Grade 11 : Chemistry - Atom Structure (Set 2)

Explanation: Cathode rays consist of negatively charged subatomic particles known as electrons, which are deflected toward the positive plate in an electric field.

Explanation: J.J. Thomson measured the ratio of electric charge ($e$) to mass ($m$) of the electron using a cathode ray tube surrounded by electric and magnetic fields.

Explanation: James Chadwick discovered neutrons in 1932 by bombarding beryllium with alpha particles, observing uncharged particles with mass roughly equal to protons.

Explanation: Number of neutrons = Mass number ($A$) - Atomic number ($Z$). Therefore, $\text{Neutrons} = 23 - 11 = 12$.

Explanation: Isotopes are species of the same chemical element having identical numbers of protons ($Z$) but differing numbers of neutrons, resulting in different mass numbers ($A$).

Explanation: Isobars are atoms of different elements having different atomic numbers ($Z$) but identical mass numbers ($A$).

Explanation: Isotones have equal neutron count ($A - Z$). For $^{14}_{6}\text{C}$, $14 - 6 = 8$ neutrons; for $^{16}_{8}\text{O}$, $16 - 8 = 8$ neutrons.

Explanation: Planck's formula states that the energy of a quantum/photon is directly proportional to its frequency, expressed as $E = h\nu$, where $h$ is Planck's constant.

Explanation: The maximum number of electrons in a main shell is given by $2n^2$. For $n = 3$, $\text{Max electrons} = 2 \times 3^2 = 18$.

Explanation: The number of orbitals in a subshell is given by $(2l + 1)$. For $l = 2$, $\text{Number of orbitals} = 2(2) + 1 = 5$.

Explanation: The magnetic quantum number ($m_l$) determines the spatial orientation of the orbital relative to a set of coordinate axes.

Explanation: Pauli exclusion principle dictates that an orbital can hold a maximum of two electrons, and they must have opposite spins.

Explanation: Hund's rule of maximum multiplicity states that subshell orbitals are filled singly before pairing occurs to minimize electron-electron repulsion.

Explanation: Chromium achieves extra stability due to a half-filled $d$-subshell ($3 ext{d}^5 4 ext{s}^1$) rather than the expected $3 ext{d}^4 4 ext{s}^2$.

Explanation: Using $\nu = \frac{c}{\lambda}$: $\nu = \frac{3.0 \times 10^8m/s}{600 \times 10^{-9}m} = 5.0 \times 10^{14}\text{ Hz}$.

Explanation: $(n+l)$ values: $3 ext{s}=3+0=3$, $3 ext{p}=3+1=4$, $4 ext{s}=4+0=4$, $3 ext{d}=3+2=5$. Higher $(n+l)$ means higher energy, so $3 ext{d}$ has highest energy.

Explanation: For shell $n=4$, azimuthal quantum number $l$ can take values $0, 1, 2, 3$ (s, p, d, f), corresponding to 4 subshells.

Explanation: For any principal quantum number $n$, $l$ can range from 0 to $n-1$. For $n=2$, maximum value of $l$ is 1. Thus $l=2$ is invalid.

Explanation: $\text{Na}^+$, $\text{F}^-$, and $\text{Mg}^{2+}$ all have 10 electrons (isoelectronic with Neon). $\text{Cl}^-$ has 18 electrons.

Explanation: Rutherford observed that a small fraction of $\alpha$-particles rebounded, proving that positive charge and mass are concentrated in a tiny central region called the nucleus.