1. Bonding
Julieanne Quigley- 2018

2. What is a chemical Formula?
Chemical Symbols- chemical symbols are used to represent elements. Each element has its own symbol. Symbols for all the known elements are made up of one or two letters.
Chemical formulas are made of combinations of chemical symbols and numbers

3. What is a chemical Formula?
Chemical Formulas: Compounds are made up of two or more elements that are chemically combined. Scientists use a chemical formula to show the elements that make up a compound
A chemical formula is a way of writing the name of a compound using chemical symbols.

4. What is a Chemical Formula?
The compound water contains the elements hydrogen and oxygen, each molecule of water contains two atoms of hydrogen and one atom of oxygen.
The chemical symbol for hydrogen is H, The chemical symbol for oxygen is O. The chemical symbol for water is H2O
The chemical formula includes the symbols for each element in the compound and a number representing how many atoms are in the compound

5. What is a Chemical Formula?
Subscripts: chemical formulas also indicate how many atoms of each element are in a molecule or ion of a compounds
The number of atoms of each element is indicated buy a subscript
A subscript is a number written to the lower right of a chemical symbol
The 2 in the chemical formula H2O is a subscript
It indicates that there are two atoms of hydrogen in a molecule of water.

6. What is a Chemical Formula?
There is one atom of oxygen in a molecule of water, however, there is no subscript written after the O in H2O. This is because the number 1 is never written in a chemical formula
When there is no subscript after a symbol in a formula, you know that there is only one atom of that element

7. What is a Chemical Formula?
Writing a Chemical Formula: In some compounds, a metal is chemically combined with a nonmetal. For example, in sodium chloride is made of the metal sodium and the nonmetal chlorine
In a chemical formula, the symbol for the metallic element is always written first. The chemical formula for the chemical compound sodium chloride is NaCl.

8. What is a chemical Formula
Sometimes elements are bonded together in specific groups. These groups are always in parentheses ( )
When elements are in ( ) with a subscript you have to multiple each element by the subscript
Example Mg(OH)2 has:
1 Mg
2 O
2 H

9. What is Formula Mass?
Formula Mass: The total mass of the atoms in a compound or molecule
Each atom in a molecule has its own mass number
The mass number of an atom is the number of protons and neutrons in the nucleus, it is equal to the atomic mass rounded to the nearest whole number
The sum of the mass numbers of all the atoms in a molecule is called the formula mass of the molecule

10. What is Formula Mass? Finding Formula Mass-
Neon is an element that can exist as a molecule with only one atom
Therefore, a molecule of neon contains one atom of neon
The mass number of neon is 20
Because there is only one atom in a molecule of neon, the formula mass of neon is also 20
However, most molecules and ionic compounds contain more than one atom, to find the formula mass of molecules or ions in ionic compounds that contain more than one atom, use the following steps

11. What is Formula Mass?
Step 1: Write the chemical formula of the compound
Step 2: Use the periodic table to find the atomic mass of each element in the compound, round the atomic mass to find the mass number
Step 3: Multiply the mass number of each element by its subscript. If there is no subscript, multiply the mass number by 1
Step 4: Add the total masses of all the atoms in the compound. The total is the formula mass of the compound

12. Formula mass Practice
Ethyl chloride is C2H5Cl- Board Notes

13. This is the end of the lecture

14. Ionic Compounds
The force that holds two atoms together is called a chemical bond
Chemical bonds may form by the attraction between a positive nucleus and a negative electrons or the attraction between a positive ion and negative ion

15. Ionic Compounds
Previously you have learned about atomic structure, electron arrangement and periodic properties of the elements
The elements within a group on the periodic table have similar properties
Many of these properties are due to the number of valence electrons
These electrons are involved in the formation of chemical bonds between two atoms

16. Forming Ions
Electron dot diagrams showing valence electrons are especially useful when illustrating the formation of chemical bonds.
Ionization energy refers to how easily an atom loses an electron. The term electron affinity indicates how much attraction an atom has for electrons
The differences in electron reactivity are related to valence electrons
Every atom is always trying to obtain a full valence shell called the octet rule.

17. Forming Ions
Formation of positive ions: positive ions form when an atom loses one or more electrons in order to obtain noble gas configuration (octet rule).
Sodium has 11 electrons with 1 valence electron (outer shell), when sodium loses its valence electron it has achieved the noble gas configuration of Neon.

18. Forming Ions
Because Sodium now only has 10 electrons and still has 11 protons, it has a positive charge of 1
It is important to note, Na+ has 11 protons still, so even though it has the noble gas configuration of Neon, it is NOT Neon. Neon has 10 protons, Sodium has 11.
An ion with a positive charge is called a cation.
Na+ is a cation

19. Forming Ions
Formation of negative ions: Recall that nonmetals located on the right side of the periodic table have a great attraction for electrons and form a stable outer electron configuration by gaining electrons
When chlorine gains an electron it becomes negative and is written Cl-
A negative ion is called anion
Cl- is an anion

20. Ionic Bonds
Na and Cl react with each other. When they react the sodium transfers its valence electron to chlorine and becomes a positive ion (cation)
The chlorine atom accepts the electron into its outer energy shell and becomes a negative ion (anion)
The compound sodium chloride forms because of the attraction between oppositely charged sodium and chlorine ions

21. Ionic Bonds
The electrostatic force that holds oppositely charged particles together in an ionic compound is referred to as an ionic bond
Compounds that contain ionic bonds are ionic compounds
If ionic bonds occur between metals and oxygen, oxides form
Most other ionic bonds are called salts.

22. Ionic Bonds Hundreds of compounds contain ionic bonds
Many ionic compounds are binary, which means they contain only two different elements
Binary ionic compounds contain a metallic cation and a nonmetallic anion
Magnesium oxide MgO, is a binary compound because it contains two different elements: magnesium and oxygen
However, CaSO4 is not binary compound because it contains MORE than two elements

23. Ionic Bonds
Lets look at what happens when an ionic bond forms between Potassium (K) and Chlorine (Cl)
BOARD NOTES:

24. Ionic Bonds
Now lets look at the ionic compound calcium fluoride from calcium (Ca) and Fluorine (F).
Calcium has two electrons in its valence shell it wants to lose. Fluorine wants to gain one electron to reach noble gas status.
How will this ionic compound form?
BOARD NOTES

25. Ionic Bonds Both MgO and CaF2 are binary
Lets do an ionic bond for something that is not binary: LiOH
BOARD NOTES

26. Properties of Ionic Bonds
The strong attraction between the positive and negative ions in an ionic compound results in a crystal lattice
A crystal lattice is a three dimension geometric arrangement of particles
In a crystal lattice, each positive ion in surrounded by negative ions and each negative ion is surrounded by positive ions

27. This is the end of the lecture

28. Names and Formulas for Ionic Compounds
Binary compounds are composed of positively charged monoatomic ions of a metal and a negatively charged monatomic ions of a non metal
A monatomic ion is a ONE atom ion, such as MG2+ or Br-
Look at the Common Ions Based on Groups table provided for you in your notes and answer what is the charge on the following ions: O Mg Fe

29. Names and Formulas for Ionic Compounds
The charge of a monatomic ion is its oxidation number
Most transition metals (middle of the periodic table) and group 3A and 4A have more than one oxidation number
The oxidation numbers given in the table are the most common ones, for many of the elements listed, but might not be the only ones possible

30. Names and Formulas for Ionic Compounds
The term oxidation state is sometimes used and means the same thing as oxidation number.
Oxidation number of an element in an ionic compound equals the number of electrons transferred from an atom of the element to form the ion
For example when sodium and chlorine atoms react, the sodium transfers one electron to the chlorine atom forming Na+ and Cl-.
The oxidation state of sodium is +1 and the oxidation state of chlorine is -2

31. Determining the Formula of an ionic compound
Determine the correct formula for the following ionic compounds
BOARD NOTES
H+ and F-
K+ and O2-
Al3+ and S2-

32. Polyatomic Ions
Many ionic compounds contain polyatomic ions, which are ions made up of more than one atom
The charge given to a polyatomic ion applies to the entire group of atoms
Although an ionic compound containing one or more polyatomic ions contains more than two atoms, the polyatomic ion acts as an individual ion (it always bonds as one unit) and follows the same rules as binary compounds

33. Polyatomic Ions
Because a polyatomic ion exists as a unit, never change subscripts of atoms within the ion
If more than one polyatomic ion is needed, place parentheses around the ion and write the appropriate subscript outside the parentheses
An example is Mg(ClO3)2
Mg is 2+ and ClO3 is 1- (therefore two are needed to balance)

34. Polyatomic Ions
Use the Common Polyatomic Ions table provided to you to determine the following formulas:
Board Notes
Cl- and NH4+
Na+ and SO3 2-
Mg2+ and OH-

35. Naming Ionic Compounds
Chemical nomenclature (naming) is a systematic way of naming compounds
Now that you are familiar with writing chemical formulas, you will use the following general rules in naming ionic compounds when their formulas are known

36. Naming Ionic Compounds
Name the cation first and the anion second
Monatomic cations use the element name
Monatomic anions take their name from the root of the element name, plus the suffix – ide
Example: KCl is written Potassium Chloride
Example: NaF is written Sodium Fluoride
Metals with more than one oxidation number are identified with roman numerals
Example: Fe2+ and O2- (FeO) would be Iron (II) oxide.
Example: Fe3+ and O2- (Fe2O3) is written as Iron (III) oxide
If the compound contains a polyatomic ion, just use the name of the ion
Example: LiOH would be written as lithium Hydroxide
Example: (NH4)2S is written as ammonium sulfide

37. This is the end of the lecture

38. Covalent Bonding
We have previously learned that noble gases have a very stable electron configuration.
This stable arrangement consists of a full outer energy level
A full outer energy level consist of two valence electrons for helium and eight valence electrons for all noble gases
Because of this stability, noble gases don’t tend to react with other elements to form compounds

39. Covalent Bonding
With ionic compounds metals and nonmetals react to form:
Binary ionic compounds
Electrons are transferred and ions are created
The ions in the ionic compound are now in a noble gas configuration
But… sometimes two atoms both need to gain valence electrons to become stable and have a similar attraction for electrons… what do they do?

40. Covalent Bonding THEY SHARE!
Sharing electrons is another way that these atoms can acquire the electron configuration of a noble gas.
The octet rule states that atoms lose, gain or SHARE electrons to achieve a stable configuration of eight valence electrons, or an octet.
Although exceptions to the octet rule exist, the rule provides a useful framework for understanding chemical bonds

41. What is a Covalent Bond?
A covalent bond is a chemical bond that results from the sharing of valence electrons
In a covalent bond, the shared electrons are considered to be part of the complete outer energy level of both atoms involved
Covalent bonding generally occurs when elements are relatively close to each other on the periodic table
The majority of covalent bonds form between nonmetallic elements

42. What is a covalent bond?
A molecule is formed when two or more atoms bond covalently
The carbohydrates and simple sugars you eat, the proteins, fats and DNA found in your bodies, and the wool, cotton and synthetic fibers in the clothes you wear all are formed by covalently bonded atoms

43. What is a Covalent Bond?
Hydrogen (H2), Nitrogen (N2), Oxygen (O2), Fluorine (F2), Chlorine (Cl2), Bromine (Br2) and Iodine (I2) occur in nature as diatomic molecules (molecules made with two of the same atom) and not as single atoms because they are more stable than individual atoms.
How do two atoms that do not give up elections bond with each other??

44. What is a Covalent Bond?
Lets look at Fluorine. Fluorine has 7 valence electrons and wants 1 more to complete an octet.
As two fluorine atoms approach each other two forces become important:
A repulsive force occurs between the like-charge electrons and between the like-charged protons of the two atoms
An attractive force also occurs between the protons of one fluorine atom and the electrons of the other atom

45. What is a covalent bond?
As the fluorine atoms move closer, the attraction of both nuclei for the other atom’s electrons increases until the maximum attraction is achieved
At the point of maximum attraction, the attractive forces balance the repulsive forces
If the two nuclei move even closer, the repulsion between the like- charged nuclei and the electron clouds will increase, resulting in repulsive forces that exceed attractive forces

46. What is a Covalent Bond?
The most stable arrangement of atoms exists at the point of maximum attraction
At that point, the two atoms bond covalently and molecules form
Fluorine exists as a diatomic molecule because the sharing of one pair of electrons will give BOTH fluorine atoms stable noble gas configuration
Each fluorine atom in the fluorine molecule has one bonded pair of electrons and three lone pairs, which are unshared pairs of electrons

47. Single Covalent Bonds
Lets look at the formation of a hydrogen molecule
Each covalently bonded atom equally attracts one pair of shared electrons
Thus, two electrons shared by two hydrogen nuclei belong to each atom simultaneously
Both hydrogen atoms have the noble gas configuration of helium. The hydrogen molecule is more stable than individual hydrogen atoms

48. Single Covalent Bond
When a single pair of electrons is shared, such as in a hydrogen molecule, a single covalent bond forms
The shared electron pair, often referred to as the bonding pair, is represented by either a pair of dots or a line in the Lewis structure for eh model
Lewis structures use electron dot diagrams to show how electrons are arranged in molecule

49. Single Covalent bond
H:H or H-H is how a hydrogen molecule is represented.
Hydrogen gas also is represented by the molecular formula H2, which reflects the number of atoms in each molecule
Lets draw some covalent bonds:
H2O
NH3
CH4

50. Multiple Covalent Bonds
In many molecules, atoms attain a noble gas configuration by sharing more than one pair of electrons between two atoms, forming multiple covalent bonds.
Atoms of the elements carbon, nitrogen, oxygen and sulfur most often form multiple bonds
A double bond two electron pairs are shared
A triple bond, three electron pairs are shared

51. Molecular Structure
One of the most useful molecular models is the structural formula, which uses letter symbols and bonds to show relative positions of atoms
The structural formula for many molecules can be predicted for many molecules by drawing the Lewis structure.
Although it is fairly easy to draw Lewis structures for most compounds formed by nonmetals, it is a good idea to follow rules.

52. Rules for determining Lewis structure:
Predict the location of certain atoms:
Hydrogen is always a terminal, or end, atom. Because it can only share one pair of electrons, hydrogen can be connected only to one other atoms
The atom with the least attraction for shared electrons in the molecule is the central atom. This element usually is the one closer to the left on the periodic table. Find the total number of electrons available for bonding. This total is the number of valence electrons in the atoms in the molecule
Find the total number of electrons available for bonding. This total is the number of valence electrons in the atoms of the molecule
Determine the number of bonding pairs by dividing the number of electrons available for binding by two
Place one bonding pair (single bond) between the central atom and each of the terminal atoms
Subtract the number of pairs you used in step 45 from the number of bonding pairs in step 3, place the electrons around the terminal atoms first, and the the remaining pairs to the central atom
If the central atoms in not surrounded by four electron pairs, it doesn’t have an octet, you must convert one or two of the lone pairs on the terminal atoms to a double bond as needed

53. Lewis Structures Board Notes: Draw an ammonia molecule (NH3)
Draw carbon dioxide molecule (CO2)
Draw the polyatomic ion phosphate (PO43-)

54. This is the end of the lecture

55. Molecular Shapes
The shape of a molecule determines many of its physical and chemical properties.
Molecular shape, in turn, is determined by the overlap of orbitals that share electrons
Theories have been developed to explain the overlap of boring orbitals and are used to predict the shape of the molecule

56. VSEPR Model
Many chemical reactions, especially those in living things, depend on the ability of two compounds to contact each other
The shape of the molecule determines whether or not molecule can get close enough to react
Once a Lewis structure is drawn, you can determine the molecular geometry, or shape, of the molecule

57. VSEPR Model
The model used to determine the molecular shape is referred to as the Valence Shell Electron Pair Repulsion or VSEPR
This model is based on an arrangement that minimizes the repulsion of shared and unshared pairs of electrons around the central atom

58. VSPER Model
In short, the repulsion between electrons makes them want to be as far part from each other as possible.
This repulsion makes it so molecules form predictable shapes
The bond angle between electrons changes with the number of electrons present
We are going to learn the different shapes

59. Molecular Shapes Example Pairs Shared Pairs Lone Pairs Molecular Shape
Bond Angle (degrees)
Hybrid orbitals
BeCl2 2
Linear
180 Sp
AlCl3 3
Trigonal planar
120
Sp2
CH4 4
Tetrahedral
109.5
Sp3
PH3 1
Trigonal pyramidal
107.3
H2O
Bent
104.5

60. This is the end of the lecture

61. Electronegativity and Polarity
Now you know that the type of bond that is formed when two elements react depends on which elements are involved.
What makes one type of bond form when carbon burns and another type form when iron corrodes?
The answer lies in how much attraction each type of atom has for electrons

62. Electronegativity and Polarity
Electron affinity is a measure of the tendency of an atom to accept an electron.
Excluding noble gases, electron affinity increases as the atomic number increases within a given period and decreases with an increase in atomic number within a group.
The scale of electronegativities allows a chemistry to evaluate the electron affinity of specific atoms when they are incorporated into a compound

63. Electronegativity and Polarity
Look at the electronegativity trends on the periodic table. Fluorine has the highest electronegativity value of 3.98, while francium has the lowest, 0.7.
The same trends appear with electronegativities than can be observed with electron affinities
Because noble gases do not generally form compounds, individual electronegativities for noble gases like helium are not given

64. Polarity
The character and type of a chemical bond can be predicted using the electronegativity difference of the elements that are bonded.
Example: Electronegativity of chlorine is 3.16, and hydrogen is
3.16
-2.20
=0.96

65. Polarity Unequal sharing of electrons results in a polar covalent bond
Sometimes sharing is equal, but a lot of the time sharing is not equal
When the electronegativity is equal, the bond is said to be nonpolar
When the electronegativity is unequal, the bond is said to be polar

66. Polarity
Molecules are either nonpolar or polar, depending on the location and nature of the covalent bonds they contain.
In addition to the electronegativity numbers, shape is really important in deciding polarity
Let’s look at a few molecules on the board and decide if they are polar or non polar
HCl
H2O
CH4

67. This is the end of the lecture