Principles of Chemistry Unit 1 Exam

What is chemistry?

The study of the composition, properties, and interactions of matter.

Why is chemistry called the central science?

It connects physics, biology, medicine, materials science, environmental science, and more.

What is the scientific method?

A process involving hypothesis, experiments, laws, and theories to explain natural phenomena.

Difference between hypothesis, law, and theory?

Hypothesis: tentative explanation. Law: summarizes observations. Theory: tested, well-substantiated explanation.

What are the three domains of chemistry?

Macroscopic (visible), microscopic (atoms, molecules), symbolic (formulas, equations).

What are the three states of matter?

Solid (definite shape/volume), liquid (definite volume, takes shape of container), gas (takes both shape and volume).

What is plasma?

A high-energy state of matter with charged particles, found in stars and lightning.

Difference between mass and weight?

Mass = amount of matter (constant). Weight = force of gravity on matter (changes with location).

Law of Conservation of Matter?

Matter cannot be created or destroyed during physical or chemical changes.

What is a pure substance?

Matter with constant composition (elements and compounds).

Difference between homogeneous and heterogeneous mixture?

Homogeneous = uniform composition (solution). Heterogeneous = non-uniform composition.

SI unit of mass?

Kilogram (kg).

SI unit of length?

Meter (m).

SI unit of time?

Second (s).

SI unit of temperature?

Kelvin (K).

SI unit of amount of substance?

Mole (mol).

What is an extensive vs. intensive property?

Extensive depends on amount (mass, volume). Intensive does not (density, boiling point).

Formula for density?

d = m/V.

Rules for sig figs in multiplication/division?

Answer has same number of sig figs as factor with fewest sig figs.

Rules for sig figs in addition/subtraction?

Answer has same number of decimal places as number with fewest decimals.

Convert 90°C to Kelvin.

363 K.

Convert 25°C to Fahrenheit.

77°F.

Who proposed that matter is indivisible atoms?

Leucippus and Democritus (5th century BC).

What did Aristotle believe about matter?

It was composed of four elements: earth, fire, air, water.

Who developed modern atomic theory in 1807?

John Dalton.

Dalton’s postulate about conservation?

Atoms are neither created nor destroyed in chemical reactions.

What is the law of definite proportions?

All samples of a compound have the same element ratios by mass.

What is the law of multiple proportions?

When two elements form multiple compounds, their mass ratios form small whole numbers.

Who discovered the electron?

J.J. Thomson with cathode ray tubes.

What did Millikan’s oil drop experiment measure?

The charge of the electron (1.6 × 10^-19 C).

What did Rutherford’s gold foil experiment show?

Atoms have a small, dense, positively charged nucleus.

Who discovered isotopes?

Frederick Soddy.

Who discovered neutrons?

James Chadwick (1932).

What are the three subatomic particles?

Protons (+1, in nucleus), neutrons (0, in nucleus), electrons (-1, outside nucleus).

What is atomic number (Z)?

Number of protons in an atom.

What is mass number (A)?

Protons + neutrons.

What is an isotope?

Atoms of the same element with different neutron numbers.

Formula for average atomic mass?

Σ(isotope mass × fractional abundance).

What does the periodic table arrange elements by?

Increasing atomic number.

Define ion.

An atom or molecule that has gained or lost electrons.

Cation vs Anion?

Cation = positive (lost electrons). Anion = negative (gained electrons).

Which groups are most reactive?

Alkali metals (group 1) and halogens (group 17).

What group is inert?

Noble gases (group 18).

What is Avogadro’s number?

6.022 × 10^23 particles per mole.

Formula for moles?

Moles = mass / molar mass.

Formula for atoms/molecules?

Number = moles × 6.022 × 10^23.

What is molar mass?

Mass of one mole of a substance, in g/mol.

How many atoms in 2 moles of O2?

2 × 6.022 × 10^23 × 2 = 2.41 × 10^24 atoms.

What is percent composition?

Mass percent of each element in a compound.

Formula for empirical formula?

Divide % composition by molar mass of each element, reduce to smallest whole ratio.

Formula for molecular formula?

Molecular formula = (empirical formula) × n, where n = molar mass/empirical mass.

Difference between ionic and covalent bond?

Ionic = transfer of electrons (metal + nonmetal). Covalent = sharing of electrons (nonmetals).

What is bond energy?

The energy required to break one mole of bonds.

What is formula mass?

Sum of atomic masses in a formula unit.

Examples of ionic compounds?

NaCl, MgO.

Examples of covalent compounds?

H2O, CO2, SO2.

How do you name ionic compounds?

Metal + nonmetal with -ide ending (ex: NaCl = sodium chloride).

How do you name covalent compounds?

Use prefixes (mono-, di-, tri-) and -ide ending (ex: CO2 = carbon dioxide).

What is an acid naming rule?

Binary acids: hydro- + nonmetal + -ic acid. Oxyacids: based on polyatomic ion name.