A chemical bond results from the simultaneous attraction of electrons by two atomic nuclei.

+ +

-

-

-AttractionAttraction

Electrons are located at certain specific energy levels around the nucleus.The max. number of electrons in each energy level equals the number of elements in each period.

The number of energy levels occupied by electrons equals the period number.

The electrons that occupy the outermost energy level are called valence electrons.

1 e- 2 e-

1 e- 6 e- 8 e- 8 e- 8 e-

1 e- 2 e- 2 e- 2 e- 2 e- 2 e-

1 p+ 3 p+ 8 p+ 10 p+ 11p+ 12 p+

H Li O Ne Na Mg

Valence electrons

Draw the remaining energy level diagrams of the first 18 elements and their ions.

• Electrons exist in orbitals– region of space

where there is a high probability of finding electrons of a particular energy

• Orbitals may be occupied by one or two electrons.

• In 1916, G.N. Lewis created a simple model of the arrangement of the valence electrons in atoms.

• A Lewis dot diagram of an atom includes:– the chemical symbol– dots that represent the

valence electrons

F

1) Write the element symbol.

2) Using a dot to represent each valence electron, place a single dot into each of the four sides (orbitals) of the elemental symbol.

3) If additional locations are required for electrons repeat step two.

Note: Maximum of eight electrons

• Bonding electron a single electron occupying an orbital.

• Lone pair a pair of electrons occupying a filled orbital. Non-bonding electrons. S

lone pair

Bonding electron

Bonding Capacity: The maximum number of single covalent bonds formed by an atom.Determined by the number of bonding electrons.

Cl

low electronegativityhigh electronegativity

e-Li

Lithium loses the e- tug-of-war with chloride.

- +

3.0 1.0

the tendency for an atom to attract electrons to itself when it is chemically combined with another element.

Electronegativity decreases as we move down a group.

Electronegativity increases from left to right in a period.

Li Be B C N O F

Li

Na

K

Rb

Cs

Fr

Practice

P.82 # 1- 5

Covalent bonds form between non-metal atoms

Covalent bonds involve sharing a pair of electrons, each atom thinking it has a complete outer shell because of the shared electrons

+

electrons are transferred from metal to non-metal ions arrange themselves so they are near the opposite charge this forms an ionic crystal lattice

• Metallic bonds are caused by the attraction of the free electrons for the cations of the metal.

• Pure metals do not consist of metal atoms, but of closely packed cations suspended in a “sea” of free electrons which can move between the cations (+ ions).

Free e- move rapidly in response to electric fields, thus metals are excellent conductors of electricity.

Free e- transmit kinetic energy rapidly, thus metals are excellent conductors of heat.

However, individual atoms are held loosely to other atoms, so atoms slip easily past one another, so metals are ductile.

Section 3.1 Questions

P.84 # 1 – 10,12