Chemistry Chapter 4 Test Review

Questions and Answers

What is an atom?

The smallest particle of an element that retains its identity in a chemical reaction.

What were the limitations of Democritus's ideas about the atoms?

He did not test his theory and had no scientific evidence to back it up.

Using Dalton's atomic theory, describe how atoms interact during a chemical reaction.

During a chemical reaction, atoms are either joined, separated, or rearranged. They are never changed into atoms of a different element.

What experimental evidence did Thomson have for 'electrons have a negative charge'?

The positive plate attracted the cathode ray, indicating the ray consisted of tiny negatively charged particles called electrons. Signup and view all the answers

What experimental evidence did Thomson have for 'atoms of all elements contain electrons'?

Thomson found the same results regardless of the metal or gas used; the ratio of charge to mass of an electron remained constant. Signup and view all the answers

Would you expect 2 electrons to attract or repel?

Repel. Signup and view all the answers

How do the charge and the mass of a neutron compare to the charge and mass of a proton?

Their masses are nearly equal, but protons have a positive charge and neutrons have a neutral charge. Signup and view all the answers

Why does it make sense that if an atom loses electrons, it is left with a positive charge?

Losing negative charge leads to more positive charge than negative charge. Signup and view all the answers

Describe the location of the electrons in Thomson's plum pudding model of the atom.

The electrons are stuck in a lump of positive charge. Signup and view all the answers

How did the results of Rutherford's gold-foil experiment differ from his expectations?

Rutherford expected alpha particles to pass through with slight deflection, but some faced major deflection. Signup and view all the answers

What is the charge of the nucleus of every atom?

Positive. Signup and view all the answers

In the Rutherford atomic model, which subatomic particles are located in the nucleus?

Protons and neutrons. Signup and view all the answers

Why is an atom electrically neutral?

The number of electrons is equal to the number of protons. Signup and view all the answers

What does the atomic number of each atom represent?

The number of protons in the atom. Signup and view all the answers

What is the difference between the mass number and the atomic number of an atom?

Mass number is the number of protons and neutrons, atomic number is only the number of protons. Signup and view all the answers

Name 2 ways that the isotopes of an element differ.

Mass number and number of neutrons. Signup and view all the answers

How can there be more than 1000 different atoms when there are only about 100 different elements?

Each atom has a different number of isotopes. Signup and view all the answers

What data must we know about the isotopes of an element to calculate the atomic mass of the element?

The mass and the natural percentage abundance of an isotope. Signup and view all the answers

How is an average mass different from a weighted average mass?

Average mass assumes equal abundance; weighted average reflects both average mass and relative abundance. Signup and view all the answers

What is the atomic mass of an element?

The weighted average mass of the atoms in a naturally occurring sample of the element. Signup and view all the answers

How are the elements arranged in a modern periodic table?

By atomic number. Signup and view all the answers

Characterize the size of an atom.

Small/Microscopic; made up of mostly empty space. Signup and view all the answers

Compare the size and the density of an atom with the nucleus.

The nucleus is denser and smaller than the atom, which is mostly empty space. Signup and view all the answers

Describe the numbers and kinds of subatomic particles in a boron-11 nucleus.

5 protons and 6 neutrons. Signup and view all the answers

What parts of Dalton's atomic theory no longer agree with the current picture of the atom?

Atoms are now known to be divisible and not all atoms of a particular element are identical. Signup and view all the answers

How did Millikan calculate the mass of an electron?

He conducted a simple algebraic procedure after finding the charge and using Thomson's charge to mass ratio. Signup and view all the answers

How is the number of electrons in an atom of a given element related to the atomic number of that element?

The number of electrons equals the atomic number if the atom is neutral. Signup and view all the answers

Dalton's atomic theory was not correct in every detail. Should this be taken as a criticism of Dalton as a scientist?

No, because scientific truth is not absolute; new data may change our results. Signup and view all the answers

Why are atoms considered the basic building blocks of matter, even though smaller particles, such as protons and electrons exist?

Atoms are the smallest particles of an element that still maintain the chemical properties of that element. Signup and view all the answers

Study Notes

Atoms and Their Properties

Atoms are the smallest units of elements that maintain their chemical identity during reactions.
An atom is electrically neutral due to equal numbers of protons (positive charge) and electrons (negative charge).

Historical Perspectives on Atoms

Democritus lacked experimental evidence to support his atomic theory, leading to limitations in his ideas.
Dalton's atomic theory posited that atoms are rearranged in chemical reactions but never transformed into different elements.

Key Discoveries in Atomic Structure

Thomson's experiments revealed that cathode rays are made of negatively charged particles, now known as electrons.
Thomson concluded that all atoms contain electrons because results were consistent across different materials, showing a constant charge-to-mass ratio.

Atomic Models and Experiments

In Thomson's "plum pudding" model, electrons are embedded in a positively charged "soup."
Rutherford's gold-foil experiment showed unexpected deflection of alpha particles, indicating a dense, positively charged nucleus.

Nuclear Components

The nucleus consists of protons (positive charge) and neutrons (neutral charge), making it dense compared to the larger, less dense atom.
The atomic number represents the number of protons in an atom, dictating elemental identity.

Isotopes and Atomic Mass

Isotopes are variations of an element with differing mass numbers due to different numbers of neutrons.
The atomic mass is a weighted average of isotopes based on their natural abundance and mass.

Periodic Table Organization

Elements in the modern periodic table are arranged by increasing atomic number, reflecting their proton count.
Atomic structure is characterized by being predominantly empty space, with a small, dense nucleus.

Fundamental Concepts in Atomic Theory

Dalton's atomic theory is outdated in aspects like the indivisibility of atoms and the identity of isotopes within elements.
Millikan determined electron charge and mass through calculated procedures based on Thomson's findings.
Atoms are the fundamental building blocks of matter, preserving the chemical properties of elements despite the existence of smaller subatomic particles.

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Prepare for your Chemistry Chapter 4 test with these flashcards. This review covers key concepts such as the definition of an atom and the limitations of early atomic theories. It's a great tool to reinforce your understanding of atomic interactions in chemical reactions.