Chemistry Test Notes

Chapters 7&8 Gauge Sheet
7.1- Ions
To find the number of valence electrons in an atom of a representative element, simply look at its group number.
Atoms of metals tend to lose their valence electrons, leaving a complete octet in the next-lowest energy level.
Atoms of some non-metals tend to gain electrons or to share with another non-metal to achieve a complete octet.
The gain of negatively charged electrons by a neutral atom produces an anion.
7.2- Ionic Bonds and Ionic Compounds
Although they are composed of ions, ionic compounds are electrically neutral.
Most ionic compounds are crystalline solids at room temperature.
Ionic compounds generally have high melting points.
Ionic compounds can conduct an electric current when melted or dissolved in water.
7.3-Bonding in Metals
The valence electrons of metal atoms can be modeled as a sea of electrons.
Metal atoms are arranged in very compact and orderly patterns.
Alloys are important because their properties are often superior to those of their component elements.
8.1-Molecular Compounds
Molecular compounds tend to have relatively lower melting and boiling points than ionic compounds.
A molecular formula shows how many atoms of each element a molecule contains.
8.2-Covalent Bonding
In covalent bonds, electron sharing usually occurs so that atoms attain the electron configurations of noble gases.
An electron dot structure such as H:H represents the shared pair of electrons of the covalent bond by two dots.
Atoms form double or triple covalent bonds if they can attain noble gas structure by sharing two pairs or three pairs of electrons.
In a coordinate covalent bond, the shared electron pair comes from one of the bonding atoms.
A large bond dissociation energy corresponds to a strong covalent bond.
The actual bonding of oxygen atoms in ozone is a hybrid, or mixture, of the extremes represented by the resonance forms.
The octet rule cannot be satisfied in molecules whose total number of valence electrons is an odd number.
There are also molecules in which an atom has fewer, or more, than a complete octet of valence electrons.
8.4-Polar Bonds and Molecules
The more electronegative atom attracts electrons more strongly and gains a slightly negative charge. The less electronegative atom has a slightly positive charge.
When polar molecules are placed between oppositely charged plates, they tend to become oriented with respect to the positive and negative plates.
Intermolecular attractions are weaker than either ionic or covalent bonds.
Melting a network solid would require breaking covalent bonds throughout the solid.
Vocabulary
1. Valence Electrons- The electrons in the highest occupied energy level.
2. Octet Rule- Atoms tend to achieve the electron configuration of a noble gas.
3. Ionic Bonds- The electrostatic force that holds ions together in ionic compounds.
4. Ionic Compound- Compounds composed of Cations and Anions,
5. Chemical Formula- The number of atoms in the smallest representative unit of a substance.
6. Formula Unit- The lowest whole-# ratio of ions in an ionic compound.
7. Coordination Number- the # of ions of opposite charge that surround the ion in a crystal.
8. Metallic Bonds- the attraction of the free-floating valence electrons for the positively charged metal ions.
9. Alloys- Mixtures composed of two or more elements, at least one of which is a metal.
10. Covalent Bond- the sharing of electrons between atoms to hold them together.
11. Molecule- A neutral group of atoms joined together by covalent bonds.
12. Diatomic Molecule- A molecule consisting of two atoms.
13. Molecular Formula- the chemical formula of a molecular compound.
14. Single Covalent Bond- the bond between two atoms that share electrons.
15. Structural Formula- shows the arrangement of covalently bonded atoms.
16. Unshared Pair- a pair of valence electrons that is not shared between atoms.
17. Polyatomic Ion- A tightly bound group of atoms that has a positive or negative charge and behaves as a unit.
18. Nonpolar Covalent Bond- All electrons are shared equally.
19. Polar Bond- a covalent bond between atoms in which the electrons are shared unequally.
20. Polar Molecule- One end of the molecule is slightly negative and the other is slightly positive.
21. Hydrogen Bonds- An attractive force in which a hydrogen is covalently bonded to a very electronegative atom is also weakly bonded to an unshared electron pair of another electronegative atom.
22. Network Solids- Solids in which all of the atoms are covalently bonded to each other.