NYU CHEM-UA 125 Chapters 1-4

Midterm

accuracy

The closeness of a measurement to the actual value.

base unit

A unit that defines the standard for one of the seven physical quantities in the SI system.

calibration

The process of correcting for systematic error of a measuring device by comparing it to a known standard.

Celsius scale

A temperature scale where water freezes at 0°C and boils at 100°C.

chemical change

A change in which substances are converted into new substances with different composition and properties.

chemical property

A characteristic that appears as a substance interacts with or transforms into other substances.

chemistry

The study of matter, its properties, changes, and the energy associated with those changes.

combustion

The process of burning in air, often with heat and light release.

composition

The types and amounts of simpler substances that make up a sample of matter.

controlled experiment

An experiment that measures the effect of one variable at a time by keeping others constant.

conversion factor

A ratio of equivalent quantities equal to 1 used to express a quantity in different units.

cubic meter (m³)

The derived SI unit of volume.

data

Pieces of quantitative information obtained by observation.

density (d)

Mass per unit volume (d = m/V). An intensive property.

derived unit

A combination of SI base units.

dimensional analysis

A calculation method using unit cancellation to ensure dimensional consistency.

energy

The ability to do work or move matter.

exact number

A number with no uncertainty, often from counting or defined quantities.

experiment

A set of procedural steps testing a hypothesis.

extensive property

A property that depends on the amount of substance (e.g., mass).

gas

A state of matter that fills its container completely.

heat (q)

Energy transferred between objects due to temperature difference.

hypothesis

A testable explanation for an observation.

intensive property

A property independent of the amount of substance (e.g., density).

Kelvin scale

Temperature scale with 0 K as absolute zero.

kelvin (K)

The SI base unit of temperature.

kilogram (kg)

The SI base unit of mass.

kinetic energy (Ek)

Energy of motion.

liquid

A state of matter with definite volume but variable shape.

liter (L)

A non-SI unit of volume equal to 1 dm³ or 0.001 m³.

mass

The quantity of matter in an object.

matter

Anything with mass and volume.

meter (m)

The SI base unit of length.

milliliter (mL)

A volume equal to 1 cm³ or 0.001 L.

model

A simplified explanation of a natural phenomenon.

natural law

A summary of universal observations, often mathematical.

observation

Information obtained using the senses or instruments.

physical change

A change in physical form but not composition.

physical property

A characteristic observed without changing composition.

potential energy (Ep)

Energy due to position or composition.

precision

Closeness of repeated measurements.

property

A characteristic that defines a substance.

random error

Error causing measurements to vary randomly around the true value.

round off

Adjusting digits to match significant figure rules.

scientific method

A process of testing and refining explanations for natural phenomena.

second (s)

The SI base unit of time.

SI unit

A unit based on the Système International d'Unités.

significant figures

Digits that show the certainty of a measurement.

solid

A state of matter with fixed shape and volume.

state of matter

Solid, liquid, or gas.

systematic error

Consistent deviation from the true value due to equipment or method flaw.

temperature (T)

A measure of average kinetic energy of particles.

thermometer

A device for measuring temperature.

uncertainty

The estimated amount by which a measurement differs from the true value.

variable

A quantity that can take more than one value.

volume (V)

The amount of space a substance occupies.

weight

The gravitational force acting on an object.

anion

A negatively charged ion.

aqueous solution

A solution where water is the solvent.

atom

The smallest unit of an element retaining its properties.

atomic mass

Weighted average mass of all isotopes of an element.

atomic mass unit (amu)

1/12 the mass of a carbon-12 atom.

atomic number (Z)

The number of protons in an atom's nucleus.

atomic symbol

One- or two-letter abbreviation of an element.

binary covalent compound

Compound of two nonmetals sharing electrons.

binary ionic compound

Compound of two elements with opposite charges.

cathode ray

Stream of electrons emitted by the cathode in a discharge tube.

cation

A positively charged ion.

chemical bond

The force holding atoms together in a compound.

chemical formula

Notation showing element symbols and subscripts for atom ratios.

chromatography

Technique separating components based on adsorption or solubility differences.

compound

A substance composed of two or more elements chemically combined in fixed ratios.

covalent bond

Bond formed by electron sharing between atoms.

covalent compound

Compound held together by covalent bonds.

crystallization

Separation technique forming solid crystals from a solution.

dalton (Da)

Same as atomic mass unit (amu).

distillation

Separation by vaporization and condensation based on volatility.

electron (e−)

A subatomic particle with negative charge.

element

A pure substance that cannot be broken down by chemical means.

filtration

Separation based on particle size.

formula mass

Sum of atomic masses in a formula unit.

formula unit

The smallest ratio of ions in an ionic compound.

fraction by mass

Mass of element ÷ mass of compound.

group

Vertical column in the periodic table.

heterogeneous mixture

Mixture with visible boundaries between components.

homogeneous mixture

Mixture with uniform composition throughout.

hydrate

Compound containing water molecules within its structure.

ion

A charged atom or group of atoms.

ionic compound

Compound made of oppositely charged ions.

isotopes

Atoms of the same element with different neutron numbers.

isotopic mass

Mass of a specific isotope relative to carbon-12.

law of definite composition

A compound has the same elements in the same proportions by mass.

law of mass conservation

Total mass remains constant during a chemical reaction.

law of multiple proportions

Element masses combine in small whole-number ratios.

mass number (A)

Total number of protons and neutrons in an atom.

mass spectrometry

Method to determine relative masses of particles by mass/charge ratio.

metal

Shiny, malleable conductor that tends to lose electrons.

metalloid

Element with properties between metals and nonmetals.

mixture

Physical combination of two or more substances.

molecular mass

Sum of atomic masses in a molecule.