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Covalent BondingCovalent bonding in compounds
Covalent bonding can take place between atoms of different elements to create molecules of covalent compounds. These covalent bonds can be single, double or triple.
Both hydrogen (1) and chlorine (2.8.7) need 1 more electron to fill their outer shell. By sharing one electron each, they can fill their outer shells and become stable.
HCl or H Cl
Covalent bonding in water
Oxygen (2.6) needs 2 more electrons, but hydrogen (1) only needs 1 more. How can these two elements be covalently bonded?
The oxygen atom shares 1 electron with 1 hydrogen atom, and a second electron with another hydrogen atom.
O
H
H
2.5 1
3 1
1 3
H
H
2.4 1
4 1
1 4
H
H
C
H
H
H
H
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Resonance is electron delocalization on a particular molecule or polyatomic ion which bonds cannot be rendered in a single structure of Lewis.
Delocalized bonding: Resonance
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Resonance of Ozone
The structure of ozone, O3, can be represented by two different Lewis electron-dot formulas.
Experiments show, however, that both bonds are identical.
2
Resonance of Ozone
According to theory, one pair of bonding electrons is spread over the region of all three atoms.
This is called delocalized bonding, in which a bonding pair of electrons is spread over a number of atoms.
2
Hetero nuclear bonding Mixed of ionic and covalent character
Dominant Covalent Covalent bond
Dominant Ionic Ionic bond
Covalent character The power of polarization of cation and anion.
Polarization The nucleus of the cation/anion may affect or pull the electron cloud of the anion/cation
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Fajans said that a small cations able to polarize the electron cloud of an anion that forms ions no longer spheric but elipsoid (distortion)
Fajans rules
PROPERTIES OF COVALENT BOND
Most covalent compounds have relatively low melting points and boiling points.
Covalent compounds usually have lower enthalpies of fusion and vaporization than ionic compounds.
Covalent compounds tend to be soft and relatively flexible.
Covalent compounds tend to be more flammable than ionic compounds.
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Many covalent compounds don't dissolve well in water.
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Covalent bonds can be divided into several types, namely as follows:
1) a single covalent bond
Single covalent bond is a bond that involves the use of shared pairs of electrons by two bonded atoms. This bond usually occurs between the non-metallic elements with non-metallic elements in the main group. Covalent bonds occur between groups IVA.VA, VIA, VIIA.
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Example: The bond between the H atom and the Cl atom in HCl
Electron configurations between H and Cl is: H1 = 1 Cl17 = 2 8 7
Each H and Cl atoms require one electron. Thus, 1 H atom pairs with one Cl atom.
HCl bond formation
2) double covalent bond and triple covalent bond
Double covalent bond involves the joint use of more than one pair of electrons by two bonded atoms. example:
a) the double bond of the O2 molecule
3) Triple Bond
The electron configuration of N (Ar = 7) was 2.5, so that nitrogen has 5 valence electrons, so it should pair 3 electrons to be stable.
N2 bond formation.
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The dipole moment (μ)
Is a quantity used to express the polarity of a covalent bond.
formulated:
μ = Q x r; 1 D = 3.33 x 10 -30 C.m
description:
μ = dipole moment, Debye units (D)
Q = the difference in the charge, the units of coulombs (C)
r = distance between the positive charge with a negative charge, units meters (m)
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Based on the difference in electronegativity of two atoms that form the molecule dwiatom raises polar molecules.
1. polar covalent bond
Polar covalent bond occurs when one element that binds the electrons have a greater attractiveness (the electronegativity is not the same).
Examples of bonding in compounds HCl, H2O, NH3, HF, HBr, HI
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2. The non-polar covalent bond
Non-polar covalent bond occurs when elements that bind have pull the same electron (the electronegativity of each atom are same).
For example ikatam in Cl2, H2, Br2, I2, N2, BeCl2, Bcl2, O2
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Iodine is a molecular solid at room temperature.
Millions of iodine molecules are held together by weak forces of attraction to create a 3D molecular lattice.
Two iodine atoms form a single covalent bond to become an iodine molecule.
I
I
Simple covalent structures
Atoms that join together by covalent bonding can form different types of covalent structure.
Oxygen, water and carbon dioxide are molecules. They have a simple structure because they only contain a few atoms.
Most molecular substances are gas or liquid at room temperature. A few are solid and these are called molecular solids.
O
O
C
O
O
H
O
H
Properties of molecular solids
are usually insoluble in water but soluble in other solvents such as petrol;
cannot conduct electricity – there are no free electrons to carry an electrical charge.
In addition, molecular solids:
are usually soft and brittle – they shatter when hit.
*
Giant covalent structures
In some substances, millions of atoms join together by covalent bonding. This produces giant covalent structures, not molecules.
*
Allotropes of carbon
In the element carbon, atoms bond in different ways, creating different kinds of giant structures.
Two of these structures are diamond and graphite. They are called allotropes of carbon.
Allotropes have the same chemical properties because they have the same number of electrons.
*
The structure of diamond
Diamond is a rare form of carbon in which each atom is covalently bonded to four others.
This pattern arrangement is repeated millions of times to create a giant lattice.
C
C
C
C
C
The properties of diamond
All the electrons in the outer shell of the carbon atom (2.4) are used in covalent bonds. This affects diamond’s properties.
Diamond is very hard – the hardest natural substance on Earth.
Diamond has a very high melting and boiling point – a lot of energy is needed to break the covalent bonds.
*
The structure of graphite
Graphite is a much more common form of carbon. in which each atom is covalently bonded to three others.
This forms rings of six atoms, creating a giant structure containing many layers. These layers are held together by weak forces of attraction.
weak forces of attraction
The properties of graphite
Only three of the four electrons in the outer shell of the carbon atom (2.4) are used in covalent bonds. This affects graphite’s properties.
Graphite is soft and slippery – layers can easily slide over each other because the weak forces of attraction are easily broken. This is why graphite is used as a lubricant.
Graphite can conduct electricity – the only
*
Other allotropes of carbon
Other allotropes of carbon have been discovered in the last 30 years. They are large but not really giant structures.
One allotrope is buckminsterfullerene. It contains 60 carbon atoms, each of which bonds with three others by forming two single bonds and one double bond.
These atoms are arranged in 12 pentagons and 20 hexagons to form spheres, which are sometimes called ‘bucky balls’.
C
C
C
C
Sand
Sand is an impure form of silicon dioxide (quartz). It has a giant covalent structure with certain similarities to diamond.
Each silicon atom (2.8.4) is bonded to four oxygen atoms, and each oxygen atom (2.6) is bonded to two silicon atoms.
Si
O
O
O
O
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Bonding theories
A Molecular Orbital is an orbital that applies to the entire molecule, instead of just one atom
So far, the orbitals we have been discussing are atomic orbitals (s, p, d, f) for each atom
When two atoms combine, their atomic orbitals overlap and they make molecular orbitals
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Each orbital is filled with 2 electrons
A Bonding Orbital is an orbital that can be occupied by two electrons of a covalent bond (it’s the space in between the two atoms)
There are 2 types of bonding orbitals : sigma and pi
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Sigma bond ()
A Sigma Bond is when 2 atomic orbitals combine to form a molecular orbital that is symmetrical around the axis
S orbitals overlapping
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Pi bond ()
Pi bonding electrons are likely to be found in a sausage-shape above and below the axis
Pi bonds are weaker than sigma bonds because they overlap less
P orbitals overlapping side-by-side
Covalent bonding can take place between atoms of different elements to create molecules of covalent compounds. These covalent bonds can be single, double or triple.
Both hydrogen (1) and chlorine (2.8.7) need 1 more electron to fill their outer shell. By sharing one electron each, they can fill their outer shells and become stable.
HCl or H Cl
Covalent bonding in water
Oxygen (2.6) needs 2 more electrons, but hydrogen (1) only needs 1 more. How can these two elements be covalently bonded?
The oxygen atom shares 1 electron with 1 hydrogen atom, and a second electron with another hydrogen atom.
O
H
H
2.5 1
3 1
1 3
H
H
2.4 1
4 1
1 4
H
H
C
H
H
H
H
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Resonance is electron delocalization on a particular molecule or polyatomic ion which bonds cannot be rendered in a single structure of Lewis.
Delocalized bonding: Resonance
© Boardworks Ltd 2004
1 of 20
© Boardworks Ltd 2005
Resonance of Ozone
The structure of ozone, O3, can be represented by two different Lewis electron-dot formulas.
Experiments show, however, that both bonds are identical.
2
Resonance of Ozone
According to theory, one pair of bonding electrons is spread over the region of all three atoms.
This is called delocalized bonding, in which a bonding pair of electrons is spread over a number of atoms.
2
Hetero nuclear bonding Mixed of ionic and covalent character
Dominant Covalent Covalent bond
Dominant Ionic Ionic bond
Covalent character The power of polarization of cation and anion.
Polarization The nucleus of the cation/anion may affect or pull the electron cloud of the anion/cation
© Boardworks Ltd 2004
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© Boardworks Ltd 2005
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Fajans said that a small cations able to polarize the electron cloud of an anion that forms ions no longer spheric but elipsoid (distortion)
Fajans rules
PROPERTIES OF COVALENT BOND
Most covalent compounds have relatively low melting points and boiling points.
Covalent compounds usually have lower enthalpies of fusion and vaporization than ionic compounds.
Covalent compounds tend to be soft and relatively flexible.
Covalent compounds tend to be more flammable than ionic compounds.
© Boardworks Ltd 2004
1 of 20
© Boardworks Ltd 2005
Many covalent compounds don't dissolve well in water.
© Boardworks Ltd 2004
1 of 20
© Boardworks Ltd 2005
* of 34
Covalent bonds can be divided into several types, namely as follows:
1) a single covalent bond
Single covalent bond is a bond that involves the use of shared pairs of electrons by two bonded atoms. This bond usually occurs between the non-metallic elements with non-metallic elements in the main group. Covalent bonds occur between groups IVA.VA, VIA, VIIA.
© Boardworks Ltd 2004
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© Boardworks Ltd 2005
* of 34
Example: The bond between the H atom and the Cl atom in HCl
Electron configurations between H and Cl is: H1 = 1 Cl17 = 2 8 7
Each H and Cl atoms require one electron. Thus, 1 H atom pairs with one Cl atom.
HCl bond formation
2) double covalent bond and triple covalent bond
Double covalent bond involves the joint use of more than one pair of electrons by two bonded atoms. example:
a) the double bond of the O2 molecule
3) Triple Bond
The electron configuration of N (Ar = 7) was 2.5, so that nitrogen has 5 valence electrons, so it should pair 3 electrons to be stable.
N2 bond formation.
© Boardworks Ltd 2004
1 of 20
© Boardworks Ltd 2005
The dipole moment (μ)
Is a quantity used to express the polarity of a covalent bond.
formulated:
μ = Q x r; 1 D = 3.33 x 10 -30 C.m
description:
μ = dipole moment, Debye units (D)
Q = the difference in the charge, the units of coulombs (C)
r = distance between the positive charge with a negative charge, units meters (m)
© Boardworks Ltd 2004
1 of 20
© Boardworks Ltd 2005
* of 34
Based on the difference in electronegativity of two atoms that form the molecule dwiatom raises polar molecules.
1. polar covalent bond
Polar covalent bond occurs when one element that binds the electrons have a greater attractiveness (the electronegativity is not the same).
Examples of bonding in compounds HCl, H2O, NH3, HF, HBr, HI
© Boardworks Ltd 2004
1 of 20
© Boardworks Ltd 2005
2. The non-polar covalent bond
Non-polar covalent bond occurs when elements that bind have pull the same electron (the electronegativity of each atom are same).
For example ikatam in Cl2, H2, Br2, I2, N2, BeCl2, Bcl2, O2
© Boardworks Ltd 2004
1 of 20
© Boardworks Ltd 2005
Iodine is a molecular solid at room temperature.
Millions of iodine molecules are held together by weak forces of attraction to create a 3D molecular lattice.
Two iodine atoms form a single covalent bond to become an iodine molecule.
I
I
Simple covalent structures
Atoms that join together by covalent bonding can form different types of covalent structure.
Oxygen, water and carbon dioxide are molecules. They have a simple structure because they only contain a few atoms.
Most molecular substances are gas or liquid at room temperature. A few are solid and these are called molecular solids.
O
O
C
O
O
H
O
H
Properties of molecular solids
are usually insoluble in water but soluble in other solvents such as petrol;
cannot conduct electricity – there are no free electrons to carry an electrical charge.
In addition, molecular solids:
are usually soft and brittle – they shatter when hit.
*
Giant covalent structures
In some substances, millions of atoms join together by covalent bonding. This produces giant covalent structures, not molecules.
*
Allotropes of carbon
In the element carbon, atoms bond in different ways, creating different kinds of giant structures.
Two of these structures are diamond and graphite. They are called allotropes of carbon.
Allotropes have the same chemical properties because they have the same number of electrons.
*
The structure of diamond
Diamond is a rare form of carbon in which each atom is covalently bonded to four others.
This pattern arrangement is repeated millions of times to create a giant lattice.
C
C
C
C
C
The properties of diamond
All the electrons in the outer shell of the carbon atom (2.4) are used in covalent bonds. This affects diamond’s properties.
Diamond is very hard – the hardest natural substance on Earth.
Diamond has a very high melting and boiling point – a lot of energy is needed to break the covalent bonds.
*
The structure of graphite
Graphite is a much more common form of carbon. in which each atom is covalently bonded to three others.
This forms rings of six atoms, creating a giant structure containing many layers. These layers are held together by weak forces of attraction.
weak forces of attraction
The properties of graphite
Only three of the four electrons in the outer shell of the carbon atom (2.4) are used in covalent bonds. This affects graphite’s properties.
Graphite is soft and slippery – layers can easily slide over each other because the weak forces of attraction are easily broken. This is why graphite is used as a lubricant.
Graphite can conduct electricity – the only
*
Other allotropes of carbon
Other allotropes of carbon have been discovered in the last 30 years. They are large but not really giant structures.
One allotrope is buckminsterfullerene. It contains 60 carbon atoms, each of which bonds with three others by forming two single bonds and one double bond.
These atoms are arranged in 12 pentagons and 20 hexagons to form spheres, which are sometimes called ‘bucky balls’.
C
C
C
C
Sand
Sand is an impure form of silicon dioxide (quartz). It has a giant covalent structure with certain similarities to diamond.
Each silicon atom (2.8.4) is bonded to four oxygen atoms, and each oxygen atom (2.6) is bonded to two silicon atoms.
Si
O
O
O
O
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Bonding theories
A Molecular Orbital is an orbital that applies to the entire molecule, instead of just one atom
So far, the orbitals we have been discussing are atomic orbitals (s, p, d, f) for each atom
When two atoms combine, their atomic orbitals overlap and they make molecular orbitals
© Boardworks Ltd 2004
1 of 20
© Boardworks Ltd 2005
Each orbital is filled with 2 electrons
A Bonding Orbital is an orbital that can be occupied by two electrons of a covalent bond (it’s the space in between the two atoms)
There are 2 types of bonding orbitals : sigma and pi
© Boardworks Ltd 2004
1 of 20
© Boardworks Ltd 2005
* of 34
Sigma bond ()
A Sigma Bond is when 2 atomic orbitals combine to form a molecular orbital that is symmetrical around the axis
S orbitals overlapping
* of 34
Pi bond ()
Pi bonding electrons are likely to be found in a sausage-shape above and below the axis
Pi bonds are weaker than sigma bonds because they overlap less
P orbitals overlapping side-by-side
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