Isotopes and Atomic Mass

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Questions and Answers

What does Bohr's model of the atom describe regarding electron behavior?

Electrons can exist in random orbits around the nucleus.

Electrons are stationary and do not move at all.

Electrons can jump between specified orbitals, gaining or losing energy. (correct)

Electrons emit radiation continuously as they revolve around the nucleus.

Which postulate is NOT part of Dalton's atomic theory?

In a compound, atoms of different elements always combine in the same way.

Atoms of the same element are identical.

Atoms of different elements can be identical in every respect. (correct)

Matter is composed of small invisible particles called atoms.

What medieval practice aimed to transform metals into gold and contributed to the scientific revolution?

Alchemy and Astrology

Astrology

Alchemy (correct)

Physics

According to Bohr's theory, when does an electron emit radiation?

When it jumps from one orbital to another. Signup and view all the answers

Which of the following individuals is known for experimenting with dissolving metals in acid during the alchemy period?

Daniel Sennert Signup and view all the answers

What defines isotopes of the same element?

Same atomic number but different mass numbers. Signup and view all the answers

Which part of the isotopic notation represents the number of protons?

Z Signup and view all the answers

What is the atomic mass of Carbon-12?

12 amu Signup and view all the answers

Which isotope of hydrogen has two additional neutrons?

Tritium Signup and view all the answers

How is the isotope notation for a neutral uranium atom with 146 neutrons expressed?

238 U 92 Signup and view all the answers

How many protons does Carbon-14 contain?

6 Signup and view all the answers

What is true about the atomic mass of Carbon?

It is an average of the isotopes' masses. Signup and view all the answers

The equation (14.0031)(X)+(15.0001)(1-X)=14.0067 is used to calculate what?

The percent abundance of nitrogen isotopes. Signup and view all the answers

Who discovered the positively charged particle in an atom?

Ernest Rutherford Signup and view all the answers

What was a key observation of Rutherford's gold foil experiment?

Some alpha particles bounced back. Signup and view all the answers

Which particle was discovered by James Chadwick?

Neutron Signup and view all the answers

What does the atomic number (Z) of an element represent?

The number of protons in the nucleus Signup and view all the answers

What is the primary conflict between Rutherford's model and Maxwell's theory?

Electrons would spiral into the nucleus due to energy loss. Signup and view all the answers

Which scientist was noted for the development of the periodic table in relation to atomic number?

Henry Moseley Signup and view all the answers

What is a characteristic feature of an atom as described in the models discussed?

Atoms are mostly empty space with electrons orbiting a nucleus. Signup and view all the answers

What happens to the charge of an atom if it gains electrons?

The atom becomes negatively charged. Signup and view all the answers

Signup and view all the answers

Study Notes

Isotopes

Atoms of the same element with the same atomic number (Z) but different mass numbers (A)
Identified using isotopic notation (X^A_Z) where:
- X = element symbol
- A = mass number (protons + neutrons)
- Z = atomic number (number of protons)
Isotopes are distinguished by their neutron count
Neutral atoms have equal number of protons and electrons (E=0)
Isotope notation can also be written as element name/symbol-mass number (e.g., uranium-238 or U-238)

Isotopes and Mass Numbers

Hydrogen has the simplest nucleus (one proton)
Atomic mass of hydrogen is approximately 1.008 amu.
Some hydrogen isotopes have additional neutrons:
- Deuterium (one additional neutron), atomic mass ≈ 2.014 amu
- Tritium (two additional neutrons), atomic mass ≈ 3.016 amu
Deuterium and tritium are isotopes of hydrogen, but behave similarly chemically to normal hydrogen.

Atomic Mass and Isotopic Abundance

Carbon has three isotopes: Carbon-12, Carbon-13, and Carbon-14
Carbon-12 is the most common and lightest.
- Six protons
- Six electrons
- Six neutrons
Carbon-13 is of medium weight
- Six protons
- Six electrons
- Seven neutrons
Carbon-14 is the rarest and heaviest among the carbon isotopes.
- Six protons
- Six electrons
- Eight neutrons

Development of Atomic Structure

Eugen Goldstein: Discovered positively charged subatomic particles (protons) in anode rays.
Ernest Rutherford: Coined the term "proton"
J.J. Thomson: Discovered electrons
James Chadwick: Discovered neutrons

The Plum Pudding Model

Thomson's model of the atom depicted electrons embedded in a sphere of positive charge, like plums in a pudding.

Rutherford's Gold Foil Experiment

Verified Thomson's model
Alpha particles were directed at a thin gold foil
Most particles passed straight through
Some particles were deflected at large angles
A few particles bounced back
This indicated a concentrated positive charge (nucleus) within the atom, surrounded by electrons.

Atomic Models

Similarities and differences between Thomson and Rutherford's models: Thomson proposed a theory, compared an atom to a watermelon, and stated that electrons reside within a positively charged sphere. Rutherford conducted an experiment, stating electrons moved around a central nucleus.
Modern atomic model: Atom is mostly empty space with a nucleus containing protons and neutrons, with electrons orbiting the nucleus.

Modern Periodic Table

Henry Moseley: Determined the atomic number corresponds to the number of protons in an atom.
James Maxwell: Explained that the loss of energy by moving charged particles may produce radiation and affect atom stability.

Laws of Chemistry

Law of Conservation of Mass: Total mass of substances before a reaction equals the total mass after the reaction.
Law of Definite Proportions: Elements combine in fixed proportions to form a compound

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Description

Explore the fascinating world of isotopes in this quiz, which covers definitions, notation, and various isotopes of elements like hydrogen and carbon. Test your understanding of atomic mass and isotopic abundance, and learn to distinguish between different isotopes based on their neutron count.