Elements, Atoms and Compounds

An element is the simplest form of a pure substance, which cannot be split up into two or more simpler substances by any chemical reaction. A compound is a substance of atoms of two or more elements formed by the chemical combination in a definite proportion by weight. This note provides information about elements, compound, molecules, and atoms.

Summary

An element is the simplest form of a pure substance, which cannot be split up into two or more simpler substances by any chemical reaction. A compound is a substance of atoms of two or more elements formed by the chemical combination in a definite proportion by weight. This note provides information about elements, compound, molecules, and atoms.

Things to Remember

  • The substances which are composed of its unit particles of a similar kind is known as pure substances.
  • An element is the simplest form of a pure substance, which cannot be split up into two or simpler substances by any chemical reaction.
  • A symbol is defined as the abbreviation of the full name of an element
  • A matter is anything that occupies space and has mass.
  • Compound is a substance of atoms of two or more elements formed by the chemical combination in a definite proportion by weight
  • The smallest particle of an element or compound, which is capable of independent existence is called molecule.
  • The smallest particle of an element, which takes part in chemical change is called atom.
  • The number of protons or the number of electrons in an electrically neutral atom of an element is called atomic number

MCQs

No MCQs found.

Subjective Questions

Q1:

 A. Write the word, from the  above passage, which are opposite in meaning  to the following words:

(a) lowered


Type: Very_short Difficulty: Easy

Show/Hide Answer
Answer: <p>grow</p>

Q2:

 A. Write the word, from the  above passage, which are opposite in meaning  to the following words:

(b) activate


Type: Very_short Difficulty: Easy

Show/Hide Answer
Answer: <p>check</p>

Q3:

 A. Write the word, from the  above passage, which are opposite in meaning  to the following words:

(c) hesitantly


Type: Very_short Difficulty: Easy

Show/Hide Answer
Answer: <p>unhesitantly</p>

Q4:

 A. Write the word, from the  above passage, which are opposite in meaning  to the following words:

(d) shout


Type: Very_short Difficulty: Easy

Show/Hide Answer
Answer: <p>be quiet</p>

Q5:

B. Write 'T' for true and 'F' for the false statements:

(a) The cold blackboard made the writer freeze.


Type: Very_short Difficulty: Easy

Show/Hide Answer
Answer: <p>false</p>

Q6:

B. Write 'T' for true and 'F' for the false statements:

 

(b) The writer did not feel comfortable among strangers.


Type: Very_short Difficulty: Easy

Show/Hide Answer
Answer: <p>true</p>

Q7:

C. Rewrite the following sentences putting them in the correct order:

(a) Other students loudly laughed at him for a long time.

(b) He tried to write on the blackboard.

(c) He was told to go to his own place.

(d) He forgot everything.


Type: Very_short Difficulty: Easy

Show/Hide Answer
Answer: <p>(b) He tried to write on the blackboard.</p> <p>(d) He forgot everything.</p> <p>(a) Other students loudly laughed at him for a long time.</p> <p>(c) He was told to go to his own place.</p>

Q8:

D. Answer the following questions:

(a) Why did the other students laugh at the writer?


Type: Short Difficulty: Easy

Show/Hide Answer
Answer: <p>The other students laughed at the writer because he was unable to write a single letter infront of them in the blackboard.</p>

Q9:

D. Answer the following questions:

(b) What made the writer freeze?


Type: Short Difficulty: Easy

Show/Hide Answer
Answer: <p>Standing at the blackboard with the eyes of so many girls and boys looking at his back made the writer freeze.</p>

Q10:

D. Answer the following questions:

(c) Was the writer really to unable to perform the task? Why/Why not ?


Type: Short Difficulty: Easy

Show/Hide Answer
Answer: <p>The writer was really unable to perform the task because he did not feel comfortable among strangers.</p>

Q11:

D. Answer the following questions:

 

(d) How can you say he was nervous ?


Type: Short Difficulty: Easy

Show/Hide Answer
Answer: <p>We can say that he was nervous because when he lifted the white chalk to the blackboard and, as he was about to write, his mind went blank. He could not remember his name, not even the first letter.</p>

Q12:

D. Answer the following questions:

(e) What sort of punishment was given to him by the teacher?


Type: Short Difficulty: Easy

Show/Hide Answer
Answer: <p>Teacher did not give any punishment to him.</p>

Q13:

                                                                                                      

A. Answer the following questions:

(a) Why did the boy curse himself?


Type: Short Difficulty: Easy

Show/Hide Answer
Answer: <p>The boy curse himself because he always appeared so dumb when he was called to perform something in a crowd.</p>

Q14:

                                                                                                                       

A. Answer the following questions:

(b) Why did the room burst into a loud and long laugh?


Type: Short Difficulty: Easy

Show/Hide Answer
Answer: <p>The room bursted into a loud and long laugh because of a sence of the girls and boys behind him filled him to the exclusion of everything. He realised how utterly he was falling and he grew weak and leaned his hot forehead against the cold blackboard.</p>

Q15:

                                                                                                                

A. Answer the following questions:

(c) Why did the boy hate the other students?


Type: Short Difficulty: Easy

Show/Hide Answer
Answer: <p>The boy hates the other students because they laughed at him.</p>

Q16:

B. Match the words in column 'A' with their meaning in column 'B':

Column 'A'                                                Column 'B'   

(a) fluently                                                  i. excitedly

(b) utterly                                                    ii. without stopping

(c) frantically                                             iii. by explaining well

(d) expressively                                        iv. completely    


Type: Very_short Difficulty: Easy

Show/Hide Answer
Answer: <p>a) fluently- without stopping</p> <p>b) utterly- completely</p> <p>c) frantically- excitedly</p> <p>d) expressively- by explaining well</p>

Q17:

C. Rewrite the following sentences putting them in correct order:

(a) The room became full of the loud laugh for a long time.

(b) He realized that he was totally failing.

(c) The boy raised his hand to write on the board.

(d) So he leaned his hot forehead against the cold board.


Type: Very_short Difficulty: Easy

Show/Hide Answer
Answer: <p>c) The boy raised his hand to write on the board.</p> <p>b) He realized that he was totally failing.</p> <p>d) So he leaned his hot forehead against the cold board.</p> <p>a) The room became full of a loud laugh for a long time.</p>

Q18:

A. Answer the following questions:

(a) What was the boy asked to do?


Type: Short Difficulty: Easy

Show/Hide Answer
Answer: <p>The boy was asked to write his name and address on the blackboard.</p>

Q19:

                                                                                                                                                                                                                                                                                                                       

A. Answer the following questions:

(b) Why did the children laugh at the boy? 


Type: Short Difficulty: Easy

Show/Hide Answer
Answer: <p>The children laughed at the boy because the boy could not remember his name, not even the first letter.</p>

Q20:

                                                                                                                                                                                                                                                                                            

A. Answer the following questions:

 (c) Why couldn't the boy write anything


Type: Short Difficulty: Easy

Show/Hide Answer
Answer: <p>The boy could not write anything because the staring eyes at his back made him immobile, his hand refused to move.</p>

Q21:

A. Answer the following questions:

(d) What did the boy feel at last?


Type: Short Difficulty: Easy

Show/Hide Answer
Answer: <p>The boy feels cursing himself for appearing so dumb when he was called to perform something in a crowd.</p>

Q22:

B. Rewrite the following sentences indicating 'T' for true and 'F' for false statement:

(a)  The task which was given to the boy was difficult.


Type: Very_short Difficulty: Easy

Show/Hide Answer
Answer: <p>false</p>

Q23:

B. Rewrite the following sentences indicating 'T' for true and 'F' for false statement:

(b) The teacher punished the boy,


Type: Very_short Difficulty: Easy

Show/Hide Answer
Answer: <p>false</p>

Q24:

B. Rewrite the following sentences indicating 'T' for true and 'F' for false statement:

(c) The boy knew his name.


Type: Very_short Difficulty: Easy

Show/Hide Answer
Answer: <p>true</p>

Q25:

B. Rewrite the following sentences indicating 'T' for true and 'F' for false statement:

(d) The other children cursed the boy.


Type: Very_short Difficulty: Easy

Show/Hide Answer
Answer: <p>false</p>

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Elements, Atoms and Compounds

Elements, Atoms and Compounds

A matter is anything that occupies space and has mass. Book, wood, pens, water etc. are the examples of matter.

The substances which is composed of its unit particles of a similar kind are known as pure substances. The substances which are composed of unit particles of different nature are known as impure substances.

Element

An element is the simplest form of a pure substance, which cannot be split up into two or more simpler substances by any chemical reaction. All the substances are made up of elements. Hydrogen, oxygen, carbon, gold etc. are the examples of elements.

Symbol

A symbol is defined as the abbreviation of the full name of an element. Using the English alphabet symbols of elements are expressed. There are three main ways of making symbols.

    1. Using the first letter of the name of elements.
      S.N Elements Symbol
      1 Hydrogen H
      2 Fluorine F
      3 Iodine I
    1. If the name of two or more elements begins with the same letter, another significant letter is taken with the first letter.
      S.N Elements Symbol
      1 Helium He
      2 Lithium Li
      3 Silicon Si
      4 Zinc Zn
      5 Bromine Br
  1. Using letters from the name of elements of their original root also make symbols. So, symbols are derived from Latin and some are from German.
    S.N Elements Name in other language Symbol
    1 Antimony Stibnum (Latin) Sb
    2 Copper Cuprum (Latin) Cu
    3 Silver Argentum (Latin) Ag
    4 Sodium Natrium (Latin) Na
    5 Tungsten Wolfan (Germany) W

Compound

Compound is a substance of atoms of two or more elements formed by the chemical combination in a definite proportion by weight. For example, water is a liquid compound of hydrogen and oxygen in which two elements are present in a fixed ratio of 1:8 by weight. For example, water is a compound because it is made of more than one element- Hydrogen and Oxygen in the ration of 2:1. The molecular formula of water is H2O.

Molecule

The smallest particle of an element or compound, which is capable of independent existence is called molecule. It retains the properties of its own. It is very small. It is difficult to estimate the size of a molecule or to determine its shape. Some of the examples of molecules are H2O (water), CO2 (Carbon dioxide), etc.

Atom

The smallest particle of an element, which takes part in chemical change is called an atom.

Structure of the atom

Atom is made up of tiny particles. These tiny particles are called sub-atomic particles or elementary particles. They are electrons, neutrons, and protons. The protons and neutrons are located at the center of an atom called nucleus. Nucleus shows the positive charge due to the presence of protons. It helps to find the atomic weight. The electrons are revolving around the nucleus in their respective orbit or shell.

Atomic number

The number of protons or the number of electrons in an electrically neutral atom of an element is called atomic number. It is denoted by Z.

Mathematically.

Atomic number (Z) = No. pf protons (p+) = No. of electrons (e-)

Atomic weight

The sum of protons and the neutrons in the nucleus of an atom is called its atomic weight. It is also called mass number. It is denoted by A.

Mathematically,

Atomic weight (A) = No. of protons (p+) + No. of neutrons (n0)

Lesson

Classification of Elements

Subject

Science

Grade

Grade 9

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