Chapter 2.1: Elements, Compounds, and Mixtures

Flashcards from Chapter 2.1 of Chemistry: The Molecular Nature of Matter and Change.

Substance

Matter with a fixed composition; includes:

• Elements (the simplest type of matter with one type of atom)

• Compounds (two or more different elements that are bonded chemically)

Element

The simplest type of matter with unique physical and chemical properties

• Has only one kind of atom

• Visible properties are unique due to submicroscopic differences

• Some exist as molecules, like oxygen as O₂

Molecule

An independent structure of two or more atoms bound together

Atom

The smallest unit of an element that retains its chemical nature

Compound

Two or more different elements that are bonded chemically, with atoms joined in a chemical reaction; can be seen with water or sodium chloride

Defined by:

1. A fixed mass ratio of each element per compound unit (like NH₃)

2. Properties different from that of the individual elements (like NaCl not inheriting many properties of Na or Cl)

3. Simple substance possibilities via chemical changes (like NaCl being broken by electric current)

Fixed mass ratio

Property of compounds where elements are present in fixed parts by mass

Mixtures

Two or more substances that are physically intermingled, but not chemically combined; some properties include:

1. Potential variation in mass parts, like concentration in salt and water

2. Component-level retention

3. Can be separated by physical changes if needed

Examples include air, oceans, and milk

Hetrogenous mixtures

Mixtures with one more visible boundaries among the components

• Variation is distributed from one region to another

• Boundaries may only be seen with microscopes at times

Homogenous mixtures (solutions)

Mixtures with no visible boundaries

• Uniform composition and uniformly intermingled (not attached)

• Cannot visually tell whether homogenous or an element or compound

Filtration

The separation of a mixture based on particle size, used to separate solids from liquids

Crystallization

Based on solubility; impure solids can be dissolved and then re-crystallized

Solubility

Of a substance, the amount that dissolves in a fixed volume of solvent at a given temperature

Distillation

Based on volatility, where:

1. In simple procedures, more volatile contents are vaporized first and collected

2. In fractional procedures, many steps are used to separate components with small differences, like with petroleum

Volatility

The tendency of a substance to become a gas

Chromatography

Also based on solubility; components flow through a solid or viscous liquid with the lowest soluble elements moving faster