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Chemistry
Chemical bonding in Elements and Compounds
Bonding in the elements
Bonding in metals
Bonding in non-metals
Chemical bonding in compounds
Covalent compounds
Ionic compounds
Physical properties of chemical and covalent compunds
Polyatomic (compound) ions
Formula of covalent compounds
Metals, Alloys and crystals.
Chemical bonding in compounds and
elements:
We have seen many compounds like those we usually see are ammonia, water and
methane; these are only formed by chemical bonding between several elements.
Bonding in the elements:
• Atoms are able to bond to each other to make molecules and compounds. A
compound is a molecule with more than one kind of element in it. How do they
do it? It has to do with their electrons.
• These two opposite ions (metals and non-metals) attract each other and form the ionic
bond. Covalent bonding is a form of chemical bonding between two non metallic
atoms which is characterized by the sharing of pairs of electrons between atoms and
other covalent bonds.
Bonding in metals
Metallic bonding is a type of chemical bonding that rises from the
electrostatic attractive force between conduction electrons and positively
charged metal ions. It may be described as the sharing of free electrons
among a structure of positively charged ions.
In metals, the electrons leave the outer shells of metal atoms, forming
positive metal ions and a 'sea' of delocalised electrons. Metals are solids at
room temperature, so the structure of a solid metal consists of closely
packed metal ions. These ions are arranged in a regular way to form a
metallic lattice structure. The lattice has layers of metal ions.
Bonding in non-metals
A covalent bond is a chemical bond that involves the sharing of
electron pairs between atoms. These electron pairs are known as
shared pairs or bonding pairs, and the stable balance of attractive and
repulsive forces between atoms, when they share electrons, is known
as covalent bonding. This bonding gives the a stable structure as of
elements of 8th group (except hydrogen). Each atom contributes one
electron to each bond.
Structures formed:
Physical properties of ionic and covalent
compunds:
Properties of typical ionic compounds
Properties of simple covalent compounds
They are crystalline solids at room temperature
They are often liquid or gas at room temperatures
They have high melting point
They have low melting and boiling points
They are often soluble in water (not soluble in
organic solutions like Ethanol and Methylbenzene
They ate soluble in organic solvents like Ethanol and
Methylbenzene (only a few are soluble in water)
They conduct electrucity when molten or dissolved
in water (not when solid)
They do not conduct electricity
Metals, alloys and crystals.
• Metal crystals: These crystals are typically solid with a
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high melting point. An example of an ionic crystal is table
salt. Metallic crystals are crystals made of metal elements.
These crystals sparkle with the lustrous sheen we think
of metals having.
The energy is transferred throughout the rest of the metal by
the moving electrons. Metalsare described as malleable (can
be beaten into sheets) and ductile (can be pulled out into
wires). This is because of the ability of the atoms to roll over
each other into new positions without breaking
the metallic bond.
Alloys
An alloy is a combination of a metal with at least one other metal or
nonmetal. The combination must be part of a solid solution, a
compound, or a mixture with another metal or nonmetal in order for
it to be considered an alloy. The most common way to combine
metals into an alloy is by melting them, mixing them together, and
then allowing them to solidify and cool back to room temperature.
Alloys give a property of being much harder than the pure elements
they were before.
Ionic crystals
An ionic crystal consists of ions bound together by electrostatic attraction.
The arrangement of ions in a regular, geometric structure is called a crystal
lattice.
Examples of such crystals are the alkali halides, which include:
•potassium fluoride (KF)
•potassium chloride (KCl)
•potassium
These solidsbromide
tend to (KBr)
be quite hard and have high melting points, reflecting
the strong forces between oppositely-charged ions. The exact arrangement
of ions in a lattice varies according to the size of the ions in the crystal.
Giant molecular crystals
Giant molecular crystals are those in which a large number
of atoms are covalently bonded to each other creating a
network. There are four examples of molecules forming giant
structures. They are silicon and two forms of carbon called
Silicon
dioxide
called silica) is the main compound found in sand. It is an
diamond
and(often
graphite.
example of a substance with a giant covalent structure. It contains many
silicon and oxygen atoms. All the atoms in its structure are linked to each other
by strong covalent bonds. The atoms are joined to each other in a regular
arrangement, forming a giant covalent structure. There is no set number of
atoms joined together in this type of structure