Olympiad Test: Structure of Atom- 2 - Class 9 MCQ

During Rutherford's experiment, most of the α particles emitted from a radioactive source bounced back to the source when passed through a gold foil. This is possible only if positively charged heavy particle (nucleus) is present at the centre. Hence, this experiment led to the discovery of atomic nucleus.

Elements with atomic number 18 and 20 are Argon and potassium respectively.

Isobar compounds have the same mass number but the different atomic number and chemical properties depend upon the number of electrons so isobars have different chemical properties.

Atomic number is 9, which means that electrons are also 9.

Electronic configuration is 2,7. So, the atom will gain 1 electron to complete its octet. Therefore the valency is 1.

Elements with valency 1 are those elements which can either gain one electron or lose one electron in order to have stable electronic configuration.

An example is chlorine with atomic number 17. It has electronic

configuration as 2,8,7.

Hence, it accepts one electron to form Cl⁻ and attains stable octet configuration. Such elements are non-metals.

Whereas, elements like sodium with atomic number 11 have electronic configuration as 2,8,1.

It is easier to lose the outermost electron to become stable and form Na⁺. Such elements are metals.

Hence, the correct option is C.

Element chlorine has atomic number 17 and its electronic configuration is 2, 8, 7. On gaining one electron it forms chloride ions whose electronic configuration is 2, 8, 8.

Almost the entire mass of an atom is concentrated in the nucleus consisting of protons and neutrons.

The air pressure inside the cathode ray tube is low. Because if we increase the pressure of gas present inside the tube then the number of atoms of the gas increases.

ie, we have PV =nRT

If volume and temperature are kept constant then pressure is directly proportional to n which is the amount of gas in moles. If the number of atoms in the tube increases then electrons will collide with these atoms. These collisions will act as obstructions in the path of electrons thereby preventing electrons from reaching anode.

Cathode rays are a beam of fast-moving electrons. Electrons are atomic particles which are negatively charged. Charges of opposite nature always attract each other. Because there is attraction between electrons and a positive electrode, cathode rays are deflected towards positive electrode

P – 4: Has 2- valence electrons. Is an s-block metal. Can exhibit covalency and electro valency.

Q – 18: Has Octet configuration: Noble gas

R – 10: Has Octet configuration.: Noble gas

S – 16: Has valence 6 – electrons: Non-metal: Mostly shows covalency.

Beryllium metal with atomic number -4 can show electrovalency and covalency.

Compare to other elements of the group it behaves mostly covalent but with higher electronegative elements it can show electrovalency.

Element X can’t form anions as the outermost orbit contains only 1 electron.the atom will rather lose this electron to complete its octet and will become a cation.