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Chemical bonds, ((The presence of delocalized electrons explains the…
Chemical bonds
Stability of atoms
KWhen two atoms form a chemical bond, the attractive forces (dotted lines) and the repulsive forces (red arrows) are balanced. When atoms are bonded, their stability is higher.
Electronegativity
Electronegativity (En) measures the force with which an atom attracts bonding electrons.
We can determine if a bond is ionic or covalent by calculating the differences in the electronegativity (Δe) of the involved elements.
(Δe > 1,9 🡺 ionic bonds )
Δe < 1,9 🡺 covalent bonds
Δe < 0,4 🡺 pure covalent bonds
0,4 < Δe < 1,9 🡺 polar covalent bonds
Primary bonds
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metallic bond – the attraction between positively charged metal ions and their most external electrons.
Binding energy
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When two atoms form a chemical bond, a certain amount of energy is released. The released energy corresponds to the amount of energy that is necessary to break the bond (binding energy).
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Electron promotion
Many atoms have electron promotion which allows an electron to transition from a full orbital level into a higher sublayer.
It is used by the atoms of some elements, e.g. carbon, in order to increase the number of unpaired electrons.
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Molecular substances
Materials formed by the same molecules, which behave as independent units, are called molecular substances.
In molecular substances, covalent bonds determine chemical properties, while physical properties are determined by intermolecular bonds.
Apolar substances have low melting and boiling points; intermolecular bonds are very weak.
Polar substances have higher boiling points.
UThe geometry of covalent bonds, particularly bond angles, determines the shape of a molecule.
The model of hybridization explains bond angles formed in molecules with three or more atoms.
According to valence bond theory (VB theory), atoms share electrons by overlapping valence orbitals while their cores remain unchanged.
If the overlap is a full head-on bond, it is called a σ bond.
If the overlap occurs on the side it is
called a π bond.
In covalent solids, atoms form a unique pattern, creating a
gigantic molecule. In these solids, physical properties are
determined by the strength and geometry of covalent bonds.
OIn ionic compounds, positive and negative ions are strongly linked and form a stable and ordered reticulum.
The attraction between ions with opposite charges is called an ionic bond. This bond is non-directional and has the same strength in any direction.
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Metals are chemical elements with low ionization energy and a small number of electrons in the external orbital.
In solid metals, there are positive ions immersed in a sea of
delocalized electrons.
Ionic solids are neutral overall and individual molecules are
not identifiable within them.
They are very stable solids with an ordered, crystal lattice structure.