University of Colorado CHEM 1011

Law of definite (or constant) composition:
No matter the source, a particular compound is composed of the same elements in the same parts (fractions) by mass
Law of multiple proportions:
If elements A and B react to form two compounds, the different masses of B that combine with a fixed mass of A can be expressed as a ratio of small whole numbers
Law of Mass conservation:
The total mass of substance doesn’t change during a chemical reaction
Dalton’s Atomic Theory: Four Postulates
1. All matter consists of atoms
2. Atoms of one element cannot be converted into atoms of another
3. Atoms of an element are identical in mass and other properties and are different from atoms of any other element
4. Compounds result from the chemical combination of a specific ratio of atoms of different elements
Mass conservation concepts:
-Atoms cannot be created or destroyed.
or converted into other types of atoms
-Since every atom has a fixed mass, during a chemical reaction atoms are combined differently and therefore there is no mass change overall.
Definite composition: concept
-Atoms are combined in compounds in specific ratios
and each atom has a specific mass.
-Therefore each element has a fixed fraction of the total mass in a compound
Dalton: Multiple Proportions concepts:
-Atoms of an element have the same mass
and atoms are indivisible
-So when different number of atoms of elements combine, they must do so in ratios of small, whole numbers
Modern Reassessment of the atomic theory:
1. All matter is composed of atoms
2. Atoms of one element can’t be converted into atoms of another element in a chemical reaction
3. All atoms of an element have the same number of protons and electrons, which determines the chemical behavior of the element.
4. compounds are formed by the chemical combination of two or more elements in specific ratios
What is an isotope
An element with a different number of neutrons, therefore it has a different mass number. A sample of the element is treated as though its atoms have an average mass.
What is an element?
the simplest type of substance with unique physical and chemical properties.

consists of only one type of atom. Can’t be broken down into any simpler substance by physical or chemical means.
Assigned a unique atomic number equal to the number of protons in an atom of that element

Atomic Mass unit
1/12 the mass of a 12C atom
Which columns are main group elements?
1A, 2A, 3-8A
Which columns are transition elements?
What are the following columns classified as?
1A-Alkali metals
2A-Earth Alkali metals
8A-Noble Gases
Characteristics of metals:
-Characteristic luster
-Good conductors of heat and electricity
-Solid at room temperature
Characteristics of nonmetals:
-Dull in appearance
-Poor conductors of heat and electricity
Properties are a mix of other classes
What are molecules?
-Groups of atoms chemically bonded together
-Covalently bound compounds which share electrons

-H represents a hydrogen atom
-H2 represents a hydrogen molecule

Describe NaCl in terms of compounds, elements, etc.
Ionic compound made of two charged ions.
What are formula units?
an ionic compound. A mix of a metal and a non-metal

Get access to
knowledge base

MOney Back
No Hidden
Knowledge base
Become a Member