1. Lecture 4: Ionic and Molecular Compounds
Course Lecturer:
Assist.Prof. Dr. Altijana Hromić-Jahjefendić

2. Book chapter: 6
Pages:

3. In nature almost all elements are found in combination
Only noble gases do not combine (very stable)
A compound is composed of two or more elements
Can be ionic and molecular

4. Ionic compound
One or more electrons are transferred from metals to nonmetals
Forms positive and negative ions
The attraction between these ions is ionic bond
Everyday examples: kitchen salt NaCl, baking soda NaHCO3, mineral supplements etc.
Precious and semiprecious gemstones (minerals) are also ionic compounds
Sapphire and rubies are made of Al2O3 with impurities

5. Molecular compounds
Consists of two or more nonmetals that share one or more valence electrons
Resulting molecules are held by covalent bonds
Examples: water H2O, carbon dioxide CO2, alcohol, antibiotics etc.

6. Ions: Transfer of Electrons
Compounds form when electrons are transferred or shared to give stable electron arrangement to the atoms!
Ionic or covalent bond
Gain, lose or share valence electrons to acquire an octet (8 valence electrons)
Tendency to be in stable electron arrangement is octet rule

8. Positive Ions: Loss of Electrons
Ions – electrical charges
Form when atoms lose or gain electrons
Metals
Positively charged ions of metals – cations
A metal ion is named by its element name
Examples: Na+, Mg2+, etc.

9. Negative Ions: Gain of Electrons
By gaining electrons, a nonmetal atom forms a negatively charged ion
Anion
The name is formed by using the first syllable of its element name followed by ide
Example: Chloride

11. Ionic Charges from Group Numbers
Using group numbers in the periodic table to determine the charges for the ions of the representative elements
Group 1A lose one electron to form ions with 1+ charge
Example: Na+
Group 2A lose two electrons to form ions with 2+ charge
Example: Mg2+
Group 3A lose 3 electrons to form ions with 3+ charge
Example: Al3+

12. Groups 5-7 are gaining electrons to form ions with negative charge

13. Three ways to find the valence electrons: http://www. wikihow

14. Link to Health Some ions are important in the body
Physiological and metabolic function
Food provides body with ions important in regulating body functions

15. Link to Health

16. Ionic compounds - Review
Consist of positive and negative ions
Held together by ionic bons
Positive ions – formed by metals
Negative ions – formed by nonmetals

17. Properties of ionic compounds
Properties of an compound are very different from those of the original elements
Example: NaCl
Sodium (Na) is soft, shiny, very reactive metal
Chlorine (Cl) is yellow-green poisonous gas
Upon reaction they produce NaCl – ordinary table salt
Hard, white, crystalline substance

19. Cl- ions are larger
Na+ ions are smaller
Arranged in 3D structure in which Na+ ions occupy the space between the Cl- ions
Every Na+ ion is surrounded by six Cl- ions and vice versa
Many strong attractions between the positive and negative ions
Accounts for the high melting points

20. Chemical formulas of ionic compounds
The chemical formula of a compound represents the symbols and subscripts in the lowest whole-number ratio of the atoms or ions.
Thus, the total amount of positive charge is equal to the total amount of negative charge.
Na atom loses its one valence electron to form Na+, and one Cl atom gains one electron to form a Cl- ion
Formula indicates that the compound has charge balance

21. Subscripts in Formulas
Example: Mg and Cl
Mg loses 2 electrons (Mg2+)
Two Cl atoms gain one electron to form two Cl- ions
Two Cl- ions are needed to balance positive charge of Mg2+
Gives formula MgCl2
Subscript 2 indicates that 2 Cl- ions are needed for charge balance

22. Naming Ionic Compounds
Name of metal ion is the same as its element name
The name of nonmetal ion is first syllable + ide
Subscripts are not used, they are understood 

23. Metals with Variable charges
Charge detrmined from its group number
Cannot determine the charge of a transition element
Typically forms two or more positive ions
Variable charges
Then we cannot predict the ionic charge from a group number
For metals forming two or more ions – naming system

25. Determination of Variable Charges
You need to determine if the metal is a representative or a transition element
If transition element (except Zn, Cd and Ag) we need to use its ionic charge
The calculation of ionic charge depends on the negative charge of the anions in the formula
Example: CuCl2
Two chloride ions (each with 1- charge; total negative charge is 2-)
To balance this 2- charge the copper ion must have a charge of 2+

26. Polyatomic ions
An ionic compound may also contain a polyatomic ion as one of its cations or anions.
A polyatomic ion is a group of covalently bonded atoms that has an overall ionic charge.
Most polyatomic ions consist of a nonmetal such as phosphorus, sulfur, carbon, or nitrogen covalently bonded to oxygen atoms.
Almost all the polyatomic ions are anions with charges of 1-, 2-, or 3-. Only one common polyatomic ion, NH4 +, has a positive charge..

27. Names of Polyatomic Ions
Names of most of them end in ate (nitrate, sulfate)
When a related ion has one less oxygen atom – ending ite (nitrite, sulfite)
Hydroxide ion (OH-) and cyanide ion (CN-) are exceptions to this naming pattern

29. Writing formulas for compounds containing polyatomic ions
No polyatomic ion exists by itself
It must be associated with ions of opposite charge
To write correct formula – same rules as for writing simple ionic compounds
The total negative and positive charge must equal zero

30. Naming Ionic Compounds Containing Polyatomic Ions
First we write the positive ion (usually a metal)
Then we write the name for the polyatomic ion
No prefixes are used

31. Summary of naming ionic compounds

32. Summary Ions Octet/ octet rule Cations Anions
Ionic charges from group numbers
Properties of ionic compounds
Chemical formulas of ionic compounds
Naming ionic compounds
Variable charges
Polyatomic ions

33. Molecular compounds
Contains two or more nonmetals that form covalent bons
Valence electrons are shared – covalent bond
Atoms sharing electrons – form a molecule

34. Formation of a covalent bond
Hydrogen atoms (2 H)
Hydrogen
molecule (H2) +
In each hydrogen
atom, the single electron
is held in its orbital by
its attraction to the
proton in the nucleus. 1
When two hydrogen
atoms approach each
other, the electron of
each atom is also
attracted to the proton
in the other nucleus. 2
The two electrons
become shared in a
covalent bond,
forming an H2
molecule. 3

35. Covalent bond Sharing a pair of valence electrons by two atoms
Two or more atoms held together by covalent bonds constitute a molecule
Occurs in non-metals
Can be single, double and triple bond

36. Difference between single, double and triple bond
Single bond= a pair of shared electrons (hydrogen H2)
Double bond= sharing a two pairs of valence electrons (oxygen O2)
Triple bond= sharing three pairs of valence electrons (nitrogen)

37. Names and formulas of Molecular Compounds
The first nonmetal in the formula is named by its element name
Second nonmetal is named using first syllable of its element name + ide
When a subscript indicates two or more atoms of an element, a prefix is shown in front of its name

38. Prefixes are needed
Different compounds can be formed from the same two nonmetals
Example: carbon and oxygen
Carbon monoxide (CO) and carbon dioxide (CO2)
Prefix indicates the number of oxygen atoms

39. Electronegativity and Bond Polarity
Electronegativity- the attraction of a particular kind of atom for the electrons in a covalent bond
The more electronegative an atom the more strongly it pulls shared electrons toward itself
Covalent bond between two atoms of the same element are equally electronegative

41. In some cases, more electronegative atoms strip electrons away from their bonding partners
Typical example is Na and Cl
Na has 1 electron in valence shell and Cl has 7
Lone valence electron of Na is transferred to the chlorine atom and both atoms have their valence shell completed

42. Bonding capacity corresponds to the number of covalent bonds thé atom can form
Also called valence
Equal to the number of unpaired electrons in the valence shell

43. Polarity of Bonds
The difference in electronegativity values of two atoms can be used to predict the type of bond
2 types:
1. polar covalent bond
2. non-polar covalent bond

44. In a polar covalent bond
The atoms have different electronegativities
Share the electrons unequally
Vary in polarity

45. In a nonpolar covalent bond
The atoms have same electronegativities
Share the electron equally
H2 or O2

46. Dipoles and Bond Polarity
The polarity of a bond depends on the difference in the electronegativity values of its atoms
In polar bond – shared electrons are attracted to the more electronegative atom; makes them partially negative
Atom with the lower electronegativity becomes partially positive; lack of the electrons at that atom

47. A bond becomes more polar as the electronegativity difference increases
Polar covalent bond with separation of charges is called a dipole
The positive and negative ends of the dipole are indicated by the lowercase Greek letter delta with a positive or negative sign, δ+ and δ-

49. Shapes of Molecules
Using electron-dot formula we can predict 3D shapes of many molecules
Shape is important to understand of how molecules interact with enzymes or certain antibiotics
Identify the number of electron groups around central atom
Counting lone pairs of electrons and bonds as one electron group
Once we know the number of electron groups we can determine its specific shape

50. Lewis representation of electrons

51. Central Atoms with Two Electron groups
CO2 molecule
Minimal repulsion occurs when two electron groups are on opposite sides of the central C atom
Linear electron-group geometry
Bond angle of 180°

52. Central Atoms with Three Electron groups
H2CO
Central carbon attached to two H atoms by single bond and to the O by a double bond
Minimal repulsion – three groups are far apart as possible around the central C atom
Geometry: trigonal planar; 120°

53. Central Atoms with Four Electron groups
CH4 (methane)
Central C bonded to four H atoms
Minimal repulsion is tetrahedral; bond angles 109°

54. Polarity of molecules 2 types of covalent bonds
2 types of molecule polarities:
1. polar
2. nonpolar

55. Nonpolar molecules All the bonds are nonpolar
Or the polar bonds cancel each other out because of symmetrical arrangement
H2, Cl2, CH4 contain only nonpolar bonds
CO2 is linear, has two equal polar covalent bonds whose dipoles point in opposite directions
Dipoles cancel out making CO2 nonpolar molecule

56. Polar molecules
One end of the molecule is more negatively charged than the other end
Dipoles from the individual polar bonds do not cancel each other
HCl – has one covalent bond that is polar so the molecule is polar

57. Molecules with two or more electron-groups the shape determines whether or not the dipoles cancel
H2O has a bent shape
It is polar because the individual dipoles do not cancel
In CH3F, the C-F bond is polar covalent
3 C-H bonds are nonpolar covalent
Because there is only one dipole which does not cancel, this is polar molecule

58. Attractive forces in compounds
In gases the interaction between particles is minimal
In solids and liquids there are sufficient interactions between particles to hold them close together
Dipole-dipole attractions
Hydrogen bonding
Dispersion forces

59. Dipole-dipole Attractions
Between the positive end of one molecule and negative end of another
Partially positive atom of one molecule attracts partially negative atom in another molecule
HCl

60. Hydrogen Bonds
Hydrogen atoms bonded to electronegative atom of nitrogen, oxygen or fluorine
Form especially strong dipole-dipole attractions – hydrogen bond
Between partially positive H atom of one molecule and partially negative (N,O,F) atom in another molecule
Strongest types of attractive forces
Major factor in the formation and structure of biological molecules (proteins and DNA)

61. Dispersion Forces Very weak attractions between nonpolar molecules
Make it possible for nonpolar molecules to form liquids and solids
Electrons are distributed symmetrically
However, they can accumulate more in one part of the molecule than another – forms temporary dipole

63. Link to Health Proteins in our body have many different functions
Structural or metabolic functions
Composed of amino acids
α helix – stabilization by hydrogen bonds
Also form between the side chains within the protein
Ionic bonds form between positively and negatively charged R groups of acidic and basic amino acids

64. Summary Molecular compounds Covalent bond
Electronegativity and bond polarity
Polar vs.non-polar
Dipoles
Shape of molecules
Attraction forces

65. Book pages:
Homework 2: Describe attractive forces in compounds!
Send the homework per till
Bring the hard copy next time to the lecture ( )
Plagiarism!!!!! No copy-paste from the book or any internet sources!!!!! Use your own sentences!!!!!
Otherwise you loose points!!!!!