Atomic Theory and Subatomic Particles

Questions and Answers

When was the idea of an atom first developed?

John Dalton, 1803.

The 4 major ideas of Dalton's Atomic Theory are: 1. Matter is made up with atoms that are invisible and indestructible, 2. All atoms of an element are __________.

identical

Atoms of different elements have different __________ and different chemical properties.

weights

Atoms of different elements combine in simple whole numbers to form __________.

compounds Signup and view all the answers

Describe the experiment that led to the discovery of the electron. Who discovered it?

Experimented with Crookes, cathode ray, and a tube; Joseph John 'J.J.' Thomson in 1897. Signup and view all the answers

Describe Rutherford's gold foil experiment. What did this experiment tell us about the structure of the atom?

Rutherford shot a beam of alpha particles at a sheet of gold foil and concluded that a tiny, dense nucleus was causing the deflections. Signup and view all the answers

What are the 3 subatomic particles?

Proton, Neutron, and Electron. Signup and view all the answers

Who discovered the neutron?

James Chadwick. Signup and view all the answers

Who determined the charge of the electron and during what experiment?

Robert A. Millikan during the Oil Drop Experiment. Signup and view all the answers

Describe the Electron Cloud Model of the atom. What are the smallest parts of an atom we know today?

The electron cloud model includes an electron cloud around the nucleus which contains neutrons and protons. Smallest parts are electrons, protons, and neutrons. Signup and view all the answers

What does the atomic number of an element represent? What does the mass number of an atom represent?

The atomic number represents the distinct identity of an element and number of protons. The mass number represents the sum of protons and neutrons. Signup and view all the answers

What are isotopes? How are they similar to each other? How are they different?

Isotopes have the same number of protons but different number of neutrons. Signup and view all the answers

What does the atomic mass of an element represent?

The atomic mass describes a chemical element's protons and neutrons. Signup and view all the answers

Of protons, neutrons, and electrons, which of these can never change in an atom during an ordinary chemical or physical change? Explain why.

Protons, because changing the number of protons changes the element. Signup and view all the answers

What is an ion? What are the two ways in which an ion can be made?

An ion is an atom with an electrical charge due to the loss or gain of electrons; either by the loss of an electron or the gain of an electron. Signup and view all the answers

Study Notes

Historical Development of Atomic Theory

The concept of the atom originated with John Dalton in 1803.

Dalton's Atomic Theory

Matter consists of indivisible and indestructible atoms.
Atoms of a single element are identical in mass and properties.
Different elements have distinct atomic weights and chemical properties.
Atoms combine in simple whole-number ratios to create compounds.

Discovery of the Electron

Joseph John "J.J." Thomson discovered the electron in 1897.
The discovery stemmed from experiments using Crookes tubes and cathode rays, revealing that cathode rays are negatively charged.

Rutherford's Gold Foil Experiment

Conducted by Ernest Rutherford, alpha particles were directed at a thin gold foil.
The experiment led to the conclusion that atoms possess a small, dense nucleus responsible for particle deflections.

Subatomic Particles

The three fundamental subatomic particles are:
- Proton
- Neutron
- Electron

Discovery of the Neutron

The neutron was discovered by James Chadwick.

Determining Electron Charge

Robert A. Millikan determined the charge of the electron through the Oil Drop Experiment.

Electron Cloud Model

The electron cloud model depicts electrons surrounding a nucleus made up of protons and neutrons.
Key components of an atom include:
- Electrons
- Protons
- Neutrons

Atomic Number and Mass Number

The atomic number signifies the number of protons and is unique to each element.
The mass number is the total of protons and neutrons in the nucleus.

Isotopes

Isotopes are variants of elements that have the same number of protons but differ in neutrons.
They maintain identical chemical properties due to the same proton count.

Atomic Mass

The atomic mass reflects the combined number of protons and neutrons within an element.

Stability of Protons

Protons remain unchanged during ordinary chemical or physical changes; altering the proton count changes the element itself.

Ions

Ions are charged atoms formed by the loss or gain of electrons.
Two methods of ion formation include:
- Losing an electron (positive ion or cation)
- Gaining an electron (negative ion or anion)

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Description

Explore the historical development of atomic theory from John Dalton's initial concepts to J.J. Thomson's discovery of the electron and Rutherford's experiments. Understand the characteristics of atoms and subatomic particles including protons, neutrons, and electrons through this quiz.