CLASS – VII WORKSHEET.
SUBJECT – CHEMISTRY
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1. State one point of difference for each pair of the following sets: (5)
a. Molecules of elements & molecules of compounds
Molecules of elements Molecules of compounds
Consist of only one type of atom. Consist of two or more different types of atoms
chemically bonded together.
The atoms are chemically bonded together. Consist of only one type of atom.
Example: Oxygen gas (O₂) consists of two Example: Water (H₂O) consists of hydrogen and
oxygen atoms, and nitrogen gas (N₂) consists of oxygen atoms, and carbon dioxide (CO₂)
two nitrogen atoms. consists of carbon and oxygen atoms.
b. Iron & rust
Iron Rust
A pure metal found in nature and used in A compound formed when iron reacts with
construction, tools, and machinery. oxygen and water (hydrated iron(III) oxide).
Strong, malleable, and a good conductor of Weak, brittle, and flaky, leading to structural
heat and electricity. damage over time.
Shiny and metallic in appearance when freshly Reddish-brown in color and non-conductive.
cut.
c. Physical and chemical change
Physical Change Chemical Change
No new substance is formed; only the physical A new substance is formed with different
properties (shape, size, state) change. chemical properties.
The change is usually reversible. The change is usually irreversible.
Examples:
Examples:
Melting of ice into water
Burning of wood (produces ash and gases)
Tearing paper
Rusting of iron (forms iron oxide)
Dissolving sugar in water
Cooking food (new substances with different
flavors are formed)
d. Metal and non-metal
Metal Non metal
Metals are very hard except Non metals are soft except for
for sodium. diamonds.
Non metals are generally brittle
Metals are generally
and can break down into smaller
malleable and ductile.
pieces.
They are shiny and They are not shiny and are non
lustrous. lustrous except iodine.
They are electropositive in They are electronegative in
nature. nature.
Non metals are generally bad
Metals are good conductors
conductors of heat and electricity
of heat and electricity.
except graphite.
They are used in They have medicinal and
machinery. Example: chemical uses. Example: carbon,
Copper, silver, gold etc. oxygen, sulphur etc.
e. Periods & groups
Periods Groups
Periods are the horizontal rows in Groups are the vertical columns in
the periodic table. the periodic table.
All the chemical elements in this All the chemical elements in the
row have the same number of same group contain an equal
electron shells. number of valence electrons.
The elements get less metallic There are mainly 18 groups in the
when we move forward a row. periodic table.
Periods have different For example, we call the
numbers of members; there group 1 element as alkali
are more chemical elements metals and group 2 elements
in some periods than some as alkali earth metals.
other periods
2. Complete the following reactions : (5)
a. Mg + 2HCl
Mg + 2HCl → MgCl₂ + H₂
b. CaO + H2O
CaO + H₂O → Ca(OH)₂
c. BaCl2 + H2SO4
. BaCl₂ + H₂SO₄ → BaSO₄ + 2HCl
d. CuSO4 + H2S
. CuSO₄ + H₂S → CuS + H₂SO₄
e. FeSO4 + NaOH
FeSO₄ + 2NaOH → Fe(OH)₂ + Na₂SO₄
3. Define : (5)
a. Desirable change –A change that is beneficial or useful to us, such as cooking food, ripening of
fruits, or the formation of curd from milk.
b. Anion –A negatively charged ion that is formed when an atom gains one or more electrons.
Example: Cl⁻ (Chloride ion), OH⁻ (Hydroxide ion).
c. Galvanization –The process of coating iron or steel with a layer of zinc to prevent rusting. Example:
Galvanized iron pipes.
d. Anion –A negatively charged ion that is formed when an atom gains one or more electrons.
Example: Cl⁻ (Chloride ion), OH⁻ (Hydroxide ion).
e. Electroplating –A process of depositing a thin layer of metal over another metal object using
electrolysis to prevent corrosion or enhance appearance. Example: Silver plating on jewelry.
4. Mention the name of the combining elements for the following compounds. (2)
a. Methane –(CH₄) – Carbon (C) and Hydrogen (H)
b. Copper sulphide –CuS) – Copper (Cu) and Sulphur (S)
5. Write the formula of the following compounds : (3)
c. Potassium bromide –KBr
d. Aluminium hydroxide –Al(OH)₃
e. Carbon monoxide –CO
6. Write the chemical reaction of rusting of iron. Also mention the chemical name of rust. [2]
4Fe+3O2+6H2O→4Fe(OH)3
4Fe(OH)3→2Fe2O3⋅xH2O4Fe(OH)₃ \rightarrow 2Fe₂O₃·xH₂O4Fe(OH)3→2Fe2O3⋅xH2O
Chemical Name of Rust: Hydrated iron(III) oxide (Fe₂O₃·xH₂O)
7. An ion is represented as P3--, Name the element and the ion. If an ion is represented as
P³⁻, it means the element P (Phosphorus) has gained three electrons, forming a negatively
charged ion.
Element: Phosphorus (P)
Ion Name: Phosphide ion (P³⁻)
8. Mention the chemical reaction of photosynthesis process . [1]
6CO2+6H2OSunlight + ChlorophyllC6H12O6+6O2
This equation represents how plants convert carbon dioxide and water into glucose and
oxygen using sunlight.
