Atomic Structure

Question 1

Behaviour of particles in an electric (and magnetic) field

Answer 1

Experiments in which subatomic particles are deflected in electric
and magnetic fields show that electrons are deflected at large angles towards the positive pole while protons are deflected at smaller angles towards the negative pole and neutrons showed
no deflection. This suggests that electrons are negatively charged particles and lighter than protons while protons are positively charged particles. The fact that neutrons were not deflected by either electric or magnetic fields suggests that these particles do
not carry an electric charge and are therefore neutral.

Question 2

The relative masses, charges and positions of protons within the atom

Answer 2

mass= 1
charge= +1
position= in the nucleus

Question 3

The relative masses, charges and positions of electrons within the atom

Answer 3

mass= 1/1837 or 1/1836 or 1/840 (negligible)
charge= -1
position= orbiting the nucleus in shells/energy levels

Question 4

The relative masses, charges and positions of neutrons within the atom

Answer 4

mass= 1
charge= 0
position= in the nucleus

Question 5

flashcard link (quizlet)

Answer 5

https://quizlet.com/62826831/cape-chemistry-unit-1-module-1-flash-cards/?funnelUUID=1c7e1801-9936-4851-b2ea-5d107bf948fd

Question 6

What is a theory?

Answer 6

A theory explains unknown or poorly understood aspects of reality. It must be logical, align with existing knowledge, and be supported by accurate, reliable, and replicable data. As knowledge grows, theories must be adjusted to resolve contradictions.

Question 7

Dalton’s atomic theory made the following assumptions:

Answer 7

• Matter consists of small particles called atoms
• Atoms are indestructible or indivisible
• Atoms of the same elements are identical in mass and properties
• Atoms combine chemically in simple whole number ratios to form compounds
• Atoms can combine in more than one simple whole number ratio

Question 8

Dalton’s theory had two major errors.
What were they?

Answer 8

• The first was that atoms could indeed be sub-divided into subatomic particles called protons, neutrons and electrons.
• It is also known that atoms can be destroyed by nuclear reactions.
• Dalton also postulated that all atoms of the same element are identical and we now know that isotopes of atoms exist and as such they are indeed different.
• We also know that atoms of the same element can have different masses as seen in isotopes.

Question 9

Summary of the Discovery of Subatomic Particles

J.J. Thomson (1897):

Answer 9

Used cathode ray experiments to discover and prove the existence of electrons, proving atoms are divisible. He proposed the plum pudding model, where electrons are embedded in a positively charged sphere.

Question 10

E. Goldstein (1900):

Answer 10

Discovered protons while observing rays moving opposite to cathode rays, concluding that atoms must contain equal positive and negative charges.

Question 11

Ernest Rutherford (1909):

Answer 11

Conducted the gold foil experiment, revealing that atoms consist mostly of empty space with a dense, positively charged nucleus. His planetary model suggested electrons orbit the nucleus but did not explain why they remained in orbit.

Question 12

Niels Bohr (1913):

Answer 12

Proposed the quantum model of the atom, where electrons move in fixed orbits around the nucleus. Electrons can only have specific energy levels and absorb or emit energy when transitioning between orbits.

Question 13

Henry Moseley (1913):

Answer 13

Suggested that atomic number corresponds to the number of protons, and hypothesized the existence of a neutral particle (neutron) to account for extra atomic mass.

Question 14

James Chadwick (1932):

Answer 14

Discovered the neutron by bombarding beryllium with alpha particles, detecting a neutral, penetrating particle that was unaffected by electric or magnetic fields.

Question 15

the atomic number or proton
number

Answer 15

The number of protons
in the nucleus of an atom is called

Question 16

Why is the atomic number used to define the atom?

Answer 16

Atoms of the same element have the same number of
protons and hence the atomic number is used to define the atom.

Question 17

What is atomic mass/mass number or nucelon number?

Answer 17

Each atom has an atomic mass or mass number which is the
sum of the protons and neutrons in the nucleus of the atom.

Question 18

Why do isotopes differ in physical properties?

Answer 18

Since the number of protons is equal to the number of
electrons, isotopes have identical chemical properties however
their physical properties are different because they have different
masses (mass number/no. of neutrons).

Question 19

What is relative isotopic mass?

Answer 19

the mass of a single isotope compared to one twelfth the mass of
a carbon-12 isotope.

Question 20

Why is the carbon-12 isotope used as the reference?

Answer 20

The actual mass of an atom is so small that it is not practical
to work with therefore a reference is used and compared to the
actual atomic mass.

Question 21

Who developed the mass spectrometer?

Answer 21

F. Aston in 1919

Question 22

What was the mass spectrometer used for?

Answer 22

to measure the mass and relative abundance of each isotope
in a sample of naturally occurring element.

Question 23

Summary of Mass Spectrometer Operating Principles

Ionization:

Answer 23

The sample is vaporized and bombarded by high-energy electrons, removing electrons and forming positive ions.

Question 24

Acceleration:

Answer 24

The positive ions are accelerated by an electric field toward a magnetic field.

Question 25

Deflection:

Answer 25

Ions are deflected based on their mass-to-charge (*m/e* or *m/z*) ratio; lighter ions are deflected more than heavier ones.

Question 26

Detection:

Answer 26

Ions reach a detector, which records their abundance. By adjusting the electric and magnetic fields, different isotopes are measured, allowing for the calculation of relative atomic mass.

Question 27

m/e, relative abudance, atomic mass calculations

Answer 27

Chapter 2 in calculations text

Question 28

# Discovery of radioactivity Henri Becquerel (1903):

Answer 28

Discovered radioactivity when uranium-exposed photographic plates developed images, proving uranium emitted radiation. He showed that this radiation was similar to X-rays and consisted of charged particles.

Question 29

# Discovery of radioactivity Pierre and Marie Curie:

Answer 29

Discovered radium and polonium while studying uranium ore. They shared the 1903 Nobel Prize in Physics with Becquerel.

Question 30

# Discovery of radioactivity Marie Curie (1911):

Answer 30

Received a second Nobel Prize in Chemistry for isolating radium. Her research contributed to medical applications, including cancer treatment.

Question 31

Alpha particles

Answer 31

Alpha particles are helium nuclei, 4^2 He2+. In nuclear reactions, it is understood that alpha particles are formed without its electrons therefore the symbol 4^2 He is used in nuclear equations. The emission of alpha particles leads to a decrease in atomic number by 2 and mass number by 4. 238 92 U -----> 4 2 He + 234 90 Th | remember it becomes a different element!!

Question 32

Beta particles

Answer 32

Beta particles are formed when a neutron disintegrates giving a proton and an electron. The proton remains in the nucleus of the atom, so its atomic **number increases by 1.** The mass number is unchanged. 14 6C→ 14 7N+ β − 24 -11 Na -----> 0 -1 e + 24 12 Mg | changes to a different element

Question 33

Gamma rays

Answer 33

Gamma rays are electromagnetic waves of short wavelength. Emissions of alpha or beta particles are often accompanied by the emission of gamma rays. When particles are emitted, the atomic nucleus becomes excited and the excess energy is released as gamma radiation for the nucleus to return to a more stable energy level.

Question 34

Explanation of the Phenomenon of Radioactivity

Answer 34

Radioactivity is the spontaneous emission of radiation from the nucleus of an unstable atom as it undergoes transformation into a more stable state. This occurs when the nucleus has an imbalance in its neutron-to-proton (n/p) ratio, making it unstable. To become more stable, the nucleus emits radiation in the form of alpha (α) particles, beta (β) particles, or gamma (γ) rays.

Question 35

Gamma rays (condensed w/ example)

Answer 35

After alpha or beta decay, the nucleus often remains in an excited state. To release excess energy, it emits a high-energy gamma ray (γ), but its atomic and mass numbers remain unchanged. Example: 60 27 𝐶𝑜→60 28𝑁𝑖 +𝛽− +𝛾

Question 36

Neutron-to-Proton (n/p) Ratio and Stability

Answer 36

The stability of a nucleus depends on its n/p ratio: * For light elements (Z ≤ 20), a ratio close to 1:1 is stable (e.g., carbon-12 has 6 neutrons and 6 protons). * For heavier elements, the ratio increases (~1.5:1) because more neutrons are needed to counteract the repulsion between protons. * If the n/p ratio is too high (excess neutrons), beta decay occurs to convert a neutron into a proton. * If the n/p ratio is too low (too many protons), alpha decay occurs to reduce the number of protons.

Question 37

**Uses of Radioisotopes**

Answer 37

Radioisotopes have various applications in **medicine, industry, agriculture, and research** due to their ability to emit radiation. Some key uses include: **1. Medical Applications** - **Cancer Treatment (Radiotherapy):** - **Cobalt-60** is used in radiation therapy to kill cancerous cells. - **Medical Imaging & Diagnosis:** - **Technetium-99m** is used in diagnostic imaging for detecting tumors and organ function. - **Iodine-131** is used to diagnose and treat thyroid disorders. **2. Industrial Applications** - **Leak Detection in Pipelines:** - **Sodium-24** is used to detect leaks in underground pipelines. - **Quality Control in Manufacturing:** - **Americium-241** is used in smoke detectors. - **Cobalt-60** is used in non-destructive testing (NDT) to inspect metal structures and welds. **3. Agricultural Applications** - **Food Preservation:** - **Cobalt-60** is used for food irradiation to kill bacteria and increase shelf life. - **Pest Control:** - **Sterile Insect Technique (SIT)** uses **radiation-sterilized insects** to control pest populations. - **Crop Improvement:** - **Radiation-induced mutation breeding** helps develop disease-resistant and high-yield crops. **4. Scientific and Environmental Research** - **Radiocarbon Dating:** - **Carbon-14** is used to determine the age of ancient fossils and artifacts. - **Tracer Studies:** - **Phosphorus-32** is used to study plant nutrient uptake in agriculture. - **Climate and Ocean Studies:** - **Tritium (Hydrogen-3)** is used to track water movement in oceans and groundwater.

Question 38

Atomic spectra

Answer 38

Evidence for the arrangement of electrons in the atom comes mainly from atomic spectra. An atomic spectrum is formed when electromagnetic radiation is absorbed or emitted by an element. Electromagnetic radiation can be viewed as a stream of photons, which are particles with no mass each travelling in a wave-like pattern and moving at the speed of light. Each photon contains a certain quantum of energy and is related by the Planck’s equation which indicates the energy is directly proportional to the frequency of the radiation.

Question 39

planck's constant

Answer 39

6.63 x 10-34 J-sec

Question 40

E = hv

Answer 40

E = energy of a photon (Joules) h = Planck’s constant ν = frequency of the radiation (Hz or s−1)

Question 41

c=νλ

Answer 41

c = speed of light (3.00×10^8 m/s) ν = frequency (Hz) λ = wavelength (m)

Question 42

Derivation from: c=νλ, solve for frequency (𝜈): Substitute this into Planck’s equation:

Answer 42

ν= c/λ ​ E=h( c/λ) 𝐸=ℎ𝑐/𝜆 ​ ​

Question 43

quantum of energy

Answer 43

amount of energy

Question 44

a quantum of energy absorbed or emitted by an atom can be determined by?

Answer 44

measuring the frequency or wavelength of the electromagnetic radiation absorbed or emitted.

Question 45

Electromagnetic Spectrum

Answer 45

The full range of electromagnetic radiation, where energy absorbed or emitted by an atom corresponds to specific wavelengths.

Question 46

Continuous Spectrum

Answer 46

When white light passes through a prism, all visible wavelengths blend seamlessly, like a rainbow.

Question 47

Absorption Spectrum

Answer 47

When white light passes through a substance, certain wavelengths are absorbed, creating dark lines on a spectrum (discontinuous spectrum).

Question 48

Emission Spectrum

Answer 48

When atoms are excited by heat or electricity and return to their ground state, they emit light at specific wavelengths, producing bright lines on a dark background.

Question 49

Unique Spectra

Answer 49

Each element has a distinct absorption and emission spectrum, allowing for its identification.

Question 50

Atomic Emission Spectrum of Hydrogen

Answer 50

The set of discrete wavelengths of light emitted by hydrogen atoms when electrons transition between energy levels.

Question 51

Explain how the atomic emission spectrum of hydrogen is produced.

Answer 51

* Energy is added to a hydrogen atom, causing an electron to absorb a quantum of energy and move to a higher energy level (excited state). * The excited electron cannot stay in this higher state and falls back to a lower energy level. * As the electron falls, it emits a quantum of energy as light. * The wavelength (color) of the emitted light depends on the energy difference between the levels. * This results in a series of spectral lines, forming the emission spectrum of hydrogen.

Question 52

Bohr’s Energy Levels

Answer 52

Fixed orbits around the nucleus where electrons exist, assigned by the principal quantum number (n). n=1 and increasing outward

Question 53

What happens when an electron absorbs a quantum of energy?

Answer 53

The electron moves from a lower energy level (ground state) to a higher energy level (excited state).

Question 54

What happens when an electron releases energy?

Answer 54

The electron falls to a lower energy level and emits light of a specific wavelength.

Question 55

What determines the frequency of the emitted light in the hydrogen spectrum?

Answer 55

The greater the difference between energy levels, the higher the frequency of the emitted light.

Question 56

How does the hydrogen emission spectrum provide evidence for discrete energy levels?

Answer 56

Each spectral line corresponds to a transition between specific energy levels. The presence of only certain wavelengths shows that electrons can only occupy fixed energy levels, proving the quantization of energy in atoms.

Question 57

What does it mean when the spectral lines converge?

Answer 57

the frequency increases and the electrons falling from the excited states and they become continuous and undefined

Question 58

principal quantum number (n) energy levels' no of electrons

Answer 58

n=1 , 2 n=2 , 8 n=3 , 18 n=4 , 32

Question 59

Each energy level has n sublevels. angular quantum number

Answer 59

n = 1 has 1 sublevel named 1 s n = 2 has 2 sublevels named 2s and 2p n = 3 has 3 sublevels named 3s, 3p and 3d n = 4 has 4 sublevels named 4s, 4p, 4d and 4f

Question 60

magnetic quantum number

Answer 60

s has 1 orbital and can hold up to 2 electrons p has 3 orbitals and can hold up to 6 electrons d has 5 orbitals and can hold up to 10 electrons f has 7 orbitals and can hold up to 14 electrons

Question 61

The principal quantum number

Answer 61

n describes the energy level of the electron. It is the same as that used in Bohr’s model. The maximum number of electrons in n is 2n^2.

Question 62

The angular quantum number

Answer 62

l describes the** sublevels **in n and the **shape of the orbitals. **The sublevels are given letter designations s, p, d and f. Each energy level has n sublevels.

Question 63

The magnetic quantum number

Answer 63

m describes the number of orbitals within a sublevel.

Question 64

A fourth quantum number

Answer 64

s is used to describe the spin of the electron. According to the Pauli Exclusion Principle no more than two electrons can occupy an orbital and two electrons occupying the same orbital must have opposite spins therefore no two electrons in an atom can have the same four quantum numbers.