Chemical Bonds & Reactions

Ions

*A charged atom *Atoms obtain their charges by losing or gaining electrons during bonding. *Cation: positively charged atom formed from the loss of electrons -Typically metals *Anion: negatively charged atom formed from the gain of electrons -Typically nonmetals

What is a chemical bond?

*A force of attraction that holds two atoms together *Has a significant effect on chemical and physical properties of compounds *involves the valence electrons

Electron Dot Structures (Diagrams)

*A way of drawing the outer energy level electrons (valence) of an atom *Also called Lewis Symbols *The symbol for the element surrounded by as many dots as there are electrons in its outer energy level (valence). Examples

Determining the Number of Valence Electrons by Using the Periodic Table

*Atoms of elements in Groups 1 and 2 have the same number of valence electrons as their group number. *Atoms of elements in Group 3-12 do not have a general rule relating their valence electrons to their group number. However, they typically have between 1 or 2 valence electrons. *Atoms of elements in Groups 13-18 have 10 fewer valence electrons than their group number. (Exception - helium atoms have only 2 valence electrons, even though they are in group 18)

The Octet Rule

*Atoms will combine to form compounds in order to reach eight electrons in their outer energy level. -Atoms with less than 4 valence electrons tend to lose electrons. Typically metals. -Atoms with more than 4 valence electrons tend to gain electrons. Typically nonmetals. Be aware that there are some exceptions! CONSIDER EIGHT A HAPPY NUMBER FOR ATOMS!

Oxidation Number

*The charge that an atom would have if it lost or gained electrons; also known as the ionic charge *Can be helpful in determining which atoms will interact or bond with each other *Example:

IONIC BONDS

*The force of attraction between oppositely charged ions. *Occurs after a transfer or loss/gain of electrons *Usually form between atoms of metals and atoms of non-metals *Resulting compounds have a name that usually ends in -ide

Metallic Bond

A force of attraction between a positively charged metal ion and the electrons in the metal Many metal ions pass along many electrons Many properties of metals, such as conductivity, ductility, and malleability, result from the freely moving electrons in the metal Usually occurs between atoms of metals

COVALENT BOND

A force that bonds two atoms together by a sharing of electrons Each pair of shared electrons creates a bond Usually occurs between atoms of nonmetals

Covalent Bonds(single, double, and triple)

Bond length: average distance between the nuclei of two bonded atoms in a molecule Bond enthalpy (or bond energy): the energy required to break a bond As the bond order (the number of chemical bonds between atoms) increase: the bond strength increases the bond length decreases the bond enthalpy increases

Electron Dot Structures for Ions

Cations: chemical symbol of metal in brackets with the oxidation number (charge) outside the brackets as a superscript Anions: chemical symbol of nonmetal with the full valence shell electron dots surrounding it with brackets around it and the oxidation number (charge) outside the brackets as a superscript

Unequal Sharing (Polar Covalent Bond)

The unequal sharing of electrons between two atoms that gives rise to negative and positive regions of electric charge Results from an atom's electronegativity - the ability to attract electrons to itself