22.0     MODELS OF THE ATOM AND THEIR LIMITATIONS

• Dalton’s Model: Atoms are indivisible; does not explain isotopes.
• Thomson’s Model: Plum pudding model; fails to explain atomic structure.
• Rutherford’s Model: Nucleus at centre; does not explain electron orbits.
• Bohr’s Model: Electrons in fixed orbits; limited to hydrogen-like atoms.

To get your E-Book PDF Download(91 pages) of the entire Physics Key Points with well illustrative diagrams to quickly prep for JAMB & WAEC purchase here for N500 -https://dtwedustore.com/shop/physics-key-points-by-dtw-tutorials-e-book-91-pages

          22.1     DALTON’S ATOMIC THEORY

• All matter is composed of tiny, indivisible particles called atom.
• Atoms of a given element are identical in size, mass, and other properties. 
• Atoms cannot be subdivided, created, or destroyed. 
• Atoms of different elements can combine in simple whole number ratios to form chemical compounds. 

22.2     BASIC COMPONENTS OF ATOM

• Protons: Positively charged particles found in the nucleus. Each proton has a charge of +1e and a mass of approximately 1 atomic mass unit (amu).
• Neutrons: Neutral particles also located in the nucleus. Neutrons have no charge and a mass like that of protons (approximately 1 amu).
• Electrons: Negatively charged particles that orbit the nucleus. Each electron has a charge of -1e and a mass of about 1/1836 amu, which is negligible compared to protons and neutrons.

Nucleus: The nucleus is the central part of the atom, containing protons and neutrons.

To get your E-Book PDF Download(91 pages) of the entire Physics Key Points with well illustrative diagrams to quickly prep for JAMB & WAEC purchase here for N500 -https://dtwedustore.com/shop/physics-key-points-by-dtw-tutorials-e-book-91-pages

22.3     ATOMIC NUMBER AND MASS NUMBER

• Atomic Number (Z): The number of protons in the nucleus, which defines the element. The proton/atomic number determines the identity of an element.
• Mass Number (A): The total number of protons and neutrons in the nucleus:

A = Z + N           (where N is the number of neutrons).

ISOTOPES: Atoms of the same element with the same number of protons but different numbers of neutrons. Isotopes have the same chemical properties but different physical properties (e.g., different mass).

Example: Carbon-12 and Carbon-14.

          22.4     DIFFERENCE BETWEEN ENERGY LEVELS AND SPECTRA

• Electrons occupy discrete energy levels.
• Energy transitions result in emission or absorption spectra.

22.5     THERMIONIC EMISSION

It is the process by which electrons are emitted from a material (usually a metal) when it is heated to a high temperature.

MECHANISM: At elevated temperatures, some electrons gain enough thermal energy to overcome the work function (the minimum energy needed to remove an electron from the surface).

APPLICATIONS OF THERMIONIC EMISSIONS: Used in vacuum tubes, cathode ray tubes, and electron guns in devices like oscilloscopes.

To get your E-Book PDF Download(91 pages) of the entire Physics Key Points with well illustrative diagrams to quickly prep for JAMB & WAEC purchase here for N500 -https://dtwedustore.com/shop/physics-key-points-by-dtw-tutorials-e-book-91-pages

          22.6     PHOTOELECTRIC EMISSION

It is the phenomenon where electrons are emitted from a material when it absorbs light or electromagnetic radiation.

MECHANISM: When photons strike the surface of a material, they transfer energy to electrons. If the energy of the photons exceeds the work function, electrons are emitted.

KEY EQUATION: Einstein’s equation for the photoelectric effect is given by:

                              E = hf                 

Where                          E is the energy of the emitted electron,

h is Planck’s constant (6.63 x 10^-34 J·s), and

f is the frequency of the incident light.

APPLICATIONS OF PHOTOELECTRIC EMISSION: Used in solar cells, photodetectors, and photoelectric sensors.

WORK FUNCTION (WΦ): The work function of a material is the minimum energy required to remove an electron from that material.

• The energy of the emitted electron depends on the frequency of the incident light and the work function of the material.

STOPPING POTENTIAL: Stopping potential (Vs) is the minimum voltage needed to stop the most energetic photoelectrons emitted from a material.

It is related to the kinetic energy of the emitted electrons by the equation:

eVs = E

Where                 e: Charge of the electron (1.6 x 10^-19 C),

Vs: Stopping potential in volts,

E: Kinetic energy of the emitted electron.

          22.7     RELATIONSHIP BETWEEN EINSTEIN’S EQUATION AND STOPPING POTENTIAL

The stopping potential can be derived from Einstein’s equation by setting the kinetic energy equal to eVs.

Thus, we can express the stopping potential as:

Vs = (hf – Wφ) / e

BINDING ENERGY: Energy required to separate nucleons in a nucleus.

MASS DEFECT: Difference between mass of nucleus and sum of individual nucleons.

          22.8     RADIOACTIVITY

Radioactivity is the spontaneous emission of particles or radiation from an unstable atomic nucleus.

To get your E-Book PDF Download(91 pages) of the entire Physics Key Points with well illustrative diagrams to quickly prep for JAMB & WAEC purchase here for N500 -https://dtwedustore.com/shop/physics-key-points-by-dtw-tutorials-e-book-91-pages

TYPES OF RADIATION

• Alpha Radiation (α): Consists of helium nuclei (2 protons and 2 neutrons); positively charged and has low penetration power (can be stopped by paper).
• Beta Radiation (β): Consists of high-energy electrons or positrons; negatively charged (beta-minus) or positively charged (beta-plus); moderate penetration power (can be stopped by aluminum).
• Gamma Radiation (γ): High-energy electromagnetic radiation; no charge and very high penetration power (requires thick lead or concrete to stop).

RADIOACTIVE DECAY: Radioactive decay is a random process where unstable nuclei lose energy by emitting radiation. Decay can be described by the decay constant (λ) and half-life (T₁/₂).

HALF-LIFE: it is the time taken for half of the radioactive substance to decay.       

RADIOACTIVITY-DECAY LAW: The number of radioactive nuclei remaining after time t is given by:

N(t) = N₀ e^(-λt)

Where       N₀ is the initial quantity,

λ is the decay constant, and

t is time.

Half-life can be calculated using:

T₁/₂ = ln(2) / λ.

APPLICATIONS OF RADIOACTIVITY

• Used in medical treatments (e.g., cancer radiotherapy).
• Used in radiography for imaging and inspection. iii)Used in smoke detectors and carbon dating.

DETECTION OF RADIATION – Radioactivity can be detected using instruments such as Geiger counters, scintillation counters, and ionisation chambers.

          22.9     NUCLEAR REACTION

A nuclear reaction is an interaction between two nuclear particles or two nuclei that results in the formation of new nuclei different from the original ones. It involves the collision and separation of particles or nuclei, resulting in elastic scattering or inelastic collisions.

NUCLEAR ENERGY: Nuclear energy is the energy released during nuclear reactions, particularly through processes such as nuclear fission and nuclear fusion.

TYPES OF NUCLEAR REACTIONS

• Nuclear Fission: This is the process where a heavy nucleus splits into two smaller nuclei, along with the release of a significant amount of energy, neutrons, and gamma radiation.
• Nuclear Fusion: This is the process where two light atomic nuclei combine to form a heavier nucleus, releasing energy in the process.

22.10     DUALITY OF MATTER

Matter exhibits both wave-like and particle-like properties. 

WAVE-PARTICLE DUALITY: Matter behaves as both waves and particles.

DE BROGLIE WAVELENGTH: λ = h/p (where h = Planck’s constant, p = momentum).

HEISENBERG’S UNCERTAINTY PRINCIPLE: It states that certain pairs of physical properties, like position (x) and momentum (p), cannot be simultaneously known to arbitrary precision. The more accurately one property is known, the less accurately the other can be known.

It is given by the formula: Δx · Δp ≥ h/(4π)         (uncertainty in position and momentum)