Mr. Bouyer - Day 1

Whether atoms will interact depends almost entirely on the arrangement of their outer energy level electrons.

Electrons in the outer energy level can be called valence electrons. It is these electrons that determine the formation of chemical bonds. There are certain numbers of valance electrons that are more stable than others. Atoms will gain or lose electrons in order to become more stable.

Only s and p sublevel electrons will be valence electrons. Electrons in the d and f sublevels are never in the outer energy level of an atom.

Types of chemical bonds:

1. Ionic bonds - electrons are transferred between atoms.
   • One atom gains electrons while another atom loses electrons.
   • When this happens, the charges within each atom are no longer balanced.
   • The atoms have become ions - one with a positive charge, the other with a negative charge.
   • The force of attraction between these opposite charges holds the ions together in an ionic bond.

   • Important Terms:
     • Ionization - the process of removing an electron from an atom to form an ion.
     • Ionization energy - the energy needed to remove an electron from an atom. For this to occur, the attraction between the negatively charged electron and the positively charged nucleus must be overcome.
       • First ionization energy - the energy required to remove the most loosely bound electron from an atom.
       • It takes more energy to remove an electron from a positively charged ion, as this chart of second and third ionization energies shows.
         • Notice the jump in energy required between the outer energy level and the next lowest level.
     • Electron affinity - the tendency of an atom to attract electrons. This characteristic determines the type of bond formed between atoms.

       Metals generally have a low electron affinity. Nonmetals generally have a high electron affinity.

   
   
   
   

2. Covalent bonds - electrons are shared between atoms.
   • Atoms that do not lose electrons easily usually form covelent bonds.
   • The positive nucleus of both atoms has an equal attraction for the electrons being shared.
   • The shared electrons spend most of their time between the two atoms.
   • The force of attraction between both nuclei and the shared electrons hold the atoms together in a covalent bond.

   • Covalent bonding can occur between atoms of the same element. Listed below are the 7 diatomic molecules. When found alone in nature, these elements exist only as two atoms covalently bonded.

     Know the 7 diatomic molecules.

     • Hydrogen - H₂
     • Nitrogen - N₂
     • Oxygen - O₂
     • Florine - F₂
     • Chlorine - Cl₂
     • Bromine - Br₂
     • Iodine - I₂

   • Polyatomic ion - a group of covalently bonded atoms that acts like a single atom when combining with other atoms. Overall, this group of atoms is not electrically balanced and does have a total charge.

3. Metallic bonds - electrons are distributed equally through a metallic crystal.
   • The electrons in metals can be thought of as being property of all the atoms.
   • The positive nuclei are surrounded by a "sea of electrons" that are all attracted by the nuclei at the same time.

Metals tend to lose valence electrons easily. Compounds formed between an atom that easily looses electrons and an atom that easily gains electrons tend to form ionic bonds. The greater the distance between the two atoms on the periodic table, the more ionic the bond.

Some of the nonmetals, such as carbon and oxygen, form compounds with each other. Since these elements have similar electron affinities, they tend to form covalent bonds. The closer the two atoms are to each other on the periodic table, the more covalent the bond.

It is important to understand that chemical bonding is almost never totally ionic or totally covalent. Chemical bonds will have some traits of each type of bond. Bond types are often expressed as a percentage of each type of bond.

Certain electron arrangements are more stable than others. An understanding of the periodic table allows us to predict the bonding characteristics of atoms.

All chemical reactions occur between electrons in the outer energy level of atoms.

The most stable atoms - their outer energy level is full. Somewhat stable atoms - the sublevels of their outer energy level are half-filled. The Octet Rule - the maximum number of electrons in the outer energy level is 8. Atoms will form compounds to reach eight electrons in their outer energy level. Atoms with less than 4 electrons in their outer level tend to lose electrons to form compounds. Atoms with more than 4 electrons in their outer level tend to gain electrons to form compounds. A helium atom only has one energy level (#1), which has only one sublevel (s). The 1s level can only hold two electrons. Helium has those two electrons, which makes the atom's outer energy level full. Because of this, helium is said to conform to the octet rule.

Electron-dot diagram - a way of drawing the outer energy level electrons of an atom.
The chemical symbol for the atom is placed in the center of an imaginary rectangle. The symbol represents the nucleus and all electrons of the atom, except the valence electrons. Each side of the imaginary box around the symbol represents an electron energy sublevel. Only s and p sublevel electrons will ever be used in an electron-dot diagram.

Electrons are represented by "dots". The first two electrons go into the s sublevel. The remaining electrons go counterclockwise around the imaginary box. Hund's Rule tells us to place one electron in each of the p sublevels before placing a second electron in any p sublevel.

Examples of electron-dot diagrams

Orbital-filling diagram - a way to represent the spin of electrons in the outer energy level of an atom. The diagram consists of a series of boxes with arrows in them. Each box represents an orbital in an electron energy sublevel. The arrows represent electrons. The first arrow drawn in a box points up, indicating it's spin. The second arrow in the box points down, indicating an opposite spin. Orbitals never have more than two electrons.

Orbital-filling diagrams might be drawn for the whole atom, but usually just show the outer electron energy level. Whatever the drawing represents, the number of boxes is determined by the number of orbitals in each energy level represented.

This is the complete orbital-filling diagram for what element?

1s2	2s2	2p6			3s2	3p1
The electron configuration is not part of the orbital-filling diagram. It is shown here to help you see how the two compare.

Homework Assignment 044:
This assignment must be turned in by the beginning of class tomorrow to receive credit.
Scoring criteria

1. NaCl is an ionic compound. What type of bond holds the atoms together?
2. How many valence electrons are in an atom of Pb?
3. How many valence electrons are in an atom of S?
4. How many valence electrons are in an atom of Ca?
5. What nonmetal on row two of the periodic table has a half-filled sublevel?
6. What nonmetal on row two of the periodic table has a full sublevel?
7. Draw the electron-dot diagram for a copper atom.
8. Draw the electron-dot diagram for a water molecule.

   Draw a combination of 3 atoms in which the outer energy level of all atoms is full.

9. Draw the orbital-filling diagram for the outer energy level of a sulfur atom.

Quantum Numbers

The orbital filling diagram is for an aluminum atom.
The last box is 3p¹, which is aluminum's location on the periodic table.
The 13 arrows represent the 13 electrons of aluminum.