2nd Term Science PS 1

Week 1: Development of Atomic Theory

What is Atomism?

Atomism is the idea that all matter is composed of extremely small, indivisible particles.

Who proposed the concept of Atomism?

Democritus proposed the concept of Atomism in the 5th Century B.C.

What did Democritus hypothesize about matter?

Democritus hypothesized that all matter is composed of extremely small, indivisible particles.

What does “Atomos” mean?

“Atomos” is a Greek word meaning “indivisible.”

What was Democritus's core idea about matter?

Democritus believed that matter cannot be divided infinitely and that there is a fundamental unit that is “uncuttable.”

Who was John Dalton?

John Dalton was the scientist who developed a more precise description of the atom and presented his atomic theory in the early 1800s.

When did Dalton propose his atomic model?

Dalton proposed his model in 1803, and his atomic theory was presented in 1808.

What is Dalton's Solid Sphere Model?

Dalton's Solid Sphere Model describes atoms as tiny, solid spheres with no internal structure.

What is Dalton's first atomic theory postulate?

Elements are made up of extremely small particles called atoms.

What is Dalton's second atomic theory postulate?

All atoms of a given element are identical in mass and properties.

What is Dalton's third atomic theory postulate?

Atoms form compounds as they combine two or more different elements.

What laws was Dalton's atomic theory based on?

Dalton's work was founded on the Law of Conservation of Mass and the Law of Definite Composition.

How did Dalton change the study of atoms?

Dalton transitioned the concept of the atom from philosophy to scientific theory.

Why were some of Dalton's original postulates later revised?

Many of Dalton's original postulates were later revised following the discovery of isotopes and subatomic particles.

Who was J.J. Thomson?

J.J. Thomson was the scientist who discovered the electron and proposed the Plum Pudding Model in 1897.

When did J.J. Thomson make his discovery?

J.J. Thomson made his discovery in 1897.

What experiment did J.J. Thomson conduct?

J.J. Thomson conducted the Cathode-Ray Tube Experiment.

What did Thomson observe in the Cathode-Ray Tube Experiment?

Thomson observed an invisible “cathode ray” that bent away from a negatively charged plate.

What did J.J. Thomson discover?

J.J. Thomson discovered negatively charged subatomic particles called electrons, which he originally called “corpuscles.”

What did Thomson's discovery prove about atoms?

Thomson's discovery proved that atoms are divisible and contain negatively charged particles.

What is the Plum Pudding Model?

The Plum Pudding Model describes electrons as being embedded in a positively charged “pudding,” similar to raisins in a dessert.

Why was Thomson's model important?

Thomson's model was the first atomic model to include an internal structure.

Who was Ernest Rutherford?

Ernest Rutherford was the scientist who proposed the Nuclear Model and discovered that an atom has a dense, positively charged nucleus.

When did Rutherford propose his Nuclear Model?

Rutherford proposed his Nuclear Model in 1911.

What experiment did Rutherford conduct?

Rutherford conducted the Gold Foil Experiment.

What did Rutherford do in the Gold Foil Experiment?

Rutherford fired alpha particles at a thin sheet of gold foil.

What happened to most alpha particles in Rutherford's experiment?

Most alpha particles passed straight through the gold foil.

What happened to some alpha particles in Rutherford's experiment?

Some alpha particles were deflected or bounced back.

What did Rutherford discover from the Gold Foil Experiment?

Rutherford discovered that the atom's mass is concentrated in a central region called the nucleus.

What is the nucleus?

The nucleus is a dense, positively charged central region of the atom where most of the atom's mass is concentrated.

What did Rutherford discover about positive charge?

Rutherford discovered that positive charges are not spread evenly throughout the atom.

What is Rutherford's Nuclear Model?

The Nuclear Model describes the atom as having a dense, positive nucleus at the center with electrons orbiting around it.

Who was Niels Bohr?

Niels Bohr was the scientist who proposed the Planetary Model in 1913.

When did Bohr propose his Planetary Model?

Bohr proposed his Planetary Model in 1913.

What limitation of Rutherford's model did Bohr address?

Bohr addressed the question of why electrons did not spiral into the nucleus.

What did Bohr's model explain?

Bohr's model explained electron stability and atomic emission spectra.

What are energy levels?

Energy levels are specific paths or levels around the nucleus that electrons occupy.

What is Bohr's idea about electron orbits?

Bohr proposed that electrons move in fixed orbits, or energy levels, around the nucleus.

Can electrons exist between Bohr's energy levels?

According to Bohr's model, electrons occupy specific paths and do not exist between them.

What happens when an electron moves between energy levels?

An electron moves between energy levels by absorbing or releasing a specific amount of energy.

Why is Bohr's model called the Planetary Model?

It is called the Planetary Model because electrons move around the nucleus similarly to planets orbiting the Sun.

Who was Erwin Schrödinger?

Erwin Schrödinger was the scientist who developed the Quantum Mechanical Model in 1926.

When did Schrödinger develop the Quantum Mechanical Model?

Schrödinger developed the Quantum Mechanical Model in 1926.

What is the Quantum Mechanical Model?

The Quantum Mechanical Model is the modern understanding of the atom, where electrons are described using mathematical probabilities rather than fixed paths.

What equation did Schrödinger use to describe the atom?

Schrödinger used complex mathematical equations known as the Schrödinger Equation to describe the atom.

What is an orbital?

An orbital is a region where there is a high probability of finding an electron.

How are orbitals different from Bohr's fixed orbits?

Unlike Bohr's fixed orbits, orbitals are regions of probability where electrons are likely to be found.

What is the dual nature of electrons?

The dual nature of electrons means that electrons exhibit both particle-like and wave-like properties.

What remains the same about the nucleus in the Quantum Mechanical Model?

The nucleus remains a dense, positively charged center, consistent with Rutherford's and Bohr's models.

Who was James Chadwick?

James Chadwick was the scientist who discovered the neutron.

What did James Chadwick discover?

James Chadwick discovered the neutron, a subatomic particle with no electric charge.

What is a neutron?

A neutron is a neutral subatomic particle found in the nucleus of an atom.

Where are protons and neutrons located?

Protons and neutrons are located in the nucleus of an atom.

What are the three main subatomic particles?

The three main subatomic particles are protons, neutrons, and electrons.

What charge does a proton have?

A proton has a positive charge.

What charge does a neutron have?

A neutron has no electric charge; it is neutral.

What charge does an electron have?

An electron has a negative charge.

Where are electrons found in the modern atomic model?

Electrons are found in orbitals, which are regions of high probability around the nucleus.

What is the chronological development of atomic theory?

The development went from Democritus's Atomism → Dalton's Solid Sphere Model → Thomson's Plum Pudding Model → Rutherford's Nuclear Model → Bohr's Planetary Model → Schrödinger's Quantum Mechanical Model.

Who came first in the development of atomic theory: Democritus or Dalton?

Democritus came first, proposing Atomism in the 5th Century B.C., long before Dalton's scientific atomic theory.

What did Democritus contribute to atomic theory?

Democritus introduced the idea that matter is made of indivisible particles called atomos.

What did Dalton contribute to atomic theory?

Dalton developed a scientific atomic theory and described atoms as tiny, solid spheres.

What did Thomson contribute to atomic theory?

Thomson discovered the electron and showed that atoms contain smaller subatomic particles.

What did Rutherford contribute to atomic theory?

Rutherford discovered the nucleus and showed that most of the atom is empty space.

What did Bohr contribute to atomic theory?

Bohr proposed that electrons occupy specific energy levels around the nucleus.

What did Schrödinger contribute to atomic theory?

Schrödinger developed the Quantum Mechanical Model, describing electrons using probability and orbitals.

What did Chadwick contribute to atomic theory?

Chadwick discovered the neutron, showing that the nucleus contains another neutral subatomic particle.

What is the main change from Dalton to Thomson?

The atom changed from being considered a solid, indivisible sphere to having internal structure containing electrons.

What is the main change from Thomson to Rutherford?

The atom changed from electrons embedded in positive material to having a dense, positively charged nucleus.

What is the main change from Rutherford to Bohr?

Bohr added specific energy levels or fixed orbits for electrons.

What is the main change from Bohr to Schrödinger?

Electrons changed from being described as moving in fixed orbits to being described as existing in orbitals based on probability.

What is the order of the major atomic models?

Solid Sphere → Plum Pudding → Nuclear → Planetary → Quantum Mechanical.

Which scientist is associated with the Solid Sphere Model?

John Dalton.

Which scientist is associated with the Plum Pudding Model?

J.J. Thomson.

Which scientist is associated with the Nuclear Model?

Ernest Rutherford.

Which scientist is associated with the Planetary Model?

Niels Bohr.

Which scientist is associated with the Quantum Mechanical Model?

Erwin Schrödinger.

Which scientist discovered the electron?

J.J. Thomson.

Which scientist discovered the nucleus?

Ernest Rutherford.

Which scientist proposed specific electron energy levels?

Niels Bohr.

Which scientist developed the modern Quantum Mechanical Model?

Erwin Schrödinger.

Which scientist discovered the neutron?

James Chadwick.

Which experiment is associated with J.J. Thomson?

The Cathode-Ray Tube Experiment.

Which experiment is associated with Ernest Rutherford?

The Gold Foil Experiment.

What is the order of the major scientists in atomic theory?

Democritus → John Dalton → J.J. Thomson → Ernest Rutherford → Niels Bohr → Erwin Schrödinger → James Chadwick.

What is the order of the major discoveries?

Indivisible particles → solid sphere → electron → nucleus → energy levels → orbitals/probability → neutron.

What year is associated with J.J. Thomson's electron discovery?

1897.

What year is associated with Rutherford's Nuclear Model?

1911.

What year is associated with Bohr's Planetary Model?

1913.

What year is associated with Schrödinger's Quantum Mechanical Model?

1926.

What year is associated with Dalton's atomic model?

1803.

What year was Dalton's atomic theory presented?

1808.

What is the key idea of Democritus?

Matter is made of indivisible particles.

What is the key idea of Dalton?

Atoms are tiny, solid spheres.

What is the key idea of Thomson?

Atoms contain electrons.

What is the key idea of Rutherford?

Atoms have a dense, positive nucleus.

What is the key idea of Bohr?

Electrons occupy specific energy levels.

What is the key idea of Schrödinger?

Electrons are found in orbitals based on probability.

What is the key idea of Chadwick?

The nucleus contains neutrons.