Chemistry laws

​Objectives

• ​To list the postulates of Dalton's Law

• To state the laws of definite and multiple proportions

• ​To count the sub-particles

• To define ions and calculate the number of subparticles

Dalton's Atomic Theory

In 1808, this English schoolteacher proposed his own atomic theory that became widely accepted

Dalton’s Atomic Theory:

–All elements are made of tiny atoms.

–Atoms cannot be subdivided.

–Atoms of the same element are exactly alike.

–Atoms of different elements can join to form molecules.

-Atoms combine together in fixed ratio

-In a reaction, atoms rearrange to form new substances​

Proust (leading up to Dalton)

• 1799 Proust observed the composition of water was always 11 percent by mass hydrogen and 89 percent by mass oxygen.

• He then studied other compounds and noticed that reguardless of the sample this was always true.

Draw

Indicate which of the following is Daltons Model?

The Law of Definite Proportions

The law of definite proportions states that a chemical compound contains the same proportions by mass regardless of the size of the sample or source of the compound.

• For example:

  • sodium chloride (table salt) always consists of:

    • 39.34% by mass of the element sodium, Na

    • 60.66% by mass of the element chlorine, Cl.

​

The Law of Multiple Proportions

The law of multiple proportions states that if two or more different compounds are composed of the same two elements, then the ratio of the masses of the second element combined with a certain mass of the first element is always a ratio of small whole numbers.​

​

For example:

• the elements carbon and oxygen form two compounds, carbon dioxide and carbon monoxide.

  • CO molecules are always composed of one C atom and one O atom.

  • CO₂ molecules are always one C atom and two O atoms.

​

History of the Atom

​Atoms

Atoms are made of protons, electrons, and neutrons

​

Protons are positive

Neutrons are neutral​

Electrons are negative ​

​

• Protons and neutrons are in the nucleus

• Electrons are on the outside

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Atom labeling - Labelled diagram

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