Chemistry Basics

Chemical Properties and Substances

• The ability of a substance to undergo a chemical change is a chemical property.
• A chemical property is a characteristic of a substance that can be observed or measured during a chemical reaction.

Composition of Substances

• Water is a compound made up of different elements.
• A compound is a pure substance formed from chemical combinations of two or more different elements.

Types of Substances

• A pure substance that cannot be broken down into any other substances by any chemical means is an element.
• An element is a pure substance that consists of only one type of atom.

Measurement of Physical Quantities

• The measure of gravity on an object is its weight.
• Weight is different from mass, which is a measure of the amount of matter in an object.
• The amount of space matter takes up is called volume.
• Volume can be measured in units such as liters or cubic centimeters.

Units of Measurement

• Mass can be measured in units called grams.
• Volume can be measured in units such as liters or cubic centimeters.
• The liter and cubic centimeter are both units used to measure volume.

Chemical Reactions

• In an endothermic reaction, energy is absorbed in the form of heat, not released.

Chemical Properties and Changes

• Chemical property: the ability of a substance to undergo a chemical change
• Chemical change: a process that alters the chemical composition of a substance

Substances and Elements

• Compound: a pure substance formed from chemical combinations of two or more different elements
• Element: a pure substance that cannot be broken down into any other substances by any chemical means

Measurement and Properties

• Mass: a measure of the amount of matter in an object
• Weight: the measure of gravity on an object
• Volume: the amount of space matter takes up
• Density: mass per unit volume of a substance
• Units of measurement: grams for mass, liters or cubic centimeters for volume

States of Matter

• Solid: particles are tightly packed and vibrate; has a definite shape and volume
• Liquid: takes the shape of its container; has a definite volume but not shape
• Gas: expands to fill the space available to it; has neither definite shape nor volume

Physical Changes

• Physical change: alters the form of a substance, but does not change it into another substance
• Examples: changes in state (solid to liquid, liquid to gas, etc.)
• Melting: change from solid to liquid
• Freezing: change from liquid to solid

Chemical Changes

• Chemical change: a process that alters the chemical composition of a substance
• Examples: burning gasoline produces carbon dioxide, lighting a match
• Chemical reaction: a process that involves a chemical change

Energy and Matter

• Thermal energy: energy of the motion of particles in a substance
• Mechanical energy: energy of motion or position of an object
• Potential energy: energy of an object due to its position or configuration

Atomic Structure

• Atom: the central core (nucleus) consists of protons and neutrons, surrounded by electrons
• Proton: positively charged particle in the nucleus
• Neutron: neutral particle in the nucleus
• Electron: negatively charged particle outside the nucleus