Chemistry chapter 3 section 1

Atom

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

Matter

Anything that has mass and takes up space

Element

A substance that cannot be broken down into simpler substances by chemical means

Compound

A substance formed when two or more elements chemically combine in fixed ratios

Chemical reaction

A process in which substances change into new substances by rearranging atoms

Democritus

Ancient Greek philosopher who proposed that matter is made of indivisible particles called atoms

Aristotle

Greek philosopher who believed matter was continuous and not made of atoms

Law of conservation of mass

Mass is neither created nor destroyed during a chemical reaction or physical change

Law of definite proportions

A compound always contains the same elements in the same fixed ratio by mass

Law of multiple proportions

When two elements form more than one compound, the masses combine in small whole-number ratios

John Dalton

Scientist who proposed the first modern atomic theory based on experimental evidence

Dalton’s atomic theory

A theory stating that matter is made of atoms that combine in whole-number ratios and are rearranged in reactions

Dalton theory: atoms

All matter is composed of extremely small particles called atoms

Dalton theory: identical atoms

Atoms of the same element are identical, while atoms of different elements differ

Dalton theory: indivisible atoms

Atoms cannot be created, destroyed, or subdivided in chemical reactions

Dalton theory: compound formation

Atoms of different elements combine in simple whole-number ratios

Dalton theory: reactions

Chemical reactions involve the rearrangement of atoms

How Dalton explains conservation of mass

Atoms are not created or destroyed, so total mass remains constant

How Dalton explains definite proportions

Compounds always contain the same combination of atoms

How Dalton explains multiple proportions

Different compounds form when atoms combine in different whole-number ratios

Modern atomic theory

Updated atomic theory that recognizes subatomic particles while keeping the idea that matter is made of atoms