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Composition of Matter and Change in Matter

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Compound

A compound is a substance formed when two or more atoms of different elements combine together in a fixed proportion by weight. Some of the common examples of a compound are water (H2O), carbon dioxide (CO2), sodium chloride (NaCl) etc. When the elements combine together, the atoms lose their individual properties and have different properties from the elements they are composed of. A chemical formula is used a quick way to show the composition of compounds.
Like, calcium oxide (CaO) is a compound made up of one atom of calcium and one atom of oxygen. Hydrogen chloride (HCl) is an atom made up of one atom of hydrogen and one atom of chloride. Similarly, water (H2O) is a compound made up of two atoms of hydrogen and one atom of oxygen.

Differences between Elements and Compounds

Elements Compounds
It is made up of only one type of atoms. It is made of two or more types of atoms.
It cannot be split into simpler substances having different properties. It can be split into simpler substances having different properties.
The smallest particle of an element is called an atom.
Examples: Hydrogen, Oxygen, Carbon etc.
The smallest particle of a compound is called a molecule.
Examples: Carbon dioxide, sodium chloride etc.

Atom

An atom can be defined as the smallest particles of an element which can take part in a chemical reaction. Elements are made up of smallest particles which are known as atoms. All the atoms of the same element are same but the atoms of different elements are different. There are total 118 elements discovered till now. The atoms of these all elements are different from each other. The atoms of element hydrogen are different than the atoms of the element carbon. Some atoms are found freely in nature whereas some are not found freely in nature. Atoms of helium, neon, argon, etc are found freely in nature whereas atoms of hydrogen, sodium, oxygen etc are not found freely in nature.
About the structure of an atom, an atom is made up of three fundamental particles which are also known as sub- atomic particles. They are the proton, neutron, and electron. Proton and neutron are located in the nucleus of an atom whereas electrons revolve around the nucleus in elliptical orbits called shells. The nucleus is the centre of an atom. Protons are positively charged, electrons are negatively charged and neutrons are chargeless.

Molecule

A molecule is the smallest particle of an element or a compound which can exist freely. A molecule has the chemical properties of element or compound. Molecules of the compounds are made up of two or more than two atoms of different elements whereas the molecules of element consists of two or more atoms of the same kind. The atoms in the molecules are held together by the chemical bond. These bonds are formed as a result of the sharing or exchange of electrons among atoms. For example, a molecule of Hydrogen (H2) consists of two atoms of hydrogen and a molecule of water (H2O) contains two atoms of hydrogen (H) and one atom of oxygen (O).

Molecular Formula

The molecular formula is the true formula representing the total number of atoms of each element present in one molecule of a compound. It is the symbolic representation of the molecule of a substance. It represents the composition of the molecule. It gives information about the names of elements and a total number of atoms present in a molecule of a compound. For example, the molecular formula of carbon dioxide is CO2. About writing the molecular formula, at first the symbol of the elements is written. After this, the total number of atoms in the molecule is also written as a subscript just after the symbol of the atoms.

Elements Molecular Formulae Compounds Molecular Formulae
1. Hydrogen H2 1. Calcium oxide CaO
2. Oxygen O2 2.Carbon tetrachloride CCl4
3. Bromine Br2 3. Carbon dioxide CO2
4. Nitrogen N2 4. Calcium oxide CaO
5. Chlorine Cl2 5. Calcium chloride CaCl2
6. Copper Cu 6. Barium oxide BaO
7. Magnesium Mg 7. Aluminium chloride AlCl3
8. Fluoride F2 8. Aluminium oxide Al2O3
9. Gold Au 9. Silver oxide Ag2O
10. Carbon C 10. Sodium chloride NaCl

Change in Matter

There are three physical states of matter. They are solid, liquid and gas. The matter changes from one state to another. For example, water is a liquid state of matter, when we put the glass of water into the refrigerator, the water freezes and changes its state from liquid to solid. Similarly, when we heat the solid water i.e. ice, the water changes from solid state to liquid state and when more amount if heat is applied, then the water starts boiling and changes its state from the liquid state to gaseous state. Here, we can change the state of water repeatedly. So, it is a temporary change. When we burn the paper, it changes into ash. Here, we cannot change ash into the paper. So, it is a permanent change. All the matters can change their state. Some changes are permanent while some are temporary. Depending upon the change in matter, there are two types of change in matter which are given below,

Physical change: The temporary and reversible change in which only the physical properties of matter are changed is called physical change. In a physical change, the chemical properties of the substance remain unchanged. Melting of ice, conversion of water into ice, ice into liquid etc are some common examples of physical change. Some of the characteristics of physical change are discussed below,

  • It is temporary and reversible change.
  • During the physical change, new types of substances are not formed.
  • There is no change in chemical properties of the substance in a physical change.

Chemical change: The permanent irreversible change in which both physical and chemical properties of matter is changed is called chemical change. Burning of wood, rusting f iron, burning of matchstick etc are the examples of chemical change. It takes place due to the chemical reactions between two or more substances. Some of the characteristics of chemical change are discussed below,

  • It is a permanent change.
  • It is irreversible change.
  • New types of substance are formed as a result of the reaction between two or more substances.
  • There is a change in physical as well as in chemical properties of substance.



  • A compound is a substance formed when two or more atoms of different elements combine together in a fixed proportion by weight. 
  • An atom can be defined as the smallest particles of an element which can take part in a chemical reaction.
  • A molecule is the smallest particle of an element or a compound which can exist freely. 
  • The temporary and reversible change in which only the physical properties of matter are changed is called physical change.
  • The permanent irreversible change in which both physical and chemical properties of matter is changed is called chemical change.
  • There are three physical states of matter. They are solid, liquid and gas.
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Very Short Questions

The differences between physical change and chemical change are given below in table,

Physical change Chemical change
It is a temporary change. It is permanent change
In this change, no new substance is formed. In this change, new substance is formed.
It is reversible change. It is irreversible change

The differences between element and compounds are given below in table,

Element Compound
They are pure substance composed of same type of atoms. They are also pure substance but composed of two or more element.
Element cannot be broken down into simple form by any chemical of physical means. They can be broken down into the form of elements by chemical process.
Till today, 113 elements are discovered. Large number of compounds are prepared till today.

The differences between atom and molecules are as follows,

Atom Molecule
Atom is the smallest particle of an element that can take part in chemical reaction without division. Molecule is the smallest particle of an element or compound, which is capable of independent existence.
Atoms are comparatively more reactive and less stable. 
For example: H, N, O, etc.
Molecules are comparatively less reactive and more stable.
For example: H2, O2, N2.

Any three characteristics of chemical change are as follows,

  • It is temporary and reversible change.
  • During the physical change, new type of substance is formed.
  • In a physical change, chemical properties of the substance remain unchanged.

A chemical change is a permanent change in which new types of substances are formed. Any three characteristics of chemical change are as follows,

  • It is permanent and irreversible change.
  • In  a chemical change, new types of substances are formed.
  • In a chemical change, physical, as well as chemical properties of substances, are changed.

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  • The substance made up of two or more atoms of different elements in a fixed proportion by weight is known as

    Molecule
    Element
    Compound
    Atom
  • What is the molecular formula of carbon dioxide?

    C2O5
    C3O
    CO
    CO2
  • What is the molecular formula of sodium chloride?

    NaCl
    Na2Cl3
    NaCl2
    Na2Cl
  • The smallest particle of an element is called

    Molecule
    Trough
    Atom
    Crest
  • The smallest particle of a compound is called

    Molecule
    Trough
    Crest
    Atom
  • How many fundamental particles are there in an atom?

    5
    6
    2
    3
  • Protons are

    Both positively and negatively charged
    Chargeless particle
    Negatively charged particle
    Positively charged particle
  • Electrons are

    Both positively and negatively charged
    Negatively charged
    Chargeless particle
    Positively charged
  • Netrons are

    Chargeless particle
    Both positively and negatively charged
    Negatively charged
    Positively charged
  • The symbolic representation of the molecule of a substance is called

    Empirical formula
    Molecular symbol
    Molecular formula
    Symbol
  • The molecular formula of Hydrogen is

    H3
    H2H
    H2
    H
  • The molecular formula of sodium hydroxide is

    Na2OH
    NaOH
    Na2H
    NaO2
  • Melting of ice is an example of

    Permanent Change
    Irreversible Change
    Chemical change
    Physical change
  • Rusting of iron is an example of

    Temporary change
    Physical change
    Chemical change
    Reversible change
  • How many types of change in matter are there?

    3
    2
    7
    6
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