Atomic Theory of Matter – Lecture Review

24 question-and-answer flashcards covering historical milestones, subatomic particles, foundational laws, and isotope concepts from the lecture on the Atomic Theory of Matter.

Who first conceived the idea that matter is made of indivisible "atomos"?

Democritus

Which English physicist is credited with pioneering modern atomic theory (1803-1807)?

John Dalton

According to Dalton’s Atomic Theory, what happens during a chemical reaction?

Atoms are rearranged.

State the Law of Conservation of Mass.

Mass is neither created nor destroyed in a chemical reaction.

What does the Law of Definite Proportion assert about chemical compounds?

A given compound always contains the same elements in the same mass ratio.

Explain the Law of Multiple Proportions.

When two elements form more than one compound, the masses of one element that combine with a fixed mass of the other are in small whole-number ratios.

What subatomic particle did J. J. Thomson discover in 1897?

The electron

Which experimental device led Thomson to the discovery of the electron?

The cathode-ray tube

Who measured the electron’s charge using the Oil Drop Experiment?

Robert Andrews Millikan

What is the charge and approximate mass of an electron?

Charge = –1 (-1.602 × 10⁻¹⁹ C); mass ≈ 9.109 × 10⁻²⁸ g (about 1⁄400 of a hydrogen atom).

Define a proton.

A positively charged subatomic particle located in the nucleus.

Which scientist’s 1886 canal-ray work contributed to the identification of protons?

Eugen Goldstein

Who discovered the atomic nucleus in 1911, and by what experiment?

Ernest Rutherford; Gold Foil Experiment

Summarize the key features of Rutherford’s atomic model (1911).

A tiny, dense, positively charged nucleus with electrons orbiting at a distance; most of the atom is empty space.

Describe a neutron.

A neutral subatomic particle in the nucleus with a mass of about 1 amu.

Who discovered the neutron in 1932?

James Chadwick

What is an isotope?

Atoms of the same element that differ in neutron number.

Which chemist introduced and proved the concept of isotopes in 1913?

Frederick Soddy

How do scientists specify different isotopes of an element?

By their mass number (total protons + neutrons).

Compare Carbon-12 and Carbon-14.

Both have 6 protons and 6 electrons; Carbon-12 has 6 neutrons, Carbon-14 has 8 neutrons.

Give an example of an element that exists naturally as three isotopes.

Magnesium (Mg-24, Mg-25, Mg-26).

What percentage of an atom’s mass is concentrated in the nucleus?

About 99.9%.

According to Dalton, are atoms of the same element identical in mass and properties?

Yes, that was one of Dalton’s postulates (though we now know isotopes vary in mass).

What did William Prout hypothesize in 1815 regarding atomic composition?

That all atoms are made up of hydrogen atoms (early hint toward protons).