Introduction to AtomsChapter 11Material on Midterm

Where is it?• How do we get information about items that we cannot see?

Section 1: Development of the Atomic Theory

•Objectives• Describe some of the experiments that

led to the current atomic theory• Compare the different models of the

atom• Explain how the atomic theory has

changed as scientists have discovered new information about the atom

Section 1: Development of the Atomic Theory• The Beginning of Atomic Theory• Democritus• The particle that was so small

it could not be ______ again• The _______ Is the smallest particle

into which an element can be divided and still be the same substance• Means not able to be divided

Section 1: Development of the Atomic Theory

• The Beginning of Atomic Theory• Democritus• Challenged by

_____________• Most believed him

(even though he was wrong!)

Section 1: Development of the Atomic Theory• Dalton’s Atomic Theory Based on

Experiments• Figured out that compounds are

made of ___________ that are made of single ___________

Section 1: Development of the Atomic Theory

• Dalton’s Atomic Theory Based on Experiments• Had three parts

1. All substances are made of ________. Atoms are small particles that cannot be created, divided, or destroyed

2. Atoms of the same element are exactly alike, and atoms of different elements are _____________

3. Atoms join with other atoms to make _________ substances

Section 1: Development of the Atomic Theory

Section 1: Development of the Atomic Theory• Thomson’s Discovery of

Electrons• Thomson used a device

called a _______________• Determined that there are

_________ particles inside of an atom

Section 1: Development of the Atomic Theory

Section 1: Development of the Atomic Theory

• _____________ are subatomic particles that have a negative charge• Thomson created the _______ _________ model

to show where the electrons go

Section 1: Development of the Atomic Theory

• Rutherford’s Atomic “Shooting Gallery”• Rutherford wanted to test Thomson’s idea• Had a sheet of gold foil (SUPER THIN)• Had a detector on the outside• Shot a beam of positive particles at it

• What he expected: all of the particles would just go ____________ _______________

Section 1: Development of the Atomic Theory

Section 1: Development of the Atomic Theory• Rutherford’s Atomic “Shooting Gallery”

• What really happened• Most went straight through (like he thought)• Some got ________ at an angle• A few bounced right back!

“It was quite the most incredible event that has ever happened to me in my life. It was almost as if you fired a fifteen-inch shell into a piece of tissue paper and it came right back to you”

Section 1: Development of the Atomic Theory

• Where are the Electrons?• Plum-pudding model was ______________!• Rutherford realized that atoms were mostly ________

______________• At the center is the _______________• The nucleus is an atom’s central region, which is made up

of protons and neutrons• __________ move around it

Section 1: Development of the Atomic Theory• Bohr’s Electron Levels• Bohr figured out electrons

move around in ________• Like rungs on a ladder

Section 1: Development of the Atomic Theory

•Modern Atomic Theory• …it’s complicated• Schrodinger & Heisenberg and others helped• Electrons ______ _______ move in paths that

are very clear• We cannot predict where electrons are ______• We’re likely to find them in electron _____,

which are regions around the nucleus where electrons are likely to be found

Section 1: Development of the Atomic Theory• Section Summary• Please answer the objectives on your objective

summary sheet1. Describe some of the experiments that led to the

current atomic theory

2. Compare the different models of the atom

3. Explain how the atomic theory has changed as scientists have discovered new information about the atom

Section 2: The Atom

• Objectives• Describe the size of an atom• Name and state information about the parts of

an atom• Describe the relationship between number of

protons and neutrons and atomic number• State how isotopes differ• Describe and calculate atomic masses• Describe the forces within an atom

Section 2: The Atom• How small is an atom?

Contains 2 x 1022

20,000,000,000,000,000,000,000

20 thousand billion billion atoms

Section 2: The Atom

•1 aluminum atom has a diameter of ___________________ cm

•How many atoms thick was our foil from chapter 1?

Section 2: The Atom• What is an Atom made of?• 3 major parts• The ________ is the subatomic particle that has a positive

charge and that is found in the nucleus of an atom• The __________ is the subatomic particle that has no

charge and that is found in the nucleus of an atom• The _________ is the subatomic particle that has a

negative charge and that is found in the electron cloud surrounding the atom

Section 2: The Atom

Section 2: The Atom• How big are these pieces• VERY SMALL!

• Scientists came up with a special term for them• The atomic mass unit is a unit of ____ the describes the mass of

an atom or molecule• Proton: ~1 amu• Neutron: ~1amu• Electron: ~_______________ amu

Section 2: The Atom

• An atom is normally _____________• Same number of protons and ___________

• If an atom changes this ratio, it becomes an _________

Section 2: The Atom

• How do Atoms of Different Elements Differ?• The atomic number is the number of _________ in

the nucleus of an atom; the atomic number is the same for all atoms of an element

• An ________ is an atom that has the same number of protons/atomic number as other atoms of the same element but has a different number of neutrons (and this a different atomic mass)

• The __________ number is the sum of the protons and neutrons in an atom

Section 2: The Atom

Subatomic particle Location Charge Key feature

Proton Nucleus __________ ________ ___________

________ Nucleus Neutral Isotopes

Electron Electron cloud __________ Charge

Section 2: The Atom

• Let’s do some practice!

• An atom has a mass number of 7. It’s atomic number is 3. What is…• The number of protons?• The number of neutrons?• The number of electrons?• The name of the element?

Section 2: The Atom• Let’s do some practice!

•An atom has a mass number of 32. It’s atomic number is 16. What is…• The number of protons?• The number of neutrons?• The number of electrons?• The name of the element?

Section 2: The Atom

• Let’s do some practice!

•An atom has a mass number of 1. It’s atomic number is 1. What is…• The number of protons?• The number of neutrons?• The number of electrons?• The name of the element?

Section 2: The Atom

Boron-10

• 5 protons• 5 neutrons• 5 electrons

• Atomic number:• Mass number:

Boron-11• 5 protons• 6 neutrons• 5 electrons

• Atomic number:• Mass number:

• Naming isotopes• Remember, they are the SAME ELEMENT but differ in neutron number

Section 2: The Atom• Calculating the mass of an element• The atomic mass is not really a whole number• The atomic mass is the mass of an atom expressed in

__________ _________ ________

• Hydrogen has an atomic mass of _______________• Where does this number come from?

Section 2: The Atom

•Calculating the Mass of an Element• The atomic mass is a weighted average

of the masses of all naturally occurring __________ of the element• Takes into account that not all isotopes

are found equally on earth

Section 2: The Atom• Calculating the mass of an element• There are two different isotopes of copper• Copper-63 (69% of earth’s copper is this type)• Copper-65 (31% of earth’s copper is this type

• Steps1. Convert percentages into decimals2. Multiple decimal value by atomic mass3. Add these amounts together to find the mass

Section 2: The Atom

• Calculating the mass of an element• There are two different isotopes of copper• Copper-63 (69% of earth’s copper is this type)• Copper-65 (31% of earth’s copper is this type

• Steps1. Convert percentages into decimals• 69% 0.69• 31% 0.31

Section 2: The Atom• Calculating the mass of an element• There are two different isotopes of copper

• Copper-63 (69% of earth’s copper is this type)• Copper-65 (31% of earth’s copper is this type

• Steps2. Multiple decimal value by atomic mass

• (0.69 x 63) = 43.47• (0.31 x 65) = 20.15

Section 2: The Atom• Calculating the mass of an element• There are two different isotopes of copper

• Copper-63 (69% of earth’s copper is this type)• Copper-65 (31% of earth’s copper is this type

• Steps3. Add these amounts together to find the mass

• (43.47 + 20.15) = 63.62 amu

Section 2: The Atom• You try!• There are two different isotopes of chlorine

• Chlorine-35 (76% of earth’s chlorine is this type)• Chlorine-37 (24% of earth’s chlorine is this type

• Steps1. Convert percentages into decimals2. Multiple decimal value by atomic mass3. Add these amounts together to find the mass

Section 2: The Atom

• Forces in Atoms• Four basic forces that are working even

inside teeny atoms!• ______________ __________• ______________ __________• Strong Force•Weak Force

Section 2: The Atom• Section Summary• Please answer the objectives on your objective summary sheet1. Describe the size of an atom

2. Name and state information about the parts of an atom

3. Describe the relationship between number of protons and neutrons and atomic number

4. State how isotopes differ

5. Describe and calculate atomic masses

6. Describe the forces within an atom