ISOTOPES

Q20: Define isotopes. Discuss isotopes of Hydrogen, Carbon, Chlorine, and Uranium?

Isotopes

Word History

The word "isotope" comes from Greek: "isos" meaning equal and "topos" meaning place. This refers to their position in the periodic table.

Discovery

In 1913, a scientist named Soddy discovered isotopes. He won the Nobel Prize in Chemistry in 1921 for this discovery.

Definition

Isotopes are different forms of the same element. They have the same atomic number but different mass numbers.

Explanation

Since isotopes have the same number of protons and electrons, their chemical properties remain the same. However, they have different numbers of neutrons, which affects their mass.

Because of these mass differences, their physical properties like density, melting point, and boiling point can vary.

Isotopes of Elements

Hydrogen

Name	Protons	Neutrons	Electrons	Abundance
Protium	1	0	1	99.985%
Deuterium	1	1	1	0.015%
Tritium	1	2	1	Very rare

Carbon

Name	Protons	Neutrons	Electrons	Abundance
Carbon-12	6	6	6	98.9%, stable
Carbon-13	6	7	6	~1.1%, stable
Carbon-14	6	8	6	Trace, unstable

Oxygen

Name	Protons	Neutrons	Electrons	Abundance
Oxygen-16	8	8	8	N/A
Oxygen-17	8	9	8	N/A
Oxygen-18	8	10	8	N/A

Chlorine

Name	Protons	Neutrons	Electrons	Abundance
Chlorine-35	17	18	17	75.53%
Chlorine-37	17	20	17	24.47%

Uranium

Name	Protons	Neutrons	Electrons	Abundance
Uranium-234	92	142	92	0.05%
Uranium-235	92	143	92	0.75%
Uranium-238	92	146	92	99.245%

Q21: How does the discovery of isotopes contradicted Dalton's atomic theory?

Dalton's Atomic Theory

Dalton's atomic theory said that all atoms of an element are the same in mass and properties. But later, scientists found isotopes. Isotopes are atoms of the same element with different masses. This happens because they have different numbers of neutrons. For example, carbon-12 and carbon-14 are both carbon atoms but have different masses. This discovery changed Dalton's theory. Now, we know that atoms of the same element can have different masses but still act the same in chemical reactions.

Q22: Give comparison of ordinary water and heavy water.

Comparison of Ordinary Water and Heavy Water

Property	Ordinary Water (H₂O)	Heavy Water (D₂O)
Chemical Composition	H₂O (Hydrogen, Oxygen)	D₂O (Deuterium, Oxygen)
Hydrogen Isotope	Protium (H)	Deuterium (D)
Molecular Weight	18 g/mol	20 g/mol
Density	1 g/cm³	1.1 g/cm³
Boiling Point	100°C (212°F)	101.4°C (214.5°F)
Freezing Point	0°C (32°F)	3.8°C (38.8°F)
Uses	General Purpose	Nuclear Reactors, Research

Uranium has three isotopes with mass numbers 234, 235, and 238. Among these, the ²³⁵U isotope is used in nuclear reactors and atomic bombs, whereas ²³⁸U lacks the necessary properties for such applications. The ²³⁵U isotope is relatively rare.

The natural abundance of Uranium isotopes is as follows:

²³⁴U = 0.009%
²³⁵U = 0.72%
²³⁸U = 99.27%

Fill in the blanks:

1. ²³⁴U has ___ protons, ___ electrons, and ___ neutrons.

2. ²³⁵U has ___ protons, ___ electrons, and ___ neutrons.

3. ²³⁸U has ___ protons, ___ electrons, and ___ neutrons.

ANS: U-234: 92 protons, 92 electrons, 142 neutrons
U-235: 92 protons, 92 electrons, 143 neutrons
U-238: 92 protons, 92 electrons, 146 neutrons

Q29: Write a note on radioactivity and how the identity of an element chan,, by radioactivity?

Radioactivity

Radioactivity ek process hai jisme kuch elements apni energy loose karte hain aur radiation nikalte hain. Yeh naturally hota hai uranium aur thorium jaise elements mein, ya artificially nuclear reactions se.

Radioactive Decay

Teen tareeqe ke radioactive decay hote hain:

Alpha Decay: Alpha particle (helium nucleus) nikalta hai. Isse atomic number 2 kam hota hai aur mass number 4 kam hota hai.
Beta Decay: Ek electron ya positron nikalta hai. Isse atomic number 1 zyada ya kam hota hai.
Gamma Decay: High-energy gamma rays nikalti hain, lekin atomic number aur mass number nahi badalte.

Radioactivity Element Ko Kaise Change Karti Hai?

Jab ek atom radiation emit karta hai, to iska atomic number badal sakta hai. Isse ek element doosre element mein badal sakta hai.

Alpha Decay: Atomic number 2 kam ho jata hai, aur mass number 4 kam hota hai.
Example: Uranium-238 → Thorium-234 + Alpha particle
Beta Decay: Atomic number 1 badhta ya kam hota hai.
Example: Carbon-14 → Nitrogen-14 + Beta particle
Gamma Decay: Koi change nahi hota, sirf energy release hoti hai.

Second Answer

The proton number decides which element it is. Normally, forces in the nucleus are balanced. But sometimes, they aren't. When that happens, the atom's nucleus breaks down and changes into another atom. This process is called radioactive decay, and we call this behavior radioactivity.

This continues until the nucleus becomes stable. When an atom loses a neutron, it turns into a different isotope. If it loses a proton, it becomes a different element. This means radioactivity can change an atom’s identity.

Examples:

Carbon-14: A radioactive form of carbon found in the air. Living things absorb carbon-14 and carbon-12. Over time, carbon-14 turns into nitrogen-14.
Uranium-238: A radioactive form of uranium. It slowly changes and finally becomes stable lead-206.

Q30: What is Carbon dating?
OR
Explain how, through carbon dating scientists determine the age of ancient artifacts or human remains?

Carbon Dating

What is Carbon Dating?

Carbon dating is a way to find out how old things made from once-living materials are. It works for items up to 50,000 years old.

How Does It Work?

Cosmic rays from space hit the Earth's atmosphere every day. These rays create tiny particles called neutrons. When these neutrons hit nitrogen in the air, they turn into carbon-14. This carbon-14 mixes with oxygen to make carbon dioxide.

Plants take in this carbon dioxide during photosynthesis. Animals and humans eat these plants, so they also take in carbon-14. The amount of carbon-14 in living things stays the same.

But when an organism dies, it stops taking in carbon-14. Over time, carbon-14 slowly turns into nitrogen-14. Scientists can measure the amount of carbon-14 left in a sample. This helps them find out how old it is.

Carbon dating is a powerful tool for studying the past!

Q31: Write a note on how radio isotopes use in medical imaging technology along applications of different isotopes?

Radioisotopes in Medical Imaging

Radioisotopes help doctors see inside the body. They allow for accurate disease diagnosis and treatment.

Common Uses:

PET Scans: F-18 for cancer, O-15 for brain studies, N-13 for heart scans.
SPECT Scans: Tc-99m for bones, I-131 for thyroid, Ga-67 for infection detection.
Radiation Therapy: I-125 and Ir-192 for treating cancer.
Bone Scans: Tc-99m for bone cancer diagnosis.
Thyroid Scans: I-123 for thyroid function tests.

How It Works:

Radioisotopes attach to specific body parts.
They emit radiation, captured by imaging tools.
Doctors analyze images to diagnose conditions.

Why It’s Beneficial:

Quick and painless.
Detects diseases early.
Highly accurate results.
Helps doctors plan the best treatments.

Interesting Fact:

Gamma rays are best for imaging because they pass through the body easily, creating clear pictures. Alpha and beta particles don’t travel far, making them less useful.

Q32: Discuss some differences between chemical reaction and nuclear reactions?

Chemical and Nuclear Reactions

Chemical Reactions

In chemical reactions, atoms stay the same because their atomic numbers do not change. Usually, only the outer electrons take part in these reactions.

Nuclear Reactions

In nuclear reactions, atoms change since the number of protons and neutrons shifts. This affects both atomic number and mass.

These reactions involve protons and neutrons. The outer electrons do not matter here.

Exam Resources

Since NBF and Cantab books are both recommended for FBISE students, exercises from both books are included. This helps students understand concepts from different textbooks used in Pakistan.

These resources also assist with SLO-based exam preparation.

Q23: Calculate the Relative Atomic Mass of Carbon

The relative atomic mass of an element can be calculated from the relative masses of its isotopes and their relative abundance.

Natural abundance of isotopes of carbon is as follows:

¹²C = 98.8%
¹³C = 1.1%
¹⁴C = 0.009%

Solution:

The relative atomic mass is a weighted average of all the naturally occurring isotopes of an element, taking into consideration their natural abundance. The general formula used is:

Relative atomic mass of element = (atomic mass × abundance) / 100

Substituting values:

Relative atomic mass of C = (98.8 × 12 + 1.1 × 13 + 0.009 × 14) / 100

= (1185.6 + 14.3 + 0.126) / 100

= 12.00026 amu

Calculate the Isotopic Mass of B

The relative atomic mass of an element is 35.5 amu. The relative abundance of isotope A is 75.77% with an isotopic mass of 35. Find the isotopic mass of isotope B if its relative abundance is 24.23%.

Solution:

Let the isotopic mass of B be m_B. We use the formula:

Relative atomic mass = (atomic mass × abundance) / 100

Substituting the given values:

35.5 = ((35 × 75.77) + (m_B × 24.23)) / 100

35.5 = (2652 + 24.23m_B) / 100

Multiplying both sides by 100:

3550 = 2652 + 24.23m_B

24.23m_B = 3550 - 2652

24.23m_B = 898.05

m_B = 898.05 / 24.23

m_B = 37

Thus, the isotopic mass of B is 37.

Q24: Explain different uses of isotopes.

Uses of Isotopes

Isotopes have many uses in science and medicine. Some common uses are:

Doctors use radioactive iodine-131 to check thyroid problems.
Sodium-24 helps find blockages in blood flow.
Iodine-123 is useful for brain imaging.
Cobalt-60 helps in treating cancer by shrinking tumors.
Carbon-14 helps scientists study how plants use carbon in photosynthesis.
Scientists use isotopes like sulfur-35 to study molecule structures.
Chemists use radioactive isotopes to understand how reactions work.
Archaeologists use them to date rocks, soil, and ancient objects.

Second Answer

Isotopes are used in many ways, such as in medicine, industry, and energy production. Here are some key uses:

1. Medical Uses

Certain isotopes help treat diseases like cancer.
Doctors use them to locate tumors and check blood conditions.
They also help detect blood clots and anemia.

2. Radiocarbon Dating

Scientists use carbon isotopes to determine the age of ancient objects like fossils and old wood.

3. Tracer Technique

Special isotopes help scientists study how plants use carbon dioxide during photosynthesis.

4. Industrial Uses

They help detect cracks in gas, oil, and water pipelines.
Used in steel production to check for phosphorus removal.
Help track wear and tear in engine parts.

5. Agriculture

Help in fertilizer production and tracking nutrient absorption.
Used to create better seeds and preserve food.

6. Nuclear Energy

Isotopes like uranium and plutonium provide fuel for nuclear power plants, producing electricity in an efficient way.

Q25: Why do the chemical properties of isotopes of same element remains the same?

Isotopes and Their Chemical Properties

Isotopes of the same element have the same chemical properties because they have the same number of protons and electrons. Protons decide the element, and electrons control chemical reactions. Since isotopes only differ in neutrons, which do not affect reactions, their chemical properties stay the same.

Second Answer

Isotopes of an element have the same chemical properties because:

They have the same atomic number (same number of protons).
Their electron arrangement is identical.
They have the same number of valence electrons.

Since isotopes only differ in neutrons, their chemical properties do not change. Their tiny mass difference does not affect reactivity. So, all isotopes of an element behave the same way chemically.

Isotopes and Atomic Mass Calculations

(i) Zinc Isotopes

Zinc consists of five naturally occurring isotopes: Zn, Zn, Zn, and Zn. None of these isotopes has the atomic mass of 65.41 listed for zinc on the periodic table.

Explanation:

Zinc consists of five natural isotopes. None of these isotopes has the atomic mass of 65.41 because this is the average atomic mass of all isotopes.

(ii) Gallium Isotopes

Two isotopes of gallium occur naturally:

Ga at 60.11% (68.93 amu)
Ga at 39.89% (70.92 amu)

Calculation:

Average atomic mass = (68.93 × 60.11%) + (70.92 × 39.89%) / 100

Result: 69.72 amu

(iii) Rubidium Isotopes

Two isotopes of rubidium occur naturally:

Rb at 72.17% (84.91 amu)
Rb at 27.83% (86.91 amu)

Calculation:

Average atomic mass = (84.91 × 72.17%) + (86.91 × 27.83%) / 100

= (6127.9 + 2418.7) / 100

Result: 85.4 amu

Why do we find average atomic mass of an element?

Average atomic mass is found because elements have different types called isotopes. Each isotope has its own mass. The average mass depends on how much of each isotope is present in nature. This helps in chemistry calculations.

Chlorine Average Mass Calculation

Given Data:

Isotope: Cl-35, Mass Number: 35, Relative Abundance: 75.76%
Isotope: Cl-37, Mass Number: 37, Relative Abundance: 24.24%

Average Atomic Mass Calculation:

(35 × 75.76 + 37 × 24.24) ÷ 100 = (2651.6 + 896.88) ÷ 100

= 35.4 amu

Student Learning Outcomes:

Describe how positive (cation) and negative (anion) ions form from atoms.
Interpret and use symbols for atoms and ions.

3.5 Isotopes

Definition and Characteristics

Isotopes: Atoms of an element with the same atomic number but different mass numbers

Similarities:
a) Same number of protons
b) Same number of electrons
c) Same atomic number

Differences:
d) Different numbers of neutrons
e) Different mass numbers

Historical Context

Term "isotope" first used by Soddy
Greek origin: "isos" (same) + "tope" (place)
Contradicts Dalton'satomic theory of identical atoms for a given element

Isotopes of Hydrogen

Protium (H)
Deuterium (D)
Tritium (T)

Heavy water: Contains Deuterium instead of Protium

Isotopes of Carbon

Carbon-12
Carbon-13
Carbon-14

Isotopes of Chlorine

Chlorine-35
Chlorine-37

Natural abundance details

Isotopes of Uranium

Uranium-234
Uranium-235
Uranium-238

Natural abundance and applications
Fission of Uranium-235

Determination of Relative Atomic Mass

Calculation method using isotopic masses and relative abundance
Example with carbon

Uses of Isotopes

Medical applications (e.g., Iodine-131, Sodium-24, Cobalt-60)
Scientific applications (e.g., Carbon-14 in photosynthesis research)
Archaeological dating

Carbon Dating

Process of using Carbon-14 to estimate age of carbon-containing substances
Principle and application in archaeology