INTRO CHEMISTRY I CHEM 1305

Matter exists in three physical states:

• Solid
• Liquid
• Gas

Homogeneous matter is uniform in:

• composition
• properties

Heterogeneous matter is not uniform in:

• composition
• properties

Heterogeneous matter consists of two or more substances unequally distributed and is often referred to as a mixture.

Heterogeneous matter is composed of two or more pure substances which can be separated.

Solutions are homogeneous mixtures composed of two or more pure substances.

Pure substances are characterized by definite and constant:

• Composition
• Properties

Pure substances are divided into two groups:  

• Compounds - pure substances which can be broken down by chemical means to two or more simpler substances elements and are composed of molecules.
  
  
• Elements - pure substance which cannot be decomposed into simpler substances by ordinary chemical means and are composed of atoms.

Common elements and symbols

Molecular formulas contain a collection of elemental symbols which as a group represents one molecule.

Examples:

Formula	Name	Proportions
CO	carbon monoxide	1 atom of carbon   1 atom of oxygen
H2O	water	2 atoms of hydrogen   1 atom of oxygen

Molecular formulas tell us:

• the atoms of each element present
• the number of atoms of each element (subscript)

Law of definite proportions -   a given pure compound always contains: the same elements in exactly the same proportions by mass.

Water will always consist of 2 atoms of hydrogen and one atom of oxygen.

Physical properties can be observed without changing the composition of the substance.

Types of physical properties are:

• color
• odor
• taste
• solubility
• density
• melting point
• boiling point

Chemical properties can be observed when a substance undergoes a change in composition.

Types of chemical properties:

• iron rusting
• gasoline burning in air
• water undergoing electrolysis
• chlorine reacts with sodium

Physical changes occur without a change in the composition of the substance. Conversions from one state of matter to another is an example of a physical change.

Chemical changes are observed when a change in the composition of a substance occurs. New substances are formed with different physical and chemical properties.

Cl₂ + Na ---> 2 NaCl

chlorine gas (poisonous) plus sodium (reactive metal) produces a new substance, sodium chloride (table salt) which has totally different physical and chemical properties.

Energy is defined as the ability to do work or to transfer heat.

The principle types of energy are:

• mechanical
• heat
• electrical
• chemical
• light

Energy can either be

• potential energy - energy possessed by its position in space or its chemical composition or
• kinetic energy - due to motion

Heat energy - energy is transferred from one substance to another when there is a temperature difference between the substances.

Measurement of Energy (units)

• Calorie (cal)
• Joule (j)
• 1 cal = 4.184 j

A calorie is  the quantity of heat required to raise the temperature of 1 gram of water from 14.5 ^oC to 15.5 ^oC.

Specific heat is a physical property.

Specific heat (SpH) is the amount of energy (calories) required to produce a given change in temperature ( ^oC) in relation to the mass of a substance.

Example:

Calculate the SpH of a metal with a mass of 25 grams and it takes 250 calories of heat energy to raise the temperature of the metal from 20 ^oC to 25 ^oC.

Law of Conservation of Mass:  Mass can neither be created nor destroyed. The total mass of any system always remains constant.

Law of Conservation of Energy: Energy can neither be created nor destroyed. Energy may be transformed from one type to another .

• metals
• nonmetals
• metalloids

Metals have certain physical properties:

• high luster
• conduct electricity
• malleable
• ductile
• most have high densities
• many have high m.p.
• most are hard

Metals have certain chemical properties:

• do not readily combine with other metals
• do combine with nonmetals
• few are found in the free state (example Au, Ag, Cu, and Pt)

Nonmetals have certain physical properties:

• Not lusterous
• poor conductors
• not malleable or ductile
• brittle
• most have low densities
• many have low melting points (mp)
• most are soft

Nonmetals have certain chemical properties:

• combine with metals or other nonmetals
• few exist in nature in the free state