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Step-by-Step Guidance for Sample Midterm 2 (GOB Chemistry)

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Q1. Bismuth-213 decays through alpha emission with a half-life of 46 minutes. Determine the number of half-lives in each case as whole number values.

Background

Topic: Radioactive Decay and Half-Life

This question tests your understanding of half-life and how to calculate the number of half-lives that have passed over a given time period.

Key Terms and Formulas:

  • Half-life (): The time required for half of a radioactive sample to decay.

  • Number of half-lives ():

Step-by-Step Guidance

  1. Identify the half-life of Bismuth-213: minutes.

  2. For each time period (e.g., 92 minutes, 276 minutes), divide the total time by the half-life to find the number of half-lives: .

  3. Round your answer to the nearest whole number, as requested.

Try solving on your own before revealing the answer!

Q2. Identify each compound as covalent or ionic.

Background

Topic: Types of Chemical Bonds

This question tests your ability to distinguish between covalent and ionic compounds based on their composition.

Key Terms:

  • Covalent compound: Formed by sharing electrons between nonmetals.

  • Ionic compound: Formed by transfer of electrons from a metal to a nonmetal.

Step-by-Step Guidance

  1. Look at the elements in each compound. If the compound contains a metal and a nonmetal, it is likely ionic. If it contains only nonmetals, it is likely covalent.

  2. Recall common metals (e.g., Mg, Cs) and nonmetals (e.g., C, H, O, Cl).

  3. Classify each compound accordingly.

Try solving on your own before revealing the answer!

Q3. Enter the element symbol and electric charge on each ion described here.

Background

Topic: Ions and Their Charges

This question tests your understanding of how to determine the symbol and charge of an ion based on the number of protons and electrons.

Key Terms and Formulas:

  • Protons determine the element (atomic number).

  • Charge = number of protons - number of electrons.

  • Ion symbol: Element symbol with charge as superscript (e.g., ).

Step-by-Step Guidance

  1. Identify the element by the number of protons (use the periodic table).

  2. Calculate the charge: .

  3. Write the element symbol with the correct charge.

Try solving on your own before revealing the answer!

Q4. Write formulas for the ionic compound formed from the following pairs of elements.

Background

Topic: Writing Ionic Compound Formulas

This question tests your ability to write correct formulas for ionic compounds formed from given elements.

Key Terms:

  • Cation: Positively charged ion (usually a metal).

  • Anion: Negatively charged ion (usually a nonmetal).

  • Balance charges to ensure the compound is neutral.

Step-by-Step Guidance

  1. Determine the charge of each ion using the periodic table.

  2. Balance the charges so the total positive and negative charges are equal.

  3. Write the formula using subscripts to indicate the number of each ion needed.

Try solving on your own before revealing the answer!

Q5. Write the correct name for each of the ionic compounds.

Background

Topic: Naming Ionic Compounds

This question tests your ability to name ionic compounds, including those with transition metals.

Key Terms:

  • For transition metals, indicate the charge with Roman numerals.

  • Name the cation first, then the anion (ending in -ide for simple anions).

Step-by-Step Guidance

  1. Identify the cation and its charge (especially for transition metals).

  2. Name the anion, changing the ending to -ide if it is a simple ion.

  3. Combine the names, using Roman numerals for transition metals as needed.

Try solving on your own before revealing the answer!

Q6. Write formulas for these ionic compounds.

Background

Topic: Writing Formulas for Ionic Compounds with Polyatomic Ions

This question tests your ability to write correct formulas for ionic compounds, including those with polyatomic ions.

Key Terms:

  • Polyatomic ion: An ion composed of more than one atom (e.g., sulfate ).

  • Use parentheses if more than one polyatomic ion is needed.

Step-by-Step Guidance

  1. Determine the formula and charge of each ion (use a polyatomic ion table if needed).

  2. Balance the charges to make the compound neutral.

  3. Write the formula, using parentheses for multiple polyatomic ions.

Try solving on your own before revealing the answer!

Q7. In a molecule composed of covalently bonded atoms, ________.

Background

Topic: Covalent Bonding

This question tests your understanding of the nature of covalent bonds and which types of atoms form them.

Key Terms:

  • Covalent bond: A bond formed by sharing electrons between nonmetal atoms.

Step-by-Step Guidance

  1. Recall that covalent bonds typically form between nonmetal atoms.

  2. Consider whether the bond involves sharing or transfer of electrons.

  3. Choose the statement that best describes covalent bonding.

Try solving on your own before revealing the answer!

Q8. How many covalent bonds and lone pairs does each element typically have?

Background

Topic: Lewis Structures and Valence Electrons

This question tests your knowledge of how many bonds and lone pairs are typical for certain elements based on their position in the periodic table.

Key Terms:

  • Valence electrons: Electrons in the outermost shell.

  • Lone pairs: Pairs of valence electrons not involved in bonding.

Step-by-Step Guidance

  1. Determine the number of valence electrons for each element (use the periodic table).

  2. Recall the typical bonding patterns for each element (e.g., oxygen usually forms 2 bonds and has 2 lone pairs).

  3. Fill in the number of bonds and lone pairs for each element.

Try solving on your own before revealing the answer!

Q9. Draw the Lewis structure for each molecule, including lone pairs of electrons.

Background

Topic: Lewis Structures

This question tests your ability to draw Lewis structures, showing all valence electrons as either bonds or lone pairs.

Key Terms:

  • Lewis structure: Diagram showing the arrangement of valence electrons around atoms in a molecule.

  • Lone pairs: Non-bonding pairs of electrons.

Step-by-Step Guidance

  1. Count the total number of valence electrons for the molecule.

  2. Arrange the atoms, usually with the least electronegative atom in the center.

  3. Distribute electrons to form bonds and satisfy the octet rule, adding lone pairs as needed.

Try solving on your own before revealing the answer!

Q10. Predict the shape of the following molecules.

Background

Topic: Molecular Geometry (VSEPR Theory)

This question tests your ability to predict molecular shapes using the Valence Shell Electron Pair Repulsion (VSEPR) theory.

Key Terms:

  • VSEPR theory: Predicts the shape of molecules based on electron pair repulsion.

  • Common shapes: linear, trigonal planar, tetrahedral, bent, pyramidal.

Step-by-Step Guidance

  1. Draw the Lewis structure for each molecule.

  2. Count the number of bonding pairs and lone pairs on the central atom.

  3. Use VSEPR theory to determine the molecular shape based on these counts.

Try solving on your own before revealing the answer!

Q11. Name each of the following molecular compounds.

Background

Topic: Naming Molecular (Covalent) Compounds

This question tests your ability to name covalent compounds using prefixes to indicate the number of each atom.

Key Terms:

  • Prefixes: mono-, di-, tri-, tetra-, etc.

  • Name the more metallic element first, then the second element with an -ide ending.

Step-by-Step Guidance

  1. Identify the number of each type of atom in the formula.

  2. Apply the appropriate prefix to each element (except mono- is often omitted for the first element).

  3. Write the name, ending the second element with -ide.

Try solving on your own before revealing the answer!

Q12. Write the formula for each of the following molecular compounds.

Background

Topic: Writing Formulas for Molecular Compounds

This question tests your ability to translate compound names into chemical formulas using prefixes.

Key Terms:

  • Prefixes indicate the number of each atom: di- (2), tri- (3), tetra- (4), etc.

  • Write the element symbols in the order given in the name, using subscripts for numbers greater than one.

Step-by-Step Guidance

  1. Identify the elements and the number of each from the name and prefixes.

  2. Write the correct element symbols in order.

  3. Add subscripts to indicate the number of each atom (omit subscript 1).

Try solving on your own before revealing the answer!

Q13. Select the more polar covalent bond in each pair.

Background

Topic: Bond Polarity and Electronegativity

This question tests your understanding of how differences in electronegativity between atoms affect bond polarity.

Key Terms:

  • Electronegativity: The tendency of an atom to attract electrons in a bond.

  • Greater difference in electronegativity = more polar bond.

Step-by-Step Guidance

  1. Look up or recall the electronegativity values for each atom in the bonds.

  2. Calculate the difference in electronegativity for each bond in the pair.

  3. The bond with the greater difference is more polar.

Try solving on your own before revealing the answer!

Q14. Draw the Lewis dot structures of the following molecules and determine if each is polar or nonpolar.

Background

Topic: Molecular Polarity and Lewis Structures

This question tests your ability to draw Lewis structures and use them to determine molecular polarity.

Key Terms:

  • Polar molecule: Has an uneven distribution of electron density, resulting in a dipole moment.

  • Nonpolar molecule: Electron density is evenly distributed.

Step-by-Step Guidance

  1. Draw the Lewis structure for each molecule, showing all bonds and lone pairs.

  2. Assess the symmetry of the molecule and the electronegativity of the atoms.

  3. Determine if the molecule has a net dipole moment (polar) or not (nonpolar).

Try solving on your own before revealing the answer!

Q15. For each compound shown, identify the major type of intermolecular forces experienced between molecules identical to itself.

Background

Topic: Intermolecular Forces

This question tests your understanding of the different types of intermolecular forces (IMFs) present in various compounds.

Key Terms:

  • Types of IMFs: ion-ion, ion-dipole, hydrogen bonding, dipole-dipole, London dispersion forces.

  • Hydrogen bonding occurs when H is bonded to N, O, or F.

Step-by-Step Guidance

  1. Determine if the compound is ionic or molecular.

  2. For molecular compounds, check for hydrogen bonding (H with N, O, or F).

  3. If not, check for dipole-dipole or London dispersion forces.

  4. For ionic compounds, the major force is ion-ion attraction.

Try solving on your own before revealing the answer!

Q16. Balance the reaction by adding the necessary coefficients.

Background

Topic: Balancing Chemical Equations

This question tests your ability to balance a chemical equation by ensuring the same number of each type of atom on both sides.

Key Terms:

  • Coefficient: Number placed in front of a formula to indicate the number of units.

  • Law of Conservation of Mass: Atoms are neither created nor destroyed in a chemical reaction.

Step-by-Step Guidance

  1. Write down the number of each atom on both sides of the equation.

  2. Adjust coefficients to balance one element at a time, starting with metals, then nonmetals, and finally hydrogen and oxygen.

  3. Check your work to ensure all atoms are balanced.

Try solving on your own before revealing the answer!

Q17. Identify reaction type

Background

Topic: Types of Chemical Reactions

This question tests your ability to classify reactions as combination, decomposition, single replacement, or double replacement.

Key Terms:

  • Combination: Two or more reactants form one product.

  • Decomposition: One reactant breaks into two or more products.

  • Single replacement: One element replaces another in a compound.

  • Double replacement: Two compounds exchange ions.

Step-by-Step Guidance

  1. Analyze the reactants and products to see how atoms are rearranged.

  2. Match the pattern to one of the four reaction types.

  3. Assign the correct reaction type to each equation.

Try solving on your own before revealing the answer!

Q18. Identify the charge of the ions formed when elements from the following Groups react.

Background

Topic: Predicting Ion Charges from the Periodic Table

This question tests your ability to predict the charge of ions formed by main group elements based on their group number.

Key Terms:

  • Group 1A (1): Forms ions.

  • Group 2A (2): Forms ions.

  • Group 6A (16): Forms ions.

  • Group 7A (17): Forms ions.

Step-by-Step Guidance

  1. Recall the group number and typical charge for each group.

  2. Write the charge as a number followed by a plus or minus sign (e.g., 2+ or 1-).

  3. Enter the correct charge for each group.

Try solving on your own before revealing the answer!

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