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
- metals
- metalloids
- non-metals
- inert gases
Which of the following is a short and scientific way of representing one molecule of an element or compound?
- Mathematical formula
- Chemical formula
- Mathematical symbol
- Chemical symbol
The metal which is liquid at room temperature is
- chlorine
- sulphur
- mercury
- silver
An element which is always lustrous, malleable and ductile is
a. non-metal b. metal c. metalloid d. gas
Fill in the blanks.
- The smallest particle of matter that can exist by itself is……….[ATOM]
- A compound containing one atom of carbon and two atoms of oxygen is………..[Carbon Dioxide CO2]
- ……….. is the only non-metal which conducts electricity.[Graphite]
- Elements are made up of………….kinds of atoms.[One]
- ………of some elements are derived from Latin or Greek names of the elements.[Symbols]
- There are ……….known elements.[118]
- Elements are the……….for of pure substances.[simplest]
- The first letter of an element is always written in ……….letter.[capital]
- Molecule containing more than three atoms are known as………[polyatomic molecules]
- ……….is the most abundant gas in the atmosphere.[Nitrogen]
Analogy.
- Mercury Liquid at room temperature :: Oxygen:……………[Gas at room temperature]
- Non-metal conducting electricity:[GRAPHITE]:: Metal conductingelectricity: Copper
- Elements: Combine to form compounds :: Compounds:…[COMBINE TO FORM MIXTURES]
- Atoms: Fundamental particle of an element::[MOLECULES]: Fundamental particles of a compound.
State true of false. If false, give the correct statement.
- Two different elements may have similar atoms. [False]
- Compounds and elements are pure substances. [True]
- Atoms cannot exist alone. They can only exist as groups called molecules.[False]
- NaCl represents one molecule of sodium chloride.[True]
- 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)
Symbol: Hg
State: Liquid
Hydrogen (H)
Symbol: H
State: Gas
Helium (He)
Symbol: He
State: Gas
Classify the following as metals, non-metals and metalloids.
Sodium, Bismuth, Silver, Nitrogen, Silicon, Carbon, Chlorine, Iron, Copper
Metals:
- Sodium (Na)
- Bismuth (Bi)
- Silver (Ag)
- Iron (Fe)
- Copper (Cu)
Non-metals:
- Nitrogen (N)
- Carbon (C)
- Chlorine (Cl)
Metalloids:
- Silicon (Si)
Classify the following as elements and compounds.
Water, Common salt, Sugar, Carbon dioxide, Iodine and Lithium
Elements:
- Iodine
- Iodine (I) is an element.
- Lithium
- Lithium (Li) is an element.
Compounds:
- Water
- Water (H₂O) is a compound.
- Common salt
- Common salt (NaCl) is a compound.
- Sugar
- Sugar (C₆H₁₂O₆) is a compound.
Carbon dioxide
- Carbon dioxide (CO₂) is a compound.
Write the chemical formula for the following elements.
- Hydrogen: H₂
- Nitrogen: N₂
- Ozone: O₃
- Sulfur (Sulphur): S
What are elements? What are they made of? Give two examples.
Elements are substances that consist of only one type of atom. They are the simplest form of matter and cannot be broken down into simpler substances by chemical means. Each element is characterized by its unique atomic number, which represents the number of protons in the nucleus of its atoms.
Elements are made up of atoms, which are the smallest units of an element that retain its chemical properties. Atoms consist of a nucleus containing protons and neutrons, surrounded by a cloud of electrons orbiting the nucleus.
Two examples of elements are:
Oxygen (O): Oxygen is an element that exists as diatomic molecules (O₂) in its natural state. It is essential for respiration and combustion, among other biological and chemical processes.
Iron (Fe): Iron is a metal element commonly found in the Earth’s crust. It is known for its strength and durability, and it is used in various industrial applications, including construction and manufacturing.
Define molecule.
A molecule is a group of two or more atoms that are chemically bonded together. These atoms can be of the same element (as in diatomic molecules like oxygen, O2) or different elements (as in compound molecules like water, H2O). Molecules are the smallest units of a compound that retain the chemical properties of that compound. They can exist as discrete units or as part of larger structures. Molecules can vary in size and complexity, from simple diatomic molecules to large, complex molecules like proteins or DNA.
What are compounds? Give two examples.
Compounds are substances composed of two or more different elements that are chemically bonded together in fixed proportions. These elements combine through chemical reactions to form compounds with properties different from those of the individual elements.
Two examples of compounds are:
Water (H2O): Water is a compound composed of two hydrogen atoms bonded to one oxygen atom. It is essential for life and is commonly found in liquid form on Earth.
Carbon dioxide (CO2): Carbon dioxide is a compound composed of one carbon atom bonded to two oxygen atoms. It is a gas that is produced during combustion and respiration and plays a crucial role in the Earth’s carbon cycle.
Give an example for the elements derived from their Latin names.
One example of an element derived from its Latin name is:
Ferrum (Fe): The element with the symbol Fe is derived from its Latin name “ferrum.” In English, it is known as iron.
What is atomicity of elements?
The atomicity of an element refers to the number of atoms that are chemically bonded together to form a single molecule of that element in its natural state.
For example:
Oxygen (O2) has an atomicity of 2 because two oxygen atoms are chemically bonded together to form a single molecule of oxygen gas.
Phosphorus (P4) has an atomicity of 4 because four phosphorus atoms are chemically bonded together to form a single molecule of white phosphorus.
Calculate the atomicity of H2SO4
To calculate the atomicity of H2SO4H2SO4, which is sulfuric acid, we need to count the total number of atoms in one molecule of sulfuric acid.
The chemical formula for sulfuric acid (H2SO4H2SO4) indicates that there are:
2 hydrogen atoms (H)
1 sulfur atom (S)
4 oxygen atoms (O)
So, the total number of atoms in one molecule of sulfuric acid is 2+1+4=72+1+4=7.
Therefore, the atomicity of H2SO4H2SO4 is 7.
Answer in detail.
Differentiate metals and non-metals.
Metals:
- Metals are typically solid at room temperature (except mercury).
- They are lustrous (shiny) in appearance.
- Metals are good conductors of heat and electricity.
- They are malleable (can be hammered into thin sheets) and ductile (can be drawn into wires).
- Metals tend to lose electrons to form positively charged ions (cations) in chemical reactions.
- Examples of metals include iron, copper, aluminum, and gold.
Non-metals:
- Non-metals can exist in various states at room temperature: solid (like sulfur), liquid (like bromine), or gas (like oxygen).
- They are typically dull or have a matte appearance.
- Non-metals are poor conductors of heat and electricity.
- They are brittle (break easily) and are not malleable or ductile.
- Non-metals tend to gain electrons to form negatively charged ions (anions) in chemical reactions.
- Examples of non-metals include oxygen, sulfur, carbon, and nitrogen.
Explain the characteristics of compounds
Characteristics of Compounds:
- Compounds are pure substances composed of two or more different elements chemically bonded together.
- The ratio of elements in a compound is fixed, giving compounds specific chemical properties distinct from their constituent elements.
- Compounds can be represented by chemical formulas, indicating the types and numbers of atoms in a single molecule of the compound.
- Compounds have specific physical and chemical properties different from those of the elements they are composed of.
- Compounds can be decomposed into simpler substances (elements or other compounds) through chemical reactions, but the elements cannot be separated by physical means.
Differentiate between elements and compounds.
Elements:
- Elements are pure substances composed of only one type of atom.
- They cannot be broken down into simpler substances by chemical means.
- Each element has a unique set of properties determined by the number of protons in its nucleus.
- Examples: Oxygen (O), Iron (Fe), Hydrogen (H).
Compounds:
- Compounds are pure substances composed of two or more different elements chemically bonded together.
- They have fixed ratios of elements and distinct chemical properties.
- Compounds can be broken down into simpler substances (elements or other compounds) by chemical reactions.
- Examples: Water (H2O), Carbon dioxide (CO2), Sodium chloride (NaCl).
Write any five characteristics of compounds.
- Compounds are composed of two or more different elements chemically bonded together.
- The ratio of elements in a compound is fixed, giving compounds specific chemical properties.
- Compounds have distinct physical and chemical properties different from their constituent elements.
- Compounds can be represented by chemical formulas, indicating the types and numbers of atoms in a single molecule.
- Compounds can be decomposed into simpler substances through chemical reactions, but the elements cannot be separated by physical means.
Compare the properties of metals and non- metals. Give three examples for each.
Properties of Metals:
- Metals are typically solid at room temperature (e.g., iron, copper, aluminum).
- They are good conductors of heat and electricity (e.g., copper wires).
- Metals are malleable and ductile, allowing them to be hammered into thin sheets and drawn into wires (e.g., gold leaf, aluminum wires).
Properties of Non-metals:
- Non-metals can exist in various states at room temperature (e.g., oxygen gas, sulfur solid, bromine liquid).
- They are poor conductors of heat and electricity (e.g., rubber, sulfur).
- Non-metals are brittle and not malleable or ductile (e.g., sulfur, carbon in the form of graphite).
Write down the properties of metalloids.
Properties of Metalloids:
- Metalloids have properties intermediate between metals and non-metals.
- They can exhibit characteristics of both metals and non-metals depending on the conditions.
- Metalloids are typically semiconductors, meaning they have electrical conductivity between that of metals and non-metals.
- Examples of metalloids include silicon (Si), germanium (Ge), and arsenic (As).
VII. Rewrite the given sentence in correct form.
Elements contain two or more kind of atoms and compounds contain only one kind of atom.
Elements contain only one kind of atom, while compounds contain two or more different kinds of atoms.
