Quarter 1 Unit 2 “ Atomic Structure”
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Transcript of Quarter 1 Unit 2 “ Atomic Structure”
Quarter 1 Unit 2“Atomic Structure”
Defining The Atom
Early Models of the Atom
Atom: the smallest particle of an element
The Greek philosopher Democritus (460 B.C. – 370 B.C.) was the first to suggest the existence of atomsHe believed that atoms were indivisible and indestructible
His ideas were not based on experiments, just philosophy
Lavoisier: The Law of Conservation of Mass
Changed chemistry to a quantitative science
Measured the mass of a system before and after a reaction in a closed system▪ Stoichiometry
Isolated and named hydrogen and oxygen
Discovered how respiration and combustion are related
Major experiment involved cinnabar: red mercury oxide
Lavoisier’s Cinnabar Experiment
Proust: The Law of Definite Proportions
Copper carbonate from a variety of sources Lab-made was 57.48% Cu, 5.43% C, 0.91% H, and 36.18% O Natural was 57.48% Cu, 5.43% C, 0.91% H, and 36.18% O
Definite Proportions A compound always contains the same
elements in certain, definite proportions Also known as the law of constant composition
Dalton’s Atomic Theory~2000 years pass before more was known about the atom
John Dalton; English Chemist & School teacher; 1803
Thought the atom looked like a marble.(Round, solid sphere)
His findings were based on scientific experiments, not philosophy
Dalton Dalton (1803) Known as the FOUNDER of the atomic theory Dalton invented the word ATOM as the basic
unit of matter Dalton also claimed that all atoms of a given
element are IDENTICAL He also discovered that atoms of different
elements have different PROPERTIES AND MASSES
Found that combining atoms of different elements formed COMPOUNDS
Dalton’s Postulates
1. Compounds are composed of elements
2. Atoms of the same elements are identical and differ from other elements.
3. Atoms chemically combine in whole-number ratios
4. Atoms cannot be created or destroyed
Sizing up the Atom
Atoms are extremely small A penny containing pure copper
contains 2,400,000,000,000,000,000,000,000 atoms
Population of our planet: ~6,000,000,000
If you could line up 100,000,000 copper atoms in a single file, they would be approximately 1 cm long
Can only be observed using a scanning tunneling (electron) microscope
SEM Microscope
Dmitri Mendeleev1869
Arranged elements into 7 groups with similar properties. He discovered that the properties of elements "were periodic functions of their atomic weights". This became known as the Periodic Law.
Crookes Tube (CRT)
A magnet will deflect the cathode ray
Particles in the cathode ray are negatively charged
Drag picture to placeholder or click icon to addhttp://www.youtube.com/watch?v=IdTxGJjA4Jw
J.J. Thomsom 1897
• While using a CATHODE RAY TUBE he discovered that the ray was deflected (due to a magnetic/electrical field
• From this discovery he concluded that atoms contain small negatively charges particles called ELECTRONS
• Theory famously referred to as the PLUM PUDDING model because he visualized the ELECTRONS being EMBEDDED within the structure of the atom (just like raisin bread)
• The MASS of the rest of the atom (besides the electrons) was thought to be EVENLY DISTRIBUTED and POSITIVELY CHARGED
Thomson’s Atomic Model
“Plum Pudding” model: the electrons were like plums embedded in a positively charged “pudding,”
J. J. Thomson
The philosopher who first suggested the existence of atoms was ____________.
A. John DaltonB. DemocritusC. Ernest Rutherford
The three subatomic particles that make up an atom are
.
A. proton, neutron, electronB. nucleus, proton, electronC. cathode rays, canal rays,
neutrons
True or False? A Scanning Tunneling Electron Microscope is the only device we can use to see atoms.
A. TrueB. False
John Dalton’s model of the atom looked like a ___________
A. soccer ballB. marbleC. football
Democritus believe that atoms were _____
A. Indivisible & InvisibleB. Indestructive & InvisibleC. Indivisible & Indestructive
True or False? There were only ~200 years between Democritus’ theory and John Dalton’s work with the atom.
A. TrueB. False
The scientist who discovered the electron was _____________
A. JJ ThomsonB. Robert MillikanC. Ernest Rutherford
Mass of the Electron
1916 – Robert Millikan determines the mass of the electron: 1/1840 the mass of a proton
Mass of the electron is 9.11 x 10-28 g
The oil drop apparatus
Goldstein (1886) Discovered the
“Proton” Goldstein proved
that when negative particles are formed, so are positive
These positive particles were found to have a mass 1837x that of an electron
932 – James Chadwick (1932)
discovered the “neutron”a particle with no charge, but a mass equal to a proton
Ernest Rutherford
In 1911, Designed the Gold Foil Experiment
Aimed a beam of alpha (α) particles at a thin piece of gold foil (only a few atoms thick.)
Most α particles passed through the foil…
A small amount of the α particleswere deflected
To their surprise, some α particlesbounced straight back.
1 in ~8000 did not go through the foil
Alpha Particle Experiment
Actual Results Most went straight through
Mostly empty space
Some were deflected at huge angles Positive charge in center of atom
Others bounced straight backwards!! Small, dense solid area in center of atom
Nuclear Model
A Visual Example
Rutherford’s Atomic Model
Conclusions:There is a nucleus in the center of the atom where most of its mass is.
The nucleus is positiveAtoms are mostly empty space
Disproved J.J. Thomson’s Plum Pudding Model
If an atom is the size of a football stadium, the nucleus is the size of a marble
Niels Bohr1885-1962 Planetary Model 1913
Nucleus surrounded by orbiting electrons at different energy levels
Electrons have definite orbits
Utilized Planck’s Quantum Energy theory
Worked on the Manhattan Project (US atomic bomb)
Bohr Model for Nitrogen
Change to Dalton’s atomic theory: atoms are divisible into subatomic particles:
Electrons, protons, and neutrons
Subatomic Particles
Particle Charge Mass Location
Electron(e-) -1 virtually
nothingElectron
cloud
Proton +1 1 Nucleus
Neutron 0 1 Nucleus
Atomic Number
Elements are different because they contain different numbers of PROTONS
atomic number = the number of protons in the nucleus
# protons in an atom = # electrons
Mass Number
Mass number = number of protons and neutrons in the nucleus
Mass # = p + nElement p n e Mass #
Oxygen - 8
- 33 42
- 31 15
8 8 1616
Arsenic 75 33 75
Phosphorus 15 3116
Nuclide SymbolsContain the symbol of the element, the
mass number and the atomic number.
X Massnumber
Atomicnumber
Subscript →
Superscript →
Symbols Find each of these:
a) number of protonsb) number of neutronsc) number of electronsd) Atomic numbere) Mass Number
Br80
35
Symbols If an element has an atomic number
of 34 and a mass number of 78, what is the: a) number of protonsb) number of neutronsc) number of electronsd) complete symbol
Symbols If an element has 91 protons and
140 neutrons what is the a) Atomic numberb) Mass numberc) number of electronsd) complete symbol
Symbols If an element has 78 electrons
and 117 neutrons what is the a) Atomic numberb) Mass numberc) number of protonsd) complete symbol
IsotopesAtoms of the same element can
have different numbers of neutrons.
Thus, different mass numbers.Isotopes change the number of
neutrons & the mass number for an atom
Frederick Soddy proposed the idea of isotopes in 1912
Isotopes: atoms of the same element having different masses, due to varying numbers of neutrons.
Elements occur in nature as mixtures of isotopes.
Naming IsotopesElement name – mass number:carbon-12carbon-14uranium-235
Isotope Protons Electrons Neutrons NucleusHydrogen–1 (protium)
1 1 0
Hydrogen-2(deuterium)
1 1 1
Hydrogen-3(tritium)
1 1 2
Atomic Mass The Gold number on the P.T. is the
Average Atomic Mass of the element This is based on the abundance of each
variety of that element in nature.Instead of grams, the unit we use is the
Atomic Mass Unit (amu)It is defined as one-twelfth the mass of a
carbon-12 atom.
The Periodic Table: A Preview
Each horizontal row is called a periodEach vertical column is called a group, or familyElements in a group have similar chemical and physical properties