Unit 1: Matter, Atoms, Elements, and Particles - Vocabulary Flashcards

A set of vocabulary flashcards covering core terms from Unit 1 notes: matter, atoms, subatomic particles, isotopes, ions, the mole, isotopes, and periodic table concepts.

Matter

Anything that has mass and occupies space.

Chemistry

The science of the properties of matter and the changes matter undergoes; the central science.

Element

A substance that cannot be broken down into simpler substances by chemical means; may consist of atoms or diatomic molecules.

Pure substance

Matter with a definite composition and distinct properties (either an element or a compound).

Mixture

A physical combination of two or more substances; components retain identities and can be separated by physical means.

Homogeneous mixture

A mixture that is uniform throughout (also called a solution).

Heterogeneous mixture

A mixture that is not uniform; components are distinguishable.

Phase of matter

Solids, liquids, and gases; phases can interconvert without changing chemical composition.

Condensed phase

Solids and liquids; the dense phases of matter.

Physical change

A change in matter that does not alter the chemical composition.

Chemical change

A change that alters the chemical composition, forming new substances; mass is conserved in the overall reaction.

Law of Conservation of Mass

In a chemical reaction, matter is neither created nor destroyed; total mass before equals total mass after.

Law of Definite Proportions

A given compound contains elements in a fixed, definite proportion by mass.

Law of Multiple Proportions

If two elements form more than one compound, the mass ratios are simple whole-number ratios.

Dalton’s Atomic Theory

Elements are made of atoms; atoms of a given element are identical; atoms combine in simple whole-number ratios to form compounds; atoms cannot be transformed into other elements in chemical reactions.

Modern Atomic Theory

All matter is made of atoms with subatomic particles; atoms of the same element have the same number of protons and electrons; isotopes exist; chemical bonds involve electron rearrangement.

Atomic Number (Z)

The number of protons in an atom’s nucleus; defines the element and equals the number of electrons in a neutral atom.

Mass Number (A)

The total number of protons and neutrons in the nucleus.

Isotope

Atoms of the same element with different numbers of neutrons; same Z but different A.

Isotope notation

Two common representations: symbol with mass number (A) or mass number and atomic number (superscript and subscript) next to the symbol.

Atomic Mass Unit (amu)

1 amu is 1/12 the mass of a carbon-12 atom; used to express atomic and molecular masses.

Nucleus

Dense center of the atom containing protons and neutrons; accounts for most of the atom’s mass.

Electron cloud

Region surrounding the nucleus where electrons reside; electrons are negatively charged.

Proton

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

Neutron

Neutral subatomic particle in the nucleus; mass ≈ 1 amu.

Electron

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

Ion

An atom or group of atoms with a net electric charge due to gain or loss of electrons.

Cation

A positively charged ion formed when electrons are lost (more protons than electrons).

Anion

A negatively charged ion formed when electrons are gained (more electrons than protons).

Avogadro’s Number

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

Mole

The amount of substance that contains Avogadro’s number of particles; unit is mol.

Molar Mass

Mass of one mole of a substance, expressed in g/mol.

Diabetic elements

Molecules composed of two atoms, e.g., O2, N2, H2; diatomic elements exist naturally.

Periodic Table

Organization of elements by increasing atomic number with recurring properties (periodic law).

Group/Family

Vertical column in the periodic table; elements with similar properties.

Period

Horizontal row in the periodic table; properties vary across a period.

Noble Gases

Group 8A; very unreactive in general (He, Ne, Ar, Kr, Xe, Rn).

Metals vs. Nonmetals

Metals tend to lose electrons to form cations; nonmetals tend to gain electrons to form anions.

Metalloids

Elements with properties between metals and nonmetals (semimetals).

Ion notation

Ions are shown by the element symbol with a superscript indicating charge (e.g., Na+).