Question

Give complete symbols of each atom, including the atomic number and the mass number. a) an oxygen atom with 8 protons and 8 neutrons b) a potassium atom with 19 protons and 20 neutrons c) a lithium atom with 3 protons and 4 neutrons

Short answer

Oxygen: \( ^{16}_{8} \text{O} \) Potassium: \( ^{39}_{19} \text{K} \) Lithium: \( ^{7}_{3} \text{Li} \)

Step-by-step solution

Understanding Atomic Number and Mass Number

The atomic number is the number of protons in an atom, which defines the element. The mass number is the sum of protons and neutrons in the nucleus. The complete symbol of an atom includes its element symbol, mass number, and atomic number.

Oxygen Atom Calculation

Oxygen has 8 protons and 8 neutrons. - Atomic number (Z) = 8 (protons) - Mass number (A) = 8 (protons) + 8 (neutrons) = 16 The symbol is written with the element symbol 'O', mass number as a superscript and atomic number as a subscript: \[ ^{16}_{8} \text{O} \]

Potassium Atom Calculation

Potassium has 19 protons and 20 neutrons. - Atomic number (Z) = 19 (protons) - Mass number (A) = 19 (protons) + 20 (neutrons) = 39 The symbol is written with the element symbol 'K', mass number as a superscript and atomic number as a subscript: \[ ^{39}_{19} \text{K} \]

Lithium Atom Calculation

Lithium has 3 protons and 4 neutrons. - Atomic number (Z) = 3 (protons) - Mass number (A) = 3 (protons) + 4 (neutrons) = 7 The symbol is written with the element symbol 'Li', mass number as a superscript and atomic number as a subscript: \[ ^{7}_{3} \text{Li} \]

Key concepts

Atomic Number

Atoms are defined by the number of protons they contain, which is known as the atomic number. This number is unique to each element and helps us identify an element on the periodic table.

• For example, oxygen has an atomic number of 8, meaning it has 8 protons.
• Potassium has an atomic number of 19, indicating 19 protons.
• Lithium, with 3 protons, has an atomic number of 3.

The atomic number is a fundamental characteristic of an element and determines the element's identity. In atomic symbols, it is usually displayed as a subscript to the left of the element symbol, such as in different² font: \( _Z\text{X} \) where \( Z \) is the atomic number and \( X \) is the element symbol.

Mass Number

While the atomic number tells us about the protons, the mass number gives us information about the entire contents of an atom's nucleus—both protons and neutrons.
To find the mass number of an atom, simply add the number of protons and the number of neutrons together:

• For an oxygen atom with 8 protons and 8 neutrons:
  • Mass Number \( = 8 + 8 = 16 \)
• For a potassium atom with 19 protons and 20 neutrons:
  • Mass Number \( = 19 + 20 = 39 \)
• For a lithium atom with 3 protons and 4 neutrons:
  • Mass Number \( = 3 + 4 = 7 \)

In atomic notation, the mass number is written as a superscript, directly above the atomic number in front of the element symbol, like \( ^AX \), where \( A \) is the mass number.

Element Symbols

Element symbols are shorthand notations used to represent elements on the periodic table. Each symbol is derived from the element's English or Latin name and typically includes one or two letters. The first letter is always capitalized, while the second, if present, is lowercase.
Here's how you might see it:

• O for oxygen
• K for potassium
• Li for lithium

When combined with the atomic number and mass number, the element symbols provide a complete picture of an atom's structure, like \( ^{A}_{Z}X \). For example, the notation for an oxygen atom is written as \( ^{16}_{8}\text{O} \), giving information about both the number of protons (8) and the total number of nucleons (16) in the atom. Understanding these symbols can make it easier to quickly identify elements and their isotopes.