Problem 63 - Introductory Chemistry Atoms First

Question

Which of the following are elemental substances and which are compounds: baking soda, \(\mathrm{NaHCO}_{3}\); graphite, \(\mathrm{C} ;\) dry ice, solid \(\mathrm{CO}_{2}\); metallic sodium, Na; metallic mercury, Hg?

Step-by-Step Solution

Answer

Baking soda, \(\mathrm{NaHCO}_{3}\), and dry ice, solid \(\mathrm{CO}_{2}\), are compounds. Graphite, \(\mathrm{C}\), metallic sodium, Na, and metallic mercury, Hg, are elemental substances.

Step 1: Determine the number of elements present in NaHCO3

In \(\mathrm{NaHCO}_{3}\), we have three different elements: \(\mathrm{Na}\) (Sodium), \(\mathrm{H}\) (Hydrogen), \(\mathrm{C}\) (Carbon), and \(\mathrm{O}\) (Oxygen).

Step 2: Classify NaHCO3

Since \(\mathrm{NaHCO}_{3}\) consists of more than one type of atoms, it is a compound. 2. Graphite, \(\mathrm{C}\)

Step 3: Determine the number of elements present in Graphite

Graphite is made up of only one element, \(\mathrm{C}\) (Carbon).

Step 4: Classify Graphite

Since graphite is made up of only one type of atom, it is an elemental substance. 3. Dry ice, solid \(\mathrm{CO}_{2}\)

Step 5: Determine the number of elements present in CO2

In solid \(\mathrm{CO}_{2}\), we have two different elements, \(\mathrm{C}\) (Carbon) and \(\mathrm{O}\) (Oxygen).

Step 6: Classify Solid CO2

Since solid \(\mathrm{CO}_{2}\) consists of more than one type of atoms, it is a compound. 4. Metallic sodium, Na

Step 7: Determine the number of elements present in Metallic Sodium

Metallic Sodium is composed of only one element, \(\mathrm{Na}\) (Sodium).

Step 8: Classify Metallic Sodium

Since metallic sodium is made up of only one type of atom, it is an elemental substance. 5. Metallic mercury, Hg

Step 9: Determine the number of elements present in Metallic Mercury

Metallic Mercury is composed of only one element, \(\mathrm{Hg}\) (Mercury).

Step 10: Classify Metallic Mercury

Since metallic mercury is made up of only one type of atom, it is an elemental substance. In conclusion, baking soda and dry ice are compounds, while graphite, metallic sodium, and metallic mercury are elemental substances.

Key Concepts

Elemental Substance

An elemental substance is composed entirely of one type of element. This means that all the atoms in the substance are the same kind.
For example, consider graphite. Its chemical symbol is \( \mathrm{C} \), which stands for carbon. Graphite is made exclusively of carbon atoms, making it an elemental substance. The same goes for metallic sodium (\( \mathrm{Na} \)) and metallic mercury (\( \mathrm{Hg} \)), which are made entirely of sodium and mercury atoms, respectively.

• Graphite (C)
• Metallic Sodium (Na)
• Metallic Mercury (Hg)

Each of these substances consists of only one type of atom, meaning that they cannot be broken down into simpler substances through chemical reactions because they already exist in their simplest form.

Compound

A compound, unlike an elemental substance, consists of two or more different types of elements that are chemically bonded together.
In compounds, the elements combine in specific ratios and structures to form a new substance with distinct properties. A good example is baking soda, known as \( \mathrm{NaHCO}_{3} \). Baking soda is a compound composed of sodium (Na), hydrogen (H), carbon (C), and oxygen (O) atoms.
Similarly, dry ice, which has a chemical formula of \( \mathrm{CO}_{2} \), is a compound made of carbon (C) and oxygen (O) elements.
The distinct arrangements and combinations of elements in these substances give them unique features differing from the individual elements themselves.

• Baking Soda (\( \mathrm{NaHCO}_{3} \))
• Dry Ice (\( \mathrm{CO}_{2} \))

Molecular Composition

Molecular composition refers to the specific makeup of a molecule in terms of the types and numbers of atoms it contains.
For instance, the molecular composition of baking soda \( (\mathrm{NaHCO}_{3}) \) includes one atom of sodium, one atom of hydrogen, one atom of carbon, and three atoms of oxygen. Each molecule of baking soda thus consists of multiple elements arranged in a precise form, creating its distinctive qualities in chemical reactions and interactions.
Understanding the molecular composition allows us to predict how a compound behaves chemically and physically, such as how it reacts when exposed to other substances or changes in environment.
Dry ice \( (\mathrm{CO}_{2}) \) has a molecular composition that includes one carbon atom and two oxygen atoms.

• Recognize the arrangement affects chemical properties.
• Molecular composition determines reactivity.
• Aids in understanding properties like phase changes.

Elements in Compounds

Elements in compounds are the different types of atoms present that form the compound itself.
When these elements come together, they do so in specific ratios. For example, in water (though not part of this exercise), hydrogen and oxygen are combined in a 2:1 ratio, forming \( \mathrm{H}_{2} \mathrm{O} \).
In our examples, baking soda has a balanced formula of \( \mathrm{NaHCO}_{3} \), which unites sodium, hydrogen, carbon, and oxygen.
Such a compilation of elements results in new properties, distinct from those of elemental substances. For instance, baking soda acts as a base in chemical reactions, a property arising from its unique combination of elements.
Dry ice \( (\mathrm{CO}_{2}) \) showcases how elements can form carbon dioxide when carbon atoms pair with two oxygen atoms.

• Elements determine a compound's properties.
• Compounds have fixed ratios of elements.
• Understanding these elements helps in chemical manipulations.