CHM 101 ONIPEDE’s Part
Recommended texts: 1. Concise Inorganic Chemistry by J.D. Lee, 2. Inorganic Chemistry
by Catherine E. Housecroft and Alan G. Sharpe, Modern Inorganic Chemistry by C.
Chamber and A.K. Holliday, Principles of General Chemistry by Martin S. Silberberg
Atoms, molecules, elements and compounds and chemical reactions
Around 1900 two scientists Joseph John Thomson (1856 – 1940) and Ernest Rutherford (1871 –
1937) established a model of the atom, and this is the basis of modern atomic theory. The model
places the more massive positive proton and neutral neutron in very small nucleus and this
contain all the positive charge and mass of the atom. Electron with a much smaller mass(1/1835)
than proton or neutron surrounds the nucleus and occupies most of the volume. In a neutral atom
the number of electrons equals the number of protons.
All atoms of a given element have the same number of
protons.in the nucleus. The number of protons in the
nucleus of an element is given by its atomic number which
is generally indicated by Z. and hence element are written
as 23
11 Na,.
Between 18th and 19th century Antoine Laurent Lavoisier
(1743 – 1794) chemist tried how elements combined with
another. They learned that the substances they produced
had constant composition so they could define the relative
masses of elements that would combine to produce a new
substance. At the beginning of 19th century, John Dalton
(1766 – 1844). Suggest that the combination of elements
involves atoms and proposed a relative scale of atom
masses and for simplicity 1 for hydrogen on which to base
the scale. Mass of atomic particle is expressed in atomic
mass unit (u). One atomic mass unit 1u is one-twelfth of the
mass of an atom of carbon with six protons and six
neutrons. One atomic mass unit (u) = 1.661 x 10 – 24 g.
Mass number
1
,The sum of the number of protons and neutrons for an atom is called it mass number and its
given the symbol A.
A = mass number = number of protons + number of neutrons
Dalton’s atomic theory
1. All matter consists of atom tiny indivisible particles of an element that cannot be created
or destroyed.
2. Atom of one element cannot be converted into atom of another element. i.e. In chemical
reactions the atoms of the original substances recombines to form different substances.
3. Atoms of an element are identical in mass and other properties and are different from
atoms of any other element
4. Compounds result from the chemical combination of a specific ratio of atoms of different
elements.
Isotopes
Atoms of the same atomic number but different mass numbers are called isotopes.
1 2 3
eg 1 H (Protium) 1 H (Deuterium), 1 H (Tritium). They differ by their number of neutrons and
hence have different mass number.
2
, Isotope abundance
Isotope abundance is the percentage of a specific isotope within a sample of an element. It refers
to the relative proportion of the different isotopes of a chemical element as they naturally occur.
number of atoms of a givenisotope
Percent abundance = x 100%
total number of atoms of all isotopes of that element
The abundance of 1H is 99.985%, for deuterium is 0.015%, while that of tritium is trace.
The relative atomic mass or atomic weight or average atomic weight
This is the average of the atomic masses of all of the element’s isotopes.
Atomic weight = ¿) (mass of isotope1) + ¿) (mass of isotope 2) + ……
Use the table above to determine the relative atomic masses of H, B, Ne and Mg.
Questions
3
Recommended texts: 1. Concise Inorganic Chemistry by J.D. Lee, 2. Inorganic Chemistry
by Catherine E. Housecroft and Alan G. Sharpe, Modern Inorganic Chemistry by C.
Chamber and A.K. Holliday, Principles of General Chemistry by Martin S. Silberberg
Atoms, molecules, elements and compounds and chemical reactions
Around 1900 two scientists Joseph John Thomson (1856 – 1940) and Ernest Rutherford (1871 –
1937) established a model of the atom, and this is the basis of modern atomic theory. The model
places the more massive positive proton and neutral neutron in very small nucleus and this
contain all the positive charge and mass of the atom. Electron with a much smaller mass(1/1835)
than proton or neutron surrounds the nucleus and occupies most of the volume. In a neutral atom
the number of electrons equals the number of protons.
All atoms of a given element have the same number of
protons.in the nucleus. The number of protons in the
nucleus of an element is given by its atomic number which
is generally indicated by Z. and hence element are written
as 23
11 Na,.
Between 18th and 19th century Antoine Laurent Lavoisier
(1743 – 1794) chemist tried how elements combined with
another. They learned that the substances they produced
had constant composition so they could define the relative
masses of elements that would combine to produce a new
substance. At the beginning of 19th century, John Dalton
(1766 – 1844). Suggest that the combination of elements
involves atoms and proposed a relative scale of atom
masses and for simplicity 1 for hydrogen on which to base
the scale. Mass of atomic particle is expressed in atomic
mass unit (u). One atomic mass unit 1u is one-twelfth of the
mass of an atom of carbon with six protons and six
neutrons. One atomic mass unit (u) = 1.661 x 10 – 24 g.
Mass number
1
,The sum of the number of protons and neutrons for an atom is called it mass number and its
given the symbol A.
A = mass number = number of protons + number of neutrons
Dalton’s atomic theory
1. All matter consists of atom tiny indivisible particles of an element that cannot be created
or destroyed.
2. Atom of one element cannot be converted into atom of another element. i.e. In chemical
reactions the atoms of the original substances recombines to form different substances.
3. Atoms of an element are identical in mass and other properties and are different from
atoms of any other element
4. Compounds result from the chemical combination of a specific ratio of atoms of different
elements.
Isotopes
Atoms of the same atomic number but different mass numbers are called isotopes.
1 2 3
eg 1 H (Protium) 1 H (Deuterium), 1 H (Tritium). They differ by their number of neutrons and
hence have different mass number.
2
, Isotope abundance
Isotope abundance is the percentage of a specific isotope within a sample of an element. It refers
to the relative proportion of the different isotopes of a chemical element as they naturally occur.
number of atoms of a givenisotope
Percent abundance = x 100%
total number of atoms of all isotopes of that element
The abundance of 1H is 99.985%, for deuterium is 0.015%, while that of tritium is trace.
The relative atomic mass or atomic weight or average atomic weight
This is the average of the atomic masses of all of the element’s isotopes.
Atomic weight = ¿) (mass of isotope1) + ¿) (mass of isotope 2) + ……
Use the table above to determine the relative atomic masses of H, B, Ne and Mg.
Questions
3
