CHEM 0105 - Chapter 3: Basic Definitions and Classification of Matter

Study flashcards covering basic definitions and the classification of matter from Chapter 3 (CHEM 0105).

What is chemistry?

The study of matter and its changes.

Define matter.

Anything that has mass and occupies space.

What is mass?

The amount of matter present in a given sample.

What is an atom?

The smallest particle that retains a unique chemical identity.

What are the two main categories of matter?

Pure Substances and Mixtures.

What are pure substances composed of?

Elements and Compounds.

What is an element?

The simplest kind of matter; the smallest unit is an atom; seven elements exist on Earth as diatomic molecules.

List the seven diatomic elements.

Hydrogen (H2), Fluorine (F2), Nitrogen (N2), Oxygen (O2), Chlorine (Cl2), Bromine (Br2), Iodine (I2) (as diatomic molecules).

What is a covalent bond?

A bond formed by sharing one or more pairs of electrons; diatomic molecules are covalently bonded.

What is a compound?

A substance formed by a specific combination of atoms with fixed composition, connectivity, and a definite 3D arrangement.

What are two examples of molecular compounds mentioned?

Water (H2O) and Hydrogen peroxide (H2O2).

What is the difference between a molecule and a formula unit?

A molecule is the smallest unit of a molecular compound; a formula unit is the smallest unit of an ionic compound.

What are the two types of compounds?

Molecular (covalent bonds) and Ionic (ionic bonds) compounds.

How is an ionic bond formed?

By the transfer of electrons, creating oppositely charged ions that attract ( coulombic attraction ).

What is a cation?

An ion with fewer electrons, giving it a positive charge.

What is an anion?

An ion with more electrons, giving it a negative charge.

Why are ionic compounds drawn without covalent bonds?

Because they are held together by ionic bonds between ions, not shared electrons.

What does Mg2+ indicate in MgCl2?

Magnesium has lost two electrons to become Mg2+; there are two Cl− ions accompanying it.

What does the subscript in MgCl2 indicate?

There are two chloride ions (two Cl−) in the formula.

What is a chemical formula?

A shorthand using elemental symbols to represent a compound; molecular formulas for molecules and formula units for ionic compounds.

What are the two kinds of chemical formulas?

Molecular formulas (for molecules) and formula units (for ionic compounds).

Give an example contrasting a molecular formula with a formula unit.

H2O is a molecular formula; NaCl is a formula unit.

How are molecules drawn to convey 3D structure?

Lines show covalent bonds; wedges show 3D orientation (in-plane, in front of plane, or behind plane as applicable). Water is bent; H2O2 has central oxygens in the same plane.

What is a homogeneous mixture?

A mixture with a constant composition and visibly indistinguishable parts.

What is a heterogeneous mixture?

A mixture with visibly distinguishable parts and typically multiple phases.

What is the main characteristic of a mixture?

Variable composition.

How can mixtures be separated?

By physical methods such as distillation or filtration.

What indicates a mixture is heterogeneous by phases?

The presence of two or more phases in the sample.

How many categories are used to classify matter?

Four: element, compound, homogeneous mixture, and heterogeneous mixture.