unit 6a: ionic and covalent bonding. ions why do elements in the same group behave similarly? they...
TRANSCRIPT
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–