Mix Example - STRUCTURE OF THE ATOM Questions in English

(C) The chronological order of the development of atomic models is as follows:
$1$. Thomson's atomic model was proposed in $1904$.
$2$. Rutherford's atomic model was proposed in $1911$.
$3$. Bohr's atomic model was proposed in $1913$.
Therefore,the correct chronological order is $(ii), (i)$ and $(iii)$.

(B) The proton was discovered by $E. Goldstein$ in $1886$ through his canal ray experiments.
The neutron was discovered by $J. Chadwick$ in $1932$ when he bombarded beryllium with alpha particles.
Therefore,the correct association is that protons were identified by $E. Goldstein$ and neutrons by $J. Chadwick$.

(A) $J.J.$ Thomson discovered the electron through his cathode ray tube experiments and proposed that they are part of the atom.
Later,$E.$ Rutherford performed the alpha-particle scattering experiment,which led to the discovery of a small,dense,positively charged center called the nucleus.
He suggested that electrons revolve outside this nucleus.

(B) In a neutral atom, the number of electrons is equal to the number of protons, which is the atomic number $(Z)$.
Given: Number of electrons = $15$, so Atomic number $(Z)$ = $15$.
The mass number $(A)$ is the sum of the number of protons and neutrons.
$A = Z + \text{Number of neutrons} = 15 + 16 = 31$.
The standard representation of an element is given by $_{Z}^{A}X$, where $A$ is the mass number and $Z$ is the atomic number.
Therefore, the correct representation is $_{15}^{31}X$.

(C) Dalton's atomic theory was proposed to explain the fundamental laws of chemical combination.
$(i)$ Law of conservation of mass: Dalton's theory states that atoms can neither be created nor destroyed in a chemical reaction,which explains this law.
$(ii)$ Law of constant composition (or definite proportions): The theory states that the relative number and kinds of atoms are constant in a given compound,which explains this law.
$(iii)$ Law of radioactivity: This law relates to nuclear physics and the instability of atomic nuclei,which was not part of Dalton's atomic theory.
$(iv)$ Law of multiple proportion: Dalton's theory explains this law by stating that atoms combine in simple whole-number ratios to form compounds.
Therefore,Dalton's theory successfully explained $(i), (ii),$ and $(iv)$.

(D) $1$. The mass number $(A)$ of an atom is the sum of protons $(p)$ and neutrons $(n)$. Given $A = 27$ and $n = 14$,we can find the number of protons: $p = A - n = 27 - 14 = 13$.
$2$. $A$ neutral atom has an equal number of protons and electrons. Thus,a neutral atom of this element has $13$ electrons.
$3$. The ion has $3$ positive charges,which means it has lost $3$ electrons.
$4$. Therefore,the number of electrons in the ion = $13 - 3 = 10$.

(TRUE) The statement is True.
Atomic radius is extremely small and is typically measured in nanometres $(nm)$.
By definition,$1 \, m = 10^9 \, nm$ (or $1 \, nm = 10^{-9} \, m$).

(FALSE) The statement is False.
According to Dalton's Atomic Theory,atoms of a given element are identical in both mass and chemical properties.
Furthermore,the existence of isotopes (atoms of the same element with different masses but identical chemical properties) contradicts the claim that they differ in chemical properties.

(A) The statement is $True$.
According to Dalton's Atomic Theory,atoms of different elements combine in small whole number ratios to form compounds. This is also known as the Law of Multiple Proportions or the Law of Definite Proportions.

(TRUE) The statement is True.
According to the Law of Constant Proportions,a chemical compound always consists of the same elements combined in the same fixed proportion by mass,irrespective of the source from which it is obtained.
In a water molecule $(H_2O)$,the atomic mass of hydrogen is $1 \text{ u}$ and oxygen is $16 \text{ u}$.
Since there are two hydrogen atoms,the total mass of hydrogen is $2 \times 1 = 2 \text{ u}$.
The mass of one oxygen atom is $16 \text{ u}$.
The ratio of the mass of hydrogen to the mass of oxygen is $2:16$,which simplifies to $1:8$.

(FALSE) The statement is False.
According to the Law of Constant Proportions (also known as the Law of Definite Proportions),in a chemical substance,the elements are always present in definite proportions by mass,regardless of the source or method of preparation of the substance.

(TRUE) The statement is True.
By definition,one atomic mass unit ($amu$ or $u$) is defined as a mass exactly equal to one-twelfth $(1/12)$ of the mass of one carbon-$12$ atom.

(FALSE) The statement is False.
Historically,oxygen-$16$ was used as a reference standard for atomic mass,but it was replaced by carbon-$12$ in $1961$. Currently,the relative atomic mass of an element is defined as the average mass of the atoms of the element compared to $1/12$th the mass of a carbon-$12$ atom.

(FALSE) False.
According to the Law of Constant Proportions,a chemical compound always consists of the same elements combined together in the same fixed proportion by mass. Therefore,the relative number and kinds of atoms in a given compound are constant,not varying.

(FALSE) False.
An isotope of an element consists of atoms that have the same number of protons but a different number of neutrons. Since all atoms in a sample of a pure isotope have the same atomic number and the same chemical properties,it is considered a pure substance. Isotopes are different forms of the same element,not impurities.

(TRUE) True.
Valency is defined as the combining capacity of an atom of an element. It represents the number of electrons an atom needs to lose,gain,or share to achieve a stable electronic configuration (usually an octet in its outermost shell).