topic 7. 1 atomic structure
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Topic 7. 1 Atomic Structure . 7.1.1 Describe a model of the atom that features a small nucleus surrounded by electrons. . The modern atom has gone through a few stages of development Dalton’s Atomic Therory – idea of an atom JJ Thompson – 1890 – negative charge (electrons) - PowerPoint PPT PresentationTRANSCRIPT
Topic 7. 1 Atomic Structure
The modern atom has gone through a few stages of development
Dalton’s Atomic Therory – idea of an atomJJ Thompson – 1890 – negative charge
(electrons)Earnest Rutherford – 1911 - positive nucleus
(protons)Niels Bohr – 1913 – orbital shellsChadwick – 1932 – neutrons
7.1.1 Describe a model of the atom that features a small nucleus surrounded by electrons.
This is a VERY simplified idea of the atomNucleus
Protons – positive charge – 1.6 x 10-19CNeutrons – no chargeDiameter order of 10-15m
Electron “cloud”Electrons – negative charge – 1.6 x 10-19CDiameter order of 10-10m
7.1.1 Describe a model of the atom that features a small nucleus surrounded by electrons.
The nucleus is about 100,000 times smaller than the electron orbits.
Imagine a pea in the center of a football field with the track being the orbits.
Protons and Neutrons have very similar mass. Protons and Neutrons are about 1800 times
bigger than electrons.
****IB DATA***See the data book for actual values.
7.1.1 Describe a model of the atom that features a small nucleus surrounded by electrons.
7.1.2 Outline the evidence that supports a nuclear model of the atomDalton’s Atomic Theory1. All matter is composed of extremely small particles
called atoms.2. All atoms of a given element are identical.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 a chemical reaction, atoms are separated,
combined or rearranged.
Deomcritus
Atoms
Differences in atoms
Dalton’s Atomic Theory1. All matter is composed of extremely small particles
called atoms.2. All atoms of a given element are identical.3. Atoms cannot be created, divided into smaller
particles, or destroyed. (This part proven wrong)4. Different atoms combine in simple whole number
ratios to form compounds.5. In a chemical reaction, atoms are separated,
combined or rearranged.
Deomcritus
Atoms
Differences in atoms
Dalton• Atoms
• Sameness• Created/destroyed
• Combination• Rearragement
Subatomic Particles and the AtomJ. J. Thomson – 1890-1900
Used cathode ray tube to prove existence of electron.Proposed “Plum Pudding Model”
Cathode ray tubeStream of charged particles (electrons).
Subatomic Particles and the AtomPlum Pudding
J. J. ThompsonPlum Pudding Model
Deomcritus
Atoms
Differences in atoms
Dalton• Atoms
• Sameness• Created/destroyed
• Combination• Rearragement
Thompson• Atoms composed
of electrons
Ernest RutherfordGold Foil experiment
Used to prove the existence of a positively charged core (Nucleus)
Fired alpha particles(2protons and 2 neutrons) into very thin gold foil.
The results were “like firing a large artillery shell at a sheet of paper and having the shell come back and hit you!”
Ernest RutherfordWhat should have
happened • What DID happened
Ernest RutherfordAfter performing hundreds of tests and calculations,
Rutherford was able to show that the diameter of the nucleus is about 105 times smaller than the diameter of the atom
Deomcritus
Atoms
Differences in atoms
Dalton• Atoms
• Sameness• Created/destroyed
• Combination• Rearragement
Thompson• Atoms composed
of electrons
Rutherford• Positively Charged
Nucleus
Subatomic Particles and the AtomChadwick
Worked with Rutherford.Noted there was energy in the nucleus, but wasn’t the
protons.Concluded that neutral particles must aslo exist in nucleus.
Subatomic Particles and the AtomJames Chadwick – 1932Bombarded a beryllium target with alpha
particlesAlpha particles are helium nucleus
Discovered that , carbon was produced with another particle.
**** Write reaction on board****Concluded this particle had almost identical
mass to proton but no charge. Called it a neutron
Deomcritus
Atoms
Differences in atoms
Dalton• Atoms
• Sameness• Created/destroyed
• Combination• Rearragement
Thompson• Atoms composed
of electrons
Rutherford• Positively Charged
Nucleus
Chadwick• Neutrons
exist in Nucleus
Subatomic Particles and the AtomThree main particles:
ProtonPositiveIn nucleus
NeutronsNeutralIn nucleus
ElectronsNegativeOrbiting the nucleus (not inside)
If low-pressure gases are heated or current is passed through them they glow.
Different colors correspond to their wavelengths.
Visible spectrum 400nm(violet) to 750nm(red)
7.1.3 Outline one limitation of the simple model of the nuclear atom.7.1.4 Outline evidence for the existence of atomic energy levels.
When single element gases such as hydrogen and helium are excited only specific wave lengths were emitted.
These are called emission line spectra
7.1.3 Outline one limitation of the simple model of the nuclear atom.7.1.4 Outline evidence for the existence of atomic energy levels.
If white light is pass through the gas the emerging light will show dark bands called absorption lines.
They correspond to the emission lines.
7.1.3 Outline one limitation of the simple model of the nuclear atom.7.1.4 Outline evidence for the existence of atomic energy levels.
Rutherford’s model didn’t explain why atoms emitted or absorbed only light at certain wavelengths.
1885 JJ Balmer showed that hydrogen’s four emission lines fit a mathematical formula.
This “Balmer series” also show the pattern continued into non-visible ultra-violet and infra-red.
LIMITATION
Bohr called these “energy levels” Reasoned that the electrons do not lose
energy continuously but instead, lose energy in discrete amounts called “quanta”.
He agreed with Rutherford that electrons orbit the nucleus but only certain orbits were allowed.
LIMITATION
Bohr explained the emission and absorption line spectra with the idea that electrons absorbed only certain quantity of energy that allowed it to move to a higher orbit or energy level.
Each element has its own “finger print”.
LIMITATION
Nuclear Structure
IB DefinitionsNucleon – any of the constituents of a nucleus.
Protons and neutrons.Atomic Number – The number of protons in the
nucleus.Nucleon Number – The number of nucleons in the
nucleus. AKA the mass number. (protons + neutrons)
Isotope – Nuclei which contain the same number of protons but different numbers of neutrons.
Nuclide – the nucleus of an atom. The nuclides of isotopes are different, even though they are the same element.
7.1.5 Explain the terms nuclide, isotope and nucleon7.1.6 Define nucleon number A, proton number Z, and neutron number N.
Atomic Number (proton number), ZHow many protons there are.This is what defines the element.Ex. Hydrogen Z =1, Oxygen Z = 8 Carbon Z = 6
Nucleon Number (mass number), AHow many nucleons there are. Protons + neutrons
Number of neutrons, NMass number = atomic number + number of
neutronsA = Z + N
7.1.5 Explain the terms nuclide, isotope and nucleon7.1.6 Define nucleon number A, proton number Z, and neutron number N.
Standard notation is: A over Z in front of element(X)
*****Draw on board*****
IsotopesMore evidence for neutrons is the existence of
isotopes. When nuclei of the same element have different
numbers of neutrons.Carbon has 6 isotopes: Carbon-11, Carbon-12,
Carbon-13, Carbon-14, Carbon-15, Carbon-16.All have 6 protons but each has different number of
neutrons.
7.1.5 Explain the terms nuclide, isotope and nucleon7.1.6 Define nucleon number A, proton number Z, and neutron number N.
The different isotopes don’t exist in nature in equal amounts.
Carbon: C – 12 is most abundant (98.9%)C – 13 is next (1.1%)
This is where atomic mass comes from. It’s the weighted average mass of all the different isotopes.
7.1.5 Explain the terms nuclide, isotope and nucleon7.1.6 Define nucleon number A, proton number Z, and neutron number N.
Nuclei of different atoms are known as nuclides. Ex. C – 12, C – 14Both are carbon but different isotopesTheir nuclei have different numbers of neutrons.These are different nuclides.
7.1.5 Explain the terms nuclide, isotope and nucleon7.1.6 Define nucleon number A, proton number Z, and neutron number N.
How do like charge (protons), stay stuck together?
We already know that like charges repel each other.
We have also seen that they are stronger than gravitational forces.
Strong Force – The force that binds the nucleus together.
It is an attractive force that acts between all nucleons.
Short – range interactions only (up to 10-15m)
7.1.7 Describe the interactions in a nucleus