Week 1

Question 1

What are the three main components of an atom according to the modern electronic theory?

Answer 1

Protons, neutrons, and electrons

Protons and neutrons reside in the nucleus, while electrons occupy energy levels around the nucleus.

Question 2

What is the charge and approximate mass of a proton?

Answer 2

Charge: 1+, Mass: 1.6 × 10^-27 kg

Protons are positively charged subatomic particles found in the nucleus.

Question 3

What is the atomic number of an element?

Answer 3

The number of protons in the nucleus

For example, hydrogen has an atomic number of 1, while iron has an atomic number of 26.

Question 4

What are isotopes?

Answer 4

Atoms of the same element with different numbers of neutrons

For example, deuterium and tritium are isotopes of hydrogen.

Question 5

What is the maximum number of electrons present in a shell determined by?

Answer 5

The 2n² rule

Where ‘n’ is the principal quantum number of the shell.

Question 6

What are the four main types of orbitals?

Answer 6

s, p, d, f

Each type of orbital has a different shape and orientation.

Question 7

What does the Aufbau principle state?

Answer 7

Electrons occupy the lowest available energy levels first

This principle explains the order of filling orbitals.

Question 8

What is Hund’s rule?

Answer 8

Electrons fill separate orbitals with the same spin before pairing

This rule helps determine the lowest-energy arrangement of electrons.

Question 9

Fill in the blank: The _______ principle states that no two electrons in an atom can have the same set of quantum numbers.

Answer 9

Pauli Exclusion

This principle restricts the occupancy of orbitals by electrons.

Question 10

What is periodicity in the context of the periodic table?

Answer 10

Regular periodic variation of properties of elements with atomic number

Elements in the same group exhibit similar properties.

Question 11

Who proposed the concept of grouping elements in triads?

Answer 11

Johannes Dobereiner

He noticed that elements with similar properties could be grouped in sets of three.

Question 12

What did John Newlands discover about the arrangement of elements?

Answer 12

Every seventh element has similar properties

This led to his ‘law of octaves’.

Question 13

What was the significant contribution of H. G. J. Moseley to the periodic table?

Answer 13

Established that the order of elements is based on atomic number, not atomic mass

His work clarified the arrangement of elements in the periodic table.

Question 14

What are the four blocks of the periodic table?

Answer 14

S block, P block, D block, F block

Each block corresponds to the type of orbital being filled.

Question 15

True or False: The modern periodic table is based on atomic mass.

Answer 15

False

The modern periodic table is based on atomic number.

Question 16

What is the significance of isotopes in the modern periodic table?

Answer 16

Isotopes have the same atomic number but different mass numbers

This allows them to fit into the modern periodic table despite having different properties.

Question 17

What is the definition of an Isotope?

Answer 17

Element with the same atomic number but different mass number; they have identical chemical properties.

Isotopes fit into the modern periodic table due to their same atomic number.

Question 18

What was a notable exception in Mendeleev’s periodic table?

Answer 18

The positions of cobalt and nickel. Cobalt should come first due to its lower atomic number compared to nickel.

The modern periodic table is based on atomic number, not atomic mass.

Question 19

What does the periodic law state?

Answer 19

When elements are arranged by atomic number, their physical and chemical properties vary periodically.

This leads to noticeable properties such as atomic radius, ionization energy, and electronegativity.

Question 20

What is the trend in atomic radius across a period?

Answer 20

Atomic radius decreases from left to right.

For example, carbon (C) has a smaller radius than silicon (Si) in Group 4A.

Question 21

What is the trend in ionic radius down a group?

Answer 21

Ionic radius increases as you move from top to bottom on the periodic table.

This is because atoms gain an electron shell.

Question 22

How does ionic radius compare to atomic radius?

Answer 22

Ionic radius may be larger or smaller than atomic radius depending on the electrical charge.

Ionic radius increases with negative charge and decreases with positive charge.

Question 23

What is the first ionization energy?

Answer 23

The minimum energy needed to remove the highest-energy electron from a neutral atom in the gaseous state.

For lithium, the first ionization energy is 520 kJ/mol.

Question 24

How does ionization energy vary across a period?

Answer 24

Ionization energy tends to increase with atomic number across a period.

The lowest values are found for Group 1A elements, while noble gases have the highest ionization energies.

Question 25

What is electron affinity?

Answer 25

The energy required to remove an electron from the atom’s negative ion or the energy change when a neutral atom picks up an electron. ## Footnote A large positive value indicates a strong affinity for an electron.

Question 26

What defines electronegativity?

Answer 26

An atom’s ability to attract electrons towards itself in a chemical bond. ## Footnote The Pauling scale is a common method for measuring electronegativity.

Question 27

How does electronegativity vary on the periodic table?

Answer 27

Electronegativity increases from left to right across a period and decreases down a group. ## Footnote The most electronegative element is fluorine, while cesium is among the least electronegative.

Question 28

What is the relationship between ionization energy and metallic character?

Answer 28

Elements with low ionization energy tend to be metallic, while those with high ionization energy tend to be nonmetallic. ## Footnote This relationship contributes to the periodic trends observed in metallic and nonmetallic character.

Question 29

What is a basic oxide?

Answer 29

An oxide that reacts with acids, typically metal oxides. ## Footnote Most metal oxides are classified as basic.

Question 30

What is a modern definition of an atom according to the electronic theory?

Answer 30

An atom consists of protons, neutrons, and electrons, with protons and neutrons in the nucleus and electrons in energy levels. ## Footnote The number of protons defines the atomic number of an element.

Question 31

What is the approximate mass and charge of a proton?

Answer 31

Mass: 1.6 × 10⁻²⁷ kg; Charge: 1+. ## Footnote Protons are located in the nucleus of an atom.

Question 32

What is the atomic number of an element?

Answer 32

The number of protons in the nucleus of an atom, which defines the element. ## Footnote For example, hydrogen has an atomic number of 1, while iron has an atomic number of 26.

Question 33

Atoms of the same element can have different numbers of neutrons, however. Atoms of the same element (i.e., atoms with the same number of protons) with different numbers of neutrons are called isotopes. Most naturally occurring elements exist as isotopes. For example, most hydrogen atoms have a single proton in their nucleus. However, a small number (about one in a million) of hydrogen atoms have a proton and a neutron in their nuclei. This particular isotope of hydrogen is called deuterium. A very rare form of hydrogen has one proton and two neutrons in the nucleus; this isotope of hydrogen is called tritium. The sum of the number of protons and neutrons in the nucleus is called the mass number of the isotope. 2. Electron Shells and Subshells Electron shells are the energy levels that electrons occupy around the nucleus. These shells are further divided into subshells, which are designated by the letters s, p, d, and f. Each subshell has a specific capacity for electrons, and the arrangement of electrons in these subshells determines the chemical properties of an element. Characteristic of Shells The principal quantum number is denoted by ‘n’. It represents the name, size and energy of the shell to which the electron belongs. The value of n lies between 1 to ∞.