see this link for info about exams
http://cbse.nic.in/PRE_EXAM_PRESS_NOTE_2010_IN_ENGLISH.pdf
Saturday, December 4, 2010
Our environment
1) Our environment is composed of various biotic and abiotic factors which
interact with each other.
2) Human activities have a great impact on the functioning of the environment.
3) The wastes generated by the various human activities may be biodegradable
or non- biodegradable.
4) The enzymes present in the body of decomposers are capable of breaking
down the biodegradable substances, but not the non- biodegradable
materials.
5) The non-biodegradable materials like plastic and synthetic pesticides persist
in the environment for a long duration and may harm its biotic factors.
6) In an ecosystem, the abiotic and biotic factors interact to form a stable unit.
7) The size of an ecosystem ranges in size from as small as a pond or a
backyard garden to as large as an entire rain forest.
8) An ecosystem may be natural (like lakes and forests) or artificial (like cropfields
and aquarium).
9) The biotic factors may be classified as producers, consumers and
decomposers depending on their mode of nutrition.
10) The food manufactured by the producers from simple inorganic substances is
utilized directly or indirectly by the consumers.
11) Herbivores, carnivores, omnivores and parasites are the various types of
consumers.
12) The decomposers break down the dead bodies and wastes of organisms and
help in nutrient recycling.
13) Food chains are present in every ecosystem. Each food chain is composed of
three to five trophic levels.
14) There is flow of energy between the various trophic levels.
15) Producers convert solar energy into chemical energy, which is then utilized
by the consumers and decomposers.
16) About 1% of solar energy falling on leaves is utilized by plants in
photosynthesis to produce food.
17) A large amount of energy loss occurs when the organisms of the higher
trophic level feeds on the lower trophic level organisms.
18) There is only 10% flow of energy from one trophic level to the next higher
level. Due to this energy loss, only 4 or 5 trophic levels are present in each
food chain.
19) The number of individuals in a trophic level decreases as we go up the food
chain.
20) Food webs, consisting of several interconnected food chains, are more
common in mature.
21) Flow of energy is unidirectional and cannot be utilized by the previous trophic
levels.
22) The non-biodegradable chemicals like pesticides and insecticides enter the
food chains in land and aquatic ecosystems and then accumulate
progressively at each trophic level. This is known as biological magnification.
23) Human activities can cause several environmental problems like ozone layer
depletion and waste disposal.
24) Ozone, composed of three oxygen atoms, is a toxic chemical. It is formed by
the combination of free oxygen atom with molecular oxygen.
25) The atmospheric ozone layer prevents the entry of solar ultraviolet rays and
thus protects all organisms on Earth.
26) Use of chemicals like chlorofluorocarbons has greatly depleted the
atmospheric ozone layer, which could endanger the environment.
27) The disposal of large amounts of garbage produced in any human settlement,
especially in cities and towns is causing major environmental problems.
28) Changes in our lifestyle and attitude have created many disposable items,
many of which are non-biodegradable.29) Effective methods of waste disposal should be found in order to reduce the
harmful effects on our environment.
Heredity and Evolution
1. Variations arise during the process of reproduction. They may be few in asexual reproduction, but many in case of sexual reproduction.
2. The minor variations arising during asexual reproduction are caused by slight inaccuracies in DNA copying. In sexual reproduction, variations are also caused by crossing over process of meiosis.
3. Beneficial variations help the species to survive better in the environment.
4. Nature selects the beneficial variations thereby leading to evolution.
5. Reproduction produces offsprings with similar body design of the parents. However the offspring are not identical, but show a great deal of variation from the parents.
6. Sexually reproducing organisms like humans have 2 (or more) versions of genes for each trait, called alleles.
7. Gregor Johann Mendel carried out several experiments on pea plants. He carried out large number of monohybrid and dihybrid crosses using many contrasting characteristics and put forward several important conclusions.
8. In case of monohybrid cross with pure variety of plants, the phenotypic ratio obtained in F2 generation is 3:1.
9. In case of dihybrid cross involving 2 pairs of contrasting characters, the phenotypic ratio obtained in F2 generation is 9:3:3:1.
10. Mendel concluded that out of any pair of contrasting characters, one is dominant and the other recessive.
11. The homozygous dominant trait is denoted by two capital letters whereas the homozygous recessive trait is denoted by two small letters. 
12. The factors or genes controlling a particular trait separate from each other during gamete formation. Hence gamete is always pure as far as contrasting characters are considered. Each gamete will possess only one gene set.
13. In crossing if two or more traits are involved, their genes assort independently, irrespective of the combinations present in the parents.
14. Genes carry information for producing proteins, which in turn control the various body characteristics. 15. For a particular trait, the offspring receives one allele from the father and one allele from the mother.
16. The combination of the male and female germ cells gives a diploid zygote. Thus the normal diploid number of chromosomes in the offspring is restored.
17. Different mechanisms are used for sex determination in different species.
18. The sex of human offspring is genetically determined.
19. Humans have 22 pairs of autosomes and one pair of sex chromosomes.
20. Females have similar sex chromosomes XX, whereas males have an imperfect pair i.e. XY. All eggs carry X chromosome.
21. The sex of the child depends on whether the egg fuses with the sperm carrying X chromosome (resulting in a girl) or with the sperm carrying Y chromosome (resulting in a boy).
22. Variations beneficial to a species have a greater chance of flourishing in the species than the harmful or neutral variations.
23. Genetic drift can alter gene frequencies in small population and provide diversity without any survival benefits.
24. Several factors like environment, mutations, reproduction etc can cause alterations in gene frequencies in a population over generations, leading to evolution.
25. Changes occurring in the DNA of germ cells are heritable whereas changes taking place in the non-reproductive tissues are not inherited.
26. Charles Darwin proposed that evolution of species occurred by natural selection, but he did not know the underlying mechanism.
27. Natural selection, genetic drift, variations and geographical isolation can lead to speciation in sexually reproducing organisms.
28. Gene flow between the members of a population prevents speciation.
29. The fundamental characteristics used to classify organisms are:
o presence of prokaryotic or eukaryotic cells.
o whether the organism is unicellular or multicellular.
o ability to perform photosynthesis.
o presence of endoskeleton or exoskeleton in heterotrophic organisms.
30. Classification of living organisms is closely related to their evolution.
31. As we go back in time to trace common ancestors, we find that all organisms must have arisen and radiated from a single species, which in turn originated from non-living material. Thus life arose from non-living matter.
32. Study of homologous organs, e.g. hand of man and wing of bird, helps in tracing the evolutionary relationship between different species.
33. Analogous organs, e.g. wing of insect and wing of bird, do not have common origins, but arose in different species to fulfill similar functions.
34. Fossils help in tracing evolutionary pathways.
35. The age of fossils can be determined by using the relative method or the isotope dating method.
36. Evolution is not a one-step process, but a continuous process occurring in several stages.
37. Complex organs are formed slowly over many generations, sometimes with intermediate forms playing an important role.
38. Sometimes the use of certain features gets modified with time. For example,feathers may have provided insulation initially but later became associated with flight
39. Evolutionary studies have shown that birds are closely related to reptiles.
40. Humans have carried out artificial selection for various features of cabbage and produced different vegetables.
41. Molecular phylogeny can also be used to trace evolutionary relationships. Here the DNA of different species is compared. Greater the differences in DNA, more distantly related are the species.
42. Disappearance of the existing species is not a requirement for formation of new species.
43. The new species formed are better adapted to the environment, but they need not be superior to the existing species.
44. The common ancestor of humans and chimpanzees evolved in different ways to produce the present forms.
45. Evolution produces more diverse and complex body forms over time, but the newly formed species are not more progressive than the already existing ones. So it is wrong to say that evolution produces progressive higher forms from lower ones.
46. All human beings, whether fair skinned or dark skinned, belong to the same species i.e. Homo sapiens that originated in Africa.
47. The human ancestors gradually migrated from Africa to various parts of the world like Asia, Europe, Australia and America. Thus, they spread to different parts of the Earth and adapted as best as they could to their environmental conditions.
How Do Organisms Reproduce?
Key Learnings
1) Reproduction is the biological process by which new individuals of the
same kind are produced.
2) Reproduction is not essential for the survival of an organism, but is
vital for the survival of a species.
3) Reproduction produces identical copies of the body design.
4) DNA is the informational macromolecule of our body. It provides
information for protein synthesis.
5) During cellular reproduction, DNA duplication occurs followed by
creation of an additional cellular apparatus.
6) The process of DNA copying is not accurate, resulting in variations
arising during reproduction, which is the basis for evolution.
7) Variations may or may not be beneficial for the individual, but help in
the survival of the species during adverse conditions.
8) Depending on their body design, the modes of reproduction differ in
different organisms.
9) Reproduction is broadly divided into asexual and sexual reproduction.
10) Fission, fragmentation, regeneration, budding, vegetative propagation
and spore formation are various modes of asexual reproduction.
11) Fission occurs in unicellular organisms like bacteria and protozoa
through simple cell division. Depending on the number of individuals
formed, fission may be binary or multiple fission.
12) On maturation, certain multi-cellular organisms (with simple body
makeup) break up into smaller fragments, each of which develops into
new individual. This reproductive method is called fragmentation.
13) Simple reproductive methods cannot occur in higher multi-cellular
organisms, since they have a complex and carefully organized body
structure.
14) In complex multi-cellular organism, reproduction is brought about by a
single, specialized cell type that is capable of proliferating and forming
all other cell types of the body.15) Regeneration is found in many completely differentiated simple
organisms, like
several parts, most of the parts will develop into complete organisms.
16) Regeneration involves specialized totipotent cells which proliferate and
differentiate to form the complete body.
17) Certain organisms like
which mature into new individuals and separate from parent body.
18) Vegetative propagation is used by many plants, especially those
incapable of producing seeds. Here, new plants are produced from
roots, stems or leaves of parent plant. This reproductive method is
widely used by plant breeders.
19) Spore formation is an asexual mode of reproduction found in certain
multicellular organisms like
capacity to develop into new individuals under suitable conditions.
20) Sexual reproduction requires both male and female sexes to produce
the offspring.
21) Sexual reproduction creates large number of novel variations.
22) In comparison to the non-reproductive body cells, the germ cells
contain only half the chromosome number.
23) The male gamete is smaller and motile whereas the female gamete is
larger and stores food.
24) When the offspring is produced by the union of the male and female
gametes, its specific chromosome number and DNA content is reestablished.
25) In angiosperms, flower is the reproductive organ of the plant.
26) Stamen, the male reproductive part of flower, is made up of anther
and filament. Carpel is the female reproductive part and is composed
of stigma, style and ovary.
27) The pollen grain is present in the anther whereas the egg cell is
enclosed in the ovary.
28) Pollination and fertilization are two essential events in reproduction of
angiosperms.
29) Pollination is the transfer of pollen grains from anther to stigma. It
may be either self-pollination or cross-pollination.30) Pollen tube carries the male gamete from stigma to the female gamete
in ovary.
31) Fertilization of male and female gametes produces the zygote, which
then forms the embryo.
32) Following fertilization, the ovule develops into seed whereas the ovary
forms the fruit. On germination, the seed develops into a seedling.
33) In humans, reproduction occurs sexually.
34) Puberty is the time when the juvenile body of a person starts sexual
maturation.
35) Before puberty, the body resources are used mainly to grow and
develop the organism to its adult size. Once this is achieved, puberty
sets in.
36) Some changes occurring during puberty are common to boys and girls,
whereas other changes are specific to boys and girls.
37) Changes such as appearance of pimples on face, growth of thick hair
in armpits and genital areas occur in both boys and girls.
38) Increase in breast size, darkening of nipples and occurrence of
menstruation are puberty associated changes in girls. In boys, facial
hair growth, cracking of voices and occasional enlargement of penis
occur during puberty.
39) Changes associated with puberty are slow and gradual and does not
occur uniformly in everyone.
40) The changes taking place during puberty, signals the occurrence of
sexual maturation in an individual to other members of the same
population.
41) In humans, the male reproductive system is composed of testes, vas
deferens, seminal vesicles, prostate gland, urethra and penis.
42) Testis is situated outside the abdominal cavity. It produces sperms and
secretes testosterone.
43) Sperm shows a small head containing the genetic material and a long
tail, which helps in motility.
44) Vas deferens and urethra are the thin tubes through which sperms are
transported from testes to outside. The sperms are nourished in the
seminal fluid.45) The female reproductive system is made up of ovaries, fallopian tubes,
uterus, cervix and vagina.
46) Ovaries are responsible for production of ova/egg as well as for
secreting the hormones, estrogen and progesterone.
47) On reaching puberty, ovulation occurs once a month in females,
wherein one immature egg present in any one of the ovaries becomes
mature and is released. This egg is carried by the fallopian tube.
48) Sperms which are introduced into the vagina of females during
intercourse, may encounter the egg on reaching the fallopian tube,
resulting in fertilization.
49) The zygote gets implanted in the uterus and develops into the embryo.
50) The placenta provides nourishment and oxygen to the embryo and
removes the waste generated by the embryo.
51) Gestation period is nine months in humans after which the child is
born due to uterine contractions.
52) In case fertilization does not occur, the released egg along with the
thickened lining of the uterus is shed out through the vagina in a
process called menstruation.
53) Engaging in unprotected sexual intercourse can cause pregnancy as
well as spreading of sexually transmitted diseases like gonorrhea,
syphilis and AIDS.
54) Condoms help to control the spread of sexually transmitted diseases.
55) Unwanted pregnancies can be avoided through several contraceptive
methods.
56) Mechanical barrier methods prevent sperm from reaching the egg, e.g.
– condom.
57) Oral contraceptive pills alter the hormonal balance, thereby preventing
the egg from being released.
58) Surgical blocking of vas deferens in male or fallopian tube in female
can also prevent pregnancy.
59) Abortions remove unwanted pregnancies, but this method is being
misused to carry out female foeticide.
60) Birth control methods are essential to keep the human population in
check and thereby improve the standard of living for everyone.Hydra and Planaria. If such an organism is split intoHydra produce buds on their body surface,Rhizopus. The thick walled spores have the
Periodic classification of elements
1. Dobereiner’s triads: Johann Wolfgang Dobereiner, a German chemist,
classified the known elements in groups of three elements on the basis
of similarities in their properties. These groups were called triads.
•
a. Properties of elements in each triad were similar.
b. Atomic mass of the middle elements was roughly the average of the
atomic masses of the other two elements.
Characteristic of Dobereiner’s Triads:• 
•
able to prepare triads of all the known elements
2. Newlands’ Law of Octaves: John Newlands, an English scientist,
arranged the known elements in the order of increasing atomic masses
and called it the ‘Law of Octaves’. It is known as ‘Newlands’ Law of
Octaves’
Limitations: Dobereiner could identify only three triads. He was not•
a. It contained the elements from hydrogen to thorium
b. Properties of every eighth element were similar to that of the first
element
Characteristics of Newlands’ Law of Octaves• 
Limitations of Newlands’ law of Octaves:
a. The law was applicable to elements upto calcium (Ca) only
b. It contained only 56 elements. Further it was assumed by Newlands
that only 56 elements existed in nature and no more elements would
be discovered in the future.
c. In order to fit elements into the table. Newlands’ adjusted two
elements in the same slot and also put some unlike elements under
same note. For example cobalt and nickel are in the same slot and
these are placed in the same column as fluorine, chlorine and bromine
which have very different properties than these elements. Iron, which
resembles cobalt and nickel in properties, has been placed differently
away from these elements
3. Mendeleev’s Periodic Table: Dmitri Ivanovich Mendeleev, a Russian
chemist, was the most important contributor to the early development
of a periodic table of elements wherein the elements were arranged on
the basis of their atomic mass and chemical properties.
.•
a. Mendeleev arranged all the 63 known elements in an increasing order
of their atomic masses.
b. The table contained vertical columns called ‘groups’ and horizontal
rows called ‘periods’.
c. The elements with similar physical and chemical properties came
under same groups.
Characteristic of Mendeleev’s Period Table:•
function of their atomic masses.
Mendeleev’s Periodic Law: The properties of elements are the periodic•
a. Through this table, it was very easy to study the physical and
chemical properties of various elements.
b. Mendeleev adjusted few elements with a slightly greater atomic mass
before the elements with slightly lower atomic mass, so that elements
with similar properties could be grouped together. For example,
aluminum appeared before silicon, cobalt appeared before nickel.
c. Mendeleev left some gaps in his periodic table. He predicted the
existence of some elements that had not been discovered at that time.
His predictions were quite true as elements like scandium; gallium and
germanium were discovered laterd. The gases like helium, neon and argon, which were discovered later,
were placed in a new group without disturbing the existing order
•
a. He could not assign a correct position to hydrogen in the periodic table
b. Positions of isotopes of all elements was not certain according to
Mendeleev’s periodic table
c. Atomic masses did not increase in a regular manner in going from one
element to the next. So it was not possible to predict how many
elements could be discovered between two elements
4. Modern Periodic Table: Henry Moseley gave a new property of
elements, ‘atomic number’ and this was adopted as the basis of
Modern Periodic Table’.
Limitations of Mendeleev’s Periodic Table :•
their atomic number
Modern Periodic Law: Properties of elements are a periodic function of•
a. The modern periodic table consists of 18 groups and 7 periods
b. Elements present in any one group have the same number of valence
electrons. Also, the number of shells increases as we go down the
group.
c. Elements present in any one period, contain the same number of
shells. Also, with increase in atomic number by one unit on moving
from left to right, the valence shell electron increases by one unit
d. Each period marks a new electronic shell getting filled
Position of elements in Modern Periodic Table:•
(i) Valency: Valency of an element is determined by the number of
valence electrons present in the outermost shell of its atom
distance between outermost electrons and nucleus which increases the
size of atom
(iii) Metallic and Non- metallic Properties:
•
called metallic character of an element
The tendency to lose electrons from the outermost shell of an atom, is•
group
Metallic character decreases across a period and increases down the•
called non- metallic character of an element
The tendency to gain electron in the outermost shell of an atom, is•
the group
Non-metallic character increases across a period and decreases down•
characteristic of both metals and non-metals are called as semi-metals
or metalloids
5. Metals have a tendency to loose electrons while forming bond. Hence
they are electropositive in nature
6. Non-metals have a tendency to gain electrons while forming bond.
Hence they are electronegative in nature
7. Oxides formed by metals are generally basic and oxides formed by
non-metals are generally acidicElements intermediate between metal and non-metals that show• Valency of elements in a particular group is same
• Valency of elements in a particular period increases by one unit from
left to right with the increase in atomic number by one unit
(ii) Atomic Size: Atomic size refers to the radius of an atom.
Trends in the Modern Periodic Table:•
due to increase in nuclear charge which tends to pull the electrons
closer to nucleus and reduces size of atom
In a period, atomic size and radii decreases from left to right. This is•
because on moving down, new shells are added. This increasesIn a group, atomic size and radii increases from top to bottom. This isAchievements of Mendeleev’s Periodic Table:Table showing Newlands’ Octaves:Example of Dobereiner’s Triads :
Carbon And Its Compounds
1. Covalent bond: A covalent bond is a bond formed by sharing of electrons between atoms. In a covalent bond, the shared pair of electrons belongs to the valence shell of both the atoms.
2. Conditions for formation of covalent bond:
a. The combining atoms should have 4 to 7 electrons in their valence shell.
b. The combining atoms should not lose electrons easily.
c. The combining atoms should gain electrons readily.
d. The difference in electronegativities of two bonded atoms should below.
3. Properties of covalent compounds:
a. Physical states: They are generally liquids or gases. Some covalent
compounds may exist as solids.
b. Solubility: They are generally insoluble in water and other polar
solvents but soluble in organic solvents like benzene, toluene etc.
c. Melting and boiling point: They generally have low melting and boiling
points.
d. Electrical conductivity: They do not conduct electrical current.
4. Steps for writing the Lewis dot structures of covalent compounds:
a. Write the electronic configuration of all the atoms present in the
molecule.
b. Identify how many electrons are needed by each atom to attain noble
gas configuration.
c. Share the electrons between atoms in such a way that all the atoms in
a molecule have noble gas configuration.
d. Keep in mind that the shared electrons are counted in the valence
shell of both the atoms sharing it.
5. Electronic configuration of some non- metals:
6. Carbon forms covalent bonds.
7. Electronegativity – It is the ability of an atom to attract a shared pair
of electrons towards itself.
8. If the atoms forming a covalent bond have different
electronegativities, the atom with higher electronegativity pulls the
shared pair of electron towards itself. Thus, the atom with the higher
electronegativity develops a partial negative charge and the atom with
the lower electronegativity develops a partial positive charge. This
covalent bond with some polarity is called polar covalent bond.
9. Carbon forms a large number of compounds because of two unique
properties:
a. Tetravalency
b. Catenation
10. Tetravalency of carbon:
Atomic number = 6
Electronic configuration: 2, 4
Valence electrons = 4
Valency = 4
So, carbon needs four electrons to attain noble gas configuration.
Or in other words, carbon has the ability to form four bonds with
carbon or atoms of other mono-valent elements.
11. Catenation: Carbon has the unique ability to form bonds with other
atoms of carbon, giving rise to large molecules. This property is called
catenation.
12. Steps for writing the Lewis dot structures of Hydrocarbons:
a. Write the electronic configuration of all the atoms present in the molecule.
b. Identify how many electrons are needed by each atom to attain noble gas configuration.
c. First complete the noble gas configuration of all the hydrogen atoms
by bonding each hydrogen atom with a carbon atom by a single bond.
d. The remaining valency of each carbon is completed by forming carbon
– carbon single, double or triple bonds.
e. Keep in mind that the shared electrons are counted in the valence
shell of both the atoms sharing it.
13. Classification of hydrocarbons:
a. Aliphatic or open chain hydrocarbons: These are the carbon
compounds which have carbon carbon long open chains. They are
classified as:
i. Saturated hydrocarbons: These hydrocarbons have all carbon – carbon
single bonds.
ii. Unsaturated hydrocarbons: These hydrocarbons have at least one
carbon – carbon double or triple bonds.
• Hydrocarbons with at least one carbon-carbon double bond are called
alkenes.
General formula = CnH2n where n = number of carbon atoms
• Hydrocarbons with at least one carbon-carbon triple bond are called
alkynes.
General formula = CnH2n-2 where n = number of carbon atoms
b. Cyclic or closed chain hydrocarbons: These are the
hydrocarbons which have carbon carbon closed chain.
They are classified as:
i. Alicyclic hydrocarbons: These are the hydrocarbons which
do not have benzene ring in their structure.
ii. Aromatic hydrocarbons: These are the hydrocarbons which have
benzene ring in their structure. When hydrogen bonded to carbon of
benzene is substituted with halogens, radicals or other functional
groups, the derivatives are called aromatic compounds.
14. Benzene: It is an aromatic hydrocarbon which has the molecular
formula C6H6. It has alternating carbon - carbon single and double bonds.
15. IUPAC name of hydrocarbon consists of two parts:
a. Word root: Number of carbons in the longest carbon chain
b. Suffix: Depends on the type of carbon – carbon bond: for single
bond, suffix is –ane ; for double bond, suffix is –ene, and for triple
bond suffix is –yne
16. Steps to write the IUPAC nomenclature of hydrocarbons:
a. Select the parent carbon chain:
i. Select the longest carbon chain as the parent chain.
ii. If a double or a triple bond is present in the carbon chain, it should be
included in the parent chain.
b. Number the parent carbon chain from that carbon end such that the
double bond, triple bond or side chain gets the lowest number.
c. Identify and name the side chain if any: -CH3 is named as methyl, -
C2H5 is named as ethyl etc. Also identify the position of the side chain.
d. Write the name of the hydrocarbon as:
Position number-name of the side chain word root – Position
number- suffix
Example: 2-Methyl but-1-ene
e. Remember if the hydrocarbon is an alkane, the position number of
suffix is not written.
17. Types of formula for writing hydrocarbons:
a. Molecular formula: The actual number of each type of atom present in
the compound.
b. Structural formula: The actual arrangement of atoms is written
c. Condensed formula: It is the shortened form of the structural formula
18. Conditions for Isomerism:
a. Only alkanes with more than three carbon atoms can have isomers.
b. The side chains cannot be present on the terminal carbons.
19. How to write different chain isomers of hydrocarbons:
a. First draw the different carbon chains keeping in mind the conditions
for isomerism.
b. Complete the tetravalency of carbon by forming single covalent bonds
with hydrogens.
c. In the end, check that the molecular formula of each isomer should be
same.
20. How to write different position isomers of unsaturated hydrocarbons:
a. First draw the different carbon chains keeping in mind the conditions
for isomerism.
b. If it is an alkene draw the first isomer always by drawing a double
bond between C1 and C2 or if it is an alkyne draw the first isomer
always by drawing a triple bond between C1 and C2
c. The next isomers will be dawn by drawing the same chain and
changing the positions of the double and triple bonds in alkenes and
alkynes respectively.
d. Complete the tetravalency of carbon by forming single covalent bonds
with hydrogens.
e. In the end, check that the molecular formula of each isomer should be
same.
21. Homologous Series: A series of organic compounds in which every
succeeding member differs from the previous one by –CH2 or 14 u.
The molecular formula of all the members of a homologous series can
be derived from a general formula.
22. Properties of a homologous series: As the molecular mass increases in
a series, so physical properties of the compounds show a variation, but
chemical properties which are determined by a functional group
remain the same within a series.
23. Homologous series of alkanes: General formula: CnH2n+2 where n =
number of carbon atoms
24. Homologous series of alkenes: General formula: CnH2n where n =
number of carbon atoms
25. Homologous series of alkynes: General formula: = CnH2n-2 where n =
number of carbon atoms
26. Functional group: An atom or a group of atoms which when present in
a compound gives specific properties to it, regardless of the length and
nature of the carbon chain is called functional group.
a. Free valency or valencies of the group are shown by the single line.
b. The functional group is attached to the carbon chain through this
valency by replacing one hydrogen atom or atoms.
c. Replacement of hydrogen atom by a functional group is always in such
a manner that valency of carbon remains satisfied.
d. The functional group, replacing the hydrogen is also called as hetero
atom because it is different from carbon, and can be nitrogen, sulphur,
or halogen etc.
27. Some functional groups in carbon compounds:
28. Steps to write the IUPAC name of organic compounds:
i. Select the parent carbon chain:
1. Select the longest carbon chain as the parent chain. If a double or a
triple bond is present in the carbon chain, it should be included in the
parent chain.
2. If a functional group is present, the carbon chain should include the
functional group.
ii. Number the parent carbon chain from that carbon end such that the
functional group, double bond, triple bond or side chain gets the
lowest number.
Remember here that the aldehyde and carboxylic acid functional group
are present on the terminal carbon atom.
iii. Identify the name and position of the functional group, double bond,
triple bond or side chain.
iv. The name of the functional group is written with either a prefix or a
suffix as given in the above table.
v. If the name of the functional group is to be given as a suffix, the name
of the carbon chain is modified by deleting the final ‘e’ and adding the
appropriate suffix. For example, a three-carbon chain with a ketone
group would be named in the following manner – Propane – ‘e’ =
propan + ‘one’ = propanone.
vi. Remember that in the compounds which have carbon containing
functional groups, the name of the word root includes the functional
group carbon atom also.
vii. If the carbon chain is unsaturated, then the final ‘ane’ in the name of
the carbon chain is substituted by ‘ene’ or ‘yne’ as given in the table
above. For example, a three-carbon chain with a double bond would be
called propene and if it has a triple bond, it would be called propyne.
29. Difference between chemical properties of saturated and unsaturated hydrocarbons
30. Catalysts are substances that cause a reaction to occur or proceed at a
different rate without the reaction being affected.
31. Oxidizing agents are substances which are capable of providing oxygen
to other compounds for their oxygen. Example: Alkaline KMnO4,
acidified K2Cr2O7 etc.
34. Catalysts are substances that cause a reaction to occur or proceed at a
different rate without the reaction being affected.
35. Soaps are sodium or potassium salts of long chain carboxylic acids.
36. Structure of soap molecule: The structure of soap molecule consists of
a long hydrocarbon tail at one end which is hydrophobic in nature. The
other end is the ionic part which is hydrophilic in nature.
37. Cleansing action of soap: When soap is at the surface of water, the
ionic end of soap orients itself towards water and the hydrocarbon ‘tail’
orients itself aligns itself along the dirt. Thus, clusters of molecules are
formed in which the hydrophobic tails are in the interior of the cluster
and the ionic ends are on the surface of the cluster. This formation is called a micelle.
Soap in the form of a micelle is able to clean, since the oily dirt will be
collected in the centre of the micelle. The micelles stay in solution as a
colloid and will not come together to precipitate because of ion-ion
repulsion. Now, when water is agitated, the dirt suspended in the
micelles is also easily rinsed away.
38. When hard water is treated with soap, scum is formed. This is caused
by the reaction of soap with the calcium and magnesium salts, which
cause the hardness of water.
39. Detergents are generally ammonium or sulphonate salts of long chain
carboxylic acids.
40. Detergents do not form scum with hard water. This is because the
charged ends of these compounds do not form insoluble precipitates
with the calcium and magnesium ions in hard water. Thus, they remain
effective in hard water.
41.
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