Unit 18 & Unit 1 Chemistry: Atomic Structure & Measurement Vocabulary

A set of vocabulary flashcards covering subatomic particles, isotopes, radioactive decay, key scientists, sig figs, and basic measurement concepts from the notes.

Proton

Positively charged subatomic particle located in the nucleus; mass ~1 amu.

Neutron

Electrically neutral subatomic particle located in the nucleus; mass ~1 amu.

Electron

Negatively charged subatomic particle orbiting the nucleus; mass ~1/1836 amu.

Atomic number

Number of protons in the nucleus; identifies the element.

Mass number

Total number of protons and neutrons in the nucleus (A).

Isotope

Atoms of the same element (same protons) with different numbers of neutrons.

Neutral atom

An atom with equal numbers of protons and electrons; overall charge is zero.

Average atomic mass

Weighted average of the masses of an element's isotopes; on the periodic table.

Fractional abundance

Proportion of a particular isotope relative to the total isotopic population.

Atomic mass unit (AMU)

Unit used to express atomic masses; defined relative to carbon-12.

Most abundant isotope

The isotope with the largest natural abundance; largely determines the element’s average mass.

Radioactive decay

Spontaneous process by which an unstable nucleus loses energy by emitting particles or radiation.

Alpha decay

Emission of an alpha particle (2 protons + 2 neutrons); reduces Z by 2 and A by 4.

Beta decay

Emission of a beta particle; beta-minus converts a neutron to a proton (Z +1); beta-plus (positron) changes Z by -1.

Gamma emission

Emission of high-energy photons; no change in Z or A.

Plum pudding model

Early atomic model by Thomson describing electrons embedded in a positively charged sphere.

Democritus

Ancient philosopher who proposed that matter is composed of indivisible atoms.

John Dalton

Formulated Modern Atomic Theory; atoms are the basic units and combine to form compounds.

Sir William Crookes

Invented the Crookes Tube; studied cathode rays in vacuum.

J. J. Thomson

Discovered the electron through cathode ray experiments; proposed the plum pudding model.

Millikan

Oil drop experiment; measured the charge of the electron.

Rutherford

Gold foil experiment; discovered the atomic nucleus and protons; disproved the plum pudding model.

Chadwick

Discovered the neutron and contributed to understanding nuclear structure.

Significant figures (sig figs)

Rules for rounding measurements: for multiplication/division, round to the least number of sig figs; for addition/subtraction, round to the least precise decimal place.

Percent error

(|experimental − accepted| / accepted) × 100%; measures experimental accuracy.

Absolute value

The nonnegative value of a number, disregarding sign.

Accuracy

Closeness of a measurement to the true value.

Precision

Closeness of repeated measurements to each other.

Density

Mass per unit volume (density = mass/volume).

Mass

Quantity of matter in an object; commonly measured in grams.

Volume

Amount of space an object or substance occupies (mL or cm^3 in lab).

Oil drop experiment

Millikan’s experiment that determined the charge of the electron and its mass relationship.

JJ Thomson

Who made the plum pudding model

Crookes tube

A vacuum tube used to study cathode rays and electron behavior.

Nucleus

Where is the neutron located?

Nucleus

Where is the proton located?

Electron cloud

Where is the electron located?

Protons and electrons

Atomic number=

Neutrons and protons

Mass number=

Positive and neutral charges

Why are the nuclei of all atoms positively charged?

Average mass of all isotopes

Concept of of average atomic mass?

Volume

Mass/Density=

Density

Mass/Volume=

Mass

Density x Volume=

Alpha

4 2

Beta

0 -1

0 0

Gamma