Chemistry - Matter

[Concept] What is matter?

Anything that has mass and takes up space.

[Concept] What four broad features of matter do the slides organize chemistry around?

State, properties, changes, and composition.

[Rule] How do you distinguish a physical property from a chemical property?

A physical property can be observed without changing the substance's identity; a chemical property describes its ability to become a new substance.

[Practice] Classify color, melting point, and physical state.

Physical properties.

[Practice] Classify flammability, tendency to rust, and reactivity.

Chemical properties.

[Rule] How do you distinguish a physical change from a chemical change?

A physical change alters appearance or state but not composition; a chemical change changes composition and produces different substances.

[Practice] Classify melting ice.

Physical change: the state changes, but the substance remains H2O.

[Practice] Classify iron rusting.

Chemical change: iron is converted into new substances.

[Concept] What is a pure substance?

One kind of matter with definite, constant composition and characteristic properties; it cannot be separated by physical means.

[Concept] What is a mixture?

A physical combination of two or more pure substances whose proportions can vary and whose components can be separated physically.

[Rule] Homogeneous versus heterogeneous mixture

Homogeneous: one visible phase and uniform composition. Heterogeneous: two or more visible phases and nonuniform composition.

[Practice] Classify saltwater.

A homogeneous mixture, assuming all of the salt is dissolved.

[Practice] Classify chicken noodle soup.

A heterogeneous mixture because different visible phases are present.

[Practice] Why can a magnet separate iron filings from a mixture?

Mixture components retain their physical properties, so magnetic iron can be removed physically.

[Concept] Element versus compound

An element cannot be broken into simpler substances chemically; a compound contains multiple elements and can be decomposed chemically.

[Concept] What is an atom?

The smallest particle of an element that retains the properties of that element.

[Concept] What is a molecule?

A group of two or more bonded atoms that functions as one unit.

[Concept] What is a formula unit?

The lowest whole-number ratio of ions represented by the formula of an ionic compound.

[Rule] What information does a chemical formula provide?

The element symbols identify the elements; subscripts show how many atoms of each element are present in one molecule or formula unit.

[Practice] How many total atoms are represented by H2O?

3 atoms: 2 H and 1 O.

[Practice] How many atoms of each element are in Mg3(PO4)2?

3 Mg, 2 P, and 8 O.

[Practice] Classify each: oxygen gas, carbon dioxide, air.

Oxygen gas is an element; carbon dioxide is a compound; air is a mixture.