3. The covalent bonding in the ammonia molecule

Doc Brown's Chemistry: Chemical Bonding and structure GCSE level, IGCSE, O, IB, AS, A level US grade 9-12 level Revision Notes


Covalent bonding diagram for AMMONIA covalent molecule, molecular formula NH3

* metals \ non-metals (zig-zag line)

Pd metals Part of the modern Periodic Table

Pd = period, Gp = group

metals => non–metals
Gp1 Gp2 Gp3 Gp4 Gp5 Gp6 Gp7 Gp0
1 1H  Note that hydrogen does not readily fit into any group but is a non-metal 2He
2 3Li 4Be atomic number Chemical Symbol eg 4Be 5B 6C 7N 8O 9F 10Ne
3 11Na 12Mg 13Al 14Si 15P 16S 17Cl 18Ar
4 19K 20Ca 21Sc 22Ti 23V 24Cr 25Mn 26Fe 27Co 28Ni 29Cu 30Zn 31Ga 32Ge 33As 34Se 35Br 36Kr
5 37Rb 38Sr 39Y 40Zr 41Nb 42Mo 43Tc 44Ru 45Rh 46Pd 47Ag 48Cd 49In 50Sn 51Sb 52Te 53I 54Xe
6 55Cs 56Ba Transition Metals 81Tl 82Pb 83Bi 84Po 85At 86Rn
The covalent molecule ammonia from nitrogen combining with hydrogen

 

(c) doc bThree atoms of hydrogen (1) combine with one atom of nitrogen (2.5) to form the molecule of the compound ammonia NH3

Each hydrogen atom is one electron short of a helium structure (full shell) and nitrogen is three electrons short of a full outer shell (of 8), so three hydrogen atoms share their electrons with the five outer electrons of nitrogen, so all four atoms effectively have full outer shells.

three of (c) doc b and one (c) doc b combine to form (c) doc b so that the hydrogen atoms are electronically like helium and the nitrogen atom becomes like neon (only the outer shell of nitrogen's electrons are shown).

dot and cross diagram of the ammonia moleculeElectronically, hydrogen (1) becomes like helium (2) and nitrogen (2.5) becomes like neon (2.8), so the hydrogen and nitrogen atoms effectively have full outer shells in forming the covalent bonds when the atoms share their outer electrons.

(Lewis diagram of ammonia) simplified 'dot and cross' electronic diagram for the covalently bonded ammonia molecule

The ammonia molecule is held together by the strong N–H nitrogen–hydrogen single covalent bonds by sharing electrons.

Note that the inner shell of nitrogen's electrons are not shown (as in the diagrams on the right), only the outer shell of nitrogen's electrons are involved in the covalent bonding here.

 

The molecule can be shown as  (displayed formula) with three nitrogen – hydrogen single covalent bonds (AS note: called a trigonal pyramid shape, the H–N–H bond angle is 107o.  This displayed formula does indicate the shape of the ammonia molecule as well as how the three N-H single covalent bonds are arranged, but no relative size of atoms or electronic detail of covalent bond formation by electron sharing. It does indicate the pyramidal shape of the molecule (A level comment).

The double dots represent a pair of electrons not involved in the covalent bonding in ammonia. PH3 will be similar since phosphorus (2.8.5) is in the same Group 5 as nitrogen. Valency of nitrogen or phosphorus is 3 here.

Above on the right two of the full 'dot and cross' electronic Lewis diagram for the covalent bonding in the ammonia molecule.

Covalent bond molecule diagrams come in a variety of forms e.g. for ammonia, as well as those above ...

    all ammonia!

dot and cross electronic diagram, 3D ball and stick model, 3D space-filling model and 2D displayed formula

 


Comments

Melting point of ammonia -78 oC

Boiling point of ammonia -33 oC

Ammonia is a colourless pungent gas at room temperature


Its worth making the following comments on the different representations of simple covalent molecules of >2 atoms

So, reminders:

(i) Dot and cross diagrams are good for showing the electronic detail of the structure, and whether the bonds are single (ox) or double (ox) etc. However, it gives no idea on the shape of the molecule i.e. the 3D spatial arrangement of the bonds and atoms (its effectively a 2D diagram, but the molecule might not be flat!) and no information about the relative size of the atoms.

(ii) Displayed formulae clearly shows how the atoms are bonded together, e.g. the arrangement of the three N-H single bonds, but only gives a 2D view of the molecule.

(iii) It needs a 3D ball and stick model diagram to give an idea of the spatial arrangement of the atoms, but not the relative size of the atoms. A space filling model would give the shape of the molecule and the relative size of the atoms. However, neither of these two models show any electronic details of how the covalent bond is formed.


What next?

Recommend next: The covalent bonding in the methane molecule

Explaining the properties of small covalently bonded molecules

 

Sub-index for Part 3. Covalent Bonding: small molecules & properties

 

Index for ALL chemical bonding and structure notes

 

Perhaps of interest?

?

 

Use My Google search box

Website map buttons below


TOP OF PAGE

KS3 BIOLOGY QUIZZES ~US grades 6-8 KS3 CHEMISTRY QUIZZES ~US grades 6-8 KS3 PHYSICS QUIZZES ~US grades 6-8 HOMEPAGE of Doc Brown's Science Website EMAIL Doc Brown's Science Website
GCSE 9-1 BIOLOGY NOTES GCSE 9-1 CHEMISTRY NOTES and QUIZZES GCSE 9-1 PHYSICS NOTES GCSE 9-1 SCIENCES syllabus-specification help links for biology chemistry physics courses IGCSE & O Level SCIENCES syllabus-specification help links for biology chemistry physics courses
Advanced A/AS Level ORGANIC Chemistry Revision Notes US K12 ~grades 11-12 Advanced A/AS Level INORGANIC Chemistry Revision Notes US K12 ~grades 11-12 Advanced A/AS Level PHYSICAL-THEORETICAL Chemistry Revision Notes US K12 ~grades 11-12 Advanced A/AS Level CHEMISTRY syllabus-specificatio HELP LINKS of my site Doc Brown's Travel Pictures
Website content © Dr Phil Brown 2000+. All copyrights reserved on revision notes, images, quizzes, worksheets etc. Copying of website material is NOT permitted. Exam revision summaries & references to science course specifications are unofficial.

 Doc Brown's Chemistry 

*

TOP OF PAGE