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2.1Compound Structure and Properties

Types of Chemical Bonds — AP CHEMISTRY Revision Notes & Topical Questions

5 min read 9 parts Lesson 5 of 13 1 quiz

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Lesson summary

2.1 Types of Chemical Bonds — Notes — AP CHEMISTRY notes: Explain how electronegativity differences and electron behaviour determine ionic, covalent and metallic bonding.A bond forms because the bonded arrangement has lower potential energy than the separated atoms, owing to Coul…

  • Covalent bond
  • Nonpolar covalent
  • Ionic bond
  • Bond dipole
  • Electronegativity increases from left to right across a period and decreases down a group
  • The trends are explained by electronic structure, the shell model and Coulomb's law

Part 1 of 7Why bonds form

  • A bond forms because the bonded arrangement has lower potential energy than the separated atoms, owing to Coulombic attractions.

Part 2 of 7Electronegativity trends

Electronegativity trends
Electronegativity increases from left to right across a period and decreases down a group.
The trends are explained by electronic structure, the shell model and Coulomb's law.
Fluorine is the most electronegative element.

Part 3 of 7Covalent bonds

Covalent bond
Covalent bond a shared pair of electrons between two nonmetal atoms, attracted to both nuclei.
Nonpolar covalent
  • Nonpolar covalent electrons shared between atoms of similar electronegativity, as in H2, Cl2 and effectively C–H bonds.
Polar covalent
  • Polar covalent electrons shared unequally; the atom with higher electronegativity develops a partial negative charge (δ−) and the other a partial positive charge (δ+),
    • as in H–Cl.
A bond dipole points from δ+ to δ−, and a larger electronegativity difference gives a larger dipole.

Part 4 of 7Ionic bonds

Ionic bond
Ionic bond electrostatic attraction between cations and anions, formed when electrons transfer from a metal to a nonmetal.
All polar bonds have some ionic character, and the difference between ionic and covalent bonding is not distinct.
Generally metal-nonmetal bonds are ionic and nonmetal-nonmetal bonds are covalent.
The best way to characterise bonding is to examine the properties of the compound.
Some compounds have both types, as in NaNO3, where the N–O bonds are covalent and the Na+/NO3− attraction is ionic.

Part 5 of 7Metallic bonds

Metallic bonds
In a metallic solid the valence electrons are delocalised and not associated with any individual atom.
Metallic bonding is a lattice of positive ions surrounded by a sea of delocalised electrons.
Delocalised electrons explain electrical and thermal conductivity, malleability and ductility.

Part 6 of 7Classifying a bond

TypeElectronegativity differenceElectronsExample
Nonpolar covalentAbout 0 to 0.4Shared equallyCl2, CH4
Polar covalentAbout 0.4 to 1.8Shared unequallyHCl, H2O
IonicAbove about 1.8TransferredNaCl
MetallicNot applicableDelocalisedCu
1
Decide whether each atom is a metal or nonmetal.
2
Metal with metal gives metallic bonding.
3
Metal with nonmetal gives ionic bonding.
4
Two nonmetals give covalent bonding; compare electronegativities.
5
Equal electronegativity gives nonpolar; unequal gives polar with δ− on the more electronegative atom.

Part 7 of 7More from the specification

More from the specification
Covalent electrostatic attractive forces
  • Covalent electrostatic attractive forces shared pairs of valence electrons experience mutual attractive forces toward both positively charged atomic nuclei.
Outer shell
  • Highest-energy occupied shell.
Ionic radius
  • Distance from the nucleus to the outermost electrons of an ion.
Attractive force
  • The pull between particles that holds them together.
Pauling scale
  • The scale of electronegativity values, with fluorine highest at 4.0.

Key terms

TermMeaning
Ionic bondElectrostatic attraction between a cation and anion.
Nonpolar covalent bondElectron pair shared equally between similar atoms.
Polar covalent bondElectron pair shared unequally, giving partial charges.
Metallic bondAttraction between cations and a sea of delocalised electrons.
ElectronegativityAbility of an atom to attract bonding electrons.
Bond dipoleSeparation of partial charges along a bond.

Avoid these mistakes

1
Treating bond types as sharply separate — bonding is a continuum
2
Stating that carbon-hydrogen bonds are strongly polar — they are effectively nonpolar
3
Placing δ− on the less electronegative atom
4
Classifying only by electronegativity difference and ignoring metal and nonmetal character

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