Chapter 3 Chemistry

The idea of atoms has been around since the time of the anicent Greeks. In the nineteenth century, John Dalton propsed a scientific theory of atoms that can still be used to explain properties of most chemicals today.

States that mass is neither created nor destoryed during ordinary chemical reactions or physical changes.

States that s chemical compound contains the same elements in exactly the same proportions by mass regardless of the size of the sample or source of the compound.

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.

• 1. All matter is composed of extremely small particles called atoms.
• 2. Atoms of a given element are identical in size, mass, and other properties; atoms of different elements differ in size, mass, and other properties. 
• 3.Atoms cannont be subdivided, created, or destroyed. 
• 4. Atoms of different elements combine in simple whole number ratios to form chemical compounds.
• 5. In chemical reactions, atoms are combined, seperated, or rearranged.

Atoms are divisible into even smaller particles (subatomic particles; protons, neutrons, and electrons). Elements can have atoms with different masses.

Atom is based on the Greek word meaning "indivisble."

Rutherford found evidence for the existence of the atomic nucleus by bombarding metal foil witha beam of positively charged particles. (He discovered protons).

The cathode ray tube supplied evidence of the existence of electrons, which are negatively charged subatomic particles that have relatively little mass.

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

Protons: +

Electrons: -

Neutrons: Neutral

Further proved that electrons were negatively charged.

Atomic nucleus are made up of protons and neutrons.

The atomic number of an element is equal to the number of protons of an atom of that element.

If the atoms lose e^- =positive charge (cation).

If the atoms gain an e^- = negative charge (anion).

Isotopes are atoms of the same element that have different masses. The isotopes of an element have the same number of protons and electrons but different number of neutrons.

The mass number is the total number of protons and neutrons that make up the nucleus of an isotope.

Average atomic mass is the weighted average of the atomic masses of the natrually occuring isotopes of an element.

The mole is the SI unit for an amount of a substance.

The number of particles in a mole can be expressed; 6.022 x 10²³

The mass of one mole of a pure substance is called the molar mass of a substance.

A general term for a specific isotope of an element.

1 amu is exactly 1/12 the mass of a carbon-12 atom.

• Horzontial; periods
• vertical; groups, similiar characterstics