IONIC AND COVALENT BONDINGChapter 7 and 8

VALENCE ELECTRONS

Valence electrons are responsible for the bonding between two atoms.

OCTET RULE

In forming compounds, atoms tend to achieve the electron configuration of a noble gas.

An octet is the set of eight electrons in the outermost energy level 

CATIONS AND ANIONS

Atoms of metals tend to lose their valence electrons, leaving a complete octet in the next lowest energy level.

Atoms of some nonmetals tend to gain electrons or share electrons with another nonmetal to achieve a complete octet. The ions that are produced when atoms of

chlorine and other halogens gain electrons are called halides.

IONIC COMPOUNDS Ionic compounds are usually composed

of a metal cation and a nonmetal anion. Although they are composed of ions, ionic

compounds are electrically neutral.

ELECTROSTATIC FORCES

Cations and anions have opposite charges and attract one another by means of electrostatic forces. The electrostatic forces that hold ions together in ionic compounds are called ionic bonds.

CHEMICAL FORMULA

A chemical formula shows the kinds and numbers of atoms in the smallest representative unit for a substance

  A formula unit is the lowest whole

number ratio of ions in an ionic compound Ex. NaCl 1:1 Ex. MgCl2 1:2

PROPERTIES OF IONIC COMPOUNDS

Most ionic compounds are crystalline solids at room temperature

Dissolve in water (soluble) Ionic compounds generally have high

melting points Ionic compounds can conduct an

electric current when melted or dissolved in water

METALLIC BONDS

The valence electrons of metal atoms can be modeled as a sea of electrons

Metallic bonds consist of the attraction of the free-floating electrons for the positively charged metal ions.

COVALENT BONDING

Molecules and Molecular Compounds A covalent bond is described as the

sharing of electrons between two atoms. Covalent compounds are a combination of two or more nonmetals

MOLECULES

A molecule is a neutral group of atoms joined together by covalent bonds. A diatomic molecule is a molecule

consisting of two atoms of the same element.

Br I N Cl H O F

PROPERTIES OF MOLECULAR COMPOUNDS

Molecular Compounds tend to have relatively lower melting and boiling points than ionic compounds

Typically do not dissolve well in water Do not conduct electricity when

dissolved in water

MOLECULAR FORMULA

A molecular formula is the chemical formula of a molecular compound A molecular formula shows how many

atoms of each element a molecule contains.

THE OCTET RULE

In covalent bonds, electron sharing usually occurs so that atoms attain the electron configurations of noble gases. Single Covalent bond: Sharing of one pair

of electrons Double Covalent bond: Sharing of two pairs

of electrons Triple Covalent bond: Sharing of three pairs

of electrons

COORDINATE COVALENT BOND

A coordinate covalent bond occurs when one atom provides the shared electron pair Ex. Carbon Monoxide

DRAWING LEWIS DOT STRUCTURES FOR MOLECULES

1. SUM THE VALENCE ELECTRONS FROM ALL ATOMS

2. Use the first atom of the chemical formula as the central atom (except hydrogen) and connect all other elements to that central atom with a single bond (---).

3. Complete the octets of the atoms bonded to the central atom. (Don’t forget that hydrogen only needs two electrons)

4. If there are not enough electrons to give the central atom an octet, try multiple bonds!.

PRACTICE PROBLEMS

H2O

CF4

CO2

BOND POLARITY

Nonpolar covalent bond Atoms in the bond pull equally

Bonding electrons are shared equally Ex. Diatomic molecules

BOND POLARITY

Polar Covalent bond Atoms in the bond pull with different

strengths Bonding electrons are not shared equally Ex. HF

BOND POLARITY

Bond Polarity is based on the difference between two atoms electronegativity values Remember that electronegativity is the

ability of an atom to attract electrons in a chemical bond.