Chemistry is the study of matter and its interactions. The basic units that make up all matter are atoms, which combine to form molecules. Atoms are made up of protons, neutrons, and electrons. The number of protons in an atom determines its atomic number, while the total mass of an atom is determined by its atomic mass number. Molecules are combinations of atoms that are bonded together chemically. The mole is a unit used to measure amounts of substances, equal to 6.022x1023 particles. Stoichiometry uses mole ratios to calculate amounts of reactants and products in chemical reactions.
19. Law of conservation mass
Total masses of reactants =
Total masses of products +
Masses of unreacted reactants.
This law was proposed by Antoine
Lavoisier in 1744
58. Atomic mas
• the number of times an atom of
that element is heavier than an
atom of Carbon -12.
• One atomic mass unit is defined
as a mass equal to 1/12th the
mass of Carbon -12 atom.
59. Average atomic mass
• Elements are found in different
isotopic forms (different mass
from)
• Isotope -atoms of same elements
having different atomic mass.
• Average Atomic Mass = Sum of
abundance(rare) of each isotope X
precise atomic mass
61. Molecular mass
• The molecular mass of substance (element
or compound) is the number of times the
molecule of the substance is heavier than
1/12ththe mass of an atom of Carbon -12.
• Example:
Molecular mass of H2O = (2 x Atomic mass of
H2) + Atomic mass of O
= (2 x 1.008) + 16.0
= 18.02 u
62. Atomicity
• total number of atoms of elements
combined to form a molecule.
• eg.Atomicity of Oxygen (O2) is two,
while that of Ozone (O3) is three.
Note:
• He and Ne are monoatomic O2, N2 and
H2 are diatomic O3 is triatomic
• P4 is tetraatomic S8 is Polyatomic.
63. Atom is distinguished from its molecule
• Consider the formation of hydrogen chloride from
hydrogen and chlorine.
• Hydrogen and chlorine do not exist in free atomic
state but exist in molecular state hydrogen chloride.
H2 + Cl2 --> 2HCl
[1v] [1v] [2 volumes]
[n molecules] [n molecules] [2n molecules]
½ ½ 1
64. MOLE
• Amount of the substance that contains the
number of particles as present in 12g of C-12.
• This number of particles is determined to be
equal to 6.022 x1023 particles(Avogadro no.N A)
• Atoms and molecules are too small to count. To
solve this problem their numbers are expressed
in terms of Avogadro’s number (NA = 6.023
1023). Mole is the number equal to Avogadro’s
number just like a dozen
65.
66. It is defined as the
percentage by weight of
each element present in
the compound.
67. Percentage composition:
• Eg. C2H5OH , Molecular mass=?, Then %=?
• 2 moles of C atom =12x2 =24g
• 1 mole of O atom = 16 x 1 = 16 g
• 6 moles of H atom = 1 x 6 = 6 g
• Hence, the percentages of constituent
elements are:
68. Percentage composition:
• the percentages of constituent elements are:
• Percentage of carbon = 24 X 100 = 52.17%
• 46
Percentage of oxygen = 16 x 100 = 34.78%
• 46
Percentage of hydrogen = 6 x 100 = 13.04%
• 46
• Therefore, Each 100 g sample of ethanol
contains 52.17 g carbon, 34.78 g oxygen and
13.04 g hydrogen.
70. Empirical formula:
• chemical formula indicating the number
of atoms in a molecule in the simplest
ratio.
eg.
• The empirical formula of ethanol
(C2H5OH) is C2H6O and that of benzene
(C6H6) is CH.
72. Molecular formula
• The formula which gives the actual
number of each kind of constituent
atoms in one molecule of the compound is
called the molecular formula of the
compound.
eg.
• The molecular formula of ethanol is
C2H5OH and that of benzene is C6H6.
74. Chemical Stoichiometry
• Derived from Greek word
• Stoichio – element and
• Metery measure.
• Chemical stoichiometry is a process
of making calculations based on
formulae and balanced chemical
equations.
75. Chemical Stoichiometry
Eg. 1N2(g) + 3H2(g) ⎯> 2NH3(g)
• Numbers 1, 3 and 2 are coefficients.
• 1 mole of N2(g) (28 g) react with 3
moles H2(g) (6 g) giving 2 moles of
NH3(g) (34 g).
• Hence from the amount of the
reactants, the amount of products
that would be formed can be
calculated.
77. limiting and excess reactants
• The limiting reactant.(less amt)
• It is the reactant which is taken as
less that reacts completely, but limits
further progress of the reaction.
• The excess reactant (Large amt)
• It is the reactant which is taken in
excess. Hence, some amount of it
remains unreacted.
Notas do Editor
If 2 same element have same no.. Of proton. When we combine proton and neutron called amu. Electron revolve around the nucleus like planet and sun.
Electron revolve attracted proton they attract both each other.
Laws Of Chemical Combination And Dalton's Atomic Theory - Lesson Summary
The five basic laws of chemical combination that govern every chemical reaction are: Laws of Conservation of Mass
Law of Constant Composition or Definite Proportions
Law of Multiple Proportions
Law of Combining Volumes (Gay-Lussac’s Law of Gaseous Volumes)
Avogadro’s Law
Laws of Conservation of Mass: In 1789, Lavoisier proposed the law of conservation of mass. It states that in all physical and chemical changes, the total mass of the reactants is equal to the total mass of the products.
After shaking reaction take place and white ppt formed.
During chemical reaction matter neither gain nor loss. This law is called law of conservation energy or also called law of indestructibility of matter.
If isotope is there where this law is not followed for eg.
One more demerit in this law is which is above there.
Here one of the best example.
Carbon atomic mass no is 12 and O atomic mass no. is 16. here fixed amount of carbon is react with fixed amount of oxygen to fomr co2. it only possible in particular amount.
Suulfur atomic mass no. 32 and
Co efficient check karne ka.
Molecule single compound. They said atom hosake hai or nahi bhi hossakte hai environemnt me free form me present eg. Iron soil ke saath mix rehta but molecule exist in one form eg. Water.
He conclude that jo smalllest particle of gas jo independently hai. Wo molecule hai na ke atom. So volume of gas must be related to no. of gas.
Matlab ek type ka volume mean container hai to usme gas ki quantity bhi utni hai. Mean same volume container me same no. of gas rahegi.
Scientist use theory for century for understanding matter.
This scinetis research delton theory and find the demerits of their theory.
Now scientist modify this theory and make modern atomic theory.
By x-ray bomberdment nitrogen is converted into carbon.