Problem 114 - Chemistry Matter and Change

Question

Phosphorus has the atomic number 15 and an atomic mass of 31 amu. How many protons, neutrons, and electrons are in a neutral phosphorus atom? (Chapter 4)

Step-by-Step Solution

Answer

Phosphorus has 15 protons, 15 electrons, and 16 neutrons.

Step 1: Identify Protons

The atomic number of an element is the same as the number of protons in its nucleus. For phosphorus, the atomic number is 15, which means there are 15 protons.

Step 2: Determine Electrons in a Neutral Atom

In a neutral atom, the number of electrons is equal to the number of protons to balance the electrical charge. Since phosphorus has 15 protons, it also has 15 electrons.

Step 3: Calculate Neutrons

The atomic mass of an atom is approximately the sum of its protons and neutrons. For phosphorus, the atomic mass is 31 amu. Using the formula: \[ \text{Neutrons} = \text{Atomic Mass} - \text{Protons} \] we find: \[ \text{Neutrons} = 31 - 15 = 16 \] Hence, there are 16 neutrons in a phosphorus atom.

Key Concepts

Atomic Number

The atomic number is an essential concept in atomic structure as it defines the identity of an element. It tells us how many protons an atom of an element possesses. Every element has a unique atomic number, making it an identifying characteristic. For example, phosphorus has an atomic number of 15. This means every atom of phosphorus has 15 protons in its nucleus.

Understanding the atomic number is crucial for several reasons:

• It determines the chemical properties of the element.
• It helps in identifying the position of the element in the periodic table.
• It indicates the number of electrons in a neutral atom, which we'll discuss next.

So, when you hear the term "atomic number," think about the protons since they're the key to identifying elements!

Neutral Atom

A neutral atom is one where the overall charge is zero. This neutrality is achieved when the number of protons equals the number of electrons. Electrons are negatively charged, while protons are positively charged. Thus, in a neutral atom, these charges balance each other out perfectly.

Neutral atoms play a significant role in chemistry because:

• They represent the most stable state of an element under normal conditions.
• They are typically the form in which elements exist in nature.

Using phosphorus as an example, which has an atomic number of 15, a neutral phosphorus atom must have 15 electrons to balance its 15 protons. This balance ensures that the atom has no net electrical charge.

Protons

Protons are subatomic particles found in the nucleus of an atom. They carry a positive charge, and the number of protons in an atom's nucleus defines the element's atomic number.

Key points about protons include:

• They contribute to the atom's mass as each proton has a mass of about 1 amu (atomic mass unit).
• They determine the chemical identity and properties of the element.

When we refer to phosphorus with an atomic number 15, we're indicating that each phosphorus atom has 15 protons. These protons are paired with neutrons in the nucleus, contributing to the atom's stability.

Neutrons

Neutrons are neutral particles located in the atomic nucleus alongside protons. They have no electrical charge. The number of neutrons can vary even among atoms of the same element, leading to different isotopes. This variance does not affect the chemical behavior of the element but does alter its atomic mass.

In phosphorus, whose atomic mass is 31 amu, we calculate the number of neutrons as follows:
Using the formula \[\text{Neutrons} = \text{Atomic Mass} - \text{Protons}\]\[\text{Neutrons} = 31 - 15 = 16\]This means phosphorus has 16 neutrons. Neutrons play a crucial role in stabilizing the nucleus by counteracting the repulsive forces among positively charged protons.

Electrons

Electrons are negatively charged particles that orbit the atom’s nucleus. They are much lighter than protons and neutrons. Electrons are involved in forming chemical bonds and determining the chemical behavior of atoms.

Vital points about electrons include:

• In a neutral atom, the number of electrons equals the number of protons.
• They're positioned in regions known as electron shells or energy levels around the nucleus.

For phosphorus, with 15 protons, there are also 15 electrons in a neutral atom. These electrons are key players in chemical interactions and bonding, making them fundamental to the study of chemistry.