What does CH.1 expect on the Chemistry SOL?

CH.1 is scientific investigation, reasoning and experimental design. You should identify the independent, dependent and controlled variables in an investigation, use a control for comparison, work safely, and report measurements in SI units with the right significant figures. You should also tell accuracy (closeness to the true value) from precision (closeness of repeats), and use hypothesis, theory and law correctly. These skills are tested directly and embedded in content items across the whole test.

How do I count significant figures and use them in calculations?

All nonzero digits count, zeros between nonzero digits count, and trailing zeros after a decimal point count, but leading zeros never do. When multiplying or dividing, keep the fewest significant figures of any factor; when adding or subtracting, keep the fewest decimal places. Round only at the end. Scientific notation, written $a \times 10^{n}$ with $1 \le a < 10$, removes ambiguity for very large or small values.

What defines an element and what defines an isotope?

The atomic number, the number of protons, defines the element. The mass number is protons plus neutrons. Isotopes are atoms of the same element (same protons) with different numbers of neutrons, so they have different mass numbers but the same chemistry. The atomic mass on the periodic table is the weighted average of the isotope masses, each weighted by its natural abundance, which is why it is usually a decimal.

How do the periodic trends run, and why?

Across a period (left to right) atoms get smaller while ionization energy and electronegativity increase, because the nuclear charge rises while electrons fill the same energy level. Down a group (top to bottom) atoms get larger while ionization energy and electronegativity decrease, because each element adds an energy level and the outer electrons are farther out and more shielded. Metals get more reactive down a group; nonmetals get more reactive up a group.

How do I handle nuclear decay and half-life on the SOL?

Alpha decay drops the mass number by 4 and the atomic number by 2; beta decay raises the atomic number by 1 with no mass change; gamma is energy only. Balance a nuclear equation by making the total mass numbers and the total atomic numbers equal on both sides. For half-life, count how many half-lives have passed (total time divided by the half-life), then halve the sample that many times: after $n$ half-lives, $(1/2)^n$ of the original remains.

VirginiaChemistry

Virginia SOL Chemistry scientific investigation and atomic structure: a complete skills guide to experimental design, measurement, the atom, the periodic table and nuclear chemistry

Q: What defines an element and what defines an isotope?

The atomic number, the number of protons, defines the element. The mass number is protons plus neutrons. Isotopes are atoms of the same element (same protons) with different numbers of neutrons, so they have different mass numbers but the same chemistry. The atomic mass on the periodic table is the weighted average of the isotope masses, each weighted by its natural abundance, which is why it is usually a decimal.

Q: How do the periodic trends run, and why?

Across a period (left to right) atoms get smaller while ionization energy and electronegativity increase, because the nuclear charge rises while electrons fill the same energy level. Down a group (top to bottom) atoms get larger while ionization energy and electronegativity decrease, because each element adds an energy level and the outer electrons are farther out and more shielded. Metals get more reactive down a group; nonmetals get more reactive up a group.

Q: How do I handle nuclear decay and half-life on the SOL?

Alpha decay drops the mass number by 4 and the atomic number by 2; beta decay raises the atomic number by 1 with no mass change; gamma is energy only. Balance a nuclear equation by making the total mass numbers and the total atomic numbers equal on both sides. For half-life, count how many half-lives have passed (total time divided by the half-life), then halve the sample that many times: after $n$ half-lives, $(1/2)^n$ of the original remains.

A deep-dive Virginia SOL Chemistry guide to scientific investigation and atomic structure (CH.1 and CH.2): variables and fair tests, accuracy and precision, significant figures and dimensional analysis, the subatomic particles, isotopes and average atomic mass, electron configuration, the periodic table and its trends, and nuclear decay and half-life, with SOL exam technique.

Generated by Claude Opus 4.817 min readCH.1-CH.2Updated 2026-06-13

Reviewed by: AI editorial process; not yet individually human-reviewed

Jump to a section

Why this reporting category anchors the whole test
Designing a fair test (CH.1)
Measurement and the math of chemistry (CH.1)
The atom and its electrons (CH.2)
The periodic table and its trends (CH.2)
Nuclear chemistry (CH.2)
Check your knowledge

Why this reporting category anchors the whole test

The first SOL reporting category, Scientific Investigation, Atomic Structure and the Periodic Table, combines the scientific-method skills of CH.1 with the atomic-theory content of CH.2. It matters out of proportion to its size: the investigation skills (reading data, judging accuracy, handling units) are tested everywhere on the exam, and atomic structure underpins bonding, the mole and reactions. This guide ties together the matching dot-point pages, each with its own practice: scientific investigation and experimental design, measurement, significant figures and dimensional analysis, structure of the atom, isotopes and average atomic mass, electron configuration and energy levels, the periodic table and periodic trends, and nuclear chemistry and radioactivity.

Designing a fair test (CH.1)

A fair investigation changes one independent variable, measures the dependent variable that responds, and holds every other factor constant as a controlled variable, with a control group for a baseline. Accuracy is closeness to the true value; precision is closeness of repeats. A systematic error (a mis-calibrated balance) hurts accuracy; random scatter hurts precision and is reduced by averaging more trials. Keep the words straight: a hypothesis is a testable proposed explanation, a theory is a broad evidence-backed explanation, and a law describes a consistent pattern, often as an equation.

Measurement and the math of chemistry (CH.1)

Report in SI units and use significant figures honestly:

d = \frac{m}{V}, \qquad \text{percent error} = \left|\frac{\text{measured} - \text{accepted}}{\text{accepted}}\right| \times 100

Convert units by dimensional analysis, arranging conversion factors so unwanted units cancel. If the units do not cancel to the target, a factor is upside down. Count significant figures by the rules (leading zeros never count; trailing zeros after a decimal do), and round at the end.

The atom and its electrons (CH.2)

The nucleus holds protons (charge $+1$ ) and neutrons (neutral); electrons (charge $-1$ ) occupy energy levels around it. The atomic number (protons) defines the element; the mass number is protons plus neutrons; neutrons $= A - Z$ . Isotopes share the proton count but differ in neutrons, so the periodic-table mass is a weighted average:

\text{average atomic mass} = \sum_i (\text{isotope mass}_i \times \text{fractional abundance}_i)

Electrons fill energy levels from the lowest up; the valence electrons in the outermost level drive bonding. Absorbing energy excites an electron, and it emits a photon of a specific color when it falls back, producing a bright-line spectrum, the historic evidence for quantized energy levels.

The periodic table and its trends (CH.2)

The table is ordered by atomic number into groups (same valence electrons, similar properties) and periods (filling a new energy level), with metals on the left, nonmetals on the upper right and metalloids on the staircase. The trends:

Property	Across a period (left to right)	Down a group (top to bottom)
Atomic radius	decreases	increases
Ionization energy	increases	decreases
Electronegativity	increases	decreases
Metal reactivity	decreases	increases

Each trend comes from two ideas: nuclear charge rising across a period, and added energy levels with more shielding down a group.

Nuclear chemistry (CH.2)

Alpha decay emits a helium nucleus (mass $-4$ , atomic number $-2$ ); beta decay emits an electron (atomic number $+1$ , mass unchanged); gamma is energy only. Balance nuclear equations by conserving total mass number and total atomic number. Fission splits a heavy nucleus, fusion joins light nuclei (the Sun). Half-life is the time for half a sample to decay; after $n$ half-lives, $(1/2)^n$ remains.

A combined atomic-structure problem

An element X has two isotopes, X-63 (mass $62.93$ u, $69.2\%$ ) and X-65 (mass $64.93$ u, $30.8\%$ ). (a) Find the average atomic mass. (b) Using the periodic table, identify the element. (c) State its number of valence electrons.

step 1 Weighted average

$(62.93)(0.692) + (64.93)(0.308) = 43.55 + 20.00 = 63.55$ u.

step 2 Identify from the periodic table

An average atomic mass of about $63.55$ matches copper (atomic number $29$ ).

step 3 Valence electrons

Copper is a transition metal; its outermost principal level ( $4s$ ) holds the valence electrons it loses in bonding, so it commonly forms $+1$ and $+2$ ions.

step 4 Sense-check

The average lies near $63$ rather than midway between $63$ and $65$ , because X-63 is the more abundant isotope, so the result is reasonable.

A fair test changes one independent variable, measures the dependent variable, and controls the rest; accuracy is closeness to the true value and precision is closeness of repeats. Use SI units, significant figures (leading zeros never count) and dimensional analysis, with $d = m/V$ and percent error $= |\text{measured} - \text{accepted}|/\text{accepted} \times 100$ . The atomic number (protons) defines the element, the mass number is protons plus neutrons, and isotopes differ only in neutrons, so the periodic-table mass is a weighted average of the isotopes. Electrons fill energy levels from the lowest up, and valence electrons drive chemistry. Across a period atoms shrink while ionization energy and electronegativity rise; down a group atoms grow while those fall. Alpha decay loses 4 and 2 from the mass and atomic numbers, beta raises the atomic number by 1, and after $n$ half-lives $(1/2)^n$ of a sample remains.

Check your knowledge

Attempt these under timed conditions, then check the solutions.

A student tests how temperature affects reaction rate. Name the independent and dependent variables. (2 marks)
How many significant figures are in $0.003050$ ? (1 mark)
An atom has $20$ protons, $20$ neutrons and $20$ electrons. State its mass number and whether it is neutral. (2 marks)
Bromine-79 (mass $78.92$ u, $50.7\%$ ) and bromine-81 (mass $80.92$ u, $49.3\%$ ) are the isotopes of bromine. Calculate the average atomic mass. (2 marks)
State the trend in atomic radius across Period 3 and explain it. (2 marks)
An isotope with a half-life of $10$ days starts at $80$ g. How much remains after $30$ days? (2 marks)

Solutions

Q1: Independent: the temperature. Dependent: the reaction rate (or amount of product per unit time).
Q2: Four significant figures (the 3, the 0 between, the 5, and the trailing 0 after the decimal; the leading zeros do not count).
Q3: Mass number $= 20 + 20 = 40$ ; it is neutral because protons equal electrons ( $20$ each). The element is calcium.
Q4: $(78.92)(0.507) + (80.92)(0.493) = 40.01 + 39.89 = 79.9$ u.
Q5: Atomic radius decreases across Period 3, because the nuclear charge increases while electrons fill the same energy level, pulling the electron cloud inward.
Q6: $30$ days is three half-lives, so $80 \rightarrow 40 \rightarrow 20 \rightarrow 10$ g; $10$ g remains.

Sources & how we know this

2018 Science Standards of Learning - Chemistry — Virginia Department of Education (2018)
Chemistry Curriculum Framework — Virginia Department of Education (2018)