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CHEMISTRY [5 Mark Question Answer]

Elements and Compounds · ICSE STD 7 (ICSE - English Medium). 5 questions.

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[5 Mark Question Answer]

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Question 14 Marks
Write the difference between monoatomic ions and polyatomic ions with the help of examples.
Answer
An ion that consists of only a single atom with a charge is called a simple ion or monoatomic ion. For example, a sodium ion $(Na^+)$ is a simple ion because it is formed from a single sodium ion. Magnesium ion $(Mg^{2+}),$ aluminium ion $(Al^{3+}),$ oxide ion $(O^{2-}),$ chloride ion $(Cl^–),$ etc are other monoatomic ions.
An ion that consists of a group of atoms with an overall charge $1$ is called a polyatomic or compound ion. For example ammonium ion $(NH^+_4)$ is a polyatomic ion which is made up of nitrogen and hydrogen with a positive charge. Carbonate ion $(CO_3^{2-}),$ hydroxide ion $(OH^–),$ etc are other polyatomic ions.
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Question 24 Marks
What happens when atoms combine to form a compound? Explain with an example.
Answer
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Question 34 Marks
What is the difference between a molecule of an element and a molecule of a compound ? Give an example of each.
Answer
The molecules of an element are made up of the same type of atoms. Examples $:$
$1.$ molecules $(He),$ argon $(Ar),$ etc are made up of only one atom of that element.
$2.$ molecules of oxygen, are made up of two oxygen atoms combined together.
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Depending on the atomicity, molecules of an element can be monoatomic $($helium $= He),$ diatomic $($oxygen $= O_2),$ triatomic $($ozone $= O_2)$ or polyatomic $($phosphorous $= P_4)$.
The molecules of a compound are made up of atoms of different elements combined together in a definite proportion.
Examples $:$
$1.$ Water $(H_2O)$ represent a molecule of the compound water in which two atoms of hydrogen combine with one atom of oxygen.
$2.$ Hydrogen chloride $(HCl)$ is a molecule of compound having one atom of hydrogen and one of chlorine.
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Question 44 Marks
Describe the structure of an atom.
Answer
An atom consits of three subatomic particles : electrons, protons and neutrons. At the centre of an atom, the protons and neutrons form a tiny central core called nucleus. The electrons in an atom move around the nucleus in definite paths called oibits.
Electron : Negatively charged particle which carries one unit negative charge and has mass nearly 1/1837 time that of a hydrogen atom.
Mass : The mass of an atom and subatomic particles are expressed in atomic mass units (amu or u).The mass of a
proton is equal to 1 amu or u. The mass of a neutron is 1 u. The mass of an electron is negligible.
electron
Proton : Positively charged particle which carries one unit positive charge and has mass nearly equal to that of a hydrogen atom. Thus, a proton is 1837 times heavier than an electron.
Neutron : A neutron is electrically neutral, that is, it does not cany any charge. The mass of a neutron is equal to the mass of a proton.
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Question 54 Marks
What is the difference between an atom and a molecule?
Answer
Atom $:$
  • An atom of an element is the smallest particle that exhibits the properties of that element.
  • Atoms generally cannot exist independently.
  • Example $:$ Atom of hydrogen is $H$.
  • It consists of sub atomic particles $-$ protons, electrons and neutrons.
Molecule $:$
  • A molecule is a group of two or more atoms that are chemically joined together.
  • Molecules can exist independently.
  • Example $:$ Molecule of hydrogen is $H_2$
  • It consists of two or more atoms of same or different elements.
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[5 Mark Question Answer] - CHEMISTRY STD 7 Questions - Vidyadip