Unit 1 – The Diversity of Matter and Chemical

Bonding

water ammonia

methane

Structural formulas show the way in which atoms are bonded to each other.

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.

Bonding Theory: Valence Electrons and Orbitals

Electrons exist in orbitals.

An orbital is a region of space where there is a high probability of finding electrons of a particular energy.

An orbital can be occupied by either one or two electrons.

The maximum number of bonding electrons determines an atom’s bonding capacity, the maximum number of single covalent bonds formed by an atom.

Bonding electron: a single electron occupying an orbital

Lone pair: two electrons occupying a filled orbital (non-bonding)

Electron Energy Level Diagrams

H

1 p+

1 e-

Li

3 p+

2 e-

1 e-

O

8 p+

2 e-

6 e-

Ne

10 p+

2 e-

8 e-

Na

11 p+

2 e-

8 e-

1 e-

Mg

12 p+

2 e-

8 e-

2 e-

valence electrons Level Max. # of Electrons

1 2

2 8

3 8

4 18

Electrons “spread out” to occupy any empty valence orbitals before forming electron pairs.

Atomic Models: Lewis Symbols

Gilbert Lewis(1875 – 1946)

In a Lewis symbol (or Lewis dot diagram), valence electrons are represented as dots.

two lone pairs and two bonding electrons

Electronegativity

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

Cl

low electronegativity

e-Li

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

- +

3.0 1.0high electronegativity

Metals tend to have low electronegativities and non-metals tend to have high electronegativities.

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

Trends in Electronegativity

e.g. period 2

e.g. group 1 (alkali metals)

Read pgs. 78 – 81

pg. 82 Practice #’s 1 – 5

Covalent Bonding

Covalent bonds form between non-metal atoms (all with high electronegativities).

Covalent bonds involve sharing a pair of electrons, each atom approximating a complete outer shell because of the shared electrons.

Ionic Bonding

Electrons are transferred from metal (low electronegativity) to non-metal (high electronegativity) atoms.

The result is the formation of positive cations and negative anions.

All ionic compounds are arranged in a 3-dimensional crystal lattice structure.

Each positive ion is surrounded by negative ions and vice versa.

Metallic Bonding

Metal atoms generally have lower electronegativity.

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).

The electrons act like a “glue” that holds the positive nuclei together.

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

The free electrons move rapidly in response to an electric field, making metals excellent conductors of electricity.

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

Read pgs. 82 – 84

pg. 84 Section 3.1 Questions #’s 1 – 10, 12