chapter 4 – the atom
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CHAPTER 4 – THE ATOM. John Dalton’s Atomic Theory (19 th Century). 1) All matter is composed of small particles called atoms 2) All atoms of an element are identical in size, mass, and chemical properties 3) Atoms cannot be created, divided into smaller particles or destroyed - PowerPoint PPT PresentationTRANSCRIPT
CHAPTER 4 – THE ATOM
John Dalton’s Atomic Theory (19th Century)
1) All matter is composed of small particles called atoms
2) All atoms of an element are identical in size, mass, and chemical properties
3) Atoms cannot be created, divided into smaller particles or destroyed
4) Different atoms combine in simple whole number ratios to form compounds
5) In chemical reactions, atoms are separated, combined, or rearranged
FALSE
FALSE
Rule #4
+
ELEMENT A ELEMENT B COMPOUND of A and B
Rule #5
+
What is an atom?
• Defn – smallest particle of an element that retains properties of the element
How many copper atoms can fit on a penny?
29,000,000,000,000,000,000,000 atoms(29 x 1021)
Electron
• Discovered by J.J. Thomson (1909) using a cathode ray tube (CRT)
• Electron – negative charged particle of matter (-1)
- has no relative mass
Nucleus
• Discovered by Ernest Rutherford (1911) using Gold Foil Experiment
• Nucleus – dense, positively charged region in center of atom
http://www.mhhe.com/physsci/chemistry/essentialchemistry/flash/ruther14.swf
Composition of Nucleus
a) Proton – positive (+1) charged particle of nucleus
b) Neutron – neutral (0) charged particle of nucleus
Particle Symbol Location ChargeRelative
Mass
Electron e- around nucleus -1 0
Neutron n0 nucleus 0 1
Proton p+ nucleus +1 1
What makes an atom of one elementdifferent from an atom of another element ?
Atomic Number
• Defn – number of protons in an atom
• How is periodic table arranged?by increasing atomic number
• How many electrons do atoms have?# electrons = # protons
atomic number identifies atoms
reading the periodic table
H
Hydrogen
1
1.008
Element
Atomic number
SymbolAtomic mass
Mass Number
• Defn – total number of protons and neutrons
NOT SAME AS ATOMIC MASS!!!!!!
H
Hydrogen
1
1.008
Cannot be found on periodic table
NO NO NO NO NO!!!!
Mass Number
• Remember this formula to find # neutrons:
MANM – A = N (Mass #) – (Atomic #) = Neutrons
Refresh!!!!
• I’ve given you 3 numbers:
1) Atomic number2) Atomic mass3) Mass number
The ones with the word “ATOMIC” is on the periodic table
Not on periodictable
What’s in a cheeseburger?
Isotope• Defn – atoms with same number of
protons, but different number of neutrons
HYDROGEN - 1 HYDROGEN - 2 HYDROGEN - 3
= neutrons= protons
= electrons
3 Different Hydrogen IsotopesHYDROGEN – 1
(protium)
1 proton0 neutrons1 electron
HYDROGEN – 2(deuterium)
HYDROGEN – 3(tritium)
1 proton1 neutron1 electron
1 proton2 neutrons1 electron
Ways to write isotopes
1) Hyphen notation (2 parts)
name of element – # OR symbol – #
ex: carbon-14 OR C-14 chlorine-35 OR Cl-35 hydrogen-3 OR H-3
MASSNUMBER
Ways to write isotopes
2) Nuclear symbol (3 parts)
C14
6elementsymbol
mass number
atomic number
Ex problem
K
Potassium
19
39.10
# protons
# neutrons
# electrons
Nuclearsymbol
Potassium-39 Potassium-40 Potassium-41
19
19
1919
19
2220 21
19
K KK39
19
41
19
40
19
Mass of individual atoms
• Atoms have very very tiny masses to work with (~10-27 kg)
• Instead we use a relative mass – atomic mass unit (amu)
• Atomic Mass Unit (amu) – 1 amu ≈ mass of 1 proton or 1 neutron
amu’s and subatomic particles
particle Mass (amu)
e-
p+
n0
0.000549
1.007276
1.008665
0
1
1
Atomic Mass
• Defn – weighted average mass of all isotopes of an element
• Where can it be found?found on periodic table K
Potassium
19
39.10
Ex problem: Calculate atomic mass of chlorine.
Isotope mass (amu) percent abundance
35Cl 35 75.770%37Cl 37 24.230%
What do you expect the average to be?About 35 amu
Actual = 35.453 amu
Which isotope is most abundant?Ar-38, Ar-40, or Ar-41?
Ar
Argon
18
39.948
Ar-40