Covalent bond Flashcards
how do atoms of non-metals achieve duplet/ octet structure
Atoms of non-metals achieve duplet/ octet structure by sharing electrons with each other
why don’t non-metal atoms want to lose its valence electron
Both non-metals have relatively large ionization energy and neither non-metal atom wants to lose its valence electron(s)
what is covalent bond
It is the electrostatic force of attraction between the shared pair(s) of electrons and the positive nuclei of the two
bonding atoms.
how do most of the non-metal elements exist as
they exist as diatomic molecules (except noble gases)
Relationship between group number and number of
covalent bonds formed (4)
valence: 4
bonding pairs: 4
lone pairs: 0
Relationship between group number and number of
covalent bonds formed (5)
valence: 5
bonding pairs: 3
lone pairs: 1
Relationship between group number and number of
covalent bonds formed (6)
valence: 6
bonding pairs: 2
lone pairs: 2
Relationship between group number and number of
covalent bonds formed (7)
valence: 7
bonding pairs: 1
lone pairs: 3
covalent bond of halogens, group VII, 17
Hydrogen and Group VII/ 17 elements form single covalent bonds by each atom sharing one pair of electrons :
covalent bond of group VI, 16
Group VI/ 16 elements form double bonds by sharing 2 pairs of electrons
covalent bond of group V, 15
Group V/ 15 elements form triple bonds by sharing 3 pairs of electrons
what is bond length
it is the distance between the nuclei of the two bonding atoms joined by covalent bond
what is bond strength
it is the strength of electrostatic force between the shared pair of electrons and the nuclei of the two bonding atoms.
how can bond strength be measured
Bond strength can be measured in terms of bond energy (unit : kJ mol-1).
what is bond energy
It is the energy required to break one mole of covalent bonds from gaseous molecules.
Relationship between bond length and bond strength
● As the atomic radius increases, the bond length
increases.
● The shared pair of electrons in the covalent bond
are further away from the nuclei of the two
bonding atoms.
● Weaker electrostatic force of attraction →
weaker covalent bond → lower bond energy.
Relationship between number of bonds and bond strength
● As the number of shared pair electrons in the covalent bond increases, the
electrostatic force of attraction from the nuclei increases.
● The atoms are held closer and so the covalent bond is shorter and stronger.
● Bond strength: triple bond > double bond > single bond
incomplete octet example
● Some atoms, like Be(Beryllium) and B(Boron),
form stable compounds with
incomplete octets.
● They prefer to form covalent bond
rather than ionic bond because of
their comparatively high ionization
energies.
how is octet structure formed in atoms like Be and B
To achieve octet structure in atoms like Be and B, they form dative covalent bond
what is dative covalent bond
it is a covalent bond which both electrons in the shared pair are contributed by the same atom
dative covalent bond examples
Dative covalent bond is also formed when species with lone pair electrons, such as ammonia and water, react with hydrogen ions (H+), it is also found in carbon monoxide
what is the arrow used to represent in dative covalent bonds
An arrow is usually used to
represent the presence of a
dative covalent bond.
how to draw lewis structure
Step 1 : Identify the total number of valence electrons.
Step 2 : Identify both central atom and surrounding atoms of the species and arrange the “skeleton”
of the species.
Step 3 : Put the valence electrons to the “skeleton” of the species as bonding electrons in such a
way that the surrounding atoms can form the expected number of covalent bonds.
Step 4 : Put the remaining valence electrons to the surrounding atoms as their lone pair(s) of
electrons in such a way that they can achieve octet structure of electrons.
If some still remain, put to the central atom as its lone pair(s).
naming and formulae of covalent compounds
● Limited to the binary covalent compounds - formed between
two different non-metals.
- The first element written in the formula should be named first
using its full name. - The second element in the formula should be named after the
first one with the suffix of “ide”. - Prefix(es) should be included to indicate the number of each
atom present in the molecule. - If the number of atom of the first element is one, then no prefix
is needed.
number of atoms 1-10
mono
di
tri
tetra
penta
hexa
hepta
octa
nona
deca
what are acids
A group of covalent compounds that dissociate to give H+ ions when dissolved in water
the two types of acid and examples
- Hydro-acids: acids that do not contain oxygen
Example - hydrochloric acid, HCl (aq) - Oxo-acids: acids containing oxygen
Example - nitric acid, HNO3 (aq)
what are hydro-acids
Generally contain hydrogen atoms and non-metal atoms (except oxygen).
When the acid dissolves in water, they can react with water molecules to
give a hydronium ion, H3O+
(aq) and an anion (more will be discussed in Topic 6 Acids and bases)
naming of hydro-acids
The name of this group of acids consists of two parts:
● The first part is named with a prefix “hydro”, which is followed by the name of the non-metal with a suffix of “ic”.
● The second part is named with the word “acid”.
what are oxo-acids
● Contain hydrogen atoms, oxygen atoms and non-metal atoms.
● When the acid dissolves in water, they react with water molecules to give a
hydronium ion, H3O+
(aq) and a polyatomic oxoanion.
naming of oxo-acids
● The first part of their names: a prefix with “part of the name of the non-metal”
and a suffix of “ic” for the one with more oxygen and “ous” for the one with
fewer oxygen.
● The second part is named with the word “acid”.
