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Tamil Nadu Board Class 7 Science Chapter 3 Matter Around Us

if you are looking for Tamil Nadu Board Class 7 Science Chapter 3 Matter Around Us then you are at the right place. Here we are providing solutions as well as additional QA / Important Notes.

 

Choose the appropriate answer.

 

Which one of the following is an example for a metal?

a. Iron b. Oxygen c. Helium d. Water

 

Oxygen, hydrogen, and sulphur are examples for

  1. metals
  2. metalloids
  3. non-metals
  4. inert gases

 

Which of the following is a short and scientific way of representing one molecule of an element or compound?

  1. Mathematical formula
  2. Chemical formula
  3. Mathematical symbol
  4. Chemical symbol

 

The metal which is liquid at room temperature is

  1. chlorine
  2. sulphur
  3. mercury
  4. silver

 

An element which is always lustrous, malleable and ductile is

a. non-metal b. metal c. metalloid d. gas

 

Fill in the blanks.

  1. The smallest particle of matter that can exist by itself is……….[ATOM]
  2. A compound containing one atom of carbon and two atoms of oxygen is………..[Carbon Dioxide CO2]
  3. ……….. is the only non-metal which conducts electricity.[Graphite]
  4. Elements are made up of………….kinds of atoms.[One]
  5. ………of some elements are derived from Latin or Greek names of the elements.[Symbols]
  6. There are ……….known elements.[118]
  7. Elements are the……….for of pure substances.[simplest]
  8. The first letter of an element is always written in ……….letter.[capital]
  9. Molecule containing more than three atoms are known as………[polyatomic molecules]
  10. ……….is the most abundant gas in the atmosphere.[Nitrogen]

 

Analogy.

  1. Mercury Liquid at room temperature :: Oxygen:……………[Gas at room temperature]
  2. Non-metal conducting electricity:[GRAPHITE]:: Metal conductingelectricity: Copper
  3. Elements: Combine to form compounds :: Compounds:…[COMBINE TO FORM MIXTURES]
  4. Atoms: Fundamental particle of an element::[MOLECULES]: Fundamental particles of a compound.

 

State true of false. If false, give the correct statement.

  1. Two different elements may have similar atoms. [False]
  2. Compounds and elements are pure substances. [True]
  3. Atoms cannot exist alone. They can only exist as groups called molecules.[False]
  4. NaCl represents one molecule of sodium chloride.[True]
  5. Argon is mono atomic gas. [True]

 

Answer in brief.

Write the chemical formula and name the elements present in the following compounds.

 

Sodium chloride

Chemical formula: NaCl

Elements present: Sodium (Na) and Chlorine (Cl)

 

Potassium hydroxide

Chemical formula: KOH

Elements present: Potassium (K), Oxygen (O), and Hydrogen (H)

 

Carbon dioxide

Chemical formula: CO2

Elements present: Carbon (C) and Oxygen (O)

 

Calcium oxide

Chemical formula: CaO

Elements present: Calcium (Ca) and Oxygen (O)

 

Sulphur dioxide

Chemical formula: SO2

Elements present: Sulphur (S) and Oxygen (O)

 

What do you understand by chemical formula of a compound? What is its significance?

A chemical formula is a symbolic representation of a compound that indicates the types and numbers of atoms present in a single molecule of that compound. It uses element symbols from the periodic table and numerical subscripts to convey this information.

Significance of Chemical Formulas:

  • A chemical formula reveals the exact number of atoms of each element in a molecule.
  • It uniquely identifies a chemical substance. Different compounds have different chemical formulas
  • Chemical formulas are essential in writing and balancing chemical equations
  • Knowing the chemical formula can help predict the properties of a compound

 

Define the following terms with an example for each.

Element

Definition: An element is a pure substance made up of only one type of atom. It cannot be broken down into simpler substances by chemical means.

Example: Hydrogen (H) is an element. It consists of hydrogen atoms only.

 

Compound

Definition: A compound is a pure substance formed when two or more different elements chemically combine in a fixed ratio. Compounds have properties that are different from those of their constituent elements.

Example: Water (H₂O) is a compound composed of two hydrogen atoms and one oxygen atom.

 

Metal

Definition: Metals are elements that are typically hard, shiny, malleable, ductile, and good conductors of heat and electricity.

Example: Iron (Fe) is a metal. It is hard, shiny, and a good conductor of electricity.

 

Non-metal

Definition: Non-metals are elements that are generally not shiny, not malleable, not ductile, and poor conductors of heat and electricity.

Example: Sulfur (S) is a non-metal. It is not shiny and is a poor conductor of electricity.

 

Metalloid

Definition: Metalloids are elements that have properties intermediate between metals and non-metals. They can exhibit characteristics of both classes.

Example: Silicon (Si) is a metalloid. It has a shiny appearance like a metal but is brittle and a semiconductor, which is typical of metalloids.

 

Write the symbols for the following elements and classify them as solid, liquid and gas. Aluminum, Carbon, Chlorine, Mercury, Hydrogen and Helium

 

Aluminum (Al)

Symbol: Al

State: Solid

 

Carbon (C)

Symbol: C

State: Solid

 

Chlorine (Cl)

Symbol: Cl

State: Gas

 

Mercury (Hg)

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