2A1 Atomic and Subatomic Structures

Question 1

Define:

Atom

Answer 1

The smallest unit of matter that retains the properties of an element and serves as the building block of all substances in the universe.
## Footnote

‘Atom’ derives from a Greek word meaning ‘indivisible’.

Question 2

What is the atomic structure?

Answer 2

It refers to the arrangement of protons, neutrons, and electrons in an atom.

Protons and neutrons form the nucleus, while electrons orbit around it. Atomic structure also determines the atom’s chemical and physical properties.

Question 3

Explain the difference between an atom and a molecule.

Answer 3

• An atom is the smallest unit of an element.
• A molecule is a group of two or more atoms chemically bonded together.

Question 4

True or false:

All atoms of the same element have the same number of protons.

Answer 4

True

The number of protons, called the atomic number, identifies the element.

Question 5

Fill in the blank:

Protons and neutrons are found in the _______ of an atom.

Answer 5

nucleus

The nucleus accounts for nearly all the atom’s mass.

Question 6

What is the net charge of a neutral atom?

Answer 6

Zero

The positive charges of protons and the negative charges of electrons balance each other.

Question 7

True or false:

The nucleus of an atom carries a positive charge.

Answer 7

True

This is due to the presence of positively charged protons.

Question 8

Define:

Isotopes

Answer 8

Atoms of the same element that have the same number of protons but different numbers of neutrons, leading to variations in atomic mass.

Isotopes can have varying stability and are used in applications like radiocarbon dating.

Question 9

True or false:

Atoms of the same element always have the same number of neutrons.

Answer 9

False

Atoms of the same element can have different number of neutrons, forming isotopes. Isotopes share chemical properties but differ in mass.

Question 10

How many elements are known to exist?

Answer 10

118 different elements

Around 92 occur naturally and 26 are created in laboratories.

The number of created elements may fluctuate as new elements are discovered.

Question 11

What information does the Periodic Table of Elements provide?

Answer 11

It organizes all known elements based on their atomic number, electron configuration, and chemical properties, revealing periodic trends.

Each element is composed entirely of one type of atom.

Question 12

What is the standard unit for quantifying the amount of substance in chemistry?

Answer 12

Mole

One mole is equal to 6.02 X 10^23 atoms.

Question 13

What does the term atomic mass unit (amu) refer to?

Answer 13

It is a unit of mass used to express atomic and molecular weights.

An atomic mass unit (amu) is a unit of mass defined as one-twelfth the mass of a carbon-12 atom.

Question 14

True or false:

Neutrons have no mass.

Answer 14

False

Neutrons have a mass similar to that of protons. They both contribute to the atom’s mass.

Question 15

Fill in the blank:

Atoms bond together to form ________.

Answer 15

molecules

These molecules, including compounds, have unique properties and include everything from water to complex biological structures.

Question 16

Fill in the blank:

Electrons are located in the _______ surrounding the nucleus of an atom.

Answer 16

Electron shells or orbitals.

These regions determine the atom’s chemical properties.

Question 17

How are quarks related to protons and neutrons?

Answer 17

Protons and neutrons are composed of three quarks each.
## Footnote

Quarks are elementary particles held together by the strong force. A proton consists of two up quarks and one down quark, while a neutron consists of two down quarks and one up quark.

Question 18

What is the mass of an electron compared to a proton?

Answer 18

An electron’s mass is about 1/1836th that of a proton.

This small mass makes electrons negligible when calculating atomic mass.

Question 19

Fill in the blanks:

The atomic mass of an atom is primarily determined by the number of _______ and _______.

Answer 19

protons; neutrons

Electrons have negligible mass and don’t significantly affect atomic mass.

Question 20

Why are electrons important in chemical reactions?

Answer 20

Electrons participate in forming bonds between atoms.

Their arrangement in orbitals determines reactivity.

Question 21

True or false:

Protons determine the chemical reactivity of an atom.

Answer 21

False

Protons define the element, but electron arrangement dictates reactions.

Question 22

Define:

Valence electrons

Answer 22

The electrons in the outermost shell of an atom.

They determine how atoms interact and bond with others.

Question 23

Fill in the blank:

John Dalton’s atomic model is called the ________, which describes atoms as indivisible particles.

Answer 23

solid sphere model

Dalton developed this model in 1803 based on his experiments with gases.

Question 24

Fill in the blanks:

According to Dalton’s atomic theory, atoms cannot be ________ or ________.

Answer 24

created; destroyed

Dalton also stated that all atoms of a pure element are identical.

Question 25

What was the **main limitation** of Dalton's model of the atom?

Answer 25

It failed to account for the existence of **subatomic particles**. ## Footnote This model couldn't explain phenomena like electrical conductivity or radioactive decay.

Question 26

What is the **plum pudding model**?

Answer 26

An atomic structure model that describes an atom as a **positively charged sphere with negatively charged electrons embedded throughout**, resembling raisins in a pudding. ## Footnote This model was proposed by J.J. Thomson.

Question 27

# True or false: The **plum pudding model** accurately explained the distribution of positive and negative charges in the atom.

Answer 27

False ## Footnote Rutherford's gold foil experiment demonstrated that most of the atom is empty space, disproving the idea of a uniform positive charge.

Question 28

What key discovery did Ernest Rutherford make from his **gold foil experiment**?

Answer 28

The **nucleus** of the atom. ## Footnote Rutherford's experiments showed that atoms have a dense center (nucleus) with electrons orbiting around it.

Question 29

# Fill in the blank: A **limitation of Rutherford’s model** was that it couldn’t explain why \_\_\_\_\_\_\_ do not lose energy and collapse into the nucleus due to electrostatic attraction.

Answer 29

electrons ## Footnote According to classical physics, orbiting electrons would lose energy and collapse into the nucleus, which doesn’t happen in reality.

Question 30

What **key idea** did Niels Bohr introduce in his atomic model?

Answer 30

Electrons orbit the nucleus in **specific energy levels**. ## Footnote These **orbits are quantized**, meaning electrons can only exist in specific energy levels, not between them.

Question 31

# True or false: According to the Bohr model, electrons can **occupy positions between discrete energy levels**.

Answer 31

False ## Footnote Electrons transition between energy levels by absorbing or emitting energy in discrete amounts.

Question 32

What **experimental evidence** supported Bohr’s atomic model?

Answer 32

The **hydrogen emission spectrum** experiment. ## Footnote This experiment showed distinct spectral lines, which the Bohr model successfully explained.

Question 33

What are the **limitations** of the Bohr model?

Answer 33

It accurately describes hydrogen-like atoms (single-electron systems) but **fails for multi-electron atoms**. ## Footnote This failure is because the Bohr model does not account for electron-electron interactions or the effects of quantum mechanics.

Question 34

How did Bohr’s model influence **future atomic models**?

Answer 34

It laid the groundwork for **quantum mechanics**. ## Footnote Bohr’s introduction of quantized energy levels was a pivotal step toward modern atomic theory.

Question 35

# Define: Photon

Answer 35

A **particle of light** emitted or absorbed during electron transitions. ## Footnote Photons carry energy equal to the difference between the initial and final energy levels of the electron.

Question 36

# Fill in the blank: When an **electron moves** to a lower energy level, it ____ a photon.

Answer 36

emits ## Footnote The energy of the photon corresponds to the energy difference between the two levels.

Question 37

What atomic model did **Erwin Schrödinger** develop?

Answer 37

The quantum model. | Also known as the electron cloud model. ## Footnote This model predicts the probability of finding an electron in certain areas around the nucleus.

Question 38

Why is the **quantum mechanical model** more complex to understand than earlier models?

Answer 38

It describes electrons as **probability clouds** rather than fixed orbits. ## Footnote This model relies on abstract mathematics, like wave functions, which can be challenging for beginners.

Question 39

# Fill in the blank: The Bohr atomic model includes the notion that **electrons orbit** a fixed nucleus with \_\_\_\_\_ \_\_\_\_\_ \_\_\_\_\_\_ \_\_\_\_\_\_\_.

Answer 39

quantized orbital angular momentum. ## Footnote This leads to discrete energy states.

Question 40

What is the **quantization formula** for angular momentum in the Bohr model?

Answer 40

L = nℏ ## Footnote Where L is angular momentum, n is a quantum number, and ℏ is the reduced Planck's constant.

Question 41

What determines the **frequency of radiation** emitted when an electron transitions between energy levels in the Bohr model?

Answer 41

By the energy difference between the initial and final energy levels, given by ΔE = hƒ, where h is Planck’s constant and ƒ is the frequency. ## Footnote This principle is a cornerstone of quantum mechanics, demonstrating that energy is quantized and transitions involve discrete energy packets (photons).

Question 42

What is the significance of the **Coulomb force** in the Bohr model?

Answer 42

It acts as the **centripetal force that keeps electrons in circular orbits** around the nucleus. ## Footnote It balances the attractive force between the negatively charged electron and the positively charged nucleus. The force is proportional to the product of the charges and inversely proportional to the square of the distance.

Question 43

# Define: Electron configuration

Answer 43

The **arrangement of electrons** in an atom's orbitals, following specific rules. ## Footnote Electron configuration helps predict an element's chemical properties and behavior.

Question 44

# Fill in the blank: The **Aufbau principle** states that electrons fill the \_\_\_\_\_\_\_ energy orbitals first.

Answer 44

lowest ## Footnote This principle ensures that the atom's total energy is minimized.

Question 45

# True or false: In electron configuration, **orbitals within the same subshell** are always filled with paired electrons before being singly occupied.

Answer 45

False ## Footnote According to Hund's rule, electrons fill orbitals singly with the same spin before pairing up.

Question 46

# Define: Spin

Answer 46

A quantum property of electrons that **represents their intrinsic angular momentum**. ## Footnote It is quantized and can have values of +½ ('up') or -½ ('down'). Spin determines how electrons pair up in orbitals and influences magnetic properties.

Question 47

# Fill in the blank: The \_\_\_\_\_\_\_\_ \_\_\_\_\_\_\_ principle explains why two **electrons in the same orbital** must have opposite spins.

Answer 47

Pauli exclusion ## Footnote This rule helps organize electrons in atoms and explains their unique arrangements.

Question 48

What does the **angular momentum quantum number (ℓ)** describe in an atom?

Answer 48

The **shape of an atomic orbital**, categorizing it into s, p, d, or f orbitals. ## Footnote It's represented by letters: 0 is 's', 1 is 'p', and 2 is 'd'.

Question 49

Why is it important to study **atomic models**?

Answer 49

They help us **understand the structure and behavior of matter**, including chemical reactions and physical properties. ## Footnote Each model builds upon previous ones, refining our understanding of the atom.

Question 50

How does studying **subatomic particles** contribute to advancements in science?

Answer 50

It leads to discoveries in fields like chemistry, physics, and medicine, including innovations like nuclear energy and medical imaging. ## Footnote Knowledge of protons, neutrons, and electrons is foundational to modern science and technology.