FTCE Chemistry 6-12 key terms

A cyclical process of asking questions, forming testable hypotheses, designing controlled experiments, collecting and analyzing data, and revising explanations based on evidence rather than authority or intuition alone.

A tentative, falsifiable statement predicting a relationship between variables that can be tested by observation or experiment; it must be worded so that data could potentially disprove it.

A procedure in which all variables except the one being tested are held constant, often including a comparison group receiving no treatment, so observed effects can be attributed to the manipulated variable.

The factor deliberately changed or selected by the experimenter in a study; it is plotted on the x-axis and its effect on the measured outcome is what the investigation seeks to determine.

The measured response in an experiment that is expected to change as a result of manipulating the independent variable; it is plotted on the y-axis and recorded as data.

The comparison set in an experiment that does not receive the treatment under study, providing a baseline against which the treated group's results are judged for significance.

A broad, well-tested explanation supported by extensive converging evidence that accounts for many observations and predicts new ones; in science it is stronger than a hypothesis, not weaker.

A concise statement, often mathematical, describing a consistent regularity observed in nature under specified conditions, such as conservation of mass, without necessarily explaining why the pattern occurs.

The digits in a measurement that carry meaningful information about its precision, including all certain digits plus one estimated digit; rules govern how they are counted and retained in calculations.

Precision describes how closely repeated measurements agree with one another, while accuracy describes how close a measurement is to the accepted true value; a set can be precise yet inaccurate.

A measure of accuracy calculated as the absolute difference between an experimental value and an accepted value, divided by the accepted value, then multiplied by 100 to give a percentage.

Unpredictable variation in measurements caused by uncontrollable factors such as fluctuations in instrument response or human estimation; it affects precision and can be reduced by averaging repeated trials.

A consistent, repeatable deviation in one direction caused by faulty calibration, biased technique, or flawed instrument design; it shifts all results and is not reduced by averaging trials.

A problem-solving technique that tracks units through calculations, multiplying by conversion factors equal to one so that unwanted units cancel and the answer carries the desired unit.

The process by which independent experts evaluate a study's methods, analysis, and conclusions before publication, helping to screen out flawed or unsupported work from the scientific literature.

An inert or inactive treatment given to a comparison group in clinical or behavioral research so that participants' expectations are matched, isolating the effect of the active treatment being tested.

Anything that has mass and occupies volume, existing as solids, liquids, gases, and plasmas; it is composed of atoms and can be classified as pure substances or mixtures.

A form of matter with a fixed, definite composition and uniform properties throughout, either an element made of one kind of atom or a compound made of chemically bonded elements.

A pure substance consisting of only one kind of atom, defined by its atomic number, that cannot be broken down into simpler substances by ordinary chemical means.

A pure substance formed when two or more different elements combine chemically in a fixed mass ratio, with properties distinct from those of its constituent elements.

A physical combination of two or more substances that retain their individual identities and can be separated by physical means; it may be homogeneous or heterogeneous in composition.

A transformation that alters a substance's form, state, or appearance without changing its chemical identity, such as melting, dissolving, or grinding; the original substance can usually be recovered.

A transformation in which one or more substances are converted into new substances with different compositions and properties, typically accompanied by energy change and evidence such as gas, precipitate, or color change.

The principle that mass is neither created nor destroyed in a chemical reaction; the total mass of reactants equals the total mass of products, which is why chemical equations must be balanced.

The number of protons in an atom's nucleus, which uniquely identifies the element and determines its position in the periodic table; in a neutral atom it equals the electron count.

The sum of protons and neutrons in an atom's nucleus, expressed as a whole number; atoms of the same element with different mass numbers are isotopes.

One of two or more atoms of the same element that have identical proton counts but different neutron counts, and therefore different mass numbers and slightly different atomic masses.

The weighted mean mass of an element's naturally occurring isotopes, calculated from each isotope's abundance and mass, reported in atomic mass units and shown on the periodic table.

An arrangement of elements in order of increasing atomic number, organized into groups with similar valence-electron configurations and periods whose length reflects filling of electron shells.

A predictable, repeating variation in a property such as atomic radius, ionization energy, or electronegativity across a period or down a group, explained largely by effective nuclear charge and shielding.

A relative measure of an atom's ability to attract shared electrons in a bond; it generally increases across a period and decreases down a group, and differences in it predict bond polarity.

The minimum energy required to remove an electron from a gaseous atom or ion; it increases across a period and decreases down a group, with large jumps after noble-gas configurations are reached.

The SI amount-of-substance unit equal to 6.022 x 10^23 representative particles, chosen so that one mole of a substance has a mass in grams numerically equal to its formula mass.

The mass of one mole of a substance in grams per mole, obtained by summing the atomic masses of all atoms in its chemical formula; it converts between mass and moles.

The quantitative relationship among reactants and products in a balanced equation, used to convert amounts of one substance into amounts of another through mole ratios.

The ratio of coefficients for two substances in a balanced chemical equation, serving as the conversion factor that links moles of one substance to moles of another in stoichiometric calculations.

The reactant that is completely consumed first in a reaction, determining the maximum amount of product that can form; other reactants are present in excess.

The maximum mass or amount of product calculated from stoichiometry when the limiting reactant is fully consumed, assuming complete reaction and no losses.

The ratio of actual experimental yield to theoretical yield, multiplied by 100, expressing how efficiently a reaction produced the expected product; values below 100 indicate losses or side reactions.