9th Class Chemistry Chapter 8 Chemical Reactivity Short Questions Answer
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Reactivity of metals increases down the group because down the group because down the group, size of atoms increase due to addition of shells. When the shells are added and the size of atoms increases the electropositive character metallic character increases due to which it becomes easier to lose its valence electrons.
Physical properties of metals:
Almost all metals are solids (except mercury).
Metals have high melting and boiling points.
Metals posses metallic luster.
Malleable and ductile.
Meals are good conductors of heat and electricity.
Meals have high density.
A alkaline earth metals form stable nitrides when heated with nitrogen. 3Mg + N₂ → Mg₃N₂
The first ionization energy of magnesium is high but the second ionization energy of Mg is very high. Because it becomes very difficult to remove second electron from the Mg ion as nuclear charge attracts the remaining electrons strongly.
The are less reactive towards oxygen and oxides are formed on heating 2Mg + O₂ → 2 Mg
Electro positivity depends upon the ionization energy which in turn depends upon size and nuclear charge of the atom.
Small sized atoms with high nuclear charge have high ionization energy.
Atoms having high ionization energy are less electropositive or metallic.
Electro positivity decreases across the period from left to right. It means elements in the start of periodic are more metallic. This is because of two reasons,
Size of atoms decreases.
Nuclear charges increases.
Electro positivity depends upon size and nuclear charge of an atom because when the size of atoms increases. Electro positivity increases as it becomes easier to lose electrons. It also depends upon nuclear charge. If nuclear charge increases the Electro positivity decreases because it becomes difficult to remove the electrons from outermost shell.
Alkaline earth metals have higher ionization energies than alkali metals because the electronic configuration of their valence shells is ns². Their atoms are smaller and have more nuclear charge. That is why, they are reactive but less alkali metals.
Silver and gold are least reactive because these metals do not lose their electrons easily. They do not have the tendency to make cations and due to their soft nature. They can not be used as such.
No, pure gold can’t be used for making ornaments.
Reason: Because gold is too soft to be used as such. It is always alloyed with copper, silver or some other metal.
Copper is used for making of electrical wires because copper is a good conductor of electricity and it is also ductile in nature as it can be easily drawn out into wires.
Densities of alkali metals increases down the group in the periodic table.
As the metal work, means fire work. The metals are used in fire work due to its characteristic flame colour when they ignite in air. “Na” give golden colour, “Ca” give red colour etc.
Magnesium us harder than sodium because in magnesium metallic bonding is stronger. While sodium is relatively soft metal due to weak metallic bonding in their atoms.
Calcium is more Electro Positivity than magnesium because metallic character or electropositive character or electropositive character down the group increases due to loosely held and can be easily with drawn from their shells.
Ionization energy of Na is less than Mg because Na requires less energy to lose its valence electron than magnesium. Ionization energy is that energy which is required to remove outermost electrons from the gaseous state of an element.
The ionization energy of sodium is more than K because down the group electropositive character increases and ionization energy decreases. As it become easier electrons down the group.