Introduction to Atoms

Introduction to Atoms Chapter 11 Material 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 smallit could not be ______ again • The _______ Is the smallest particleinto 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 • All substances are made of ________. Atoms are small particles that cannot be created, divided, or destroyed • Atoms of the same element are exactly alike, and atoms of different elements are _____________ • 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 • _____________ are subatomic particles that have a negative charge • Thomson created the _______ _________ modelto 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 • 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 sheet • 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 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 __________ numberis the sum of the protons and neutrons in an atom

Section 2: The Atom

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 • Naming isotopes • Remember, they are the SAME ELEMENT but differ in • neutron number Boron-10 Boron-11 5 protons 6 neutrons 5 electrons Atomic number: Mass number: • 5 protons • 5 neutrons • 5 electrons • Atomic number: • Mass 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 • Steps • Convert percentages into decimals • Multiple decimal value by atomic mass • 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 • Steps • 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 • Steps • 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 • Steps • 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 • Steps • Convert percentages into decimals • Multiple decimal value by atomic mass • 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 sheet • 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

Introduction to Atoms