3.2 ✨ defining the atom

How was an electric field used to determine the charge of a cathode ray?

• By measuring the deflection of the ray in the field

• By observing the color change of the ray

• By calculating the speed of the ray

• By determining the temperature change in the ray

A cathode-ray tube has a metal electrode at each end. The electrodes are connected to a power supply. When current flows, electrons are emitted from the cathode and travel through the tube to the anode.

• Electrons are emitted from the anode and travel to the cathode.

• Electrons are emitted from the cathode and travel to the anode.

• Electrons remain stationary within the tube.

• Electrons are emitted from both electrodes simultaneously.

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NGSS.HS-PS2-5

NGSS.HS-PS3-5

What caused the deflection of the alpha particles in Rutherford’s gold foil experiment?

• The α particles were deflected by the positively charged gold nuclei.

• The α particles were deflected by the negatively charged electrons.

• The α particles were deflected by the neutrons in the gold atoms.

• The α particles were deflected by the gold foil itself.

Explain what keeps the electrons confined in the space surrounding the nucleus.

• attraction to the positively charged nucleus

• repulsion from other electrons

• gravitational pull of the nucleus

• magnetic forces within the atom

What are the strengths and weaknesses of Rutherford’s nuclear model of the atom?

• a. Strengths: explained the results of the gold-foil experiment and why an atom is electrically neutral. Weaknesses: could not account for the total mass of an atom or the arrangement of the electrons.

• b. Strengths: explained the arrangement of electrons and the total mass of an atom. Weaknesses: could not explain the results of the gold-foil experiment.

• c. Strengths: explained the chemical properties of elements. Weaknesses: could not explain the electrical neutrality of an atom.

• d. Strengths: explained the stability of atoms. Weaknesses: could not explain the existence of isotopes.

Describe the structure of a typical atom according to modern atomic theory. Identify where each subatomic particle is located.

• An atom consists of a nucleus containing protons and neutrons, with electrons orbiting around the nucleus.

• An atom consists of a nucleus containing electrons and protons, with neutrons orbiting around the nucleus.

• An atom consists of a nucleus containing neutrons and electrons, with protons orbiting around the nucleus.

• An atom consists of a nucleus containing protons, with electrons and neutrons orbiting around the nucleus.

Compare the relative charge and mass of each of the subatomic particles by filling out the table below.

• Relative Charge: 0, Relative Mass: 1

• Particle: Proton,

• Relative Charge: +1, Relative Mass: 1

• Particle: Neutron,

• Relative Charge: -1, Relative Mass: 1/18

• Particle: Electron,