Chapter 4 Atomic Structure

Each of an element's __________ has a different number of neutrons and a different mass number.

isotopes

The center of this atom is called the __________.

nucleus

Step 2. Its mass number is __________.

19

Step 2. Its mass number is

9

The modern process of discovery about atoms began with the theories of an English schoolteacher named __________.

John Dalton

__________ used experimental methods to propose an atomic theory based on earlier ideas.

John Dalton

Why is the atomic mass unit (amu), rather than the gram, usually used to express atomic mass?

The values of atomic masses measured in grams are inconveniently small and impractical to work with.

Step 4. Is your answer reasonable? Why?

Yes it is, because the mass is greater than the atomic number.

Neon-20 and neon-22 are called __________.

isotopes

Explain why in 1911 Rutherford and his coworkers were surprised when they shot a narrow beam of alpha particles through a thin sheet of gold foil.

The expected most of the alpha particles to pass easily through the foil with only a slight deflection. They found that most alpha particles were not deflected at all, and a few were deflected at very large angles.

The __________ of an element is the weighted average of all the isotopes of the element.

atomic mass

A negatively charged particle.

electron

Step 3. The shorthand notation for beryllium-9 is:

9 Be 4

__________ first proposed that atoms are small, indestructible particles that make up all matter.

Democritus

Step 4. Is your answer reasonable? Why?

Yes it is, because the mass number is great than the atomic number.

An electron with a positive charge.

anode

What charge does a neutron carry?

none

There is a small core known as a(n) __________ in the center of an atom which contains the protons and neutrons.

nucleus

What is the mass number of a helium atom that has two protons and two neutrons?

4

How do atoms of neon-20 and neon-22 differ?

An atom of neon-22 has two more neutrons in its nucleus than an atom of neon-20.

How is the atomic theory that is accepted today different from Dalton;s atomic theory?

Atoms are now known to be divisible. They can be broken down into even smaller, more fundamental particles.

Circle the letter next to the number of units of positive charge that remain if a hydrogen atom loses an electron.

B

Circle the letter of each sentence that is true about atoms, matter, and electric charge. a. All atoms have an electric charge. b. Electric charges are carried by particles of matter. c. Electric charges always exist in whole-number multiples of a single basic unit. d. When a given number of positively charged particles combines with an equal number of negatively charged particles, an electrically neutral particle is formed.

B, C, D

Suppose you grind a sample of the element copper into smaller and smaller particles. The smallest particle that could no longer be divided , yet still has the chemical properties of copper, is __________.

a copper atom

Most of the volume of an atom is occupied by __________.

electrons

The __________ of the atom is 16.

mass number

The total number of protons and neutrons in an atom is its __________.

mass number

Elements are different because their atoms contain different numbers of __________.

protons

Is the following sentence true or false? An alpha particle has a double positive charge because it is a helium atom that has lost two electrons.

true

Is the following sentence true or false? Isotopes are chemically alike because they have identical numbers of protons and electrons.

true

Step 1. The atomic number of fluorine-19 is __________.

9

hydrogen-1

hydrogen

hydrogen-3

tritium

About how many atoms of copper when placed side by side would form a line 1 cm long?

100,000,000

Step 3. The shorthand notation for carbon-12 is:

12 C 6

Step 3. The shorthand notation for fluorine-19 is:

19 F 9

Step 1. The atomic number of beryllium-9 is

4

How many neutrons does a beryllium atom with four protons and a mass number of nine have?

5

An electron with a negative charge.

cathode

Although atoms are extremely small, scientists can observe them using instruments such as the __________.

scanning electron microscope

The particles that make up atoms—protons, neutrons, and electrons—are known as __________ particles.

subatomic

When chlorine occurs in nature, there are three atoms of chlorine-35 for every one atom of chlorine-37. Which atomic mass number is closer to the average atomic mass of chlorine?

35 amu

Circle the letter of each sentence that is true about the nuclear theory of atoms suggested by Rutherford's experimental results. a. An atom is mostly empty space. b. All the positive charge of an atom is concentrated in a small central region called the nucleus. c. The nucleus is composed of protons. d. The nucleus is large compared with the atom as a whole. e. Nearly all the mass of an atom is in its nucleus.

A, B, E

Circle the letter of each statement that is true about the average atomic mass of an element and the relative abundance of its isotopes. a. In nature, most elements occur as a mixture of two or more isotopes. b. Isotopes of an element do not have a specific natural percent abundance. c. The average atomic mass of an element is usually closest to that of the isotope with the highest natural abundance. d. Because hydrogen has three isotopes with atomic masses of about 1 amu, 2 amu, and 3 amu, respectively, the average atomic mass of natural hydrogen is 2 amu.

A, C

Circle the letter of each sentence that is true about Dalton's atomic theory. a. All elements are composed of tiny, indivisible particles called atoms. b. An element is composed of several types of atoms. c. Atoms of different elements can physically mix together, or can chemically combine in simple, whole-number ratios to form compounds. d.Chemical reactions occur when atoms are separated, joined, or rearranged; however, atoms of one element are changed into atoms of another element by a chemical reaction.

A, C, D

Thomson observed that the production of cathode rays did not depend on the kind of gas in the tube or the type of metal used for the electrodes. What conclusion did he draw from these observations?

He concluded that electrons must be parts of the atom of all elements.

What two properties of an electron did Robert Millikan determine from his experiments?

He determined that quantity of charge carried by an electron and its mass.

List two reasons why the ideas of Democritus were not useful in a scientific sense.

They did not explain chemical behavior, and they lacked experimental support because Democritus's approach was not based on the scientific method.

The __________ of a sample of the element is 10.81 __________. This number is not a whole number because the sample contains different __________ of the element.

atomic mass, amu, isotopes

Step 1. The number of protons in an atom is called its __________ number. The number of protons in an atom of carbon-12 is __________.

atomic, 6

Democritus, who lived in Greece during the fourth century B.C., suggested that matter is up of tiny particles that cannot be divided. He called these particles __________.

atoms

What isotope of carbon has been chosen as the reference isotope for atomic mass units? What is the defined atomic mass in amu of this isotope?

carbon-12; 12 amu

A glowing beam traveling between charged electrodes.

cathode ray

What subatomic particles carry a negative charge?

electrons

Is the following sentence true or false? The atomic mass of an element is always a whole number of atomic mass units.

false

Step 2. The number of protons plus the number of neutrons in an atom is called its __________ number. For carbon-12, this number is __________.

mass, 12

The positively charged subatomic particle that remains when a hydrogen atom loses an electron is called a(n) __________.

proton

The identity of an element is determined by the number of __________ it contains.

protons

The atom contains 5 __________ and 5 __________.

protons, electrons

Step 4. Except for hydrogen-1, the mass number of an isotope is always greater than its atomic number. Is the mass number reasonable?

yes

The __________ of the atom is 5.

atomic number

hydrogen-2

deuterium

The atom contains 6 __________.

neutrons