CM 03.3 TB How Atoms Differ

What is the atomic number of an element?

• The number of protons

• The number of neutrons

• The number of electrons

• The number of protons and neutrons.

Answer explanation

The atomic number of an element is defined as the number of protons in its nucleus. This number determines the element's identity and its position in the periodic table, making 'the number of protons' the correct answer.

Explain how isotopes of an element differ from each other.

Answer explanation

Isotopes of an element differ in the number of neutrons in their nuclei, resulting in different atomic masses. However, they have the same number of protons and exhibit similar chemical properties.

An isotope of carbon has 6 protons and 8 neutrons. The mass number of this isotope is ____.

Answer explanation

The mass number of an isotope is the sum of its protons and neutrons. Here, 6 protons + 8 neutrons = 14. Therefore, the mass number of this carbon isotope is 14.

Match the following terms with their definitions: Atomic Number, Mass Number, Isotope.

• Total number of protons and neutrons

• Number of protons in the nucleus

• Atoms of the same element with different numbers of neutrons

• Total number of protons and neutrons

• Number of protons in the nucleus

• Atoms of the same element with different numbers of neutrons

The atomic mass of an element is the weighted average of the masses of its (a)   .

• protons

• neutrons

• isotopes
• electrons

Answer explanation

The atomic mass of an element is determined by the weighted average of the masses of its isotopes, which are variants of the element with different numbers of neutrons. Protons and electrons do not account for the atomic mass in this context.

What is the role of atomic number in determining the identity of an atom?

Answer explanation

The atomic number, which is the number of protons in an atom's nucleus, uniquely identifies an element. It determines the element's chemical properties and its position in the periodic table.

Define an isotope.

Answer explanation

An isotope is defined as a variant of a chemical element that has the same number of protons but a different number of neutrons, leading to a difference in atomic mass number. This definition aligns with the correct answer.

Tags

NGSS.HS-PS1-8

Why are atomic masses not whole numbers?

Answer explanation

Atomic masses are not whole numbers because they represent the weighted average of all isotopes of an element, taking into account their relative abundances and different masses, resulting in fractional values.

Calculate the number of electrons, protons, and neutrons in an atom given its mass number and atomic number. For example, if an atom has a mass number of 23 and an atomic number of 11, how many neutrons does it have?

• A) 11

• B) 12

• C) 13

• D) 14

Answer explanation

To find the number of neutrons, subtract the atomic number from the mass number. Here, mass number is 23 and atomic number is 11. So, neutrons = 23 - 11 = 12. Therefore, the correct answer is B) 12.

Tags

NGSS.MS-PS1-1

Match the following terms with their definitions:

• Isotope

• Variants of elements with different neutron numbers

• Mass Number

• Number of protons in an atom

• Atomic Number

• Total number of protons and neutrons in an atom