For thousands of years
people rocks and distal plant uses to materials over the past two centuries
chemist have loved more and more about how to get materials from rocks from the
air and the sea types of plants they have also found out the right condition to
alow these materials to react together to make new substances such as dyes,
plastic, medicine.
When we make a new substance
that is important to mix the reactance in the correct proportions to
ensure that it is vested in order to do this we need to know about the relative
masses of atoms and molecules and how these are used in chemical calculation.
In order to explain how chemical substances behave, first have to understand but the substances themselves were made from. Over time a model was developed in which all substances were composed of atom of element. Originally it was thought that atom could not themselves be broken up into smaller parts but now we understand the structure inside the atoms themselves and the role of electrons protons and neutrons we cannot design and make materials and objective almost at the atomic level.
Matter
Anything and which
has mass and occupy space. For example oxygen nitrogen wood and iron
Atoms
are the smallest
particle of an element which may or may not exist independently and it can
enter in a chemical reaction for example atoms of Hydrogen oxygen nitrogen do
not exist independently but Helium Neon and Argon can exist
independently.
Diameter of atom is of the order = 2 x 10-10 meter or .2 nm.
Radius
of atom is of the order
= 10-10
Compound
A pure substance which
is formed by the chemical combination of two or more different elements in a
fixed ratio by mass is called compound. Hydrogen and Oxygen in water have a
fixed ratio by mass which is 1:8 respectively.
Molecules
The smallest particle of
an element or compound which exist independently is called molecule
Classification of Molecules
·
On
the basis of type of atoms
1) Home atomic molecules same
kind of atoms H2, O3
2) Heteroatomic
molecules different kind of atoms HCl , H2O
·
On
the basis of number of atoms
1) Monatomic
contain only one atom. For Example Helium, Neon, Argon
2) Polyatomic
contain more than one atoms. For example O2 ,CH4
,NH3
·
On
the basis of mass of molecules
1) Micro molecules: contain molecular mass less than
10000 Dalton. For example glucose
2) Macromolecules: contain molecular mass about 10000 Dalton.
For example: protein
Atomicity:
Total number of atoms in
one molecule is called atomicity for example hemoglobin has 10000 atom
Ions
The species which carry
positive or negative charge. Example Cl- ,O2-,
Types of Ions:
Cations: The ions which carry positive charge. All cations
are smaller in size than their parent Atoms and energy is required to form cations.
For example: Na+, Ca++
Isoelectronic
cations are those
have same number of electrons in them.For example
Na+, Mg++, Al+++
Anions: The ions which carry negative charge. All anions are larger than
parent atom andEnergy is released to form anions.
For Example: Cl-,SO2-2
Isoelectronic
anions are those
have same number of electrons in them. For example
Cl-, O--, N---
Molecular Ions: Molecules carry positive or negative charge is called molecular
ions.For
Example: O2-2, CH4+
Types
of Molecular Ions
Molecular Cations: molecules
carry positive charge
Molecular Anions:
molecules carry negative charge
Note: NH4+ positive is not a molecular ion:
Moles:
Atomic mass of an element expressed in gram is called gram atom or mole
For example
23 gram of sodium is = 1
mole
12 gram of carbon
is = 1 mole
Molar mass of compound expressed in gram is called gram molecule or
mole
For example
44 gram of carbon
dioxide is = 1 mole
18 gram of water
is = 1 mole
Formula mass of ionic compound
expressed in gram is called gram formula or mole
For example
58 8.5 gram of
sodium chloride is equal to 1 mole
Ionic mass of ions expressed in gram
is is called Gram ion or mole
For example
17 gram of OH-
is = 1 mole
Avogadro's
number
The number of atoms
molecules and ions in 1 mole of substance which is equal to 6.02 x 10 23.
It is a constant and denoted by NA
For example
One mole of sodium
contain 6.02 x 10 23 atoms
One mole of carbon
dioxide contain 6.02 x 10 23 molecules
One mole of
hydroxyl Ion contains 6.02 x 10 23 ions
Molar
volume
One mole of any gas at
standard temperature and pressure occupies 22.414dm-3.
For example
One mole of H2 contains
6.02 x 10 23 molecules is equal to 22.414 dm3
STOICHIOMETRY
The branch of chemistry
which deals with quantitative relations between reactants and products in a
balanced chemical equation
Limitation of
Balanced chemical equation
They do not tell
about
·
Conditions
·
Rate of reaction
·
Physical state of
reactants and products
·
Mechanism of reaction
Condition for stoichiometry
calculation
·
All reactants must be
completely converted into products
·
The side reaction must
not occur
· The law of conservation
of mass and law of Definite proportion must be obeyed while doing the
calculations
Limiting Reactant
Limiting reactant is a
reactant that controls the amount of product formed in a chemical reaction due to being less than the
required amount
Or
It can also be defined
as follows
·
It is a reactant that
produce least number of moles of product
·
It is consumed earlier
in the reaction
Identification of Limiting Reactant
·
Calculate the number of
moles from the given amount of reactants
·
Calculate the number of
moles of product formed from the given moles of each reactant
·
Identify the reactant as
a limiting reactant which produces least moles of product
Yield
The amount of product
obtained as a result of chemical reaction is called yield
Types of Yield:
Theoretical yield: The amount of product calculated from the
balanced chemical equation is called theoretical yield
Actual yield: The amount of product obtained in a chemical reactions
experimentally is called actual yield
Percentage yield: it is the ratio between actual yields
divided by theoretical yield x 100
Note: actual yield is always less than
theoretical yield
Isotopes
The atoms of same
element having same atomic number but different atomic masses are called
isotopes
For example: Hydrogen has three isotopes naming protium, deuterium and tritium
respectively Carbon has three
isotopes Chlorine has two isotopes Oxygen has three isotopes Nickel has five Calcium has six Palladium
has six Cadmium has nine and Tin has 11 isotopes the majority of
elements of the periodic table have some number of isotopes
Note: those elements which have only one isotopes are called monoisotopic elements
For example: gold,
Arsenic, Iodine and Fluorine are mono isotopic elements
Isobars: Atoms of element having same atomic message but different atomic number. For example,
Calcium have mass number
40 and atomic number is 20 but argon has mass number 40 but atomic number is 18
Isotones: Atoms of element have
same number of neutrons. For Example,
Carbon-14, Oxygen-16 and Nitrogen-15 have same number of neutrons.
Relative Abundance of Isotopes:
The percentage of a
particular isotope of element which exist naturally is called the relative
abundance of isotopes
280 different isotopes
are present naturally. They include 40 radioactive isotopes as well. About 300
isotopes are unstable radioactive produced through artificial disintegration of
atoms of different element. Out of 280, 240 isotopes are stable. The relative
abundance of isotopes can be determined by mass spectrometry
For example:
The elements like
arsenic following iodine and gold have only a single isotope they are called monoisotopic substances.
In general the element
of odd atomic number almost never possesses more than two stable isotopes the
element of even atomic number usually have much larger number of isotopes. Oxygen
magnesium silicon calcium iron farm nearly 50% of the earth crust out of 280
isotopes that occur in nature 154 are of even mass number and even atomic
number and 126 has odd Match number and atomic number. Isotopes are separated
from each other based upon their properties.
Mass
spectrometry
The technique in which atoms or molecules are
converted into ions are Separated on the basis of charge to mass ratio
Mass spectrometer: An instrument used to measure the exact mass
of different isotopes of an atom of element with their relative abundance is
called mass spectrometer
Types of mass spectrometer
·
Aston mass spectrometer
·
Dempster's Mass spectrometer
·
Modern Mass spectrometer
Aston mass spectrometer: It was designed to identify isotopes of an element on the basis of atomic masses
Dempster’s spectrometer: It was design to identify isotopes of element
which are in solid state
Parts of modern mass spectrometer
Vaporization chamber: In this chamber the sample of element is
vaporized in this chamber the Vapors pressure is reduced to 10 -7 to
10-6 Torr.
Ionization chamber: In this chamber sample of element is ionized
either by alpha rays are by Electron beam
Electric field: Electric field is applied to accelerate the positive ions the
applied potential Difference is of 500- 2000 volts.
Magnetic
field: On passing through magnetic field deflection of positive ions takes
place According to their mass to charge ratio.
Electrometer or ion collector: And collector receive positive ions
according to their mass to Charge ratio related to isotopes
1) The strength of
current measured by ions collector gives the relative abundance of isotopes of
a definite mass to charge value
2) The same experiment
is performed with carbon 12 isotopes and current strength is compared
Other techniques for the
separation of isotopes
·
Gas diffusion
·
Thermal diffusion
·
Distillation
·
Ultracentrifugation
·
Electromagnetic
separation
·
Laser separation
The mass spectrometer
tells us
·
The number of isotopes
the number of peaks represents the number of isotopes of an atom of an
element
·
The abundance of
isotopes the relative height of peaks give the direct measure of the
relative abundance of isotopes
Fractional atomic mass
Atomic mass of elements
depends upon the number of isotopes of an
element and their natural abundance.
Combustion analysis
Those compounds which simply consists of carbon hydrogen and oxygen can be analyzed by very easily by combustion analysis. The product of combustion is H2O and CO2.these two products are collected separately and weighed.
The carbon and hydrogen
present in the compound reacts with oxygen in the presence of cupric oxide and
change into carbon dioxide and water respectively. These gases are passed first
through water absorber containing magnesium dichlorate and then through carbon
dioxide absorber which contains 50% potassium hydroxide solution.
The increase in mass of these absorbers corresponds to the main source of water and carbon dioxide produce in an organic compound. The percentage to Carbon and Hydrogen from the mass of carbon dioxide and water can be determined directly and mass of Oxygen which is in excess cannot be determined directly
Note: there are two methods through which nitrogen from organic compound can be estimated and following methods are
a) Dumas
method
b) Kjeldahl
method
Empirical Formula
The simplest whole
number ratio of atoms of different elements in a compound is called empirical formula. For
example, empirical formula of glucose C6 H12 O6
is CH2 O, empirical formula of hydrogen peroxide H2O2
is HO
The empirical and
molecular formula of CH4, NH3, H2O and C12
H22 O11 are the same because they cannot be simplified.
Ionic compounds have empirical formula but no molecular formula.
Molecular Formula
Actual number of atoms
of different elements present in a molecule is called molecular formula.
For example
benzene C6 H6, ethane C2 H6, Sodium
Peroxide and Na2 O2, mercuric chloride and glucose have
molecular formulas. In all these compounds the molecular formulas are simple
multiple of empirical formulas, Hence.
Molecular formula= n x Empirical Formula
(Where n is the simple
integer. those compounds whose empirical and Molecular formulas are same or
numerous for example sodium chloride water carbon dioxide ammonia and sucrose
have same empirical and Molecular formulas
Note: Empirical Formula of hemoglobin is C759 H1208 N 210 S2 O204 Fe
