Problem 30 - Chemistry The Central Science In Si Units

Question

Fill in the gaps in the following table, assuming each column represents a neutral atom. $$ \begin{array}{l|l|l|l|l|l} \hline \text { Symbol } & { }^{89} \mathrm{Y} & & & & \\ \text { Protons } & & 78 & & & 89 \\ \text { Neutrons } & & & 123 & & \\ \text { Electrons } & & & 81 & 50 & \\ \text { Mass no. } & & 195 & & 119 & 227 \\ \hline \end{array} $$

Step-by-Step Solution

Answer

Y has 39 protons and electrons; Pt has 117 neutrons; Tl is element 81 with mass 204; Sn has mass 119; Ac has 138 neutrons.

Step 1: Filling Protons for Known Symbols

The symbol \(^ {89}\text{Y}\) represents Yttrium, which has an atomic number of 39. Hence, it has 39 protons. In a neutral atom, the number of electrons is equal to the number of protons, so it also has 39 electrons. Thus, we fill in 39 protons and 39 electrons for the first column.

Step 2: Determining Neutrons from Mass Number

In the second column with protons listed as 78, we can identify this as Platinum (Pt) since it matches the atomic number of 78. The mass number is 195, so the number of neutrons can be calculated as Mass number - Number of protons = 195 - 78 = 117 neutrons.

Step 3: Finding Protons and Symbol for Known Neutrons

For the third column, with 123 neutrons and 81 electrons, using the fact that number of protons equals number of electrons for neutral atoms, we determine this atom has 81 protons. This corresponds to Thallium (Tl) since it has an atomic number of 81. For Thallium with these neutrons, its mass number is calculated as Protons + Neutrons = 81 + 123 = 204.

Step 4: Completing Mass Number for Known Electrons

In the fourth column, there are 50 electrons indicating 50 protons, which matches Tin (Sn). With this information, we calculate the mass number using protons, known electrons, and adding 69 neutrons that result from 119 - 50 to fill the column as the atomic mass number is labeled 119.

Step 5: Calculating Neutrons for Mass Number 227

In the last column, the mass number is 227, and the number of protons is 89, matching Actinium (Ac). Calculate neutrons as Mass number - Protons = 227 - 89 = 138 neutrons. Then fill the table with this information.

Key Concepts

Proton Number

The proton number, also known as the atomic number, is a key property of an element. It tells us how many protons are in the nucleus of an atom. This number is unique to each element and defines the identity of the atom. For instance, Yttrium has a proton number of 39, meaning it always has 39 protons.
For neutral atoms, the number of protons equals the number of electrons. This balance keeps the atom electrically neutral. Understanding the proton number:

• Defines the type of element
• Helps in identifying the element on the periodic table
• Provides information about the electrical neutrality in atoms

Mass Number

The mass number is a combination of the number of protons and neutrons in the atom's nucleus. It represents the total mass of the nucleus.
It's important because:

• It helps calculate the neutron number when the atomic number is known.
• Determines the mass of an individual atom of an element.

For instance, if we look at the element Platinum, which has a mass number of 195 and a proton number of 78, we can determine various properties of the atom. This number is typically larger than the proton number because it also includes neutrons, which have a similar mass to protons.

Neutron Calculation

Neutrally charged subatomic particles within an atom's nucleus. Despite not altering the electric charge, neutrons play a crucial role in the atom's mass and stability.
The number of neutrons can be found by subtracting the number of protons from the mass number:

• Mass Number = Number of Protons + Number of Neutrons
• Number of Neutrons = Mass Number - Number of Protons

For example, if an element like Thallium has a mass number of 204 and a proton count of 81, the neutron number is calculated as 204 - 81, resulting in 123 neutrons. In this way, the neutron calculation is instrumental in identifying isotope differences and understanding atomic mass.

Electron Configuration

The electron configuration describes how electrons are arranged around the nucleus of an atom. In a neutral atom, the electron number equals the proton number. This equality keeps the atom electrically stable.
Consider elements in the periodic table:

• The element Tin has 50 electrons, matching its 50 protons.
• These electrons are organized across shells and sub-shells based on energy levels, which affects chemical properties.

Thus, the electron configuration provides insight into chemical reactivity and the formation of bonds. It is fundamental in understanding how atoms interact with one another, forming the basis for the periodic table's layout and chemical behavior.