5.5Dative Bond
In a typical covalent bond, each bonding atom contributes electrons to be shared between them. However, in certain chemical species, a unique type of covalent bond known as a dative bond (or coordinate bond) is formed. In this bond, the entire pair of shared electrons originates from only one of the participating atoms.
Learning Objectives
- Define what a dative bond (coordinate bond) is.
- Explain the formation of a dative bond in a hydroxonium ion, H3O+.
- Explain the formation of a dative bond in an ammonium ion, NH4+.
Formation of Dative Bond in Hydroxonium Ion (H3O+)
See step-by-step how a lone pair of electrons from a water molecule is shared with an electron-deficient hydrogen ion.
Oxygen has a stable octet arrangement and two lone pairs of electrons. Each hydrogen atom has a stable duplet arrangement.
A hydrogen ion has no electrons in its electron shell, so it can accept a lone pair of electrons.
The oxygen atom shares one lone pair with H+. Oxygen keeps its octet arrangement and all three hydrogen atoms achieve a stable duplet arrangement.
Brief Explanation
Understand the key ideas behind a dative bond.
1. Lone Pair of Electrons
One atom or molecule must possess at least one lone pair of electrons.
2. Empty Shell
The accepting species, such as a hydrogen ion, H+, must have an empty shell capable of accommodating the electron pair.
| Species | Role in dative bond formation | Resulting ion |
|---|---|---|
| Water molecule, H2O | Donates a lone pair of electrons from its oxygen atom. | Hydroxonium ion, H3O+ |
| Ammonia molecule, NH3 | Donates a lone pair of electrons from its nitrogen atom. | Ammonium ion, NH4+ |
Formation of the Ammonium Ion
An ammonia molecule, NH3, has one lone pair of electrons on its nitrogen atom. The nitrogen atom shares this lone pair with a hydrogen ion, H+, which has an empty shell, to form a dative bond:
NH3 + H+ → NH4+
In the ammonium ion, all four hydrogen atoms achieve stable duplet arrangements, while nitrogen retains its octet arrangement.
Try These Questions First
Answer mentally, then check the explanation.
What is another term used to refer to a dative bond?
Why can a hydrogen ion (H+) receive a lone pair of electrons from another atom?
What observable phenomenon occurs when hydrogen chloride gas (HCl) is mixed with ammonia gas (NH3)?
Common Mistakes
Avoid these errors when explaining dative bonds.
Common Misconceptions
Compare each misconception with the correct fact.
A dative bond is an ionic bond because it often involves ions like H+ or results in charged species like H3O+ and NH4+.
A dative bond is a type of covalent bond. The electrons are shared between the two atoms, not completely transferred from one to the other.
Summary
Key facts to remember.
- A dative bond (coordinate bond) is a covalent bond where the shared pair of electrons comes entirely from one atom.
- It is formed between an atom containing a lone pair of electrons and a species with an empty shell, such as H+.
- Key textbook examples include the hydroxonium ion, H3O+ (formed from H2O and H+), and the ammonium ion, NH4+ (formed from NH3 and H+).
- In the hydroxonium and ammonium examples, the oxygen or nitrogen donor atom retains an octet arrangement while the hydrogen atoms achieve stable duplet arrangements.
Quick Activity
Complete all parts before checking your score.
A. Objective Quiz
What is the definition of a dative bond?
Which species provides the lone pair of electrons in the formation of a hydroxonium ion, H3O+?
B. Fill in the Blanks
Another name for a dative bond is a ______ bond.
When ammonia gas and hydrogen chloride gas mix, white fumes of ______ are formed.
C. Match the Species or Concept with Its Description
Drag each item on desktop. On mobile, tap an item and then tap the matching box.
Answer Choices
Hydrogen ion (H+) Lone pair of electrons Hydroxonium ion (H3O+) Dative bondDescription Matching
Keywords
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