Atomic Number and Mass Number

Atomic Number:

• Each element is identified by its atomic number, which is the number of protons in the nucleus of an atom.
• The atomic number determines the element’s position on the periodic table and its chemical properties.
• Changing the atomic number of an atom changes the element itself.

Mass Number:

• The mass number of an atom is the sum of the number of protons and neutrons in its nucleus.
• Isotopes of an element have the same atomic number but different mass numbers due to varying numbers of neutrons.
• The mass number provides information about the atom’s overall mass and stability.

What is Atomic Number and Mass Number?

Atomic Number:

The atomic number of an element is the number of protons found in the nucleus of an atom of that element. It is a fundamental property that uniquely identifies each element and determines its position on the periodic table. The atomic number is represented by the symbol “Z.”

For example, the atomic number of hydrogen is 1, indicating that a hydrogen atom has one proton in its nucleus. The atomic number of carbon is 6, meaning that a carbon atom has six protons in its nucleus.

Mass Number:

The mass number of an element is the total number of protons and neutrons found in the nucleus of an atom of that element. It is represented by the symbol “A.”

The mass number provides information about the overall mass of an atom. Since protons and neutrons have approximately the same mass (approximately 1 atomic mass unit), the mass number is close to the actual mass of the atom.

For instance, the mass number of hydrogen is 1, indicating that a hydrogen atom has one proton and no neutrons. The mass number of carbon is 12, signifying that a carbon atom has six protons and six neutrons.

Relationship between Atomic Number and Mass Number:

The atomic number and mass number are closely related. The atomic number determines the number of protons in an atom, while the mass number accounts for both protons and neutrons. The difference between the mass number and the atomic number represents the number of neutrons in the atom.

For example, consider an atom of carbon with a mass number of 12 and an atomic number of 6. This means that the carbon atom has 6 protons and 12 - 6 = 6 neutrons.

Isotopes:

Elements can have different isotopes, which are variations of the same element with the same atomic number but different mass numbers. Isotopes have the same number of protons but differ in the number of neutrons.

For instance, carbon has three naturally occurring isotopes: carbon-12, carbon-13, and carbon-14. All three isotopes have six protons, but they differ in the number of neutrons. Carbon-12 has six neutrons, carbon-13 has seven neutrons, and carbon-14 has eight neutrons.

Isotopes have similar chemical properties but can vary in their physical properties, such as mass and radioactive behavior.

In summary, the atomic number represents the number of protons in an atom and determines its identity, while the mass number indicates the total number of protons and neutrons in an atom. Isotopes are variations of the same element with different mass numbers due to varying neutron counts.

Atomic Number

The atomic number of an element is a fundamental property that defines its identity and distinguishes it from other elements. It is represented by the symbol “Z” and corresponds to the number of protons found in the nucleus of an atom. Each element on the periodic table has a unique atomic number, which increases sequentially from hydrogen (Z = 1) to the heaviest known element, oganesson (Z = 118).

Examples of Atomic Numbers:

1. Hydrogen (H): Hydrogen, the first element on the periodic table, has an atomic number of 1. This means that a hydrogen atom contains one proton in its nucleus.

2. Carbon (C): Carbon, an essential element for life on Earth, has an atomic number of 6. Carbon atoms have six protons in their nuclei.

3. Oxygen (O): Oxygen, a vital component of the Earth’s atmosphere, has an atomic number of 8. Oxygen atoms contain eight protons in their nuclei.

4. Sodium (Na): Sodium, a reactive metal used in various applications, has an atomic number of 11. Sodium atoms have 11 protons in their nuclei.

5. Iron (Fe): Iron, a crucial element in many industrial processes, has an atomic number of 26. Iron atoms contain 26 protons in their nuclei.

Significance of Atomic Number:

1. Element Identification: The atomic number uniquely identifies an element. No two elements can have the same atomic number.

2. Periodic Table Organization: Elements are arranged on the periodic table according to their increasing atomic numbers. This arrangement highlights patterns in chemical properties and behavior.

3. Chemical Bonding: The atomic number determines the number of electrons an atom can have, which influences its chemical bonding behavior.

4. Isotopes: Elements can have different isotopes, which are variations of the same element with different numbers of neutrons. Isotopes have the same atomic number but different neutron counts.

5. Nuclear Reactions: The atomic number plays a crucial role in nuclear reactions, such as nuclear fission and fusion, where the number of protons and neutrons is conserved.

In summary, the atomic number is a defining characteristic of an element, providing essential information about its identity, chemical properties, and behavior. It is a fundamental concept in chemistry and plays a vital role in understanding the structure and interactions of matter at the atomic level.

Introduction to Atomic and Molecular Weight

Atomic Weight:

The atomic weight of an element is the weighted average mass of all the naturally occurring isotopes of that element. It is expressed in atomic mass units (amu), where one amu is defined as 1/12th of the mass of a carbon-12 atom.

For example, the atomic weight of carbon is 12.011 amu. This means that the average mass of all the naturally occurring isotopes of carbon is 12.011 times the mass of a single proton.

Molecular Weight:

The molecular weight of a compound is the sum of the atomic weights of all the atoms in the molecule. It is also expressed in amu.

For example, the molecular weight of water (H2O) is 18.015 amu. This means that the average mass of a single water molecule is 18.015 times the mass of a single proton.

Examples:

The following table shows the atomic weights of some common elements:

The following table shows the molecular weights of some common compounds:

Applications:

Atomic and molecular weights are used in a variety of applications, including:

• Determining the composition of compounds
• Calculating the amount of a substance needed for a reaction
• Predicting the properties of a compound

Conclusion:

Atomic and molecular weights are important concepts in chemistry. They provide information about the composition and properties of matter.

The Periodic Table

What is Atomic Number?

The atomic number of an element is a fundamental property that defines its identity and distinguishes it from other elements. It is represented by the symbol “Z” and corresponds to the number of protons found in the nucleus of an atom. Each element has a unique atomic number, which increases sequentially as we move across the periodic table.

Key Points about Atomic Number:

1. Definition: The atomic number of an element is the number of protons in its nucleus.

2. Unique Identifier: Each element has a unique atomic number, making it a defining characteristic that distinguishes one element from another.

3. Periodic Table Arrangement: Elements are arranged in the periodic table based on their increasing atomic numbers. This arrangement highlights the periodic trends and relationships between elements.

4. Number of Electrons: The atomic number also determines the number of electrons that an atom has in its neutral state. In a neutral atom, the number of protons (positive charge) is balanced by an equal number of electrons (negative charge).

5. Isotopes: Elements can have different isotopes, which are variations of the same element with the same atomic number but different numbers of neutrons. Isotopes have the same chemical properties but differ in their atomic masses.

Examples:

1. Hydrogen (H) has an atomic number of 1, indicating that it has one proton in its nucleus.

2. Carbon (C) has an atomic number of 6, meaning it has six protons in its nucleus.

3. Oxygen (O) has an atomic number of 8, corresponding to eight protons in its nucleus.

4. Uranium (U) has an atomic number of 92, signifying that it has 92 protons in its nucleus.

Understanding atomic numbers is crucial in various fields of science, including chemistry, physics, and nuclear science. It allows scientists to predict the properties and behavior of elements, classify them into groups with similar characteristics, and study their interactions and reactions.

What is Mass Number?

Mass Number

The mass number of an atom is the total number of protons and neutrons in its nucleus. It is represented by the symbol A.

For example, the mass number of carbon-12 is 12, which means that its nucleus contains 6 protons and 6 neutrons.

The mass number is an important property of an atom because it determines its atomic mass. The atomic mass of an atom is the weighted average of the masses of its isotopes.

For example, the atomic mass of carbon is 12.011 atomic mass units (amu). This means that the average mass of a carbon atom is 12.011 times the mass of a hydrogen atom.

The mass number can also be used to calculate the number of neutrons in an atom. The number of neutrons is equal to the mass number minus the atomic number.

For example, the atomic number of carbon is 6, so the number of neutrons in a carbon-12 atom is 12 - 6 = 6.

The mass number is a fundamental property of an atom that is used in a variety of calculations. It is an important concept to understand in order to gain a deeper understanding of the structure of atoms and the properties of matter.

Here are some additional examples of mass numbers:

• Helium-4 has a mass number of 4, which means that its nucleus contains 2 protons and 2 neutrons.
• Oxygen-16 has a mass number of 16, which means that its nucleus contains 8 protons and 8 neutrons.
• Iron-56 has a mass number of 56, which means that its nucleus contains 26 protons and 30 neutrons.

The mass number is a valuable tool for understanding the structure of atoms and the properties of matter. It is a fundamental concept that is used in a variety of calculations and applications.

History of Atomic Number

History of Atomic Number

The concept of atomic number has its roots in the early days of atomic theory. In the late 18th and early 19th centuries, scientists began to investigate the properties of elements and how they combine to form compounds. One of the key discoveries was that elements could be arranged in a periodic table based on their atomic masses.

In 1869, Dmitri Mendeleev published his periodic table, which arranged the elements in order of increasing atomic mass. Mendeleev’s table was a major breakthrough, as it allowed scientists to predict the properties of new elements that had not yet been discovered.

However, Mendeleev’s table was not perfect. There were some elements that seemed to be out of order, and there were some gaps in the table where elements were missing.

In 1913, Henry Moseley discovered that the atomic number of an element is equal to the number of protons in its nucleus. This discovery was a major breakthrough, as it provided a way to uniquely identify each element. Moseley’s work also led to the development of the modern periodic table, which is arranged in order of increasing atomic number.

The atomic number of an element is a fundamental property that determines its chemical properties. Elements with the same atomic number have the same number of protons and electrons, and they therefore have the same chemical properties.

The atomic number of an element can be used to predict its position in the periodic table. Elements with a higher atomic number are located to the right of elements with a lower atomic number.

The atomic number of an element can also be used to calculate its atomic mass. The atomic mass of an element is the sum of the masses of its protons and neutrons.

The atomic number is a key concept in chemistry, and it is essential for understanding the properties of elements and how they combine to form compounds.

Examples of Atomic Number

The following are some examples of atomic numbers:

• Hydrogen has an atomic number of 1. This means that hydrogen has one proton in its nucleus.
• Helium has an atomic number of 2. This means that helium has two protons in its nucleus.
• Lithium has an atomic number of 3. This means that lithium has three protons in its nucleus.
• Carbon has an atomic number of 6. This means that carbon has six protons in its nucleus.
• Oxygen has an atomic number of 8. This means that oxygen has eight protons in its nucleus.

The atomic number of an element is a unique identifier that determines its chemical properties.

Examples of Atomic Number

Atomic Number

The atomic number of an element is the number of protons in the nucleus of an atom of that element. It is a unique identifier for each element and is used to determine the element’s position on the periodic table.

Examples of Atomic Numbers

The following are some examples of atomic numbers:

• Hydrogen: 1
• Helium: 2
• Lithium: 3
• Beryllium: 4
• Boron: 5
• Carbon: 6
• Nitrogen: 7
• Oxygen: 8
• Fluorine: 9
• Neon: 10

How to Find the Atomic Number

The atomic number of an element can be found on the periodic table. It is the number located at the top of each element’s box. For example, the atomic number of hydrogen is 1, which is located at the top of the hydrogen box.

Importance of the Atomic Number

The atomic number is an important property of an element because it determines the element’s chemical properties. For example, all elements with the same atomic number have the same number of electrons in their outer shells. This means that they will react in a similar way with other elements.

The atomic number is also used to calculate the mass number of an element. The mass number is the total number of protons and neutrons in the nucleus of an atom. To calculate the mass number, add the atomic number to the number of neutrons in the nucleus. For example, the mass number of carbon is 12, which is calculated by adding the atomic number of carbon (6) to the number of neutrons in the nucleus (6).

Conclusion

The atomic number is a fundamental property of an element. It is used to identify the element, determine its chemical properties, and calculate its mass number.

Atomic Number Orbital Energy Levels

Atomic Number Orbital Energy Levels

The atomic number of an element is the number of protons in the nucleus of an atom of that element. The number of protons in an atom determines the number of electrons that the atom has, and the number of electrons in an atom determines the element’s chemical properties.

The electrons in an atom are arranged in shells around the nucleus. The shells are numbered 1, 2, 3, and so on, starting with the shell closest to the nucleus. Each shell can hold a certain number of electrons. The first shell can hold up to 2 electrons, the second shell can hold up to 8 electrons, the third shell can hold up to 18 electrons, and so on.

The electrons in an atom are also arranged in orbitals. Orbitals are regions around the nucleus where electrons are most likely to be found. Orbitals are shaped like spheres, dumbbells, or other shapes. Each orbital can hold up to 2 electrons.

The energy level of an orbital is determined by its shape and its distance from the nucleus. Orbitals that are closer to the nucleus have lower energy levels than orbitals that are farther from the nucleus. Orbitals that are shaped like spheres have lower energy levels than orbitals that are shaped like dumbbells or other shapes.

The electrons in an atom fill the orbitals in order of increasing energy level. The electrons in the lowest energy level orbitals are the most tightly bound to the nucleus, and the electrons in the highest energy level orbitals are the most loosely bound to the nucleus.

The arrangement of electrons in orbitals is important because it determines the element’s chemical properties. The electrons in the outermost shell of an atom are the most reactive, and they are the electrons that participate in chemical reactions.

Examples of Atomic Number Orbital Energy Levels

The following are some examples of atomic number orbital energy levels:

• Hydrogen has 1 proton and 1 electron. The electron is in the 1s orbital.
• Helium has 2 protons and 2 electrons. The electrons are in the 1s orbital.
• Lithium has 3 protons and 3 electrons. The electrons are in the 1s and 2s orbitals.
• Beryllium has 4 protons and 4 electrons. The electrons are in the 1s, 2s, and 2p orbitals.
• Boron has 5 protons and 5 electrons. The electrons are in the 1s, 2s, and 2p orbitals.

The arrangement of electrons in orbitals is a complex topic, but it is important for understanding the chemical properties of elements.

Difference between Valency, A and Z:

Valency

Valency is a measure of the combining capacity of an atom. It is the number of electrons that an atom can gain or lose in order to achieve a stable electron configuration. For example, sodium has a valency of 1 because it can lose one electron to achieve a stable configuration. Chlorine has a valency of 7 because it can gain seven electrons to achieve a stable configuration.

A

The atomic number of an element is the number of protons in the nucleus of an atom. It is a unique identifier for each element. For example, the atomic number of sodium is 11, which means that a sodium atom has 11 protons in its nucleus.

Z

The mass number of an element is the total number of protons and neutrons in the nucleus of an atom. It is a measure of the mass of an atom. For example, the mass number of sodium is 23, which means that a sodium atom has 11 protons and 12 neutrons in its nucleus.

Examples

The following table shows the valency, atomic number, and mass number of some common elements:

Applications

Valency is used to predict the chemical properties of elements. For example, elements with a high valency tend to be more reactive than elements with a low valency. Valency is also used to determine the formula of compounds. For example, the formula of sodium chloride is NaCl because sodium has a valency of 1 and chlorine has a valency of 7.

Atomic number is used to identify elements. It is also used to determine the number of electrons in an atom. For example, a sodium atom has 11 electrons because it has an atomic number of 11.

Mass number is used to determine the mass of an atom. It is also used to calculate the average atomic mass of an element. For example, the average atomic mass of sodium is 22.99 g/mol because it has a mass number of 23 and an atomic number of 11.

Solved Example

Solved Example: Finding the Area of a Triangle

Problem: Find the area of a triangle with base 6 cm and height 8 cm.

Solution:

1. Identify the formula for the area of a triangle: The area of a triangle is given by the formula:

Area = (1/2) * base * height

2. Substitute the given values into the formula: In this case, the base is 6 cm and the height is 8 cm. Substituting these values into the formula, we get:

Area = (1/2) * 6 cm * 8 cm

3. Simplify the expression: Multiplying the values, we get:

Area = 24 cm²

Therefore, the area of the triangle is 24 square centimeters.

Explanation:

In this example, we used the formula for the area of a triangle to find the area of a triangle with a given base and height. The formula states that the area of a triangle is equal to half the product of its base and height. In this case, the base is 6 cm and the height is 8 cm, so the area is (1/2) * 6 cm * 8 cm = 24 cm².

This example illustrates how to use a formula to solve a problem. In this case, the formula for the area of a triangle was used to find the area of a triangle with a given base and height.

Frequently Asked Questions – FAQs

What is the highest atomic number?

The highest atomic number currently known belongs to the element Oganesson, which has an atomic number of 118. It was first synthesized in 2006 at the Joint Institute for Nuclear Research in Dubna, Russia, by a team of scientists led by Yuri Oganessian. Oganesson is a superheavy element, meaning it has an atomic number greater than 104. These elements are extremely unstable and can only be produced in very small quantities through nuclear reactions.

The synthesis of Oganesson involved bombarding a target of californium-249 with ions of calcium-48. This reaction produced a single atom of oganesson, which was detected using a variety of instruments. The atom was found to have a half-life of only 0.89 milliseconds, meaning it decayed into other elements very quickly.

Oganesson is named after the Russian nuclear physicist Yuri Oganessian, who played a key role in its discovery. It is the heaviest element currently known, and its existence has been confirmed by multiple experiments. However, due to its extreme instability, very little is known about its properties. Scientists are continuing to study oganesson and other superheavy elements in order to learn more about the structure of matter and the limits of the periodic table.

Here are some additional examples of elements with high atomic numbers:

• Uranium (atomic number 92): Uranium is a radioactive element that is used as fuel in nuclear reactors. It is also the heaviest naturally occurring element.
• Plutonium (atomic number 94): Plutonium is a radioactive element that is used in nuclear weapons. It is also produced as a byproduct of nuclear power generation.
• Americium (atomic number 95): Americium is a radioactive element that is used in smoke detectors. It is also used in some medical imaging procedures.
• Curium (atomic number 96): Curium is a radioactive element that is used in some medical imaging procedures. It is also used as a power source for spacecraft.
• Berkelium (atomic number 97): Berkelium is a radioactive element that is used in some medical imaging procedures. It is also used as a target for the production of other superheavy elements.

Who discovered the atomic number?

Who Discovered the Atomic Number?

The concept of atomic number was introduced by the English physicist Henry Moseley in 1913. Moseley’s work revolutionized the understanding of the periodic table and laid the foundation for modern chemistry.

Moseley’s Experiment

Moseley’s groundbreaking experiment involved using X-ray spectroscopy to study the emission spectra of various elements. He observed that the frequency of the X-rays emitted by an element increased in a regular manner as the atomic number of the element increased.

Atomic Number

Moseley defined the atomic number as the number of protons in the nucleus of an atom. He realized that the atomic number, rather than the atomic mass, was the fundamental property that determined the chemical properties of an element.

Periodic Table

Moseley’s discovery led to a rearrangement of the periodic table based on atomic numbers instead of atomic masses. This resulted in a more accurate and systematic organization of the elements, with elements with similar chemical properties grouped together.

Examples

Here are some examples of how the atomic number helps us understand the properties of elements:

• Elements with the same atomic number have the same number of protons and electrons, making them chemically identical. For example, all atoms with an atomic number of 6 are carbon atoms, regardless of their number of neutrons.
• The atomic number determines the element’s position in the periodic table. Elements with consecutive atomic numbers are arranged in the same row (period) of the periodic table.
• The atomic number also determines the element’s chemical properties. Elements in the same group (vertical column) of the periodic table have similar chemical properties because they have the same number of valence electrons.

Conclusion

Henry Moseley’s discovery of the atomic number was a major breakthrough in chemistry. It provided a deeper understanding of the structure of atoms and led to the development of the modern periodic table. The atomic number remains a fundamental property used to classify and study elements and their chemical behavior.

How do you find atomic mass from the atomic number and the number of neutrons?

The atomic mass of an element is the sum of the masses of its protons and neutrons. The atomic number of an element is the number of protons in its nucleus, and the number of neutrons is the number of neutrons in its nucleus.

To find the atomic mass of an element, you can use the following formula:

atomic mass = atomic number + number of neutrons

For example, the atomic number of carbon is 6, and the number of neutrons in carbon-12 is 6. Therefore, the atomic mass of carbon-12 is 12.

Here are some other examples of how to find the atomic mass of an element:

• Hydrogen-1 has an atomic number of 1 and 0 neutrons, so its atomic mass is 1.
• Helium-4 has an atomic number of 2 and 2 neutrons, so its atomic mass is 4.
• Lithium-7 has an atomic number of 3 and 4 neutrons, so its atomic mass is 7.
• Beryllium-9 has an atomic number of 4 and 5 neutrons, so its atomic mass is 9.
• Boron-11 has an atomic number of 5 and 6 neutrons, so its atomic mass is 11.

The atomic mass of an element can be used to calculate its average atomic mass. The average atomic mass of an element is the weighted average of the masses of all of its isotopes. The weighting factor for each isotope is its relative abundance.

For example, the average atomic mass of carbon is 12.011. This means that the average carbon atom has a mass of 12.011 atomic mass units (amu). The majority of carbon atoms are carbon-12, which has a mass of 12 amu. However, there are also small amounts of carbon-13 and carbon-14, which have masses of 13 amu and 14 amu, respectively. The relative abundances of carbon-12, carbon-13, and carbon-14 are 98.89%, 1.11%, and 0.0000000001%, respectively.

The average atomic mass of an element can be used to calculate its molar mass. The molar mass of an element is the mass of one mole of that element. One mole of an element is the amount of that element that contains 6.022 x 10^23 atoms.

For example, the molar mass of carbon is 12.011 g/mol. This means that one mole of carbon has a mass of 12.011 grams.

Why is the atomic number denoted by Z?

The atomic number of an element is denoted by the letter Z. This is because the atomic number is equal to the number of protons in the nucleus of an atom. Protons are positively charged particles, and they are what give atoms their chemical properties. The number of protons in an atom is also what determines its place on the periodic table.

For example, the atomic number of hydrogen is 1. This means that a hydrogen atom has one proton in its nucleus. The atomic number of helium is 2, which means that a helium atom has two protons in its nucleus. And so on.

The atomic number is a fundamental property of an element. It cannot be changed without changing the element itself. This is why the atomic number is used to identify elements.

Here are some examples of how the atomic number is used:

• To identify the element: The atomic number of an element is its unique identifier. For example, the element with atomic number 1 is hydrogen, the element with atomic number 2 is helium, and so on.
• To determine the number of protons in an atom: The atomic number of an element is equal to the number of protons in the nucleus of an atom. For example, a hydrogen atom has one proton, a helium atom has two protons, and so on.
• To determine the number of electrons in an atom: The number of electrons in an atom is equal to the number of protons in the nucleus. This is because atoms are electrically neutral, meaning that they have the same number of positive charges (protons) as negative charges (electrons).
• To determine the chemical properties of an element: The atomic number of an element determines its chemical properties. This is because the number of protons in an atom determines the number of electrons in the atom, and the electrons are what interact with other atoms to form chemical bonds.

The atomic number is a very important property of an element. It is used to identify elements, determine the number of protons and electrons in an atom, and determine the chemical properties of an element.

What is the mass number?

The mass number of an atom is the sum of the number of protons and neutrons in its nucleus. It is represented by the symbol A. For example, the mass number of carbon-12 is 12, which means that it has 6 protons and 6 neutrons in its nucleus.

The mass number is an important property of atoms because it determines their atomic mass. The atomic mass of an element is the weighted average of the masses of all its isotopes, taking into account their relative abundances. For example, the atomic mass of carbon is 12.011, which means that the average mass of a carbon atom is 12.011 atomic mass units (amu).

The mass number can also be used to calculate the number of neutrons in an atom. The number of neutrons is equal to the mass number minus the atomic number. For example, the atomic number of carbon is 6, so the number of neutrons in a carbon-12 atom is 12 - 6 = 6.

The mass number is a fundamental property of atoms that plays an important role in many areas of chemistry and physics.

Here are some additional examples of mass numbers:

• Helium-4 has a mass number of 4, which means that it has 2 protons and 2 neutrons in its nucleus.
• Oxygen-16 has a mass number of 16, which means that it has 8 protons and 8 neutrons in its nucleus.
• Iron-56 has a mass number of 56, which means that it has 26 protons and 30 neutrons in its nucleus.

The mass number is a valuable tool for understanding the structure and properties of atoms.

What is an atomic number and mass number?

Atomic Number:

The atomic number of an element is the number of protons found in the nucleus of an atom of that element. It is a unique identifier for each element and determines its position on the periodic table. The atomic number is represented by the symbol “Z.”

For example, the atomic number of hydrogen is 1, which means that a hydrogen atom has one proton in its nucleus. The atomic number of carbon is 6, indicating that a carbon atom has six protons in its nucleus.

Mass Number:

The mass number of an element is the total number of protons and neutrons found in the nucleus of an atom of that element. It is represented by the symbol “A.”

For instance, the mass number of carbon-12 is 12, which means that a carbon-12 atom has six protons and six neutrons in its nucleus. The mass number of oxygen-16 is 16, indicating that an oxygen-16 atom has eight protons and eight neutrons in its nucleus.

Relationship between Atomic Number and Mass Number:

The atomic number and mass number of an element are closely related. The atomic number determines the number of protons in an atom, while the mass number accounts for both protons and neutrons. Since neutrons have a neutral charge, the mass number of an element is always greater than or equal to its atomic number.

Isotopes:

Isotopes are atoms of the same element that have the same atomic number but different mass numbers. This means that isotopes have the same number of protons but differ in the number of neutrons.

For example, carbon has three naturally occurring isotopes: carbon-12, carbon-13, and carbon-14. All three isotopes have six protons, but carbon-12 has six neutrons, carbon-13 has seven neutrons, and carbon-14 has eight neutrons.

Isotopes have similar chemical properties but can differ in their physical properties, such as density and radioactivity.

In summary, the atomic number of an element defines its identity and position on the periodic table, while the mass number represents the total number of protons and neutrons in an atom of that element. Isotopes are variations of the same element with different mass numbers.