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Understanding the Atom

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Presentation on theme: "Understanding the Atom"— Presentation transcript:

1 Understanding the Atom
Chapter 9 Material on Midterm Exam

2 Essential Questions What is an atom?
How would you describe the size of an atom? How has the atomic model changed over time? What happens during nuclear decay? How does a neutral atom change when its number of protons, electrons, or neutrons changes?

3 Section 1: Discovering the Parts of an atom
The Beginning of Atomic Theory ___________________ A particle that was so small it could not be cut again The ___________ is the smallest piece of an element that still represents that element Means not able to be divided Democritus atom

4 Section 1: Discovering the Parts of an atom
Early ideas about matter Democritus Challenged by ______________ Most believed him (even though he was wrong!) Aristotle

5 Section 1: Discovering the Parts of an atom
__________’s Atomic Model Figured out that compounds are made of elements that are made of single _________ Dalton atoms

6 Section 1: Discovering the Parts of an atom
Dalton’s Atomic Theory Based on Experiments Had three parts ______________________________________________. Atoms are small particles that cannot be created, divided, or destroyed _______________________________________________ , and atoms of different elements are different _______________________________________________ All substances are made of atoms Atoms of the same element are exactly alike Atoms join with other atoms to make new substances

7 Section 1: Discovering the Parts of an atom

8 Section 1: Discovering the Parts of an atom
________________-- Discovering electrons Thomson used a device called a cathode ray tube Determined that there are _________________ particles inside of an atom Thomson negative

9 Section 1: Discovering the Parts of an atom

10 Section 1: Discovering the Parts of an atom
__________________ are subatomic particles that have a negative charge (1-) Thomson created the ______________________ to show where the electrons go Electrons Plum-Pudding Model

11 Section 1: Discovering the Parts of an atom
__________________--Discovering the Nucleus 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 ______________________________ Rutherford right through

12 Section 1: Discovering the Parts of an atom

13 Section 1: Discovering the Parts of an atom
Rutherford’s Atomic “Shooting Gallery” What really happened Most went ________________________(like he thought) Some got __________ at an angle A few ___________________________! “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” straight through bent bounced right back

14 Section 1: Discovering the Parts of an atom
Rutherford’s Conclusions Atoms re mostly empty space The nucleus is a small area in the ___________ of an atom where most of an atom’s ________ and ____________________________ is concentrated The nucleus is positive because of protons, atomic particles that have one ______________ charge (1+) Negatively charged electrons move in the empty space ____________________ the nucleus center mass positive charge positive surrounding

15 Section 1: Discovering the Parts of an atom
Rutherford’s Atomic Model Plum-pudding model was wrong! Rutherford realized that atoms were mostly empty space At the center is the _______________ The nucleus is an atom’s central region, which is made up of _________________________ Electrons move ___________ it nucleus protons and neutrons around

16 Section 1: Discovering the Parts of an atom
Discovering Neutrons Rutherford’s colleague, James Chadwick discovered in addition to protons, the nucleus also contained neutrons Neutrons are ________________ particles that exist in the nucleus of an atom neutral

17 Section 1: Discovering the Parts of an atom
_________’s Atomic Model Bohr figured out electrons move around in ____________ Like rungs on a ladder Bohr paths

18 Section 1: Discovering the Parts of an atom
Modern Atomic Model …it’s complicated Schrodinger & Heisenberg and others helped Electrons do not move in paths that are very clear We ____________________where electrons are exactly We’re likely to find them in an ______________________, which is an area around the nucleus where an electrons is most likely to be located cannot predict electron cloud

19 Scientists Matchup __ Went against Democritus; people believed this scientist even though he was wrong ___ Used the term “electron cloud” to show where electrons are likely to be found ___ Saw that a positive particles could bounce off gold foil ___ Realized that compounds are made of elements that are made of atoms ___ Realized that atoms are mostly empty space ___ Had an atomic theory with three different parts ___ Gave us the term “atom” ___ Discovered the neutron ___ Discovered the positively charged nucleus ___ Discovered that there are negatively charged particles in an atom ___ Determined that electrons move around in paths like rungs on a ladder ___ Determined that electrons do not move around in predictable paths ___ Created the “plum pudding model” ___ A particle that is so small it cannot be divided again A. Aristotle E. Rutherford B. Bohr F. Schrodinger & Heisenberg C. Dalton G. Thomson D. Democritus

20 The Parts of an Atom Symbol Size Charge Location Electron e- - Proton
Section 2: Protons, Neutrons, and Electrons—How atoms differ 55 The Parts of an Atom Symbol Size Charge Location Electron e- ~1/1800 amu - Outside nucleus Proton p+ 1 amu + Nucleus Neutron n0 ~1 amu No charge PROTON + charge In nucleus NEUTRON No charge ELECTRON - charge Outside nucleus

21 Section 2: Protons, Neutrons, and Electrons—How atoms differ
Atomic Counting Atomic Number-number of protons in an atom of an element (= # p+) Atom’s identity EX: Oxygen has 8 protons; its atomic number is 8 Mass Number- sum of the number of protons and neutrons in an atom (= p+ + n0) (skip e-  too small) EX: Oxygen has 8 protons and 8 neutrons for a mass number of 16 The number on the periodic table is a decimal, so we have to round “5 and above...” give it a shove “4 and below…” down you go

22 Atomic Counting Neutrality Ions Atom is overall neutral (+ = -)
Section 2: Protons, Neutrons, and Electrons—How atoms differ Atomic Counting Neutrality Atom is overall neutral (+ = -) # p+ = # e- EX: Oxygen has 8 electrons to balance the 8 protons Ions Ions are when atoms are no longer neutral because they have gained or lost electrons Lose e-? Become positive (NaNa+) Gain e-? Become negative (ClCl-) EX: Oxygen atom and Oxygen ion O 8p+ 8n0 8e- O2- 8p+ 8n0 10e-

23 Atomic Counting Isotopes
Section 2: Protons, Neutrons, and Electrons—How atoms differ Atomic Counting Isotopes Atoms of the same element HAVE to have same # p+, but not # n0 Isotopes atoms of the same element with different numbers of neutrons EX: Oxygen-16 and Oxygen-18 O16 8p+ 8n0 8e- O18 8p+ 10n0 8e Some isotopes are radioactive, which means they spontaneous emit radiation in a process called nuclear decay

24 Section 2: Protons, Neutrons, and Electrons—How atoms differ
Atomic Counting The atomic number of Calcium is 20, and the mass number is 40 There are _______ protons There are _______ electrons There are _______ neutrons The mass number of Calcium is 41 What changes? Proton Neutron Electron We call atoms of the same element with different mass number ____________________ 20 20 20 isotopes

25 Section 2: Protons, Neutrons, and Electrons—How atoms differ
Atomic Counting The atomic number of Sodium is 11, and the mass number is rounded to 23 There are _______ protons There are _______ electrons There are _______ neutrons This sodium has 10 electrons What changes? Proton Neutron Electron We call atoms of the same element with electron numbers ____________________ 11 11 12 ions

26 Atomic Counting Atom 1 has 7 protons and 7 neutrons
Section 2: Protons, Neutrons, and Electrons—How atoms differ Atomic Counting Atom 1 has 7 protons and 7 neutrons Atom 2 has 8 protons and 8 neutrons How many electrons are in Atom 1? ___________ What is the mass number of Atom 1? __________ How many electrons are in Atom 2? ___________ What is the mass number of Atom 2? __________ Are these different elements , ions or isotopes? ____________ 7 14 8 16 Different elements

27 Atomic Counting 10 20 10 21 Isotopes
Section 2: Protons, Neutrons, and Electrons—How atoms differ Atomic Counting Atom 3 has an atomic number of 10 and 10 neutrons Atom 4 has an atomic number of 10 and 11 neutrons How many electrons are in Atom 3? ___________ What is the mass number of Atom 3? __________ How many electrons are in Atom 4? ___________ What is the mass number of Atom 4? __________ Are these different elements , ions or isotopes? ____________ 10 20 10 21 Isotopes

28 Atomic Counting Atom 5 has 17 protons, 17 electrons and 18 neutrons
Section 2: Protons, Neutrons, and Electrons—How atoms differ Atomic Counting Atom 5 has 17 protons, 17 electrons and 18 neutrons Atom 6 has 17 protons, 18 electrons and 18 neutrons How many protons are in Atom 5? ___________ What is the mass number of Atom 5? __________ How many protons are in Atom 6? ___________ What is the mass number of Atom 6? __________ Are these different elements , ions or isotopes? ____________ 17 35 17 35 Ions

29 Atomic Counting Atom 7 has 3 protons and 4 neutrons
Section 2: Protons, Neutrons, and Electrons—How atoms differ Atomic Counting Atom 7 has 3 protons and 4 neutrons Atom 8 has 3 protons and 3 neutrons How many electrons are in Atom 7? ___________ What is the atomic number of Atom 7? ________ What is the mass number of Atom 7? __________ How many electrons are in Atom 8? ___________ What is the atomic number of Atom 8? ________ What is the mass number of Atom 8? __________ Are these different atoms or isotopes? ____________ 3 3 7 3 3 6 Isotopes

30 Atomic Counting Calculating average atomic mass abundance
Section 2: Protons, Neutrons, and Electrons—How atoms differ Atomic Counting Calculating average atomic mass atomic mass is not really a whole number The average atomic mass of an element is the average mass of the element’s isotopes, according to the __________________of each isotope Ex: Hydrogen has an atomic mass of abundance

31 Atomic Counting—guided practice
Section 2: Protons, Neutrons, and Electrons—How atoms differ Atomic Counting—guided practice Calculating the average atomic mass of an element Convert percentages into decimals Multiply decimal value by atomic mass Add these amounts together to find the mass

32 Atomic Counting Sample problem: Steps
Section 2: Protons, Neutrons, and Electrons—How atoms differ Atomic Counting Sample problem: 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 _________________ Multiply decimal value by atomic mass _____________________ Add these amounts together to find the mass (_________ + ________) = ____________ amu 69%  0.69 31%  0.31 (0.69 x 63) = 43.47 (0.31 x 65) = 20.15 43.47 20.15 63.62

33 Atomic Counting Sample problem 2: Calculating the mass of an element
Section 2: Protons, Neutrons, and Electrons—How atoms differ Atomic Counting Sample problem 2: Calculating the mass of an element There are two different isotopes of chlorine Chlorine-35 (75.53% of earth’s chlorine is this type) Chlorine-37 (24.47% of earth’s chlorine is this type Steps

34 Atomic Counting You Try! Calculating the mass of an element Steps
Section 2: Protons, Neutrons, and Electrons—How atoms differ Atomic Counting You Try! Calculating the mass of an element There are three different isotopes of magnesium Magnesium-24 (78.70% of earth’s magnesium is this type) Magnesium-25 (10.13% of earth’s magnesium is this type Magnesium-26 (11.7% of earths’s magnesium is this type) Steps

35 Section 2: Protons, Neutrons, and Electrons—How atoms differ
Atomic “Art” Step 1: Draw the nucleus with the # of protons and neutrons Step 2: Determine # of electron shells (circles) needed to hold the electrons (2 in first, 8 in second, 8 in third) Step 3: Draw electrons as dots using this rule: North North, East South West, East South West New shell? Start over H He Li Be 1 p+ 0 n0 2 p+ 2 n0 3 p+ 4 n0 4 p+ 5 n0

36 Section 2: Protons, Neutrons, and Electrons—How atoms differ
Atomic “Art” H He Li Be 4 p+ 5 n0 1 p+ 0 n0 2 p+ 2 n0 3 p+ 4 n0

37 Atomic “Art” Drawing in electrons The rule is
Section 2: Protons, Neutrons, and Electrons—How atoms differ Atomic “Art” Drawing in electrons The rule is North North, East South West, East South West Na Al O Ar 8 p+ 8 n0 18 p+ 22 n0 11 p+ 12 n0 13 p+ 14 n0

38 Section 2: The Atom Drawing an atom EXCEPTION:
Section 2: Protons, Neutrons, and Electrons—How atoms differ Section 2: The Atom Drawing an atom The rule is North North, East South West, East South West EXCEPTION: Group 14 (carbon): ___ outer electrons Pattern: ____________ 4 NESW C 6 p+ 6 n

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