H.W. #7 Unit 3

According to the particle model of matter, all matter is

• made up of tiny particles that are in constant motion.

• made up of one type of particle.

• particles that are the same size.

• too small to see.

Answer explanation

According to the particle model of matter, all matter consists of tiny particles that are in constant motion, which explains the properties of solids, liquids, and gases. This makes the first choice the correct answer.

Identify the incorrect statement regarding Dalton’s Atomic Theory.

• All matter is composed of protons, electrons, and neutrons.

• All matter is composed of atoms.

• All atoms of a given element are identical.

• A given compound always has the same relative numbers and types of atoms.

Answer explanation

The incorrect statement is 'All matter is composed of protons, electrons, and neutrons.' Dalton's Atomic Theory states that all matter is composed of atoms, which are the basic units, not just subatomic particles.

The following are all proposals of Dalton’s atomic theory. Which part of Dalton’s atomic theory was shown to be wrong by the discovery of natural radioactivity?

• Atoms of a given element all weigh the same.

• Two or more kinds of atoms may combine in different ways to form more than one kind of chemical compound.

• Atoms combine in simple numerical ratios to form compounds.

• Atoms are permanent, unchanging, indivisible bodies.

• Compounds consist of collections of molecules made up of atoms bonded together.

Answer explanation

The discovery of natural radioactivity showed that atoms can change and decay, contradicting Dalton's claim that atoms are permanent, unchanging, indivisible bodies.

Rutherford’s α-scattering experiment showed that most α particles directed toward a thin metallic foil passed through with only slight deviations. From this evidence we can conclude that

• α particles are uncharged.

• the foil was too thin.

• α particles are too small to hit anything.

• an α particle is a type of light which should not be defected.

• the mass of the atom is concentrated in a very small area.

Answer explanation

Rutherford's experiment revealed that most α particles passed through the foil with minimal deflection, indicating that the atom's mass is concentrated in a small nucleus, as only a few particles were deflected by it.

The discovery and characterization of cathode rays was important in the development of the atomic theory because

• it indicated that all matter contains protons.

• it indicated that all matter contains alpha particles.

• it indicated that all matter contained electrons.

• None of these is correct.

• it led to the suggestion of the existence of the neutron.

Answer explanation

The discovery of cathode rays demonstrated the existence of electrons, which are fundamental components of all matter. This was crucial in shaping atomic theory, as it revealed that atoms are not indivisible but contain smaller particles.

Which statement best summarizes the general nature of investigations during the 1800s related to the acquisition and development of knowledge concerning the atomic structure of matter?

• The development and use of electrical probes to study matter lead to experimental evidence for the existence of subatomic particles in atoms.

• Qualitative observations, although often influenced by ideas related to magic and mysticism, provide glimpses of the structure of matter.

• Quantitative measurements, particularly those related to mass, lead to the formulation of fundamental laws leading to an atomic theory of matter.

• The use of new experimental and mathematical techniques provide information concerning the organization of subatomic particles in atoms.

Answer explanation

The correct choice highlights how the development of electrical probes in the 1800s provided experimental evidence for subatomic particles, marking a significant advancement in understanding atomic structure.

Neutrons eluded discovery until the 1930's because

• neutrons have no mass and thus could not be quantified.

• neutrons have no charge and thus could not be manipulated in electric or magnetic fields.

• many atoms have no neutrons.

• neutrons existed in distant orbitals that were difficult to study.

Answer explanation

Neutrons were difficult to discover because they have no charge, making them unresponsive to electric and magnetic fields. This lack of charge hindered their manipulation and detection compared to charged particles.

In the cathode ray tube experiment, it was found that a beam of cathode rays were able to turn a paddle wheel, thus proving that

• electrons are negatively charged.

• protons are positively charged.

• Electrons have mass and kinetic energy

• Protons have a much larger mass than electrons.

Answer explanation

The paddle wheel's movement indicated that cathode rays exerted force, proving they consist of particles with mass. This led to the conclusion that these particles, later identified as electrons, are negatively charged.

Identify the experimental evidence that indicates an atom has a positively charged nucleus.

• Cathode rays are attracted to the positive plate of an applied electrical field.

• α particles are deflected at large angles when projected toward a thin sheet of metal.

• Line spectra are produced from elemental gases in a gaseous discharge tube.

• Cathode rays produce diffraction patterns.

• Electrons can be ejected from a metallic surface with high energy light.

Answer explanation

The deflection of α particles at large angles when projected at a thin metal sheet indicates a concentrated positive charge, revealing the presence of a positively charged nucleus, as most particles pass through with little deflection.

The sum of the protons and neutrons in the nucleus of an atom is the

• element number.

• atomic number.

• mass number.

• atomic weight.

Answer explanation

The sum of protons and neutrons in an atom's nucleus is called the mass number, not atomic weight. The atomic number refers to protons only, while atomic weight is the average mass of an element's isotopes.