These diagrams in 2D have their limitations as they do not show the 3D shape of the molecule. Covalent bonds act in a particular direction. 3D ball and stick models or space-filling models can provide a better indication of the structures.
ball and stick Cl2 space filling model HCl
The outer electrons are written as pairs of electrons. The bond pair is written between the two symbols.
H
H
water
H
H H
N H
ball andfilling stick model H2O Cl2 space
ball and stick Cl2
chlorine space filling model Cl2 Cl
Cl
ammonia
O H
hydrogen chloride
space filling model HCl
ball and stick HCl
When atoms form covalent bonds they share pairs of electrons. This can be shown using a dot and cross diagram.
hydrogen
2.4
ball and stick HCl
space filling model H2O
ball and stick H2O
Cl
ball and stick NH3
methane H
space filling model H2O
H H
C
ball and stick NH3 H
space filling model NH3 ball and stick CH4
H
2
The displayed formula of hydrogen fluoride is H–F. Represent HF as a dot and cross diagram.
3
How many bond pairs are there in a molecule of ammonia?
(a) O
4
Determine the molecular formula of methane.
(b) space filling model O2
5
Draw a dot and cross diagram for H2S.
space filling model NH3 ball and stick CH4
6
Explain why there are two dots and two crosses between the oxygen atoms in the diagram to the right.
7
Use the dot and cross diagram to the right to explain why a molecule of nitrogen N2 has a triple bond.
8
Draw a dot and cross diagram to show the bonding in carbon dioxide CO2. (Hint: it is a linear molecule with a C atom in the middle.)
O
space filling model CH4
Multiple bonds One ‘dot and cross’ together represents a single bond, which is one bond pair of electrons. Two pairs of ‘dots and crosses’ side by side represent a double bond (as in O2). Three electron bond pairs is a triple bond (as in N2).
space filling model CH4
(a) O
(c) dot and cross diagram O2
O
(b) space filling model O2
(a) N
N
(c) space O filling model O N2
(c) dot and cross diagram O2 (a) N N
(b) dot and cross diagram N2
(c) space filling model N2
O
O
N
N
(b) dot and cross diagram N2
KEY INFORMATION N
N
The inner shells of electrons are not shown.
Google search: 'triple bonding symbol'
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