Atoms and Elements

What is Brownian motion?

• The random movement of small particles suspended in a fluid due to collisions with fast-moving molecules.

• The predictable movement of large particles in a solid due to gravitational forces.

• The uniform motion of particles in a vacuum.

• The movement of electrons around the nucleus of an atom.

Answer explanation

Brownian motion is the random movement of small particles suspended in a fluid due to collisions with fast-moving molecules.

Who first observed Brownian motion?

• Albert Einstein

• Robert Brown

• Jean Perrin

• Isaac Newton

Answer explanation

Robert Brown was the first to observe Brownian motion, not Albert Einstein, Jean Perrin, or Isaac Newton.

Which scientist's work in 1905 provided strong evidence for the existence of atoms and molecules through the description of Brownian motion?

• Robert Brown

• Albert Einstein

• Jean Perrin

• Niels Bohr

Answer explanation

Albert Einstein's work in 1905 described Brownian motion, providing strong evidence for the existence of atoms and molecules.

According to the atomic theory, what are atoms composed of?

• Destructible particles

• Indestructible particles

• Subatomic particles

• Molecules

Answer explanation

According to the atomic theory, atoms are composed of indestructible particles.

What does the atomic theory state about atoms of a given element?

• They have different masses and properties.

• They have the same mass and other properties.

• They can change into atoms of another element.

• They cannot form compounds.

Answer explanation

The atomic theory states that atoms of a given element have the same mass and other properties.

How do atoms combine to form compounds according to the atomic theory?

• In complex, fractional ratios

• In simple, whole-number ratios

• By changing into different elements

• By losing their properties

Answer explanation

Atoms combine to form compounds in simple, whole-number ratios according to the atomic theory.

What happens to atoms of one element in a chemical reaction according to the atomic theory?

• They change into atoms of another element.

• They remain unchanged.

• They change the way they are bound together with other atoms to form a new substance.

• They lose their properties.

Answer explanation

According to the atomic theory, atoms of one element change the way they are bound together with other atoms to form a new substance in a chemical reaction.

Who discovered the electron in the late 1800s through experiments with cathode rays?

• Ernest Rutherford

• Robert Millikan

• J. J. Thomson

• Niels Bohr

Answer explanation

J. J. Thomson discovered the electron in the late 1800s through experiments with cathode rays.

What did Robert Millikan measure that led to the calculation of the mass of an electron?

• The charge-to-mass ratio of the proton

• The charge of the electron

• The mass of the neutron

• The volume of the nucleus

Answer explanation

Robert Millikan measured the charge of the electron, which led to the calculation of the mass of an electron.

Who developed the nuclear theory of the atom in 1909?

• J. J. Thomson

• Robert Millikan

• Ernest Rutherford

• Niels Bohr

Answer explanation

Ernest Rutherford developed the nuclear theory of the atom in 1909.