Bond ing

Bonding A chemical bond results from the simultaneous attraction of electrons by two atomic nuclei. - - Attraction Attraction + + -

The electrons that occupy the outermost energy level are called valence electrons. The max. number of electrons in each energy level equals the number of elements in each period. Electrons are located at certain specific energy levels around the nucleus. The number of energy levels occupied by electrons equals the period number.

Electron Energy Level Diagrams 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 Draw the remaining energy level diagrams of the first 18 elements and their ions.

Electron Configuration 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.

Lewis Dot Diagram 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

Lewis Diagram for fluorine 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   F     

Types of Valence Electrons lone pair Bonding electron  a single electron occupying an orbital. Lone pair  a pair of electrons occupying a filled orbital. Non-bonding electrons.   S   Bonding electron   Bonding Capacity: The maximum number of single covalent bonds formed by an atom.Determined by the number of bonding electrons.

e- - Cl Li Electronegativity 3.0 1.0 + the tendency for an atom to attract electrons to itself when it is chemically combined with another element. e- - + Cl Li 3.0 1.0 high electronegativity low electronegativity Lithium loses the e- tug-of-war with chloride.

Trends in Electronegativity Electronegativity increases from left to right in a period. Li Be B C N O F Electronegativity decreases as we move down a group. Li Na K Rb Cs Fr

Homework Practice P.82 # 1- 5

+ Covalent Bonding 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

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

Bonding in Metals 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.

Homework Section 3.1 Questions P.84 # 1 – 10,12