base your answers to questions 53 through 55 on the data table below.
53 Record the electronegativity for the elements with atomic numbers 11 through 17.

54 Mark an appropriate scale on the axis labeled "Electronegativity."
55 On the same grid, plot the data from the data table. Circle and connect the points.

6/04

9 Covalent bonds are formed when electrons are
        (1) transferred from one atom to another (2) captured by the nucleus   (3) mobile within a metal (4) shared between two atoms

13 Which of these elements has the least attraction for electrons in a chemical bond? (1) oxygen (2) fluorine (3) nitrogen (4) chlorine

11 Which change occurs when a barium atom loses two electrons?
        (1) It becomes a negative ion and its radius decreases.         (3) It becomes a positive ion and its radius decreases.
        (2) It becomes a negative ion and its radius increases.          (4) It becomes a positive ion and its radius increases.

39 The bonds between hydrogen and oxygen in a water molecule are classified as     (1) polar covalent     (2) nonpolar covalent     (3) ionic (4) metallic

8/04

5 Which compound contains only covalent bonds?     (1) NaOH     (2) Ba(OH)2     (3) Ca(OH)2     (4) CH3OH

10 Given the Lewis electron-dot diagram:

Which electrons are represented by all of the dots?

                (1) the carbon valence electrons, only                             (2) the hydrogen valence electrons, only

                (3) the carbon and hydrogen valence electrons             (4) all of the carbon and hydrogen electrons

38 Which substance is correctly paired with its type of bonding?

                (1) NaBr—nonpolar covalent     (2) HCl—nonpolar covalent     (3) NH3—polar covalent     (4) Br2—polar covalent

Base your answers to questions 58 through 60 on the electronegativity values and atomic numbers of fluorine, chlorine, bromine, and iodine that are listed on Reference Table S.

58 Create an appropriate scale on the y axis and label  it  “Electronegativity.” An appropriate scale is one that allows a trend to be seen.

59 On the same grid, plot the electronegativity and atomic number data from Reference Table S. Circle and connect the points.

60 Explain, in terms of electronegativity, why the H–F bond is expected to be more polar than the H–I bond.

1/03

The strength of an atom's attraction for the electrons in a chemical bond is the atom's

            (1) electronegativity    (2) ionization energy    (3) heat of reaction               (4) heat of formation

6/03

1 What is represented by the dots in a Lewis electron-dot diagram of an atom of an element in Period 2 of the Periodic Table?

            (1) the number of neutrons in the atom                            (2) the number of protons in the atom

            (3) the number of valence electrons in the atom             (4) the total number of electrons in the atom

2 As a neutral sulfur atom gains two electrons, what happens to the radius of the atom?

3 Which of these formulas contains the most polar bond? (1) H-Br  (2) H-Cl  (3) H-F (4) H-I

4 Which element has atoms that can form single, double, and triple covalent bonds with other atoms of the same element?

        (1) hydrogen (2) oxygen  (3) fluorine (4) carbon

5 Which type of chemical bond is formed between two atoms of bromine? (1) metallic (2) hydrogen (3) ionic (4) covalent

8/03

11 Which type of bond is formed when electrons are transferred from one atom to another? (1) covalent (2) ionic (3) hydrogen (4) metallic

13 What occurs when an atom of chlorine forms a chloride ion?
   (1) The chlorine atom gains an electron, and its radius becomes smaller.         (2) The chlorine atom gains an electron, and its radius becomes larger.
   (3) The chlorine atom loses an electron, and its radius becomes smaller.         (4) The chlorine atom loses an electron, and its radius becomes larger.

34 As two chlorine atoms combine to form a molecule, energy is     (1) absorbed         (2) released         (3) created         (4) destroyed

6/02

1 Draw the electron-dot (Lewis) structure of calcium chloride.

2 Which compound contains ionic bonds?     (1) NO       (2) NO2    (3) CaO    (4) CO2

3Which of the following atoms has the greatest tendency to attract electrons?  (1) barium   (2) beryllium    (3) boron  (4) bromine

8/02

1 Draw an electron-dot diagram for each of the following substances:

a) calcium oxide (an ionic compound), CaO

b) hydrogen bromide, HBr

c) carbon dioxide, CO

2 Which molecule contains a triple covalent bond?  (1) H2       (2) N2     (3) O2       (4) Cl2

10 Which formula represents an ionic compound? (1) NaCl          (2) N2O        (3) HCl                (4) H2O

21Which of the following elements has the highest electronegativity?  (1) H  (2) K    (3) Al   (4) Ca

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