Chemical bonding

Chemical Bonding

CHEMICAL BONDS

• A chemical bond is the force that holds atoms together.

• There are 3 types of bonds:

• Ionic bond

• Covalent bond

• Metallic bond

Chemical bond

• Chemical bonds can form :

• A) By the attraction between opposite charged ions

• B) By the sharing of electrons between atoms

Positive Ion Formation

• A positive ion forms when an atom loses one or more valence electrons in order to attain a noble gas configuration (octet rule).

• A positively charged ion is called a cation

• Ex.

Metal Ions

• Metals atoms are reactive because they lose valence electrons easily, have Low ionization energy and low electron affinity

• The group 1 and 2 metals are the most reactive metals in the P.T.

• Metals in group 1 form +1 ions• Metals in group 2 form +2 ions• Metals in group 13 form +3 ions• Transition metals: is difficult to predict

Negative Ion Formation

• Nonmetals, located on the right side of the P.T., easily gain electrons to attain a stable outer configuration(octet rule) and form an anion.

Nonmetal Ions

• Elements in group 15 gain 3 electrons and form -3 ions

• Elements in group 16 gain 2 electrons and form -2 ions

• Elements in group 17 gain 1 electron and form -1 ions

Lewis dot diagrams for Ions

Practice

• Write the symbol of the ion and the dot structure of the following :

• a)calcium ion

• b) germanium ion

• c) phosphide

• d) oxide

The Ionic Bond

Na

e.c. 2,8,1

(Na +)

Ion

Atom

e.c. (2,8)+

The Sodium loses 1 electron to leave a complete outer shell.

It is now a Sodium ion with a charge of 1 +

The Sodium atom has 1 Electron in it’s outer shell.

+

Cl

e.c. 2,8,7

(Cl - )

Ion

Atom

e.c. (2,8,8)-

The Chlorine gains 1 electron to gain a complete outer shell.

It is now a Chlorine ion with a charge of 1 -

The Chlorine atom has 7 electrons in it’s outer shell.

-

Sodium atom

Na

Sodium ion

(Na +)

Chlorine atom

Cl

Chlorine ion

(Cl -)

The Ionic Bond

The sodium atom loses one electron to attain a complete outer shell and become a positive ion (Na +). The Chlorine atom gains one electron to attain a complete outer shell and become a negative ion (Cl –).Strong electrostatic forces attract the sodium and chlorine ions.

+ -

Ionic Bonds

Ion Cartoon

Covalent Bonds

• Atoms in nonionic compounds share electrons.

• A molecule is formed when 2 or more atoms bond covalently.

• The majority of covalent bonds form between atoms of nonmetallic elements.

Covalent Bonds

Covalent Bonds

Covalent bonds can be single, double or triple

• Single covalent bond: atoms share 1 pair of electrons

• Double covalent bond: atoms share 2 pairs of electrons

• Triple covalent bond: atoms share 3 pairs of electrons

Covalent bonds

Covalent bonds

• The halogens, group 17, form single covalent bonds with atoms of other nonmetals. They can only form 1 bond since they have 7 valence electrons.

• The chalcogens, group 16, have 6 valence electrons, can form a total of 2 bonds. These can be single or double.

• The group 15 elements, have 5 valence electrons, can form a total of 3 bonds. These can be single, double or triple.

Practice

• Draw the Lewis structures for each molecule:

• a) PH3

• b) H2S

• c) HCl

• d) CCl4

• e) SiH4

• f) OBr2

Electronegativity and Polarity

• The type of bond formed is related to each atom´s attraction for electrons.

• Electronegativity indicates the relative ability of an element´s atoms to attract electrons in a chemical bond.

• Nonmetals have higher electronegativities than do metals.

• Each element is assigned a value:

Electronegativity

Types of Bonds

Types of bonds

• Bond can be: polar covalent, nonpolar covalent and ionic.

• Polar bond: a bond in which electrons are shared unequally.

• Nonpolar bond: a bond in which electrons are shared equally.

• Ionic bond: a bond in which electrons are transferred.

• The character of a bond depends on how strongly each of the bonded atoms attracts electrons.

Practice

• Use electronegativities to classify each of the following bonds as nonpolar covalent, polar covalent or ionic:

• a) O-H

• b) O-K

• c) Cl- As

• d) N -N

POLARITY OF MOLECULES

• Nonpolar molecules: are molecules that have a symmetrical arrangement and the dipoles cancel each other.

• Polar molecules: one end of the molecule is more negatively charged than the other end, have a dipole.

POLARITY OF MOLECULES

PRACTICE

• Indicate if each of the following molecules is polar or nonpolar:

• a) BF3

• b) CH3F

• c) CCl4

• d) NF3

• e) Br2

IONIC AND COVALENT COMPOUNDS

IONIC COVALENT METALLIC

TYPE OF PARTICLE

PHYSICAL STATE

MELTING POINT

ELECTRIC CONDUCTIVITY

SOLUBILITY

EXAMPLES