Unit 6A: Ionic and Covalent

Bonding

IonsWhy do elements in the same group behave similarly?• They have the same number of valence electrons.

Valence electrons are the electrons in the highest occupied energy level of an element’s atoms.

How do you find the number of valence electrons in an atom of a representative element? • The Group number.

IonsWhat are electron dot structures?• Diagrams that show valence electrons as dots.

IonsWhy do atoms form ions?• In order to become more stable

The octet rule states that in forming compounds, atoms tend to achieve the electron configuration of a noble gas.

How do metals become stable?• By losing their valence electrons

How do nonmetals become stable?• By gaining valence electrons• By sharing valence electrons with other nonmetals

IonsHow are cations formed?• Cations are formed when an atom loses one or

more electrons.

IonsHow are anions formed?• Anions are formed when an atom gains one or

more valence electrons.

Ionic Bonds and Ionic Compounds

What is an ionic compound?• A compound that is composed of cations and

anions.

What is the electrical charge of an ionic compound?• All ionic compounds are neutral

What is an ionic bond?• The electrostatic forces that hold cations and

anions together in an ionic compound.

Ionic Bonds and Ionic Compounds

How do chemists represent the composition of a substance?

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

Examples:• H2O

• C12H22O11

• Fe2O3

• CO2

Ionic Bonds and Ionic Compounds

The smallest unit of an ionic compound is called a formula unit. • Lowest whole-number ratio of ions in an ionic

compound

Examples:Sodium chloride• NaCl

Magnesium chloride• MgCl2

Molecular CompoundsWhy do atoms form molecular compounds?• To satisfy the octet rule

How are atoms held together in covalent bonds?• Sharing of valence electrons

Molecular CompoundsWhat is a molecular formula?• The chemical formula of a molecular compound• It shows how many atoms of each element a

molecule contains

Examples:• H2O

• CO2

• NH3

MoleculesDiatomic Molecule: A molecule consisting of only two atoms.

There are seven diatomic elements:• Hydrogen (H2)

• Oxygen (O2)

• Nitrogen (N2)

• Fluorine (F2)

• Chlorine (Cl2)

• Bromine (Br2)

• Iodine (I2)

The Nature of Covalent Bonding

Single Covalent Bond

An electron dot structure represents a covalent bond using dots to represent the shared pair of electrons.

The Nature of Covalent Bonding

Unshared Electrons• A pair of electrons not shared between atoms is

called an unshared pair of electrons

A structural formula represents covalent bonds by dashes and shows the arrangement of covalently bonded atoms.

The Nature of Covalent Bonding

Double Covalent Bond

The Nature of Covalent Bonding

Triple Covalent Bond

The Nature of Covalent Bonding

Polar Bonds and Molecules

Polar Covalent Bond

A polar covalent bond is a covalent bond in which the electrons are shared unequally.

The more electronegative atom attracts electrons more strongly and gains a slightly negative charge. The less electronegative atom has a slightly positive charge.

Polar Bonds and Molecules

Differences Between Types of Bonds

Electronegativity Difference

Bond Type

Element Types

Examples

0 – 0.4NonpolarCovalent

Nonmetal-nonmetal

H―HCl―Cl

0.5 – 2.0Polar

CovalentNonmetal-nonmetal H―Cl

> 2.0 IonicMetal-

nonmetal Na+ Cl–