MA High School Chemistry Module 2 bonding and molecular structure: a complete overview of ionic, covalent, and metallic bonding, nomenclature, molecular shape, polarity, and intermolecular forces

What Module 2 actually demands

Module 2 explains why substances behave the way they do, by linking the bonding between particles to the properties you can measure. Under the Massachusetts STE framework this is HS-PS1-2 (explaining reactions from electron states), HS-PS1-3 (structure and the forces between particles), and the Massachusetts materials standard HS-PS2-6(MA). The thread running through every topic is structure determines properties: the same idea that Module 1 set up with valence electrons now explains melting points, conductivity, hardness, and solubility.

This guide ties together the matching dot-point pages, each with its own practice questions: ionic and covalent bonding, metallic bonding and material properties, chemical names and formulas, molecular geometry and polarity, and intermolecular forces and physical properties.

The three types of bonding

Atoms bond to reach a full outer shell. Ionic bonding transfers electrons from a metal to a nonmetal, making oppositely charged ions that lock into a giant lattice. Covalent bonding shares electrons between two nonmetals, usually making discrete molecules. Metallic bonding is a lattice of metal cations in a sea of delocalised electrons. Predict the type from the elements: metal plus nonmetal gives ionic, nonmetal plus nonmetal gives covalent, metal plus metal gives metallic. Each bond type leads to a characteristic set of properties.

Naming and writing formulas

An ionic formula has no overall charge, so the positive and negative charges must balance; the crossing-over shortcut sets the subscripts, and polyatomic ions (nitrate, sulfate, hydroxide, ammonium) stay together, with brackets if more than one is needed. Name ionic compounds as metal then nonmetal with an -ide ending, using Roman numerals for multivalent metals like iron(II) and iron(III). Name covalent compounds with Greek prefixes (mono, di, tri) because two nonmetals can combine in several ratios. Getting the formula right is the prerequisite for every calculation in Module 3.

Metals, alloys, and designed materials

Metallic bonding explains why metals conduct (mobile electrons), bend (sliding layers held by the electron sea), and shine. Alloys mix in different-sized atoms to disrupt the layers, making a harder material like steel. The broader Massachusetts standard generalizes this: a material's bulk properties follow from its molecular-level structure, so a flexible polymer, a brittle ceramic, and a conductive metal each suit different jobs. Engineers choose a material by matching its structure to the required function.

Molecular shape and polarity

Electron pairs around a central atom repel and spread out, setting the shape: two groups give linear, three give trigonal planar, four give tetrahedral, and lone pairs bend the shape (water is bent, ammonia is pyramidal). A bond is polar when the atoms differ in electronegativity. A whole molecule is polar only if the bond polarities do not cancel, which depends on the shape: symmetrical molecules like carbon dioxide are nonpolar, while bent water is polar. Polarity then predicts solubility and the strength of intermolecular forces.

Intermolecular forces and properties

The forces between particles set the bulk properties. From weakest to strongest: London dispersion forces (all molecules), dipole-dipole forces (polar molecules), and hydrogen bonding (H bonded to N, O, or F). These are far weaker than the bonds within ionic lattices and covalent networks. Stronger forces mean higher melting and boiling points. "Like dissolves like": polar and ionic substances dissolve in polar water, nonpolar substances in nonpolar solvents. Given an unknown's melting point, conductivity, and hardness, you can infer whether it is ionic, molecular, covalent network, or metallic.

Check your knowledge

A mix of recall and application questions covering Module 2. Attempt them under timed conditions, then check against the solutions.

1. State what happens to electrons in an ionic bond and in a covalent bond. (2 marks)
2. Predict the bond type in a compound of magnesium and chlorine, and explain. (2 marks)
3. Write the formula for aluminum oxide from the ions $\text{Al}^{3+}$ and $\text{O}^{2-}$. (1 mark)
4. Name the compound $\text{N}_2\text{O}_5$. (1 mark)
5. Explain why metals conduct electricity. (2 marks)
6. Explain why steel is harder than pure iron. (2 marks)
7. State the shape of a molecule with four bonding pairs and no lone pairs. (1 mark)
8. Explain why water is polar but carbon dioxide is not. (2 marks)
9. Name the strongest intermolecular force in water and explain its effect on the boiling point. (2 marks)
10. A solid melts above $1000\,^{\circ}\text{C}$, is very hard, and does not conduct in any state. Identify its structure type. (2 marks)