Ch 4 - Atomic Theory 4.1 Atomic Theory

Review Vocabulary – Theory

New Vocabulary – Dalton’s Atomic Theory

Main Idea -The ancient Greeks tried to explain matter, but the scientific study of the atom began with John Dalton in the early 1800's.

Greek Philosophers• Many ancient scholars believed matter was composed of such things as earth, water, air, and fire.

• Many believed matter could be endlessly divided into smaller and smaller pieces.

• _____________________ (460–370 B.C.) was the first person to propose the idea that matter was not infinitely divisible, but made up of individual particles called_______________.

• ____________________ (484–322 B.C.) disagreed with Democritus because he did not believe empty space could exist.

• Aristotle’s views went unchallenged for 2,000 years until science developed methods to test the validity of his ideas.

Democritus - Greek philosopher (470-380 B.C.)

• Came up with idea of the atom.

• Used logical thinking - _____________________.

• Atomos = Greek for _____________________.

• Everything in the universe is made up of atoms – microscopic, indestructible, solid spheres.

• Constantly in motion and can combine in different combinations.

Dalton• John Dalton _________________the idea of the ______________ in the early 1800s based on numerous

chemical reactions. (________________________!)

• Dalton’s atomic theory easily explained ___________________________________ in a reaction as the result of the combination, separation, or rearrangement of atoms.

• _________________________________

• First Atomic Theory stated:

1. Each element composed of ______________.

2. Atoms of an element are_______________.

3. Different element’s atoms have different ______________________.

4. Atoms combine in ________________________ to form compounds.

5. ____________________________ occur due to separating and rejoining or rearranging of atoms.

6. Atoms of one element ____________change into another element.

4.2 Subatomic particles and the nuclear atomReview Vocabulary

model: a visual, verbal, and/or mathematical explanation of data collected from many experiments

New Vocabulary

• atom• cathode ray• electron• nucleus• proton• neutron• Main Idea - An atom is made of a nucleus containing protons and neutrons; electrons move around the

nucleus.

The Atom• The smallest particle of an element that _______________________________ of the element is called an

atom

• An instrument called the ________________________________________ (STM) allows individual atoms to be seen.

J.J. Thomson• Identified the _________________and ___________________.

• Discovered electrons using the _______________________________ and magnets.

• Concluded that the electron was _______________ charged and the proton _________________charged.

• “_________________________” model: Positive sphere with negative electrons embedded in it. (Like chocolate chip cookie dough)

• When an electric charge is applied, a ray of radiation travels from the cathode to the anode, called a cathode ray.

• Cathode rays are a stream of particles carrying a __________________ charge.

• The particles carrying a negative charge are known as ___________________.

• This figure shows a typical cathode ray tube.

• J.J. Thomson measured the effects of both magnetic and electric fields on the cathode ray to determine the ______________________________ of a charged particle, then compared it to known values.

• The mass of the charged particle was much less than a hydrogen atom, then the lightest known atom.

• Thomson received the Nobel Prize in 1906 for identifying the __________________________—the electron

Robert Millikan• In the early 1910s, Robert Millikan used the ___________________ apparatus shown below to determine

the ________________of an electron.

• 1916 – Robert Millikan determines the mass of the electron: _________________the mass of a hydrogen atom; has one unit of __________________ charge

• Mass of the electron is ______________________ g

Conclusions about The Electrona) Cathode rays have identical properties regardless of the element used to produce them. All elements must

contain_________________ charged electrons.

b) Atoms are ________________, so there must be_______________ particles in the atom to balance the __________________charge of the electrons

c) Electrons have so _____________________ that atoms must contain other particles that account for most of the mass

The Electron (cont)• Charges change in discrete amounts—1.602 10–19 coulombs, the charge of one electron (now equated to

a single unit, 1–).

• With the electron’s charge and charge-to-mass ratio known, Millikan calculated the mass of a single electron.

• Matter is neutral.

• J.J. Thomson's plum pudding model of the atom states that the atom is a uniform, positively changed sphere containing electrons.

The NucleusEarnest Rutherford

• Discovered the nucleus.• Experimented using alpha radiation and gold foil.• Nucleus is a dense, positive core in the center of the atom• Electrons move around the nucleus.• Atom is mostly empty space.

the mass of a

The Nucleus (cont.)James Chadwick

• Identified the neutron.• Neutron has no charge.• Found in nucleus.• Has a mass greater than a proton. • Neutron served as “nuclear cement” by separating the protons and accounted for missing mass of atom.

Rutherford’s Gold Foil Experiment

• In 1911, _____________________________ studied how ____________________charged alpha particles (helium nuclei) interacted with solid matter.

• By aiming the particles at a thin sheet of ___________________, Rutherford expected the paths of the alpha particles to be only slightly altered by a collision with an electron.

• Although most of the alpha particles ____________________ the gold foil, a few of them __________________________, some at large angles.

• Rutherford concluded that atoms are mostly ________________________.

• Almost all of the atom's positive charge and almost all of its mass is contained in a dense region in the center of the atom called the ____________________.

• Electrons are held within the atom by their _____________________ to the positively charged nucleus.

• The repulsive force between the positively charged nucleus and positive alpha particles caused the _________________.

• Rutherford refined the model to include ___________charged particles in the nucleus called____________.

Rutherford (cont.)

• ___________________________ received the Nobel Prize in 1935 for discovering the existence of ________________, neutral particles in the nucleus which accounts for the remainder of an atom’s mass.

• All atoms are made of ________ fundamental subatomic particles: the electron, the proton, and the neutron

• Atoms are ___________________shaped.

• Atoms are mostly empty space,

and electrons travel around the nucleus held by

an attraction to the positively charged nucleus.

Subatomic Particles• Scientists have determined that protons and neutrons are composed of subatomic particles called

____________.

• ________________________ can be explained by considering only an atom's __________________.

Additional Important Atomic Theorists Neils Bohr

• Developed the Bohr Model of the atom.

• _______________: Electrons move around the nucleus in fixed, circular orbitals that have a set amount of energy levels.

Erwin Schrödinger• Inventor of the theory of ________________________.

• Described the______________ as a ________________________ rather than as a particle

• Assigned 4 quantum numbers to an electron in an atom to describe its location (s, p, d, f)

• Electrons in ‘________________’

4.3 How Atoms DifferReview Vocabulary

periodic table: a chart that organizes all known elements into a grid of horizontal rows (periods) and vertical columns (groups or families) arranged by increasing atomic number

New Vocabulary– atomic number– isotopes– mass number– atomic mass unit (amu)– atomic mass

• Main Idea - The number of protons and the mass number define the type of atom.

Atomic Number• Each element contains a unique positive charge in their nucleus.

• The number of______________ in the nucleus of an atom identifies the element and is known as the element’s ________________________.

• Atomic number (Z) of an element is the number of protons in the nucleus of each atom of that element.

Isotopes and Mass Number• Dalton was ______________ about all elements of the same type being _______________.

• Atoms of the same element can have different numbers of__________________.

• Thus, different ____________ numbers.

• These are called ____________________.

• All atoms of a particular element have the same number of protons and electrons but the number of neutrons in the nucleus can differ.

• Atoms with the same number of protons but different numbers of neutrons are called isotopes.

• The relative ____________________of each isotope is usually constant.

• Isotopes containing more neutrons have a ______________ mass.

• Isotopes have the ___________ chemical behavior.

• The ____________________is the sum of the protons

and neutrons in the nucleus.

Mass of Atoms• One __________________________ (amu) is defined as 1/12th the mass of a carbon-12 atom.

• One amu is nearly, but not exactly, equal to one proton and one neutron.

Mass Number of Atoms • The _______________________ of an element is the ____________________________ mass of the

isotopes of that element.

Isotope Symbols• Contain the symbol of the element, the mass number and the atomic number.

EX 1- Symbolsn Find each of these:

a) number of protons

b) number of neutrons

c) number of electrons

d) Atomic number

e) Mass Number

EX 2- Symbolsn If an element has an atomic number of 34 and a mass number of 78, what is the:

a) number of protons

b) number of neutrons

c) number of electrons

d) complete symbol

EX 3- Symbolsn If an element has 91 protons and 140 neutrons what is the

a) Atomic number

b) Mass number

c) number of electrons

d) Isotope symbol

EX 4- Symbolsn If an element has 78 electrons and 117 neutrons what is the

a) Atomic number

b) Mass number

c) number of protons

d) complete symbol

Naming Isotopes• We can also put the mass number after the name of the element:

– carbon-12– carbon-14– uranium-235

• Isotopes are atoms of the same element having different masses, due to varying numbers of neutrons.

Isotope Protons Electrons Neutrons Nucleus

Isotopes (cont) Elements occur in nature as mixtures of isotopes.

Isotopes are atoms of the same element that differ in the number of neutrons.

Atomic Mass How “heavy” (mass) is an atom of oxygen?

It depends, because there are different kinds of oxygen atoms.

We are more concerned with the _____________atomic mass.

This is based on the _____________________ (percentage) of each variety of that element in nature.

We don’t use grams for this mass because the numbers would be too ____________.

Measuring Atomic Mass• Instead of grams, the unit we use is the ___________________________ (amu)

• It is defined as one-twelfth the mass of a __________________atom.

– Carbon-12 chosen because of its isotope _______________.

• Each isotope has its own atomic mass, thus we determine the _________________from percent abundance.

• Atomic mass is the weighted average of all the naturally occurring _____________of that element.

To calculate the average:

• ___________________ the atomic mass of each isotope by it’s abundance (percentage expressed as a ___________________), then___________ the results.

• If not told otherwise, the mass of the isotope is expressed in atomic mass units (amu)

Isotope Symbol

Composition of the nucleus

% in nature

Carbon-12

12C 6 protons

6 neutrons

98.89%

Carbon-13

13C 6 protons

7 neutrons

1.11%

Carbon-14

14C 6 protons

8 neutrons

<0.01%

Ex: Oxygen has three isotopesIsotope Mass in amu Abundance

168O 15.995 99.759%

178O 16.995 0.037%

188O 17.999 0.204%

______________________________________

______________________________________

______________________________________

Atomic Mass O = 15.999 amu

4.4 Unstable Nuclei and Radioactive Decay Review Vocabulary

element: a pure substance that cannot be broken down into simpler substances by physical or chemical means

New Vocabulary• radioactivity• radiation• nuclear reaction• radioactive decay• alpha radiation

Main Idea - Unstable atoms emit radiation to gain stability.

4.4 Radioactivity• Nuclear reactions can change one element into another element.

• In the late 1890s, scientists noticed some substances spontaneously emitted radiation, a process they called _________________________.

• The rays and particles emitted are called ___________________.

• A reaction that involves a change in an atom's nucleus is called a ____________________________.

• alpha particle• nuclear equation• beta radiation• beta particle• gamma rays

Radioactive Decay• Unstable nuclei lose energy by emitting radiation in a spontaneous process called

_________________________.

• Unstable radioactive elements undergo radioactive decay thus forming stable nonradioactive elements.

Alpha radiation is made up of__________________ charged particles called ________________________.

• Each alpha particle contains two protons and two neutrons and has a 2+ charge.

• The figure shown below is a __________________________ showing the radioactive decay of radium-226 to radon-222.

• The mass is _____________________in nuclear equations.

Beta radiation is radiation that has a _______________________ charge and emits _____________________________.• Each beta particle is an electron with a 1– charge.

Radioactive Decay

_____________________are high-energy radiation with no mass and are neutral.

• Gamma rays account for most of the energy lost during radioactive decay.

Radioactive Decay• Atoms that contain too many or two few neutrons are unstable and lose energy through radioactive decay

to form a stable nucleus.

• Few exist in nature—most have already decayed to _______________________.