Problem 13 - Chemistry and Chemical Reactivity

Question

How many electrons, protons, and neutrons are there in an atom of (a) magnesium- \(24,^{24} \mathrm{Mg} ;\) (b) tin- \(119,^{119} \mathrm{Sn}\) and (c) thorium-232, \(^{232}\) Th?

Step-by-Step Solution

Answer

(a) Mg: 12 protons, 12 neutrons, 12 electrons; (b) Sn: 50 protons, 69 neutrons, 50 electrons; (c) Th: 90 protons, 142 neutrons, 90 electrons.

Step 1: Understanding the Atom

Each atom is composed of protons, neutrons, and electrons. The number of protons is given by the atomic number, the number of electrons is equal to the number of protons in a neutral atom, and the number of neutrons is the mass number minus the atomic number.

Step 2: Magnesium-24 Atom

Magnesium (Mg) has an atomic number of 12. Therefore, in a neutral magnesium atom, the number of protons and electrons is 12. The mass number is 24, so the number of neutrons is calculated as follows: \(\text{Neutrons} = 24 - 12 = 12\).

Step 3: Tin-119 Atom

Tin (Sn) has an atomic number of 50. Therefore, a neutral tin atom has 50 protons and 50 electrons. The mass number is 119 for this isotope, so the number of neutrons is: \(\text{Neutrons} = 119 - 50 = 69\).

Step 4: Thorium-232 Atom

Thorium (Th) has an atomic number of 90. Therefore, in a neutral thorium atom, there are 90 protons and 90 electrons. The mass number is 232, so the number of neutrons is: \(\text{Neutrons} = 232 - 90 = 142\).

Key Concepts

Isotopes

In chemistry, isotopes are variations of a particular element. These variants have the same number of protons but differ in the number of neutrons. This means that they have the same atomic number but different mass numbers.
For example, in the case of magnesium-24, tin-119, and thorium-232, each isotope is denoted by the number representing its mass number right after the element's name. The mass number is the sum of protons and neutrons in an atom's nucleus.

• **Magnesium-24**: This isotope has a mass number of 24.
• **Tin-119**: This one has a mass number of 119.
• **Thorium-232**: It has a mass number of 232.

Isotopes can be stable or radioactive, and they play essential roles in scientific research and practical applications, such as carbon dating and medical diagnostics.

Protons

Protons are positively charged particles found in the nucleus of an atom. They are one of the key components that make up the atomic structure. The number of protons in an atom is fundamental because it defines the element itself. This number is known as the atomic number.

Each element in the periodic table is distinct due to its number of protons. For instance:

• Magnesium has an atomic number of 12, meaning it has 12 protons.
• Tin has an atomic number of 50, meaning it carries 50 protons.
• Thorium's atomic number is 90, indicating 90 protons.

The atomic number is crucial because it ensures the chemical identity of an element, differentiating one element from another in the periodic table.

Neutrons

Neutrons are neutral particles found within the core or nucleus of an atom along with protons. They have no electrical charge and are crucial in adding mass to the atom without affecting its charge balance.
Neutrons play a key role in stabilizing the nucleus, as they help offset the repulsive forces between positively charged protons by adding strong nuclear binding forces.

• To find the number of neutrons in an atom, you simply subtract the atomic number (protons) from the mass number.
• In magnesium-24, there are 12 neutrons: \(24 - 12 = 12\).
• For tin-119, the neutron count is 69: \(119 - 50 = 69\).
• Thorium-232 boasts 142 neutrons: \(232 - 90 = 142\).

Understanding neutrons is key to grasping nuclear reactions and stability in atoms.

Electrons

Electrons are negatively charged particles found outside the nucleus of an atom in orbital clouds. They orbit the nucleus in regions called electron shells or levels. In a neutral atom, the number of electrons is equal to the number of protons, which balances the overall charge.
This balance allows atoms to be neutral and stable. The electron configuration also determines how atoms interact and bond with each other, dictating the chemical properties of the element.
Considering the examples:

• In a neutral magnesium atom, there are 12 electrons.
• For tin, a neutral atom also holds 50 electrons.
• In thorium, a neutral atom will contain 90 electrons.

These electrons are key players in forming chemical bonds in reactions, through interactions in their outermost shells or valence electrons.