History of the Atom Chapter 3. Element Symbols Rule 1 First letter is capitalized H HydrogenC...
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Transcript of History of the Atom Chapter 3. Element Symbols Rule 1 First letter is capitalized H HydrogenC...
History of the Atom
Chapter 3
Element Symbols
Rule 1 First letter is capitalizedH Hydrogen C Carbon O Oxygen
Rule 2 Second letter is lower caseCl Chlorine He Helium Ne Neon
Rule 3 Some are Latin namesNa Sodium (natrium) Fe Iron (ferrum)
Rule 4 Some elements are named for places, scientists,
greek gods…Eu Europium Am Americium
Period
Group
Foundations of Atomic TheoryLaw of conservation of mass: Antoine Lavoisier
Mass is neither created nor destroyed.
HgO Hg + O433.2 g 401.2g + 32g
Dalton’s Atomic Theory (1808)
1. All matter is made of indivisible and indestructible atoms.
2. All atoms of the same element are identical in their physical and chemical properties.
3. Atoms of different elements have different properties.
4. Atoms of different elements combine in simple whole-number ratios to form compounds.
5. Atoms cannot be subdivided, created, or destroyed when they are combined, separated, or rearranged in chemical reactions.
Changes to Dalton’s Theory
Are atoms actually indivisible?
Are all atoms identical?
The Atom
the smallest unit of an element that retains that elements properties
Made of protons, neutrons, and electrons Can you see inside an atom?
How did they know it contains protons, neutrons and electrons?
Obscertainer Activity
Ob-scertainer Solutions
#1 #2 #3 #4
#5 #6 #7 #8
#9 #10 #11 #12
Cathode Ray Tube
When connected to electric current the remaining the gas forms a BEAM OF LIGHT.
The beam always started at the NEGATIVE electrode and flowed to the POSITIVE electrode.
The electrode is named by what type of particle it attracts Cathode: Negative (-) Anode: Positive (+)
Cathode Ray Tube Experiment
Cathode Ray Conclusions
1. The beam was attracted to a POSITIVE magnet.
2. The beam must be made of NEGATIVE particles.
JJ THOMSON DISCOVERED A NEGATIVE PARTICLE CALLED THE:
ELECTRON!
Plum Pudding Model
Plum Pudding OR Chocolate Chip Cookie
Radioactivity
Becquerel discovered RADIATION
uranium would expose photographic plates in the dark
The properties of an element changed as it gave off radiation
Curie Discovered radium and polonium
The radioactive emissions of alpha, beta and gamma rays were identified.
(Uranium compound)
Types of Radioactive Decay
Decay Type
Symbol
Charge
Reaction
Particle
Strength
Can be stopped
by…
Alpha
Beta
Gamma
Radioactive Decay
Ernest Rutherford’s Gold Foil Experiment
Set up Gold Foil with a detection sheet around it.
Set up radioactive source emitting alpha particles.
ALPHA PARTICLES shot at gold foil.
Rutherford’s Gold Foil Experiment
MOST particles went through the gold foil
SOME particles BOUNCED back
Rutherford: It’s like shooting a cannon at a piece of tissue paper and having it bounce back at you!
Gold Foil Conclusions
1. The atom is made up of mostly EMPTY SPACE
2. The center of the atom contains a POSITIVE CHARGE
3. Rutherford called this positive bundle of matter the NUCLEUS
Rutherford’s Model of the Atom
–
+ NUCLEUS
EMPTY SPACE
Other scientists later confirmed that the nucleus
was made up of protons and neutrons
Niels Bohr – 1913
Developed a new diagram of the atom Electrons can only be at certain energies Electrons must gain a specific amount of
energy to move to a higher level, called a quantum
**DISCOVERED ENERGY LEVELS!!
Bohr’s Model of the Atom
SUBATOMIC PARTICLES
Atomic number (Z) = number of protons in nucleus
Mass number (A) = number of protons + number of neutrons
= atomic number (Z) + number of neutrons
XAZ
H11 H (D)2
1 H (T)31
U23592 U238
92
Mass Number
Atomic NumberElement Symbol
Isotopes: atoms of the same element (X) with different numbers of neutrons in their nuclei
Isotopes
How many protons, neutrons, and electrons are in C146 ?
How many protons, neutrons, and electrons are in C116 ?
6 protons, 8 (14 - 6) neutrons, 6 electrons
6 protons, 5 (11 - 6) neutrons, 6 electrons
Do You Understand Isotopes?
Hyphen Notation
The mass number is written with a hyphen after the name of the element.
Element – Mass#Uranium – 235Calcium – 40
An ion is an atom, or group of atoms, that has a net positive or negative charge.
cation – ion with a positive chargeIf a neutral atom loses one or more electronsit becomes a cation.
anion – ion with a negative chargeIf a neutral atom gains one or more electronsit becomes an anion.
Na 11 protons11 electrons Na+ 11 protons
10 electrons
Cl 17 protons17 electrons Cl-
17 protons18 electrons
13 protons, 14 neutrons, 10 (13 – 3) electrons
34 protons, 44 neutrons, 36 (34 + 2) electrons
Do You Understand Ions?
How many protons and electrons are in Al2713 ?3+
How many protons and electrons are in Se7834
2- ?
Average Atomic Mass
Atomic Mass Unit
Carbon is the standard for all masses on the periodic table.
Carbon: 6 p and 6 n = 12 amu
Periodic table lists weighted average atomic masses of elements (like a GPA or final grade calculation)
Relative Atomic Mass
Calculation AVERAGE Atomic Mass
Steps:1. Percent to a
decimal
2. Multiply by mass
3. ADD IT UP!
75% 133Cs20% 132Cs5 % 134Cs