Atoms- Atoms and the Periodic Table

Atoms- Atoms and the Periodic Table

Objectives:

Describe the structure of atoms in terms of neutrons, protons, and electrons and the role of the atomic structure in determining chemical properties.

Slide 1

400 B.C. - Democritus thought matter could not be divided indefinitely. • 350 B.C - Aristotle modified an earlier theory that matter was made of four “elements”: earth, fire, water, air. • Aristotle was wrong. However, his theory persisted for 2000 years. fire air water earth • This small particle he called “atomos”

John Dalton

• 1808 -Dalton proposed a modern atomic model based on experimentation not on pure reason.

• • All matter is made of atoms.

• Atoms of an element are identical.

• Atoms of different elements are distinctively different

• Atoms are rearranged in chemical reactions

• Atoms of different elements combine in constant ratios to form compounds.

• Atoms of one element cannot be changed into an atoms of different elements.

Slide 2

He thought particles would pass through and most particles did. So, atoms are mostly empty. • But some positive -particles deflected or bounced back! • He concluded that a “nucleus” existed, is positive and holds most of an atom’s mass.

Multiple Choice

What is a atoms

• In 1932, Chadwick observed that beryllium, when exposed to bombardment by alpha particles, released an unknown radiation that in turn ejected protons from the nuclei of various substances.

• The nucleus of an Atom contains PROTONS and NEUTRONS

• Protons are Positive and Neutrons are Neutral  The ELECTRONS in an atom are responsible for the chemical properties of the element