Question

What will be the atomic number of the next alkali metal to be discovered? How would you expect the physical properties of the next alkali metal to compare with the properties of the other alkali metals summarized in Table 19-4?

Short answer

The atomic number of the next alkali metal to be discovered should be 95, based on the pattern observed in the atomic numbers of the existing alkali metals. In terms of physical properties, we can expect this new alkali metal to be more reactive and have lower melting and boiling points compared to the other alkali metals in the group, following the general trend observed in the alkali metal group. However, the actual properties of the element might vary.

Step-by-step solution

Identify the alkali metals

The alkali metals are the elements in Group 1 of the periodic table. They include: 1. Lithium (Li) - Atomic number: 3 2. Sodium (Na) - Atomic number: 11 3. Potassium (K) - Atomic number: 19 4. Rubidium (Rb) - Atomic number: 37 5. Cesium (Cs) - Atomic number: 55 6. Francium (Fr) - Atomic number: 87 Observe the pattern of their atomic numbers.

Predict the atomic number of the next alkali metal

If we analyze the pattern of atomic numbers of the alkali metals provided above, we can identify that each alkali metal has eight more protons than the one that precedes it in the periodic table (except for helium to lithium where it has only two more protons). Following the pattern, the next alkali metal after francium would have 87 + 8 = 95 protons. Therefore, the atomic number of the next alkali metal to be discovered should be 95.

Compare the physical properties of the next alkali metal with those of the existing alkali metals

Generally, alkali metals are soft, highly reactive, and have low melting points. As we move down the group, the alkali metals become more reactive, and their melting points and boiling points decrease. Based on this trend, we can expect the next alkali metal (Atomic number 95) to have the following properties as compared to the other alkali metals: 1. Higher reactivity - The next alkali metal is expected to be more reactive than francium, which is already highly reactive. 2. Lower melting and boiling points - The melting point and boiling point of the next alkali metal are expected to be lower than those of the existing alkali metals. These are predictions based on the observed trends in the alkali metal group, but the actual properties of the element might vary.

Key concepts

Atomic Number

The atomic number is a fundamental property of an element that influences its position on the periodic table and its chemical behavior. It is defined as the number of protons found in the nucleus of an atom. As we explore the alkali metals, which are located in Group 1 of the periodic table, we notice they have atomic numbers that are separated by certain numerical intervals. For instance, the atomic number increases by eight when moving from one alkali metal to the next in the sequence, starting with lithium. This systematic increase correlates with their placement on the periodic table, which is structured based on electronic configurations, and helps predict properties of undiscovered elements.

When looking forward to the discovery of a new alkali metal beyond francium, we can predict its atomic number by continuing this sequence. Since francium has an atomic number of 87, the next alkali metal in line, following the pattern, would have an atomic number of 87 plus 8, totaling 95. This prediction serves as a basis for hypothesizing other properties of this not-yet-discovered element.

Periodic Table Trends

Understanding the periodic table involves recognizing the trends that appear as we move across or down the table. For alkali metals, these trends have distinct patterns due largely to their electronic structure. As we move down Group 1 from lithium to francium, alkali metals exhibit an increase in atomic and ionic size due to the addition of electron shells. This growth in size affects their melting and boiling points, ionization energies, and reactivity. Decreases in melting and boiling points are observed as we go down the group, which means that these elements become more metallic in character.

The pattern of increasing reactivity is also a critical trend for alkali metals, making elements lower in the group more prone to react with other substances. Another trend includes changes in densities and electro-negativities. These periodic table trends not only help us categorize elements but also facilitate predictions about the chemical and physical characteristics of unknown, possibly heavier alkali metals.

Chemical Properties of Alkali Metals

Alkali metals are known for a set of unique chemical properties that define their interactions with other substances and their role in various chemical reactions. Primarily, they have one electron in their outermost shell, which makes them highly prone to losing that electron to achieve a stable noble gas configuration. This single electron defines many of their properties, such as forming ionic compounds by readily giving up this electron.

They react vigorously with water to form hydroxides and hydrogen gas; this reaction is typically exothermic. Alkali metals also form halides by reacting with halogens and typically create white crystalline salts that are soluble in water. When discussing solutions, such as the dissolving of sodium in water to create a basic solution, the chemical property of alkali metals to form hydroxides is pivotal.

Key Chemical Traits of Alkali Metals:

• Low ionization energies leading to high reactivity
• Formation of strongly basic hydroxides
• Preference for the +1 oxidation state
• Production of bright colors when burned due to electron excitation

These features are essential for understanding how alkali metals behave in different settings and how they respond to various reagents.

Reactivity of Alkali Metals

Reactivity is perhaps the most pronounced characteristic of alkali metals, with their reactivity increasing as we move down the group on the periodic table. At the atomic level, this trend in reactivity is due to the lowering of ionization energy; as the atoms become larger and the outer electron is farther from the nucleus, it becomes easier to remove. This is the primary reason that the alkali metals are such reactive metals – they are always ready to lose their single valence electron in chemical reactions.

Francium, being the heaviest naturally occurring alkali metal, is the most reactive, although its high reactivity and rarity make it difficult to observe. Predictions for the next alkali metal suggest even higher reactivity, surpassing all known alkali metals, thus posing potential challenges for its storage and handling. This heightened reactivity is a critical consideration when studying the characteristics of alkali metals as well as developing safe practices for working with them in laboratory and industrial sets.

The reactivity of alkali metals makes them fascinating for scientific study, especially in chemical synthesis and the development of new compounds with unique properties.