Question

Determine whether the following atoms will form an ionic compound or a molecular compound, and give the formula of the compound. (a) sodium and chlorine (b) carbon and 4 hydrogen (c) magnesium and bromine (d) 2 bromine (e) carbon and 2 oxygen

Short answer

Ionic compounds: NaCl and MgBr2. Molecular compounds: CH4 and CO2. Diatomic molecule: Br2.

Step-by-step solution

Identify Compound Type for Sodium and Chlorine

To determine the type of compound that sodium (Na) and chlorine (Cl) will form, we look at the types of elements involved. Sodium is a metal and chlorine is a non-metal. Metals and non-metals typically form ionic compounds.

Determine Formula for Sodium and Chlorine

To write the formula for the ionic compound formed by sodium and chlorine, we must balance the charges. Sodium has a charge of +1 (Na+) and chlorine has a charge of -1 (Cl-). The formula for the compound is NaCl.

Identify Compound Type for Carbon and Hydrogen

Carbon (C) and hydrogen (H) are both non-metals. When non-metals combine, they typically form molecular compounds.

Determine Formula for Carbon and Hydrogen

The chemical formula for the molecular compound formed by carbon and hydrogen follows the valency of carbon, which is four. As each hydrogen atom has one valence electron, the formula is CH4.

Identify Compound Type for Magnesium and Bromine

Magnesium (Mg) is a metal and bromine (Br) is a non-metal. Combining a metal with a non-metal results in an ionic compound.

Determine Formula for Magnesium and Bromine

Magnesium has a charge of +2 (Mg2+) and bromine has a charge of -1 (Br-). To balance the charges, we need two bromine atoms for each magnesium atom. The formula for the compound is MgBr2.

Identify Compound Type for Two Bromines

Two bromine atoms form a diatomic molecule, not a compound. Bromine exists naturally as a molecule made up of two bromine atoms.

Determine Formula for Two Bromines

The diatomic molecule formed by two bromine atoms is written as Br2.

Identify Compound Type for Carbon and Oxygen

Carbon (C) and oxygen (O) are both non-metals, which typically combine to form molecular compounds.

Determine Formula for Carbon and Oxygen

Combining carbon with two oxygen atoms, considering the valences of carbon (4) and oxygen (2), we get the molecular formula CO2.

Key concepts

Ionic Compound Formation

Understanding the formation of ionic compounds is essential for grasping basic chemistry principles. Ionic compounds arise from the chemical bonding between metals and non-metals, involving the transfer of electrons from the metal to the non-metal. This transfer creates ions: positively charged cations and negatively charged anions.

For instance, when sodium (Na), a metal, comes into contact with chlorine (Cl), a non-metal, sodium donates one electron to chlorine, leading to the formation of Na+ (sodium ion) and Cl- (chloride ion). The opposite charges of these ions attract each other and create an ionic bond, resulting in the formation of sodium chloride (NaCl). This compound is stable because the total charge is balanced, with one Na+ ion bonding to one Cl- ion, creating a neutral compound. This process is crucial for understanding how diverse materials form and explains the properties of ionic compounds, such as high melting and boiling points, and their ability to conduct electricity when molten or dissolved in water.

Molecular Compound Formation

Molecular compounds, also known as covalent compounds, form when two or more non-metals share electrons, creating strong bonds known as covalent bonds. Unlike ionic bonds, where electron transfer occurs, covalent bonding involves the sharing of electron pairs between atoms.

A classic example is the bonding of carbon (C) and hydrogen (H) to form methane (CH₄). Carbon has four electrons in its outer shell and needs four more to achieve stability, resembling the nearest noble gas configuration. Hydrogen has one electron and needs one more to achieve the same stability. Therefore, one carbon atom shares its four electrons with four hydrogen atoms, allowing each hydrogen atom to share its one electron with carbon, effectively filling their outer shell and stabilizing the molecule.

Unlike ionic compounds, molecular compounds have distinct properties, including lower melting and boiling points, and they are poor conductors of electricity. This is because they do not have charged particles that are free to move, as in the case of ionic substances.

Chemical Formula Writing

Writing chemical formulas is a fundamental skill in chemistry that represents the elements and the number of atoms of each element in a compound. Chemical formulas are written using the symbols from the periodic table, followed by subscript numbers to indicate the quantity of each atom present.

For ionic compounds, the chemical formula is derived by balancing the charges of the ions. For example, magnesium (Mg) has a +2 charge and bromine (Br) has a -1 charge. To balance the charges, we need two bromine ions to neutralize one magnesium ion, resulting in the formula MgBr₂.

For molecular compounds, we utilize the valencies of the atoms to determine how they combine. Carbon dioxide (CO₂) is formed by one carbon atom that can form four bonds and two oxygen atoms, each needing to share two electrons. The subscript '2' after oxygen indicates that two oxygen atoms are covalently bonded to one carbon atom. It's crucial to understand that while the charges must balance in ionic compounds, the number of electrons shared in molecular compounds must produce a stable electronic configuration in each of the bonded atoms.