Question

The formulas for the oxides of sodium, magnesium, aluminum, and silicon are, respectively, \(\mathrm{Na}_{2} \mathrm{O}, \mathrm{MgO}, \mathrm{Al}_{2} \mathrm{O}_{3},\) and \(\mathrm{SiO}_{2}\). Using the periodic table, predict the chemical formulas for each of the following similar compounds: (a) lithium oxide (b) barium oxide (c) gallium oxide (d) tin oxide

Short answer

(a) Li₂O; (b) BaO; (c) Ga₂O₃; (d) SnO or SnO₂.

Step-by-step solution

Understanding the Valency

To predict the chemical formula for the oxides, we need to know the valency of each element based on its position in the periodic table. Alkali metals like lithium (Li), found in Group 1, have a valency of +1. Barium (Ba), an alkaline earth metal in Group 2, has a valency of +2. Gallium (Ga), in Group 13, typically has a valency of +3. Tin (Sn), in Group 14, can have a valency of either +2 or +4.

Writing Formulas for Lithium and Barium Oxide

For lithium oxide, which has a valency of +1, we combine lithium ( ext{Li}^+) with oxygen ( ext{O}^{2-}). The formula becomes ext{Li}_2 ext{O}. For barium, which has a valency of +2, and oxygen ( ext{O}^{2-}), they simply combine in a 1:1 ratio, giving the formula ext{BaO}.

Writing Formula for Gallium Oxide

Gallium has a valency of +3 and combines with oxygen ( ext{O}^{2-}) to balance the charges. The least common multiple of 3 (gallium) and 2 (oxygen) is 6, meaning two gallium atoms combine with three oxygen atoms. This gives us the formula ext{Ga}_2 ext{O}_3.

Writing Formula for Tin Oxide

Tin can have either a +2 or +4 valency. For stannous oxide (lower oxidation potential), use the +2 valency: Sn + ext{O}^{2-} = ext{SnO}. For stannic oxide (higher oxidation potential), use the +4 valency: Sn^{4+} + 2 ext{O}^{2-} = ext{SnO}_2.

Key concepts

Valency

Valency is an essential concept in chemistry that helps us determine how elements combine to form compounds. It refers to the number of chemical bonds an atom of an element can form. This capability is based on an atom's ability to gain, lose, or share electrons to achieve a stable electron configuration, often resembling the nearest noble gas.

In the periodic table, groups or families of elements display similar valencies due to having the same number of valence electrons. For example, Group 1 elements, such as sodium (Na) and lithium (Li), have one valence electron, giving them a valency of +1. They tend to lose one electron to form positive ions like Na⁺ and Li⁺. Alkaline earth metals, including magnesium (Mg) and barium (Ba), belong to Group 2 and usually have a valency of +2, leading to forms like Mg²⁺ and Ba²⁺.

Understanding valency is crucial for constructing chemical formulas. For instance, when forming oxides, we balance the positive valency of metals with the negative valency of oxygen, which is typically -2. This balancing act helps us predict the correct chemical formula for various oxides, as seen in lithium oxide (Li₂O) and barium oxide (BaO).

Periodic Table

The periodic table is more than just a collection of elements; it is a powerful tool that organizes elements according to increasing atomic number and similar chemical properties. This arrangement allows us to predict how elements will behave and interact.

Each row in the periodic table is called a period, and each column is a group. Elements in the same group exhibit similar chemical behaviors due to their valence electron configuration. These similar properties make it easier to determine the valency of elements, a crucial factor in writing chemical formulas.

For example, elements in Group 13, such as aluminum (Al) and gallium (Ga), generally have a valency of +3 due to possessing three valence electrons. Meanwhile, Group 14 elements like tin (Sn) can have multiple oxidation states, commonly +2 and +4. Thus, the periodic table helps to pin down details like whether tin will form stannous oxide (SnO) or stannic oxide (SnO₂), depending on its oxidation state.

Oxides

Oxides are a broad class of chemical compounds that consist of at least one oxygen atom bonded to another element. The oxygen usually has a -2 oxidation state in these compounds, requiring the metal or other elements to balance this with their respective charges.

The formation of oxides is guided by the valency of the metal or non-metal combining with oxygen. For instance, lithium (Li) with a valency of +1 forms lithium oxide (Li₂O), balancing the -2 charge of one oxygen atom. Similarly, barium (Ba) with a valency of +2 forms barium oxide (BaO), resulting in a neutral compound without additional oxygen molecules.

Some elements can form more than one type of oxide, which is reflected in the different oxidation states. Tin (Sn), for instance, can form stannous oxide (SnO) with Sn²⁺ or stannic oxide (SnO₂) with Sn⁴⁺. This versatility illustrates how understanding the valency not only helps in predicting simple oxides but also in grasping the complexity and variability of such compounds.