The main group elements in the periodic table can be
classified as either being metals or non-metals. The
vertical columns in the table are called groups. Elements
within the same group all have the same number of electrons
in their outer shell. Group I Elements
are known as alkali metals. Group II
Elements
are known as the alkaline earth metals and the group of elements between
group II and III are known as the Transition
Element.
The manufacture of ammonia involves the fixation of atmospheric nitrogen, there
by making it available for incorporation into a variety of other compounds. The
Haber Process is used industrially
for this fixation.
The manufacture of steel, which is an alloy of iron and
carbon uses the basic-oxygen process, ld process, by blowing
oxygen onto molten scrap and pig iron at high pressure. This
process removes impurities from the metal in the form of
slag and gases. The gases are burned off at high
temperature. Various other materials are then added to
the iron in order to make different types of steel. Steels
containing over 11 per cent of chromium are known as
stainless steel.
The Markownikoff Rule specifies the orientation with which a
small asymmetric molecule adds across the double bond of an
alkene in an addition reaction.
- The Markownikoff Rule
- states that In the ionic addition of
an acid to the carbon carbon double bond of an alkene, the
hydrogen of the acid attaches itself to the carbon atom
that already holds the greater number of hydrogens.
For example, when hydrogen bromide adds across the double
bond of propene, the hydrogen initially adds to that carbon
atom which already has the greater number of hydrogen atoms
directly attached to it (i.e. the terminal carbon atom)
and then the bromine then attaches to the other carbon
of the double bond (i.e. the central carbon atom) to
yield 2-bromopropane.
HH H HH H HHH
HCC=CH ==> HCC+CH ==> HCCCH
H HH H HBrH
2-bromopropane
Mass is the intrinsic characteristic of matter and
all matter has mass. Mass is the amount of matter
in a substance, and it is measured in grams and
kilograms.
The a mass spectrometer is an instrument for the separation and
analysis of ions and atoms. In the mass spectrometer a
sample (usually gaseous) is
ionised and the positive ions produced are
accelerated into a high vacuum which is exposed
to electric and magnetic fields. Ions of different types
can be sorted via a detector into a mass spectrum. The mass
spectrum consists of peaks of varying intensity to which
mass/charge values can be assigned, and from which
molecular structure can be deduced.
Francis William Aston (1877-1945) invented
the Mass Spectrometer
Matter is defined as anything that occupies space and
that has mass.
These three forms are called the States of Matter :
Examples of matter are a book, pen, ruler, the sun,
the moon, air, water, milk, etc., since each has
mass and occupies space.
Radio waves, heat and light are not matter since they
have no mass.
A maximum-boiling mixture is an azeotrope
having a boiling point higher than those of its components.
Melting is the process by which a solid changes state
from a solid to a liquid.
Melting point is the temperature at which a
substance change state from being solid to being liquid.
A metal is an element which has the physical properties of having
- a lustrous appearance,
- being malleable,
- being tenacity,
- having high densities, and
- being good conductors of heat and
- being good conductors of electricity.
Metals react with oxygen to form basic oxides.
Metals react with halogens to form halogen compounds which
are stable in presence of water.
Metals are electro-positive elements and form complex salts.
Those metals which are high on the electrochemical series
form chlorides which are non-volatile ionic solids and
have cubic ionic lattices (e.g. sodium chloride). These
ionic crystal lattices, which are composed of metal ions
and chloride ions, dissociate in water but the ions
themselves are not hydrolysed (they do not react with
water).
Many metallic chlorides liberate chlorine when treated
with sulphuric acid and manganese dioxide.
Many metallic chlorides liberate hydrogen chloride gas
when warmed with concentrated sulphuric acid.
The atoms in a metal are arranged in an orderly
manner. Because metals have low ionisation potential,
they can easily lose their outermost electrons, which
are then free to travel in a cloud between all the
atoms of the metal. The electrostatic attractive force
between the positively charged ionised atoms of the
metal and the negatively charged electronic cloud is
responsible for the bonding in the metal. The
metallic bond is very strong and accounts for the mechanical
strength of metals.
The metallic bond accounts for the physical and chemical
properties of metals. The following structure is proposed for
the metallic bond.
- Metals consist of positive ions of the metal packed
closely. The packing structure varies with the metal.
- When forming this arrangement each atom of the metal
releases its valiancy electrons, which are now free to
roam through the intervening spaces between the positive
ions. This space of moving electrons is often referred to
as the electron gas or electron atmosphere.
- The positive ions are not free to move, but
they are able to vibrate.
- The mutual sharing of this electron atmosphere
by all the positive ions of the metal establishes
a kind of diffuse bonding, which is non-directional,
and is called the metallic bond.
Methane, CH4, is the simplest hydrocarbon and first
member of the alkane series. The methane molecule
has a tetrahedral shape, and there are single covalent
bonds between the carbon atom to each hydrogen atom
in the molecule.
Migration is the movement of ions through the solution
towards the electrodes during electrolysis.
A minimum boiling mixture is an azeotrope have
a boiling point lower than those of its
components.
For example, 95% alcohol, boils at a lower temperature
than either pure ethanol or water.
When two liquids mix readily to form a solution, they
are said to be miscible.
A mixture is composed of two or more constituent
substances which are not bound together by a chemical
bond. Mixtures can occur in each of the
states of matter.
For example, air is a mixture of gases, consisting of
approximately 78% nitrogen, 20% oxygen, and smaller
quantities of carbon dioxide, argon and water vapour.
The composition of the atmosphere is changing gradually
over time, due to the burning of fossil fuels and
emissions from industry.
Mixtures can be found everywhere, as well as air. Mixtures
can be found in practically all foods, the soil in the
ground, oil and petrol and many other everyday
substances.
Alloys are a very important kind of mixture in
modern life. Alloys are made by mixing two or
more molten metals uniformly together, and allowing
the metal in metal solution to solidify on cooling.
Molal concentration is the amount of substance dissolved per unit volume and has units
of mol per dm cubed or mol per liter cubed. It has the symbol c.
Molar Mass is the amount of substance per unit mass of solvent and has units
of mol per kg. It has the symbol m.
A molar solution, M, is one which contains one gram
molecular weight (i.e. one mole) of the solute in
a liter of solution.
For example, 0.5M HCl means a hydrochloric acid
solution containing 0.5 moles of hydrochloric acid
per liter of solution.
A mole is the amount of substance which contains
as many molecules as are present in 12 grams of
Carbon 12. One mole of a compound is its molecular
weight in grams.
Every compound has a molecular formula, which shows
the elements that are present in the compound and
the number of atoms of each element in the compound.
Molecular weight, Mr, (also called relative molecular mass) is
the ratio of the average mass per molecule of naturally
occurring form of an element or compound to one twelfth (i.e. 1 / 12) of the mass of a Carbon-12 atom.
The molecular weight is equal to the sum of the
relative atomic masses of all the atoms that comprise
the molecule.
A molecule is the smallest particle of a
substance (i.e. of a chemical compound) which can
maintain an independent existence and consists two
or more atoms bonded together. In general, atoms do
not exist individually, but occur in groups called
molecules.
For example, a molecule of hydrogen consists of two hydrogen
atoms bonded together.
A molecule of oxygen consists of two oxygen atoms bonded together.
Similarly, a molecule of nitrogen consists of two nitrogen atoms
bonded together.
A molecule that consists of two atoms is known as a
Diatomic Molecule.
A molecule of helium consists of a single atom of helium,
as it has a valency of zero.
A molecule of sulphuric acid consists of two atoms of hydrogen, one
atom of sulphur and four atoms of oxygen.
Chemists give each type of molecule a chemical formula, showing
what atoms are contained in the molecule and in what proportions.
Monobasic Acids are acids that contain one ionisable
hydrogen atom in each molecule.
A monohydric alcohol contain one hydroxyl group in the
molecule. The general formula of saturated aliphatic
alcohols is CnH2n+1OH, where n=1,2,3, etc.
Monomers are the low molecular weight materials from
which high molecular weight polymers
are formed in a polymerisation process.
Mortar is a hydraulic cement, the best known of which is
known as Portland Cement.
Multiple bonds are formed between atoms in a molecule
where more than one pair of electrons are shared between
the atoms. Examples of molecules containing multiple bonds
include, the alkenes, the alkynes, and the arenes.
Start of Hypertext ....
Elements ....
Compounds ....
Index
Hypertext Copyright (c) 2000 Donal O'Leary. All Rights Reserved.