Question

The isotope of an unknown element, \(X\), has a mass number of 79 . The most stable ion of the isotope has 36 electrons and forms a binary compound with sodium having a formula of \(\mathrm{Na}_{2} \mathrm{X}\). Which of the following statements is(are) true? For the false statements, correct them. a. The binary compound formed between \(\mathrm{X}\) and fluorine will be a covalent compound. b. The isotope of \(\mathrm{X}\) contains 38 protons. c. The isotope of \(X\) contains 41 neutrons. d. The identity of \(X\) is strontium, \(S r\).

Short answer

The short answer is: Statements b, c, and d are true. Statement a is false; the binary compound formed between X and fluorine will be an ionic compound, not a covalent compound. X is Strontium (Sr), with 38 protons and 41 neutrons.

Step-by-step solution

: The exercise gives us the following information about the isotope of X: 1. It has a mass number of 79. 2. Its most stable ion forms a binary compound with sodium with the formula Na₂X. 3. It has 36 electrons in its most stable ion form. #Step 2: Determine the number of protons in isotope X#

: The compound Na₂X has a neutral charge, and we know that sodium has a charge of +1. Since there are 2 sodium atoms in the compound, the charge of X should be -2. Thus, the unknown element in its neutral form will have 2 more electrons than it has in its most stable ion form. Neutral X: # of electrons = # of protons 36 electrons (ion) + 2 electrons = 38 protons #Step 3: Verify statement b#

: Statement b says that the isotope of X contains 38 protons. From our previous step, we already concluded that the neutral form of X has 38 protons. Therefore statement b is true. #Step 4: Determine the number of neutrons in isotope X#

: To find the number of neutrons in the isotope of X, we can use the mass number formula: Mass number = Number of protons + Number of neutrons Let N represent the number of neutrons. Then we have: 79 = 38 + N N = 79 - 38 N = 41 neutrons #Step 5: Verify statement c#

: Statement c says that the isotope of X contains 41 neutrons. From our calculation in step 4, we found that the isotope has 41 neutrons. Therefore statement c is true. #Step 6: Determine the identity of X and verify statement d#

: Using the periodic table, we find that an element with 38 protons is Strontium (Sr). So, the identity of X is indeed Sr. Hence, statement d is correct. #Step 7: Determine the type of compound formed between X and fluorine#

: Since X is found in the same group as Calcium and Magnesium on the periodic table (group 2), we can infer that when it forms a binary compound with Fluorine, an electronegative halogen, it's likely to form an ionic compound rather than a covalent compound. #Step 8: Verify statement a and correct if false#

: Statement a claims that the binary compound formed between X and fluorine will be a covalent compound. As we previously determined that the compound formed with fluorine would be ionic, statement a is false. The correct statement should be: a. The binary compound formed between X and fluorine will be an ionic compound. In summary, statements b, c, and d are true. Statement a was false, but we corrected it.

Key concepts

Mass Number

The mass number is a fundamental concept in chemistry, representing the total number of protons and neutrons in the nucleus of an atom. It's denoted as 'A' and is critical for identifying isotopes of elements, as isotopes have the same number of protons (atomic number) but differ in the number of neutrons.

In the exercise, the isotope of element X has a mass number of 79. By calculating the number of neutrons (79 - 38 = 41), students can confirm the correct neutron count for this isotope. Understanding mass number is essential because it affects the isotope's stability and physical properties. Moreover, the mass number can affect isotopic abundance and average atomic masses listed on the periodic table, influencing calculations in various applications like radiometric dating or nuclear medicine.

Binary Compounds

Binary compounds are chemical compounds comprising two different elements. The name 'binary' comes from the fact there are two parts to the formula. In the context of the given exercise, the binary compound is formed between an unknown element X and sodium, with the formula Na₂X. This implies a 2:1 ratio of sodium atoms to the X element.

Understanding binary compounds is essential when examining reactions and predicting compound formation. For instance, knowing that sodium forms a Na⁺ ion, we can deduce that X must form an ion with a -2 charge in the Na₂X compound to balance the charges and create a compound with an overall neutral charge. This insight on binary compounds helps students predict compound types and related chemical behaviors.

Periodic Table

The periodic table is a comprehensive chart that organizes all known elements by increasing atomic number (number of protons) and aligns them into groups and periods based on their chemical properties. Elements in the same group (column) typically exhibit similar properties, including similar bonding behavior.

In this exercise, using the atomic number deduced (38 protons), the element is identified as strontium (Sr), which is located in group 2 of the periodic table. This knowledge not only helps us pinpoint the element but also gives us clues about its reactive nature, since group 2 elements are known to form +2 cations. Students can utilize the periodic table to predict ionic charges and reactivity, which is pivotal when deducing the types of bonds and compounds that different elements can form.

Ionic and Covalent Bonding

Ionic and covalent bonds are two primary types of chemical bonding. Ionic bonding occurs between metals and nonmetals where electrons are transferred from the metal to the nonmetal, forming ions. The resulting electrostatic attraction between the oppositely charged ions constitutes the ionic bond. In contrast, covalent bonding takes place when two nonmetals share electrons, usually to achieve a noble gas electron configuration.

In the case of element X (strontium) and fluorine, an ionic bond forms as electrons are transferred from the metal X to the highly electronegative fluorine. This forms a stable ionic compound, contrary to statement a in the original exercise, which incorrectly suggests a covalent compound would form. Students must differentiate between ionic and covalent bonding to accurately predict the properties and structures of compounds they will encounter in chemistry.