4.1-Defining the Atom-1

The smallest particle of an element that retains its identity in a chemical reaction.
It can be broken down into subatomic particles.

• Molecule
• Compound
• Atom
• Ion

Who was among the first to propose the existence of atoms, believing that they were indivisible and indestructible?

• Democritus

• John Dalton

• Isaac Newton

• Albert Einstein

Which scientist developed an atomic theory that included the postulate stating that all elements are composed of tiny indivisible particles called atoms?

• Democritus

• John Dalton

• Albert Einstein

• Isaac Newton

1. all elements are composed of tiny indivisible particles called atoms (changed, now divisible).

2. atoms of the same element are identical & atoms of different elements are different.

3. atoms of different elements can physically mix together or chemically combine in simple whole number ratios to form compounds.

4. chemical reactions occur when atoms are separated, joined, or rearranged but the atom of 1 element doesn't change.

• Democritus atomic theory

• John Dalton atomic theory

Which of the following is NOT one of Dalton's atomic theory postulates?

• Atoms of different elements can physically mix together.

• Atoms of the same element are identical.

• Atoms of different elements are different.

• Atoms are the smallest particles that exist.

What was a limitation of Democritus' proposal of atoms?

• He lacked the ability to test his hypothesis.

• He couldn't explain the existence of subatomic particles.

• He didn't have knowledge of chemical reactions.

• He believed atoms were composed of protons, neutrons, and electrons.

According to Dalton's atomic theory, what happens during a chemical reaction?

• Atoms of one element change into atoms of another element.

• Atoms of different elements combine to form a new element.

• Atoms of one element are separated, joined, or rearranged.

• Atoms combine in ratios that can't be expressed by whole numbers.