Module 2 (Part 2): Early Ideas and Evolution of Atomic Theory

Question 1

Matter is composed of tiny, indivisible particles called “atomos” (atoms)

Answer 1

Democritus

Question 2

Who is credited for composing the basic atomic theory?

Answer 2

John Dalton

Question 3

4 Postulates of the Basic Atomic Theory

Answer 3

1. Matter is composed of exceedingly small and indestructible particles called atoms.
2. Elements are made of just one type of atom that is unique to that element.
3. Compounds result from the chemical combination of a specific ratio of atoms to different elements.
4. Atoms are neither created nor destroyed during a chemical change but are instead rearranged to yield substances that are different from those present before the change.

Question 4

Why is the first postulate false?

Answer 4

Atoms are divisible into its subatomic particles.

Question 5

Why is the second postulate false?

Answer 5

Isotopes of elements exist and they all share the same atoms of that element.

Question 6

Why is the fourth postulate false?

Answer 6

This is true for chemical reactions but not for nuclear reactions.

Question 7

The only postulate that gave rise to the Mass Laws and remains correct is

Answer 7

Compounds result from the chemical combination of a specific ratio of atoms of different elements.

Question 8

Give the 3 Mass Laws

Answer 8

1. Law of Conservation of Mass
2. Law of Definite Proportions
3. Law of Multiple Proportions

Question 9

Law of Conservation of Mass

Answer 9

The total mass of substances does not change during a chemical reaction.

Question 10

Law of Definite Proportions

Answer 10

No matter the source, a particular compound is composed of the same elements in the same parts (fractions) by mass.

Question 11

Law of Multiple Proportions

Answer 11

If elements A and B react to form two compounds, the different masses of B that combine with a fixed mass of A can be expressed as a ratio of small whole numbers.

Question 12

Scientist that discovered electrons and proposed the plum-pudding model

Answer 12

JJ Thomson

Question 13

How did the scientist discover electrons?

Answer 13

Through the cathode ray experiment

Question 14

Scientist that states that atom is mostly empty space and its mass is mainly concentrated at the center

Answer 14

Ernest Rutherford

Question 15

How was Rutherford able to prove his theory?

Answer 15

Through the gold foil experiment

Question 16

What accounts for most of an atom’s volume?

Answer 16

Electrons

Question 17

What takes little volume but contains all the atom’s mass?

Answer 17

Protons and neutrons