NOTES: TYPES of CHEMICAL BONDS Name______

NOTES: TYPES OF CHEMICAL BONDS Name______Date______Block______

What is a chemical bond?

. A strong attractive force between atoms in a compound

 Ionic: attraction of ______

 Covalent: attraction of the nucleus of each atom to a ______pair of valence electrons

 Metallic: attraction of ______charged metal ions to the mobile valence electrons in the metal

The Octet Rule

. The Octet Rule:

 Atoms will lose, gain, or share valence electrons until each atom achieves…

an ______of valence electrons

a total of _____valence electrons

a ______electron configuration

. The Octet Rule is our guiding principle in the formation of chemical bonds between atoms

Types of Bonds

 Ionic: atoms lose or gain valence electrons, forming + and – ions, which are then attracted to one another because they are ______charged

 Covalent: atoms ______valence electrons, the nuclei of both atoms are strongly attracted to the shared valence electrons, forming the bond

May be nonpolar (equal sharing) or polar (______sharing)

 Metallic: the valence electrons of atoms in the metal are mobile, leaving the metal atoms with a ___ charge, the + charged metal ions are attracted to the free-floating ______

What determines the type of bond formed between two atoms?

. The “______” for electrons!

. Atoms play “tug of war” with electrons

. The ______of the atoms determines their “strength” in the tug of war

. Electronegativity is a measure of the tendency of an atom to ______a bonding pair of electrons.

. The Pauling scale is the most commonly used. Fluorine (the most electronegative element) is assigned a value of ______and values range down from there Consider two atoms…

. Atom A and Atom B form a bond…

What if atom B is a lot more electronegative than atom A?

. Sometimes one of the atoms is much stronger (more electronegative) than the other, and “wins” the electron- this results in a transfer of electron(s) to form ions, and thus an ______

. Consider a bond between two atoms, A and B.

 In this case, the electron pair is dragged right over to B's end of the bond. A has lost control of its electron, and B has complete control over both electrons. Ions have been formed.

A+1 ------:B-1

What happens if B is slightly more electronegative than A?

. Sometimes one of the atoms is a little stronger than the other, but not strong enough to “win” the electron

. This results in ______sharing of electrons, which is a polar covalent bond

. B will attract the electron pair more than A does.

. That means that the B end of the bond has more than its fair share of electron density and so becomes ______. At the same time, the A end (rather short of electrons) becomes slightly positive.

δ+A------:---Bδ-

(note that δ is pronounced “delta” means “______”, so δ+ means slightly positive and δ- means slightly negative. The δ- will always be on the more electronegative of the two atoms)

. This is described as a polar bond (or polar covalent)- a covalent bond in which there is a ______of charge between one end and the other

 in other words one end is slightly positive and the other ______.

 The electron density lies ______to one atom than the other

 Examples include most covalent bonds. The hydrogen-chlorine bond in HCl or the hydrogen-oxygen bonds in water are typical NOTES: TYPES OF CHEMICAL BONDS Name______Date______Block______

What happens if two atoms of equal electronegativity bond together?

. Sometimes the atoms are equal or nearly equal in their strength (electronegativity), and neither wins

. This results in ______sharing of the electron(s), and thus a nonpolar covalent bond

. If the atoms are equally electronegative, both have the same tendency to attract the bonding pair of electrons, and so it will be found on average ______between the two atoms.

A-----:-----B

. To get a bond like this, A and B would usually have to be the ______atom. You will find this sort

of bond in, for example, H2 or Cl2 molecules.

How to determine bond type

. The ______in electronegativity between the two atoms is what determines whether a bond is ionic, polar covalent, or nonpolar covalent

. To determine the bond type-

 Look up the electronegativity values for the two atoms in the bond

 ______to find the difference

Use the chart (next slides) to determine the type of bond

. Difference in electronegativity Type of Bond

0- 0.3 ______covalent

0.4- 1.0 moderately polar covalent

1.1- 1.7 very polar covalent

> 1.7 ______

% Ionic Character

. Bonds can also be described based on their % ionic character, which is another way to express the degree of polarity in the bond.

 100% ionic character would represent a purely ______bond

 0% ionic character would represent a purely ______bond Let’s compare ionic and covalent

IONIC:

• Transfer of electrons to form ions due to ______electronegativity difference between the two atoms

• Oppositely charged ______are attracted

• The ions build up in a 3 dimensional crystal lattice; there are not individual ______

• The chemical formula represents a ______: the lowest whole number ratio of ions that is neutral

POLAR COVALENT:

______sharing of electrons due to some electronegativity difference between the two atoms

• Electron clouds ______and electrons are shared unequally to form bond

• Individual molecules are formed

• The chemical formula represents a ______

NONPOLAR COVALENT:

• Equal sharing of electrons since the two atoms have ______or nearly equal electronegativities

• Electron clouds ______and electrons are shared equally to form the bond

• Individual molecules are formed

• The chemical formula represents a ______