1. Chemistry
Chapter 7
Chemical Bonding

2. Chemical Bonding Elements are rarely found in an uncombined form.
A chemical bond a force that holds elements together in compounds.
Compounds may be classified as two types: ionic compounds held together by ionic bonds or molecular compounds held together by covalent bonds.

3. Atoms seek to achieve lower-energy states
Combining with other elements allows an atom to achieve a lower energy state than it could reach on it’s own.
Noble gases already have the lowest energy state possible and therefore are very stable.
An element can gain the electron configuration of the noble gas of which it is closest to by gaining or losing electrons, (there are exceptions).

4. Anions Nonmetals tend to gain electrons more easily.
Electron affinity is the energy change that occurs when an electron is added to an atom or ion.
Atoms that gain electrons become negatively charged and are called anions.
Nonmetals gain electrons to form anions with a noble-gas configuration.

5. Cations
Ionization energy is the amount of energy needed to completely remove an electron
Metals tend to lose electrons thus forming a positively charged ion called a cation.
The more electrons you remove from an atom the higher the ionization energy until you can no longer remove an electron.
Losing a number of electrons that is equal to the group number produces a noble-gas configuration.

6. Transition Metals
Transition metals do not form ions in as predictable of a manner as the representative elements.
For transition metal to achieve noble gas configuration they may have to lose eleven electrons, therefore instead they will lose just enough electrons to reach a full orbital.
Because of this many of the transition metals have multiple ions they can form such as Cu 1+ and Cu2+ or V2+ , V3+ , V4+ and V5+.

7. Formation of Ionic Compounds
A chemical rxn occurs with a transfer of electrons between metals & nonmetals.
Steps in ionic cmpd formation:
Cations & anions are formed with noble-gas configurations and become stable (cont).
Stable ions attracted to each other by electrostatic forces form new ionic cmpnds.
The bond formed between oppositely charged ions is called an ionic bond.

8. Ionic Charges
All compounds are electronically neutral, therefore combining ratios of metals and nonmetals in ionic bonds can be predicted.
Group A metals can be predicted using their group number.
Exceptions to this rule are listed in Table 6.5 on page 159.
Group B metals can form ions with more than one charge and are also listed in Table 6.5.

9. Polyatomic ions
Simple ions or monatomic ions are made up of only one element.
Polyatomic ions are made up of more than one element in certain ratios, & are inseparable.
Polyatomic ions are enclosed by parenthesis if there is more than one of them. Ex. (SO4)2
SO4 is a sulfate ion. It has four oxygen atoms and one sulfur atom combined into a group held together by covalent bonds.

10. Formulas for Ionic Compounds
The formula for an ionic compound represents the ratio of atoms that exist in a molecule of the compound.
Total positive charges must equal total negative charges.
The positive ion(s) should always be written first
Charges of the ions are not written.
The number of ions present, if more than one, is written as a subscript next to the ion.

11. Nature of the Ionic Bond
Ionic bonds are formed by the electrostatic attraction between cations and anions.
Ionic compounds form when:
Ionization energy is low (energy input)
Electron affinity is high (energy release)
Lattice energy is high
Lattice energy is the energy released by the attraction between the cation and anion.

12. Lattice Structure
Ionic compounds exist in a lattice structure because of the systematic pattern in which they bond.
Lattice structure is the regular arrangement of ions in a solid.
The formula is the smallest unit of the lattice structure.

13. Law of Definite Composition
The law of definite composition states that elements always show some definite combining ratio of atoms or ions.
Therefore, this law can be used to determine the definite combining ratio by mass.
Ex. NaCl = 1:1 ratio, or 23.0 : 35.5 ratio

14. Ionic Compound Characteristics
Ionic compound characteristics include:
Form solids at room temperatue with definite shapes and angles
Crystalline structures (they form crystals that are brittle)
High melting and boiling points
When dissolved in water, they will conduct an electric current.

15. Coordination Number
For each ion in a crystal, is the number of ions of opposite charge that surround that ion

16. Metallic Bonding Metals form crystalline structures too.
However, valence e- drift around the central cations (+), so they can flow past each other rather than being brittle.
Called sea of electrons.
Hence, we get the metallic properties of ductility and malleabiity.

17. Alloys
Are mixtures of different metals, which have better properties than the simpler elements.
Bronze, brass, solder, sterling silver, cast iron, brass are examples.
HW: bring in something made of alloys along with its makeup.