Download Chemical bonds

Department “ORGANIC CHEMISRTY AND TECHNOLOGY”
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Chemistry for Engineering Logistics
Chemical Bond
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General information
Ionic bond
Covalent bond
Metal bond
Assoc. Prof. V. Grozev
1. GENERAL INFORMATION
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Atoms are the basic building blocks of all types of matter. They link
to other atoms through chemicals bonds resulting from the strong
attractive forces that exist between the atoms.
Chemical bonds are defined as a set of interactions that take
place in the electron shell of atoms, in order to join and form a molecule
or a chemical stable compound.
Chemical bonds can be divided into 3 groups:
1. Ionic bonds
2. Covalent bonds
3. Metal bonds
2. IONIG BOND
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The theory of ionic bonding was proposed by Walther Kossel in
1916.
2.1. Definitions
Definition 1: bond in which one or more electrons from one atom
are removed and attached to another atom, resulting in positive and
negative ions which attract each other.
Definition 2: An ionic bond is a chemical link between atoms
caused by the electrostatic force between oppositely-charged ions in
an ionic compaund.
2. IONIG BOND
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2.2. Formation of ionic bonding
The formation of ionic bond of sodium chloride (NaCl) can be
described through the following steps:
Step 1- ionization of Na to Na+
The sodium has lost an electron, so it no longer has equal numbers of
electrons and protons. Because it has one more proton than electron, it
has a charge of 1+. If electrons are lost from an atom, positive ions
(cations) are formed:
Na – e- = Na +
Step 2 - formation of chloride ion from chlorine atom
The chlorine has gained an electron, so it now has one more electron
than proton. It therefore has a charge of 1-. If electrons are gained by an
atom, negative ions are formed.
Cl + e- = Cl –
2. IONIG BOND
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Step 3 - formation of solid sodium chloride from Na+ and Cl- .
The sodium cations and chloride anions are held together by the
strong electrostatic attractions between the positive and negative charges.
2. IONIG BOND
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The formula of sodium chloride is
NaCl. Ionic compounds do not usually
exist as isolated molecules, such as
NaCl, but as a part of a crystal lattice.
The
crystal
lattice
is
a
three
dimensional regular array of cations
and
anions.
Each
cation
is
surrounded by several anions and
each anion is surrounded by several
anions.
2. IONIG BOND
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2.3. Properties of ionic compounds
Because of the strong binding of the crystal lattice the most
ionic compounds tend to have:
 High melting point (solid at room temperature);
 Hard but brittle (can shatter);
 Many dissolve in water;
 Conductors of electricity when dissolved or melted.
3. COVALENT BOND (Lewis theory, 1916)
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Definition: A covalent bond is a chemical link between
atoms in which electrons are shared between them.
Covalent bond is formed between nonmetallic elements
of similar electronegativity.
Examples - H2, Cl2, O2, CO2, C2H6, H2O, SiC.
3. COVALENT BOND
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Formation of covalent bond (oxygen molecule) - two oxygen
atoms share pairs of outer-shell electrons:
Oxygen Molecule (O2)
3. COVALENT BOND
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water
Covalent bonding in
(H2O)
There is a covalent bond
between the oxygen and each
hydroden atoms in a water molecule
(H2O). Each of the covalent bonds
contains two electrons - one from a
hydrogen atom and one from the
oxygen atom. Both atoms share the
electrons.
Water is a polar molecule
because
oxygen
is
more
electronegative than hydrogen, and
therefore electrons are pulled closer
to oxygen.
3. METALLIC BOND
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Definition - metallic bond is a
type of chemical bond between atoms
in a metallic element, formed by the
valence electrons moving freely
through the metal lattice.
Metals form giant structures in
which electrons in the outer shells of
the metal atoms are free to move. The
metallic bond is the force of attraction
between these free electrons and
metal ions.
Metallic bonds are strong, so
metals can maintain a regular
structure and usually have high
melting and boiling points.
valence electrons
metal ions
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