General Chemistry I - Chapter 2: Atoms, Elements, Atomic Mass, and Molar Mass – Vocabulary Flashcards

Vocabulary flashcards covering key terms from the lecture notes on atoms, elements, isotopes, atomic mass, and the periodic table.

Atom

The smallest identifiable unit of an element; consists of a nucleus (protons and neutrons) surrounded by electrons; Greek for indivisible.

Element

A substance that cannot be broken down into simpler substances by chemical means.

Atomic Mass Unit (amu)

A unit for expressing atomic masses; defined as 1/12 the mass of a carbon-12 atom.

Atomic Number (Z)

The number of protons in an atom's nucleus; determines the identity of the element.

Mass Number (A)

Total number of protons and neutrons in an atom's nucleus.

Proton

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

Neutron

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

Electron

Negatively charged subatomic particle surrounding the nucleus; very small mass.

Nucleus

Dense center of the atom containing protons and neutrons; contains most of the atom's mass.

Rutherford's Gold Foil Experiment

Demonstrated the existence of a dense nucleus and that most of the atom is empty space.

Plum Pudding Model

Thomson's model with electrons embedded in a positively charged sphere.

Law of Conservation of Mass

In a chemical reaction, mass is neither created nor destroyed; total mass remains constant.

Law of Definite Proportions (Constant Composition)

A given compound contains elements in the same proportions by mass regardless of source.

Law of Multiple Proportions

If two elements form more than one compound, the mass ratio of one element that combines with a fixed amount of the other is a simple whole-number ratio.

Dalton's Atomic Theory

All matter is made of tiny atoms; atoms of an element are identical; atoms combine in simple whole-number ratios; atoms are rearranged, not created or destroyed, in reactions.

Isotope

Atoms of the same element (same Z) that have different numbers of neutrons.

Isotope Notation

Notation using A (mass number) and Z (atomic number); e.g., Ne-20.

Atomic Mass (Average/Atomic Weight)

Weighted average mass of an element's naturally occurring isotopes; shown under the element symbol on the periodic table.

Mass Spectrometry

Analytical method that ionizes samples, separates ions by mass/charge, and detects them to determine masses.

Avogadro’s Number

6.022 x 10^23; the number of particles in one mole.

Mole

Amount of substance containing Avogadro’s number of particles; the chemist’s counting unit.

1 Mole = 6.022 x 10^23 Units

Conversion factor between moles and particles (atoms/molecules/ions, etc.).

Converting Between Moles and Atoms

1 mole of anything contains 6.022 x 10^23 particles; e.g., 2.0 mol Cu = 1.20 x 10^24 Cu atoms.

Periodic Table

Table listing elements in order of increasing atomic number with recurring properties in groups and periods.

Metals

Elements with properties like high conductivity, malleability, ductility; tend to lose electrons.

Nonmetals

Elements with varied properties, generally poor conductors; tend to gain electrons.

Metalloids (Semimetals)

Elements with mixed properties; lie along the zigzag line between metals and nonmetals; some are semiconductors.

Noble Gases

Group 8A; very unreactive gases like He, Ne, Ar, Kr, Xe.

Alkali Metals

Group 1A; highly reactive metals (e.g., Li, Na, K).

Alkaline Earth Metals

Group 2A; reactive but less so than alkali metals (e.g., Mg, Ca).

Halogens

Group 7A; highly reactive nonmetals (e.g., F, Cl, Br, I).

Ions

Charged particles formed by loss or gain of electrons; cations are positive, anions are negative.

Cation

Positively charged ion formed by loss of electrons.

Anion

Negatively charged ion formed by gain of electrons.

Periodic Law

Properties of elements recur periodically when arranged by increasing atomic number.

Mendeleev and the Periodic Table

Drew a table by arranging elements to reveal recurring properties; led to the periodic law.

Mass Spectrometry (role in isotopes)

Used to measure masses and relative abundances of isotopes.

Atomic Mass vs Mass Number

Mass number A is an integer (p+n); atomic mass is a weighted average of isotopes (in amu).