1. Distinguish between shell and sub-shell?
Ans:
Atoms have energy levels called shells. Each shell contains smaller sections called sub-shells.
Shells are numbered from 1 (K shell) onward. Sub-shells are labeled as s, p, d, and f.
Shells represent big energy levels, while sub-shells break these into smaller parts.
Electrons fill shells first, then go into sub-shells in a set order.
2. Why an atom electrically neutral?
Ans:
An atom stays neutral because it has the same number of protons and electrons. Protons are positive and sit in the nucleus. Electrons are negative and move around the nucleus. Since their charges cancel out, the atom has no overall charge. This balance keeps atoms stable and helps everything around us exist!
3. How many sub-shells are there in N shell?
The N shell has a principal quantum number of n = 4. The number of sub-shells in a shell is equal to n. So, the N shell has 4 sub-shells:
Thus, the N shell contains 4 sub-shells.
4. Give notation for sub-shells of M shell.
The M shell is written as n = 3. It has three sub-shells: 3s, 3p, and 3d.
5. List the sub-shells of M shell in order of increasing energy
Ans: 3s < 3p < 3d
6. Can you identify an atom without knowing number of neutrons in it?
Yes! You can identify an atom without knowing the number of neutrons. Just look at the number of protons!
The atomic number (Z) is the number of protons in an atom. It is unique for every element. For example, carbon (C) always has 6 protons.
Neutrons only affect the isotope of an element, not its identity. So, the atomic number alone tells you which element it is!
7. The electronic configurations listed are incorrect. Explain what mistakes have been made in each and write correct electronic configurations.
x = 1s ^ 2 y = 1s ^ 2 2s ^ 2 2s ^ 1 2p ^ 4 2p ^ 1 3s ^ 2 z = 1s ^ 2 2s ^ 2 , 2p ^ 5 3s ^ 1
Yes! You can identify an atom without knowing the number of neutrons. Just look at the number of protons!
The atomic number (Z) is the number of protons in an atom. It is unique for every element. For example, carbon (C) always has 6 protons.
Neutrons only affect the isotope of an element, not its identity. So, the atomic number alone tells you which element it is!
8. Which orbital in each of the following pairs is lower in energy.
(a) 2s,2p
(b) 3p, 2p
(c) 3s, 4s
The Afbau principle explains how electrons fill energy levels in atoms. The order of energy levels from lowest to highest is:
This means:
8. Draw Bohr's model for the following atoms indicating the location for electron, protons and neutrons.
(a) Potassium (Atomic No 19, Mass No 39)
(b) Silicon (Atomic No.14, Mass No 28)
(c) Argon (Atomic No. 18, Mass No 39)
Draw Bohr's model for these atoms. Show electrons, protons, and neutrons.
9. Write electronic configuration for the following elements
(a) Si
(b) 12 ^ 26 Mg
(c) 12 ^ 24 Mg
(d) Ar
Atomic Number: 14
Electronic Configuration: 1s² 2s² 2p⁶ 3s² 3p²
Atomic Number: 12
Electronic Configuration: 1s² 2s² 2p⁶ 3s²
Atomic Number: 13
Electronic Configuration: 1s² 2s² 2p⁶ 3s² 3p¹
Atomic Number: 18
Electronic Configuration: 1s² 2s² 2p⁶ 3s² 3p⁶
10. State the importance and uses of isotopes in various fields of life.
11. The atomic number of an element is 23 and its mass number is 56.
(a) How many protons and electrons does an atom of this element have?
(b) How many neutrons does this atom have?
Given:
The atomic number (Z) tells us the number of protons in an atom. So, this atom has 23 protons. Since neutral atoms have the same number of electrons as protons, it also has 23 electrons.
Neutrons are found using the formula:
Neutrons (N) = Mass Number (A) - Atomic Number (Z)
So, N = 56 - 23 = 33.
12. The atomic symbol of aluminum is written as Al. What information do you get from it?
The atomic symbol for aluminum is Al. It gives us important details:
From this, we can figure out:
Cantab Publishers
1: Describe the composition and charge of alpha particles emitted from certain radioactive nuclei and their impact on the original nucleus.
Alpha particles are tiny bits of matter. They are made of two protons and two neutrons. This means they have a positive charge.
Some atoms throw out alpha particles. When this happens, the atom loses two protons and two neutrons. This makes the atom lighter and changes what kind of element it is.
The atom becomes more stable. It turns into a new element with a lower atomic number. This process is called radioactive decay, and it helps the atom get rid of extra energy.
2: Describe the decay process of C-14 in carbon dating and its role in determining the age of organic materials.
Carbon-14 (C-14) is a type of carbon that slowly turns into nitrogen over time. This happens through beta decay and takes about 5,730 years. Living things take in C-14 from the air and food. But when they die, they stop absorbing it, and the C-14 starts to disappear.
Scientists use carbon dating to check how much C-14 is left in old objects. By comparing it to what a living thing would have, they can guess its age. This method helps archaeologists, historians, and geologists date things up to 50,000 years old. It gives us clues about history, cultures, and nature.
3: Explain how the strong nuclear force holds protons and neutrons together in the nucleus of an atom.
The strong nuclear force is what holds the center of an atom together. It keeps protons and neutrons bound inside the nucleus.
This force is stronger than the electromagnetic force, which would normally push protons apart because they have the same charge.
However, the strong force only works at very short distances. It acts between tiny particles called quarks, which make up protons and neutrons.
Without this force, atoms wouldn't exist, and neither would we!
Isotopes are atoms of the same element with different numbers of neutrons. Even though their masses are different, their chemical properties remain the same. Here's why:
In short, isotopes behave the same in chemical reactions because their electron configuration stays the same, and only the nucleus changes.
5: How can the presence of isotopes affect the overall atomic mass of an element?
Isotopes change an element’s atomic mass in three ways:
Take chlorine (Cl) as an example. It has two main isotopes:
The atomic mass of chlorine is 35.45 u, which is the weighted average of these isotopes.
In short, isotopes affect atomic mass through averaging, extra neutrons, and abundance.
6: Calculate the relative atomic mass of element x with isotopes x-35 (70%) and x-37 (30%).
We have two isotopes of an element:
Using the formula:
Relative Atomic Mass = ((35 × 70) + (37 × 30)) / 100
= (2450 + 1110) / 100
= 35.6 amu
7: Define relative atomic mass and its calculation, emphasizing its role in representing the average mass of isotopes in an element.
Atoms are tiny! Measuring their actual weight is extremely difficult. For example, a hydrogen atom weighs about 1.672 × 10⁻²⁴ g. Such small numbers are hard to use in calculations.
To make things easier, scientists use relative atomic mass. Instead of measuring actual mass, they compare it to carbon-12, which is assigned a mass of12 atomic mass units (amu).
The relative atomic mass of an element is the average mass of its atoms compared to 1/12th of a carbon-12 atom.
Elements often have different versions called isotopes. Their relative atomic mass is calculated using the formula:
Relative Atomic Mass = (mass × abundance) + (mass × abundance) / 100
Carbon has three isotopes with these natural abundances:
Using the formula:
(98.8 × 12 + 1.1 × 13 + 0.009 × 14) ÷ 100 = 12.00026 amu
8: Compare and contrast the properties of protons, neutrons, and electrons in terms of their charge, mass, and location within the atom.
| Particle | Charge Discovery | Charge | Relative Charge | Relative Mass |
|---|---|---|---|---|
| Electron | Discovered in cathode ray experiments | -1.602 × 10⁻¹⁹ C | -1 | 1/1836 |
| Proton | Discovered in experiments | 1.602 × 10⁻¹⁹ C | +1 | 1 |
| Neutron | Discovered by James Chadwick | 0 (neutral) | 0 | Slightly more than 1 |
9: Compare and contrast the concepts of nucleon number and atomic mass in the context of an atom's composition.
| Concept | Nucleon Number (Mass Number) | Atomic Mass |
|---|---|---|
| Definition | Total count of protons and neutrons in a nucleus. | Average mass of all isotopes of an element, considering abundance. |
| Formula | A = Z + N | (Isotopic mass × Relative abundance) summed. |
| Units | Atomic mass units (amu) | Atomic mass units (amu) |
| Example | Carbon-12 has 12 nucleons (6 protons + 6 neutrons). | Carbon's atomic mass is ~12.01 amu (average of C-12 & C-13). |
10: Describe the formation of a negatively charged ion (anion) from an atom.
A negative ion (anion) forms when an atom gains extra electrons. This happens in two ways:
Since electrons are negatively charged, the atom becomes a negative ion.
11: Illustrate and explain the pathways that positively and negatively charged particles would follow under influence of a uniform electric field.
Positively Charged Particles (e.g., Protons):
They move along the electric field lines, going from the positive plate to the negative plate.
Negatively Charged Particles (e.g., Electrons):
They move in the opposite direction of the electric field lines, from the negative plate to the positive plate.
12: For each representation of a nucleus a through e, write the atomic symbol and identify which are isotopes.
Atoms are made of protons, neutrons, and electrons.
Beryllium (Be)
Protons: 4 | Neutrons: 5
Type: Metal
Boron (B)
Protons: 5 | Neutrons: 6
Type: Metalloid
Carbon (C)
Protons: 6 | Neutrons: 6
Type: Non-metal
13: Identify the element represented by each nucleus A through E in the problem as a metal and nonmetal?
Ans: A is a metal.
E is a non-metal.