1. Bonding

2. Things We’ve Learned Atoms have the ability to gain or lose electrons
Metal lose elections to form cations, Non-metals gain electrons to form anions
Ionization energy is the amount of energy needed to remove an electron.
Electronegativity is an atoms ability to attract an electron to form a compound

3. Notes: Ions
Pyrite (FeS2) is often mistaken for gold—hence its nickname, “fool’s gold.” Pyrite is an example of a crystalline solid.

4. Valence Electrons
Valence electrons are the electrons in the highest occupied energy level of an element’s atoms.
The number of valence electrons determines the chemical properties of an element.
To find the number of valence electrons in an atom of a representative element, look at its group number.

5. Determining the Number of Valence Electrons
Atoms of the Group 1A elements (hydrogen, lithium, sodium, and so forth) all have one valence electron, corresponding to the 1 in 1A.
Exceptions: Helium 2s2 Group 8A

6. Lewis Dot Structures
Electron dot structures are diagrams that show valence electrons in the atoms of an element as dots.
Notice that all the electrons within a given group (with the exception of helium) have the same number of electron dots in their structures.
Electron Dot Structures of Some Group A Elements
Period
Group 1A 2A 3A 4A 5A 6A 7A 8A 1 2 3 4

7. Lewis Dot Practice Draw the electron dot structure for bismuth. Bi •
• • •

8. The Octet Rule
The octet rule states that in forming compounds, atoms tend to achieve the electron configuration of a noble gas.
Atoms of each of the noble gases (except helium) have eight electrons in their highest occupied energy levels and the general electron configuration of ns2np6.
Example: Neon (Ne) 1s22s22p6

9. The Octet Rule
Atoms of metals tend to lose their valence electrons, leaving a complete octet in the next-lowest energy level.
Atoms of some nonmetals tend to gain electrons or share electrons with another nonmetal atom or atoms to achieve a complete octet.

10. Formation of Cations
A positively charged ion, or cation, is produced when an atom loses one or more valence electrons.
Example: A sodium atom (Na) forms a sodium cation (Na+).
The most common cations are those produced by the loss of valence electrons from metal atoms.
Na 1s22s22p63s Na+ 1s22s22p6
–e–
octet

11. Formation of Cations
Both the sodium ion and the neon atom have eight electrons in their valence shells (highest occupied energy levels).

12. Transition Metal Cations
The charges of cations of the transition metals may vary.
An atom of iron may lose two valence electrons, forming the Fe2+ cation, or three valence electrons, forming the Fe3+ cation.

13. Transition Metals Cations
Fool’s gold is composed of iron(II) cations (Fe2+) and disulfide anions (S22–). Write the electron configuration of the Fe2+ ion.
Fe: 1s22s22p63s23p63d64s2
Fe2+: 1s22s22p63s23p63d6

14. Formations of Anions
An anion is produced when an atom gains one or more valence electrons.
Naming:
The name of the anion typically ends in -ide.
A chlorine atom (Cl) forms a chloride anion (Cl–).
Atoms of nonmetals and metalloids form anions by gaining enough valence electrons to attain the electron configuration of the nearest noble gas.

15. Bonding

16. Things We’ve Learned
Valence Electrons occupy the high energy level within an atom.
For representative elements, the group number if equal to the number of valence electrons
Lewis Dot Structures are used to show the number of valence electrons in an atom.
Atoms achieve an octet in their highest energy levels when forming compounds.
Metals lose electrons, non-metals gain electrons and transition metals find stable configuration.

17. Notes: Ionic Compounds
Where does table salt come from?
In some countries, salt is obtained by the evaporation of seawater. In other countries, salt is mined from rock deposits deep underground.

18. Formation of Ionic Compounds
An ionic compound is a compound composed of cations (metals) and anions (non-metals).
Although they are composed of ions, ionic compounds are electrically neutral.
The total positive charge of the cations equals the total negative charge of the anions.

19. Formation of Ionic Compounds
Anions and cations have opposite charges and attract one another by means of electrostatic forces.
The electrostatic forces that hold ions together in ionic compounds are called ionic bonds.

20. Formation of Ionic Compounds
When sodium and chlorine react to form a compound, the sodium atom transfers its one valence electron to the chlorine atom.
Sodium and chlorine atoms combine in a one-to-one ratio, and both ions have stable octets.

21. Formation of Ionic Compounds
A chemical formula shows the numbers of atoms of each element in the smallest ratio of a substance.
NaCl is the chemical formula for sodium chloride. Ratio 1:1 (one sodium for every 1 chlorine atom)

22. Predict The Following Compounds
lithium and fluorine
potassium and oxygen
magnesium and nitrogen

23. Properties of Ionic Compounds
Most ionic compounds are crystalline solids at room temperature.
The component ions in such crystals are arranged in repeating three-dimensional patterns.
The beauty of crystalline solids comes from the orderly arrangement of their component ions.

24. Properties of Ionic Compounds
Ionic compounds generally have high melting points.

25. Properties of Ionic Compounds
Ionic compounds can conduct an electric current when melted or dissolved in water.
To (+) electrode
To (–) electrode
Inert metal electrodes
Flow of electrons
Current meter
Power source
Cl–
Na+

26. Bonding

27. Things We’ve Learned . . .
Ionic Compounds are made of Metals and Non Metals
Metal lose electrons and to form a positive charge
Non-Metals gain electron to form a negative charge
When forming Ionic compounds, the positive and negative charges should be equal.
Example: Al3+ + O2-  Al2O3

28. Notes: Molecular Compounds
How are atoms joined together to make compounds with different structures?
Although the types of pieces are limited, you can make many different toy models depending on how many pieces you use and how they are arranged.

29. Molecules and Molecular Compounds
A molecular compound is composed of non- metal atoms.

30. Molecules and Molecular Compounds
Only the noble gas elements, such as helium and neon, exist as uncombined atoms.
They are monatomic; that is, they consist of single atoms.

31. Molecules and Molecular Compounds
An oxygen molecule is an example of a diatomic molecule—a molecule that contains two atoms.
Other elements found in nature in the form of diatomic molecules include hydrogen, nitrogen, and the halogens.

32. Properties of Molecular Compounds
Ionic compounds are generally crystalline solids with high melting points. Molecular compounds have different properties from Ionic compounds.
Examples:
Low melting point
Water (H2O) is a liquid at room temperature.

33. Sharing Electrons
Another way that atoms can combine is by sharing electrons.
Atoms that are held together by sharing electrons are joined by a covalent bond.

34. A compound composed of molecules is called a molecular compound.
Sharing Electrons
Molecules can also be made of atoms of different elements. (Non-metals)
A compound composed of molecules is called a molecular compound.
Water is an example of a molecular compound.

35. Molecular Formulas
A molecular formula shows how many atoms of each element a substance contains.
The subscript written after an element’s symbol indicates the number of atoms of each element in the molecule.
Ex: The molecular formula of water is H2O.

36. Molecular Structure
The arrangement of atoms within a molecule is called its molecular structure.
The molecular structure of water shows how the oxygen atom is in the middle between the hydrogen atoms.
The atoms in water are not arranged in a row. Instead the hydrogen atoms are mainly on one side of the water molecule.

37. Molecular Formula Practice
Acetylsalicylic acid, also known as aspirin, has a molecular formula of C9H8O4.
1. What elements make up acetylsalicylic acid?
2. How many atoms of each element are found in one molecule of acetylsalicylic acid?

38. Molecular Vs. Ionic Compounds

39. Bonding

40. Things We’ve Learned
Molecular compounds are composed of non-metal atoms
Molecular compounds are held together by the sharing of electrons
Properties of Molecular Compounds, Low melting/boiling point, wide range of physical properties (Solid Liquid Gas)
Diatomic molecules exist as pairs in nature. (H2, N2, O2 Group 7A)
Monatomic molecules are single atoms (Noble Gases)

41. Notes: Covalent Compounds
What is the difference between the oxygen you breathe and the oxygen in ozone in the atmosphere?
Our atmosphere contains two different molecules that are both made of oxygen atoms.

42. Octet Rule in Covalent Bonds
In covalent bonds, electron sharing usually occurs so that atoms attain the electron configurations of noble gases.

43. Single Covalent Bonds
Two atoms held together by sharing one pair of electrons are joined by a single covalent bond.
Hydrogen gas consists of diatomic molecules whose atoms share only one pair of electrons, forming a single covalent bond.
A structural formula represents the covalent bonds as dashes and shows the arrangement of covalently bonded atoms.

44. In F2, each fluorine atom has three unshared pairs of electrons.
Single Covalent Bonds
A pair of valence electrons that is not shared between atoms is called an unshared pair, also known as a lone pair or a nonbinding pair.
In F2, each fluorine atom has three unshared pairs of electrons.

45. Single Covalent Bonds- Examples
As you can see in the electron dot structures below, the oxygen atom in water has two unshared pairs of valence electrons.

46. Single Covalent Bonds- Examples
Methane contains four single covalent bonds.
The carbon atom has four valence electrons and needs four more valence electrons to attain a noble-gas configuration.

47. Single Covalent Bonds- Practice
Drawing an Electron Dot Structure
Hydrochloric acid (HCl (aq)) is prepared by dissolving gaseous hydrogen chloride (HCl (g)) in water. Hydrogen chloride is a diatomic molecule with a single covalent bond. Draw the electron dot structure for HCl.

48. Double and Triple Covalent Bonds
Atoms form double or triple covalent bonds if they can attain a noble gas structure by sharing two or three pairs of electrons.
A double covalent bond is a bond that involves two shared pairs of electrons.
A bond formed by sharing three pairs of electrons is a triple covalent bond

49. Double and Triple Covalent Bonds- Examples
The carbon dioxide (CO2) molecule contains two oxygens, each of which shares two electrons with carbon to form a total of two carbon–oxygen double bonds.
Double and Triple Covalent Bonds

50. Double and Triple Covalent Bonds- Examples
Nitrogen (N2), a major component of Earth’s atmosphere, contains triple bonds.
A single nitrogen atom has five valence electrons; each nitrogen atom in the molecule must share three electrons to have the electron configuration of neon.

51. Bond Dissociation Energy
A large bond dissociation energy corresponds to a strong covalent bond.
As the number of bonds increase the amount of energy required to break the bond increases.

52. Drawing Covalent Compounds
HBr
NCl3
C2H4
C2H5Cl

53. Bonding

54. Things We’ve Learned
Non-metals atoms share electrons in order to in achieve their octet.
Some atoms can share two or three pairs of electrons. (Double and Triple Bonds)
Drawing covalent compounds show the structure of the molecular compound

55. Notes: Polar and Non-Polar Covalent Compounds

56. Bond Polarity
Covalent bonds differ in terms of how the bonded atoms share the electrons.
Bond Polarity depends on structure of the molecule and number of atoms joined together.
The more electronegative atom attracts more strongly and gains a slightly negative charge. The less electronegative atom has a slightly positive charge.

57. Bond Polarity
The bonding pairs of electrons in covalent bonds are pulled between the nuclei of the atoms sharing the electrons.

58. Non-Polar Vs. Polar Covalent
When the atoms in the bond pull equally (as occurs when identical atoms are bonded), the bonding electrons are shared equally, and each bond formed is a nonpolar covalent bond.
Ex: CH4
A polar covalent bond, known also as a polar bond, is a covalent bond between atoms in which the electrons are shared unequally.
Ex: HCl

59. Bond Polarity Practice
Which type of bond (nonpolar covalent, polar covalent, or ionic) will form between each of the following pairs of atoms?
Indicate the positive and negative charge of each atom.
a. N and H
b. F and F
c. Ca and Cl
d. Al and Cl

60. Bonding