Chapter 4: Atomic Structure Notes

Which scientist demonstrated the existences of neutrons?

James Chadwick

What did Bohr contribute to modern atomic theory?

Bohr contributed the idea that electrons have energy levels with specific amounts of energy.

Almost all the mass of an atom is located in its a. protons b. electrons c. electron cloud d. nucleus

d. nucleus

BOHR'S MODEL

-Agreed with Rutherford's model of a nucleus surrounded by a large volume of space -However, unlike Rutherford's, Bohr's model focused on ELECTRONS. -A description of the arrangement of electrons in an atom is the centerpiece of the modern atomic model.

Applying Concepts: If a potassium atom has an atomic number of 19 and a mass number of 39 how many protons, electrons, and neutrons are in the atom?

19 protons, 19 electrons, 20 neutrons

Calculating: The atomic number for iron is 26. How many neutrons are in the nucleus of an iron atom with a mass number of 57? How many electrons does the iron atom have?

31 neutrons; 26 electrons

Hypothesizing: Why were the proton and electron discovered before the neutron?

A neutral particle is more difficult to detect than a charged particle because charged plates do not deflect its path.

RUTHERFORD'S MODEL

According to Rutherford's model, all of an atom's positive charge is concentrated in its nucleus (instead of the positive matter making up most of the atom with those negatively-charged chocolate chips or plums spread evenly throughout).

What part of Dalton's theory was modified after the discovery of isotopes?

All atoms of an element are identical

What theory did Dalton propose about the structure of matter?

All matter is composed of individual particles called atoms, which cannot be divided.

What did Rutherford discover about the structure of an atom?

All of the positive charge of an atom is concentrated in its nucleus.

Compare the mass and volume of the nucleus to the total mass and volume of an atom.

Almost all of the mass of an atom is located in the nucleus. The volume of the nucleus is much smaller than the volume of the atom as a whole.

Explain why it isn't possible for an atom to have a mass number of 10 and an atomic number of 12.

An atom with an atomic number of 12 has 12 protons. Because the mass number is the sum of the protons and neutrons, the mass number would need to be at least 12.

What does an electron cloud represent?

An electron cloud represents the most probable locations of an electron in an atom.

ELECTRON CONFIGURATION

An electron configuration is the arrangement of electrons in the orbitals of an atom.

Why have scientists developed atomic models?

Atoms are too small to be seen.

Why must indirect evidence be used to study the structure of atoms?

Atoms are too small to observe directly.

If the atomic number of an atom is 11, how many electrons does the atom have? Explain.

Because an atom must be neutral, it has 11 electrons to balance the charge of the 11 protons.

Predicting: How would the results of Thomson's experiment change if the beam were a stream of neutrons instead of a stream of electrons?

Because neutrons have no charge, the charge plates would not deflect the beam.

What is the main difference between Bohr's model of the atom and the atomic theory that is currently accepted?

Bohr assumed that electrons traveled in orbits around the nucleus. Current atomic theory assumes that electrons do not travel in fixed paths.

What was Bohr correct about? What was he wrong about?

CORRECT: assigning energy levels to electrons INCORRECT: assuming that electrons moved like planets in a solar system

Why was Dalton's model of the atom changed after Thomson's experiment?

Dalton assumed atoms were solid, indivisible particles. Thomson had evidence that smaller particles existed inside atoms.

Explain why scientists accepted Dalton's atomic theory but not the idea of an atom proposed by the Greek philosophers.

Dalton had data from experiments to support his theory, whereas the Greeks did not have data.

What did Dalton notice that all compounds have in common?

Dalton noticed that the ratio of masses of elements in a compound is always the same.

What is the most stable electron configuration?

The most stable electron configuration is the one in which the electrons are in orbitals with the lowest possible energies

Relating Cause and Effect: Brightly colored neon lights consist of tubes filled with gas. When an electric current passes through the tubes, different colors are emitted. Why might you conclude that the tubes in a multicolored display contain more than one element?

Each element used in neon lights produces a distinctive color when its atoms are excited. If there are multiple colors, there must be multiple elements present.

What is the difference between atoms of oxygen-16 and oxygen-17?

Each oxygen-17 atom has one more neutron than each oxygen-16 atom.

When is an electron in an atom likely to move from one energy level to another?

Electrons are likely to move from one energy level to another when atoms gain or lose energy.

BOHR'S MODEL AND ENERGY LEVELS How are electrons positioned, how do they move, and what are energy levels?

Electrons move with constant speed in fixed orbits around the nucleus (like planets around a sun) Each electron in an atom has a specific amount of energy. If the atom gains or loses energy, the energy of electrons can change. ENERGY LEVELS: the possible energies that electrons in an atom can have.

What property do protons and electrons have that neutrons do not have?

Protons and electrons are charged particles. Neutrons have no charge.

Comparing and Contrasting: The compound in blood that carries oxygen to cells throughout the bod contains iron. Iron has an atomic number of 26. Iron-59 is used to diagnose disorders in the blood. How is iron-59 different from all other isotopes of iron? How is it the same?

Iron-59 is different form other isotopes of iron because it contains 33 neutrons. It is the same as other isotopes because they all contain 26 protons.

How are the isotopes of an element different from one another?

Isotopes of an element have the same atomic number but different mass numbers because they have different numbers of neutrons.

WHOSE EXPERIMENTS provided the first evidence that atoms are made of even smaller particles?

J.J. Thomson: Tube/beam experiment.

Name three properties you could use to distinguish a proton from an electron.

Mass, charge, and location in an atom.

How do objects with the same charge behave when they come close to one another?

Objects with the same charge repel.

What does it mean to say that an atom is in an excited state?

One or more of the electrons in an atom have moved from the ground state to an orbital with a higher energy.

Name three subatomic particles.

Proton, electron, and neutron

What do neutrons and protons have in common? How are they different?

Protons and neutrons have almost the same mass and are both located in the nucleus of the atom. Protons are charged particles. Neutrons are neutral particles.

Compare the relative masses of protons, neutrons, and electrons in an atom.

Protons and neutrons have almost the same mass, which is about 2000 times greater than the mass of an electron.

Was Rutherford's model of an atom incorrect or incomplete? Explain your answer.

Rutherford's description of an atom was correct, but incomplete. It did not provide as much information about the behavior of the electrons as later models.

The discovery of _______________ __________________ allowed scientists to describe the differences between atoms of different elements.

SUBATOMIC PARTICLES

If an atom has an atomic number of 6 and a mass number of 14, how many protons, electrons, and neutrons are in the atom?

Six protons, six electrons, and eight neutrons

Rutherford based his hypothesis off of the _____________________ model.

THOMSON

Applying Concepts: Explain why a neutral atom cannot have one proton, one neutron, and two electrons.

The atom would have a negative charge, and atoms are neutral.

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

The atomic number represents the number of protons or electron in the atom. The mass number represents the number of protons and neutrons.

Which characteristic of an atom always varies among atoms of different elements?

The atoms of any element have a different number of protons than the atom of all other elements.

In Thomson's experiment, why was the glowing beam repelled by a negatively charged plate?

The beam contained negatively charged particles, and like charges repel.

What evidence did Thomson have that his glowing beam contained negative particles?

The beam was attracted to a positively charged plate and repelled by a negatively charged plate.

What model do scientists use to describe how electrons move around the nucleus?

The electron cloud model

A boron atom has two electrons in the first energy level and three in the second energy level. Compare the relative energies of the electrons in these two energy levels.

The electrons in the second energy level will have more energy than the electrons in the first energy level.

Describe the most stable configuration of the electrons in an atom.

The most stable configuration is the one in which the electrons are in orbitals with lowest possible energy.

What is the nucleus, and who discovered it?

The nucleus is a dense, positively charged mass located in the center of the atom. According to Rutherford's model, all of an atom's positive charge is concentrated in its nucleus.

In the Rutherford experiment, why weren't all the alpha particles deflected?

The nucleus is small compared with the atom as a whole. Very few of the alpha particles came close enough to a gold nucleus to be deflected.

If you observed a beam of particles being bent toward a negatively charged plate, what might you conclude?

The particles have a positive charge.

What evidence supported Thomson's hypothesis that the negative particles he observed came from inside atoms?

The particles were much less massive than the lightest known atom. The same particles were produced no matter which metal was used as the origin of the particles.

How can atoms be neutral if they contain charged particles?

The positive charge of the protons in the nucleus is balanced by the negative charge of the electrons.

What evidence convinced Dalton that elements must be made of individual particles called atoms?

The ratio of the mass of elements in a compound is always the same.

What determines the amount of energy gained or lost when an electron moves between energy levels?

The size of the jump between energy levels.

MASS NUMBER:

The sum of the protons and neutrons in the nucleus of an atom. MASS# = # protons(atomic number) + #neutrons #NEUTRONS = Mass # - #Protons(atomic number) #Protons = Mass # - #Neutrons

Classifying: The nucleus of an atom contains six neutrons and six protons. The nucleus of a second atom contains six neutrons and five protons. Are they atoms of different elements or isotopes of the same element? Explain your answer.

They are atoms of different elements because they have different numbers of protons. All atoms of a given element have the same number of protons.

What evidence did J.J. Thomson provide about the structure of an atom?

Thomson provided the first evidence that atoms are made form even smaller particles.

What did Dalton's model look like?

Tiny, solid sphere

Applying Concepts: A helium-4 atom has twice as many protons as a hydrogen atom. How many protons and how many neutrons are in the nucleus of a helium-4 atom?

Two protons and two neutrons

HOW BIG IS THE NUCLEUS OF AN ATOM?

VERY SMALL. The total volume of an atom is about a trillion times the volume of its nucleus.

GROUND STATE

When all the electrons in an atom have the lowest possible energies. (p. 118 example of lithium)

Inferring: If you see a green color when fireworks explode, can you be certain that the fireworks contained a barium compound? Give a reason for your answer.

You cannot be certain because elements other than barium also may produce a green color.

The atomic number of sulfur is 16. How many electrons are there in an atom of sulfur-34? a. 16 b. 34 c. 18 d. 50

a. 16

One of the first people to state that matter is made up of atoms was a. Democritus b. Aristotle c. Dalton d. Rutherford

a. Democritus

J.J. Thomson demonstrated that electrons a. have a negative electric charge b. have a positive electric charge c. are repelled by a positively charged object d. are attracted to a negatively charged object e. do not have an electric charge

a. have a negative electric charge

The number of neutrons in an atom equals the a. mass number minus atomic number b. atomic number plus number of electrons. c. mass number plus atomic number. d. atomic number minus mass number

a. mass number minus atomic number

Dalton's model of an atom is best described as a. a solar system b. a solid sphere c. a plum pudding d. an elctron cloud

b. a solid sphere

Which particle is the least massive? a. proton b. electron c. neutron d. nucleus

b. electron

Atoms emit energy as light when a. electrons move to a higher energy level b. electrons move to a lower energy level c. protons move to a higher energy level d. protons move to a lower energy level

b. electrons move to a lower energy level

Electrons in the first energy level of an atom a. have no energy b. have the lowest possible energy c. have the highest possible energy d. are in an excited state e. are in an unstable state

b. have the highest possible energy

According to Dalton's atomic theory, an atom is a. made of smaller particles b. a particle with a positive charge c. the smallest particle of an element d. in constant motion e. a particle with a negative charge

c the smallest particle of an element

Who provided the first evidence that atoms contain subatomic particles? a. Dalton b. Rutherford c. Thomas d. Bohr

c. Thomas

All atoms of an element have the same a. mass number b. number of isotopes c. atomic number d. number of neutrons

c. atomic number

An electron configuration describes a. regions of space around the nucleus of an atom b. possible energies that an electron can have c. the arrangement of electrons in an atom d. the emission of light from an excited atom e. the number of possible orbitals in an atom

c. the arrangement of electrons in an atom

What is the mass number of oxygen-18? a. 8 b. 10 c. 16 d. 18 e. 0.205

d. 18

An electron is a particle with a. a negative charge, found in the nucleus b. a positive charge, found in the nucleus c. no charge, found outside the nucleus. d. a negative charge, found outside the nucleus

d. a negative charge, found outside the nucleus

Most alpha particles pass through a thin layer of gold without deflection because gold atoms a. are filled with positively charged matter b. have no overall charge c. have a negatively charged nucleus. d. do not have a nucleus. e. have a dense nucleus surrounded by space

e. have a dense nucleus surrounded by space