4.1.2 Atomic Number and Mass Number

• What is an atom composed of?

  Protons, neutrons, electrons
• Electrons have a negative charge and are located in orbitals
• Neutrons are located in the nucleus and have a neutral charge.
• Match the atomic component with its charge:

  Proton ↔️ Positive

  Neutron ↔️ Neutral

  Electron ↔️ Negative
• What does the atomic number (Z) represent?

  Number of protons
• The atomic number is crucial because it identifies the element
• Oxygen has an atomic number of 8, meaning it has 8 protons in its nucleus.
• What is the mass number (A) of an atom?

  Sum of protons and neutrons
• Carbon-12 has 6 protons and 6 neutrons, resulting in a mass number of 12.
• Steps to calculate the number of neutrons in an atom

  1️⃣ Identify A and Z

  2️⃣ Apply the formula $N =$$A - Z$
• What are isotopes of an element?

  Same protons, different neutrons
• Isotopes are denoted using the format $^{\text{A}}_{\text{Z}}X$ where $A$ is the mass number, Z</latex> is the atomic number, and $X$ is the element symbol.
• What does the atomic number (Z) represent in an atom?

  Number of protons
• To find the number of neutrons (N), you subtract the atomic number (Z) from the mass number (A)
• Calculate the number of neutrons in carbon-14, where A = 14 and Z = 6.

  8 neutrons
• The number of neutrons in carbon-14 is 8.
• Isotopes are atoms of the same element with the same number of protons but different numbers of neutrons
• What does the symbol A represent in the isotope notation $^{\text{A}}_{\text{Z}}X$?


  Mass number
• Carbon-12 has 6 protons and 8 neutrons.

  False
• What are the three main components of an atom?

  Protons, neutrons, electrons
• Match the atomic component with its properties:

  Protons ↔️ +1 charge, nucleus

  Neutrons ↔️ 0 charge, nucleus

  Electrons ↔️ -1 charge, orbitals
• Where are electrons located in an atom?

  Orbitals around the nucleus
• The atomic number of oxygen is 8, which means it has 8 protons
• The atomic number is unique for each element.
• What is the mass number (A) of an atom equal to?

  Protons + neutrons
• What is the mass number of carbon-12, which has 6 protons and 6 neutrons?

  12
• The mass number is the same for all isotopes of an element.

  False
• How do you calculate the number of neutrons in an atom using its mass number (A) and atomic number (Z)?

  N = A - Z
• To find the number of neutrons, you subtract the atomic number from the mass number
• The atomic number uniquely identifies an element.
• What is the atomic number and mass number of helium, as shown in the example?

  Z = 2, A = 4
• Calculate the number of neutrons in sodium, which has an atomic number of 11 and a mass number of 23.

  12 neutrons