models of the atom ms fedor arts and college preparatory academy
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Agenda 1. Collect Assignments 2. Notes: Atomic Structure 3. Activity: Atomic Pudding HW: Students who have completed quiz 2: study and schedule Quiz 3 Students who have completed Quiz 3: work on organizing your notebook, finishing your preplanning for your element project Objectives: describe the structure of an atom, understand how atomic theory developed over timeTRANSCRIPT
Models of the AtomMs FedorArts and College Preparatory Academy
ChemCatalystThe model shown here is a tiny cube of gold. 1. What do you think a scientific model
is?2. The spheres in this model represent
atoms. What do you think atoms are?
Agenda
1. Collect Assignments2. Notes: Atomic Structure3. Activity: Atomic PuddingHW: Students who have completed quiz 2:
study and schedule Quiz 3Students who have completed Quiz 3:
work on organizing your notebook, finishing your preplanning for your element project
Objectives: describe the structure of an atom, understand how atomic theory developed over time
What I Need From YouSupplements for Quiz 2
◦Mole practice problems◦Chemical formulas/reactions
Activities: ◦A New Language ◦Copper Cycle Lab◦What Goes Around Comes Around
Earliest Ideas About Atoms
Democritus – 460 BCEPhilosopherAll matter is
made up of indivisible particles
Atoms means “indivisible”
No experimental evidence to support idea
Democritus
Greek banknote with Democritus and drawing of atom
Where did Democritus get his ideas forsmall, indestructible, indivisible
atoms?
Atoms are small…
new wedding rings old wedding ring
EVIDENCE: Old wedding rings get worn away slowly, and get thinner and thinner, but you never see the gold atoms on your finger, so gold atoms must be very small!
Atoms are indestructible…
Atoms are indivisible…
EVIDENCE: The Earth has been around a long time. Even though mountains get washed away, the rocks continue to exist. New plants grow where old plants die.
EVIDENCE: None.This was a HYPOTHESIS made by Democritus to explain nature as he saw it.
Aristotle had other ideas
ARISTOTLE: Famous Greek philosopher, born 384 BCE. He was a student of Plato (another famous philosopher) and the teacher of Alexander the Great, who later conquered the world.
Greek banknote and coin picturing Aristotle
Aristotle’s idea of matterAristotle did not believe that Democritus’s idea of atoms was correct.
He believed all matter was made from four elements:
EarthAirFireWater
Aristotle’s idea of matterAristotle was more famous than Democritus, so people believed him, even though he was wrong.
So Democritus’s idea of atomos (atoms) was lost for nearly 2000 years until John Dalton brought it back in 1803.
Then in 1803…
John Dalton, an English chemistry teacher, made several conclusions about atoms from his experiments: 1. All elements are composed of tiny particles
called atoms, and the atoms of different elements are different from one another.
2. Atoms of different elements combine to form new substances in whole number ratios.
3. Chemical reactions occur when atoms are rearranged so that they attach to different atoms.
Dalton’s Chemical Symbols
We use different symbols today.
Overarching QuestionThese ideas formed the basis of atomic theory.
Dalton was wrong about atoms being indivisible. So if atoms aren’t indivisible, then where does our modern idea of the atom come from?
HOW HAS ATOMIC THEORY CHANGED OVER TIME?
WHAT DO WE NOW KNOW ABOUT ATOMS?
Activity: Atomic Pudding
1. Examine and compare the different models
2. Use new evidence to determine the correct sequence of the models
3. Identify the parts of the atom
Objectives: • I can interpret the results of each major
experiment in the development of atomic theory
• I understand and can describe the structure of an atom, and am able to explain the differences between atoms of different elements
Atoms are the smallest units of an element
Sulfur (S)
Average Atomic Mass and Reactivity
MODEL: a simplified representation of something more complex, that facilitates understanding certain aspects of a real object or processATOMS: the smallest unit of an element that retains the chemical properties of that element.
ChemCatalystWhich model represents Dalton’s idea that atoms are indivisible?
Which model suggests that there are negative particles in an atom?
Atomic TheoryAll matter is made of atoms
Solid sphere model, 1803
Plum pudding model, 1897
nuclear model, 1911
Solar system model, 1913
cloud model, quantum model, 1927-1932
first proposal of the atom, 442 BC
How did Thomson know to run an electrical current through matter?
Michael Faraday, English chemist, born 1791.In 1834 he learned that matter would interact with electricity.He realized that electricity had to me made up of particles that could be counted, but he did not know what they were. (They were electrons.)
ChemCatalystWhat are the three particles that
make up an atom?What is the charge of each
particle?
J.J. Thomson1856-1940
Discovered electron 1897◦Cathode Ray Experiment:
electric charges make materials lose negatively charged particles.
◦Atoms contain negatively charged particles
Plum Pudding model 1904◦Electrons in a soup of
positive charges
More About Charge…Opposite charges attract, alike charges repel (push away).
Cathode Ray Experiment
Thomson’s “Plum pudding” atom
– raisin
RULE: Matter is NEUTRAL, so for every electron (one negative charge) they must also have a proton (one positive charge) to balance the math to zero charge (“neutral”).
ENGLISH PLUM PUDDING– electron
Ernest Rutherford1871-1937 Gold foil experiment:
◦Shot alpha particles (positively charged particles) at gold atoms
◦Most went through, but some bounced back
Nuclear model 1911◦An atom’s mass is
mostly in the nucleus◦The nucleus has a
positive charge◦Electrons in fixed orbit
Rutherford’s Gold Foil Experiment
Rutherford gold foil experiment
Rutherford expected the a particles to pass straight through, like this…
But what he got was most a particles went straight through, but a few were deflected, like this…
Problem with Rutherford’s Model
But there also was a problem with Rutherford’s nuclear atom!To prevent the negative (-) electrons from being attracted to the positive (+) nucleus, the electrons would have to orbit the nucleus like the Earth orbits the sun.
Why don’t the electrons crash into the nucleus?
Niels Bohr1885-1962
Each element emits specific set of wavelengths of light (colors)◦Wavelength = amount of
energy◦Electrons of those
elements have different energy levels
Solar system Model 1913◦Nucleus surrounded by
orbiting electrons at different energy levels
◦Electrons have definite orbits
Bohr’s Quantized Energy LevelsBohr’s new atomic model had quantized
energy levels, meaning the electrons could only move by jumping between levels (numbered n = 1, n = 2, n = 3, etc.). They absorb energy when they jump out, and emit (send out) energy when they jump in.
Ernest Rutherford1871-1937 Alpha particles can
knock positively charged particles out of the nucleus. ◦Nucleus contains
positively charged particles called protons
Proton model 1918◦Central nucleus made of
protons◦Tiny orbiting electrons
(negatively charged)◦Most atom is empty space
ChemCatalystWho discovered the electron?
What did Bohr’s research change about the atom?
Ernst Schrödinger 1887-1961
Quantum Mechanical Model 1926
◦Electrons are in probability zones called “orbitals”, not orbits and the location cannot be pinpointed (Heisenberg uncertainty principle)
Werner Heisenberg 1901-1976
Cloud/Quantum mechanical model
James Chadwick1891-1974
Discovered Neutron 1932
Neutrons hold positively charged nucleus together
400 BC 1803 1904 1910 1913 1926
Niels Bohr
J J Thomson
Democratus
John Dalton
Schroedinger / Heisenberg
Ernest Rutherford
Atomic Theory
The Complete Modern AtomAn atom is mostly empty space with a nucleus containing protons and neutrons which contain most of the mass of an atom.Electrons are in energy levels around the nucleus, and are very tiny.
Electrons jump between levels, emitting and absorbing energy as they jump. We often refer to these energy levels as “orbitals”, but real orbitals are much more complicated…
Simple atomic modelIncludes:1. Rutherford’s discovery of the
proton 2. Chadwick’s discovery of the
neutron3. Bohr’s discovery of electrons in
orbits
Regions of an atom
Nucleus:•center of the atom•Makes up most of its mass
Electron cloud:•Mostly empty space•Take up most of the radius of the atom
Electron Cloud
Nucleus
Subatomic Particles
Neutrons (Neutral)
electrons (-)
Protons (+)
Atomic ParticlesParticle Charge mass Relative
massproton +1 1.67 x 10-
24 g1 amu
neutron 0 1.67 x 10-24 g
1 amu
electron -1 9.11 x 10-28 g
1/1840 amu
* amu = atomic mass units
A neutral atom has no net charge: number of protons is equal to the number of electrons.
#P + #e = 0
Images of atoms Scanning tunneling electron microscope 1981Bombards
surface with electrical current (electrons)
Read changes in current, translate into image