Atomic Theory

Question 1

John Dalton

Answer 1

• English chemist and teacher (begun teaching at age 12)
• Experiments led to discovery that the ratios of the elements in the compound are whole number multiples (law of multiple proportions)
• Determined relative mass of elements

Question 2

Dalton’s atomic model

Answer 2

• “billiard ball model”

- Dalton envisioned atoms as tiny, solid, indivisible spheres, like billiard balls

Question 3

Laws that Dalton’s model was based on

Answer 3

• Law of Conservation of Matter
• Law of Constant Composition
• Law of Multiple Proportions

Question 4

Discoveries that conflicted with Dalton’s Atomic Theory

Answer 4

• Dalton’s theory failed to explain the periodic law of atomic behavior (many of the physical and chemical properties of the elements tend to recur in a systematic manner with increasing atomic number)
• Discovery of radioactivity
• Discovery of electron

Question 5

J.J. Thomson’s atomic model

Answer 5

• “plum pudding model”
• Discovery of the electron meant that atoms were made of subatomic particles contrary to Dalton
• As atoms are electrically neutral, negative electrons must be balanced by a positive charge in the atom
• Thomson proposed that the atom was a sphere of positive charge with negative electrons embedded in atom like “plums in plum pudding.”

Question 6

Law of Constant Composition

Answer 6

All of the same compound has the same composition; all water is H2O

Question 7

Law of Multiple Proportions

Answer 7

the ratios of the elements in the compound are whole number multiples

Question 8

Rutherford’s nuclear model

Answer 8

• The atom is mostly empty space (99.9999+%)
• The positive charge is centrally located in a dense nucleus (most of the mass of the atom)
• The nucleus is approximately 100,000 times smaller than the atom
• The electrons are located at a distance away from the nucleus and avoid being pulled into the nucleus by orbiting at rapid speeds
• gold foil experiment

Question 9

Mendeleev

Answer 9

• When Mendeleev arranged the elements by increasing atomic weight, he noticed a periodic repetition in atomic properties (e.g. density, melting point, reactivity)
• Mendeleev left blanks in his table, predicting elements (and their properties) not yet discovered
• This periodic table was empirical, NOT theoretical