the nature of science the natural world is understandable science demands evidence science is a...
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Atomic Structure & Theory Notes The Nature of Science
The Natural world is Understandable Science Demands Evidence Science is a Blend of Logic & Imagination Scientific Knowledge is Durable
Theory = used to explain complex natural processes. Scientific Law = often use mathematical formulas to
show relationships and make predictions about the natural world. A description of what happens.
Subject to Change Scientists Attempt to Avoid Bias Science is a complex social activity.
Scientific Method Question/Problem/Observation Hypothesis – an EDUCATED Guess proposed
reason for what is observedExperiment – To test hypothesis.
Create a controlled experiment with one experimental variable, constants, and controls. Quantitative Data = numeric data. Qualitative Data = nonnumeric data.
Analyze Data – Create Graphs, Perform calculations Etc.
Conclusion – Compare experimental results with hypothesis. Create a new hypothesis.
Experiment Theory
Law
Hypothesis
Observation
Non linear nature of science video
Observation Versus Inference
An observation is the gathering of information by using our five senses: sight, smell, hearing, taste, touch Qualitative- Quality = descriptive Ex. The shirt is blue. Quantitative- Quantity = numerical Ex. The flower has 7
petals.
An inference is something a scientist thinks is true, based on observations or evidence. They are based on your past experiences and prior knowledge. Examples:
Observation: The grass on the playground is wet. Possible inferences: It rained. The sprinkler was on. Observation: The line at the water fountain is long. Possible inferences: It's hot outside. The students just
came in from
Observation vs Inference
Examples: Observation: The grass on
the playground is wet. Possible inferences: It
rained. The sprinkler was on. There is morning dew on the grass.
Observation: The line at the water fountain is long.
Possible inferences: It's hot outside. The students just came in from
The Greek Philosophers A. Around 450 BC a Greek
philosopher, Democritus proposed the all matter is actually composed of tiny, indivisible particles, which he called atomos.
B. At the same time Aristotle and other philosophers did not agree. They thought that if matter were made up of tiny particles it would fall apart. Aristotle's view made more sense at the time, so it prevailed for 21 centuries.
A. Law of Conservation of Matter
(Antoine Lavoisier) – Matter can neither be
created nor destroyed in a chemical reaction
II. Late 1700's
Example: 16 X + 8 Y 8YX2
Mass Mass Atoms Atoms
B. Law of Constant Composition
A given compound always contains the same elements in the same proportions by mass.
Example: H2O is always 11.1 % hydrogen and 88.9 % oxygen; no matter how much water there is. Same proportions of H & O Same proportions
of H & O (by mass)
“Now that’s High Quality H2O”
Law of Multiple Proportions
-Applies to different compounds made from the same elements.
-The mass ratio for one of the elements that combines with a fixed mass of the other element can be expressed in small whole #’s
Examples:H2O : 2 H + 1 O (2:1)H2O2 : 2 H + 2 O (2:2)
1) Each element is composed of extremely small particles called atoms, which are identical in their chemical properties.
2) All atoms of a given element are identical, but they differ from those of any other element.
3) Atoms of different elements combine in simple whole number ratios to form chemical compounds.
4) Atoms are neither created nor destroyed
when they are combined, separated or rearranged in a chemical reaction.
Solid Sphere Model. Nothing smaller = no subatomic particles
Experimented with cathode raysHe concluded that there were
negatively charged particles he called electrons.
The "Plum Pudding" or "Raisin Bun" model.
Like a ball of chocolate chip cookie dough.Choc. Chips = electronsDough = positive charge
Raisins (electrons) dispersed throughout positive dough.
raisins = e-
Soft pudding-like dough = positive charge
The Charge on the electron
Robert Millikan discovered the numerical charge on the electron using the oil drop experiment
Gold Foil experimentWhen Rutherford directed a beam of
positive α particles at a thin gold foil, most of the particles passed through unaffected, but a small fraction deflected in all directions. The small number that were deflected indicated that most of the atom was empty space.
Rutherford concluded that the positive charge of the atom was concentrated in a small compact nucleus.
Rutherford’s Experiment
• Model called the "Nuclear atom"Positive charge concentrated in the nucleus, w/ e- moving around it.
• Atom is mostly empty space
• Positive Particles in nucleus later called protons
• If this dot were the nucleus of an atom, the atom would have the diameter of a football field. The nucleus is very tiny compared with the rest of the atom.
James Chadwick (1932) discovered a particle with no charge and a mass equal to a proton-he called it a neutron.
Planetary MODEL Experimented on Hydrogen proposed that e- in an atom can
reside only in certain energy levels or orbitals
The rungs on a ladder are similar to the energy levels within an atom. A person can move up or down the ladder only by standing on its rungs; it is impossible to stand between them
e-
e-
e-
e-e-
e-
e-
e-
e-
e-
• Nucleus (p+ & n0)• Concentric Circular orbits
Particle Symbol Charge Mass (AMU)
Electron e- -1 0
Proton p+ +1 1
Neutron n0 0 1
• Element = made of one kind of Atom.• Compounds = made of different atoms combined in
whole number ratios.• Mixtures are physical combinations of elements or
compounds with variable composition.
What holds nucleus together?
Nuclear Tug-Of-War Electrostatic force – like charges repel and unlike charges
attract
Strong Nuclear Force – holds nucleons (p+ & n0) together, very strong nuclear force but over short distances Stable nuclei are SMALL Large nuclei tend to be unstable (radioactive)
+ ++ -
Where do Atoms Come From?
Fusion = smaller atoms combine to form larger atoms (stars & supernovas)
Fission = large atoms split (atomic bombs, nuclear reactors)
Why don’t electron’s fly off?
Electrostatic Force Holds electrons on atom Nuclear Pull: + nucleus pulls – electrons
towards itself. More charge = more attraction
Increases
Counting Particles in Atoms NotesAtomic Number = (smaller #) = # of
p+ = unique for each element
Atomic Mass Number = mass of an atom = p+ & nº (e- have no mass)
Complete Shorthand Symbol “top heavy”
atomic Mass Sym Atomic #
Example:
Counting e-
Atoms are neutral so, p+ = e- (assume an atom is neutral unless a
charge is written) Ions = charged atoms (lost or gained e-) (charge in upper right hand corner )
Cation = positive atom (lost e-) Anion = negative atom (gained e-)
NeutronsIsotopes = atoms of the same element with diff. numbers of nº and atomic masses
Sym-massU-235 H-3 C-14 13C 6
The number is the atomic mass
Formulas:
# of p+ = Atomic Number # of nº = Atomic Mass – Atomic
Number # of e- = Atomic Number – charge
Examples: 35 Cl –1
17
Mg+2
19 F –1
9
Average Atomic Mass All masses are based on the mass of C
= 12 amu (atomic mass unit) Relative to Carbon Relative Atomic Mass
Use mass spectrometer Average Atomic Mass
Weighted average of the masses of the isotopes of that element
Reflects relative abundance of isotopes in nature
mass number exact weight percent abundance
12 12.000000 98.90
13 13.003355 1.10
To calculate the average atomic weight, each exact atomic weight is multiplied by its percent abundance (expressed as a decimal). Then, add the results together and round off to an appropriate number of significant figures.
This is the solution for carbon:
(12.000000) (0.9890) + (13.003355) (0.0110) = 12.011 amu
.Average Atomic Mass = Σ [abundance * mass] (sum of)
EX:
6329Cu 65
29Cu69.1 % 30.9 %
(63 * 0.691) = (65 * 0.309) = 63.618
Try These
Problem #3: Chlorine Problem #4: Silicon
mass number
exact weight
percent abunda
nce
mass number
exact weight
percent abunda
nce
35 34.96885 75.77 28
27.9769 92.23
37 36.96590 24.23 29
28.9764 4.67
3029.973
7 3.10
The answer for chlorine: 35.453 The answer for silicon: 28.086
Warm up 9-15-14
1. For Ca2+ find the: Electrons Protons Neutrons Atomic Mass Atomic Number
2. Find the Average mass for Silver:
Isotope nameIsotope mass (a
mu) percentage
Silver-107 106.90509 51.86
Silver-109 108.90470 remainder
Radioactive Isotopes (radioactive…radioactive)
Some types of atoms spontaneously change because they are unstable. They eject sub particles or emit energy and are transformed into different types of atoms.
Atoms that are changed in this way are called radioactive, and the transformation process is called radioactive decay.
Products of Decay
Natural Decay Products - there are three major products emitted by the decay of naturally occurring radioactive isotopes. Alpha particles (α) Beta particles (β- & β+) Gamma ray (γ)
Radiation
alpha
Radiation Interaction and Penetration Through Matter
alpha
beta
gamma
neutron
High charge, dense ionization, short path
Less mass/charge than alpha, longer path
No charge or mass, much less interaction
No charge, interacts through nuclear events
Not to scale
Characteristics
• +2 charge• 2 protons• 2 neutrons• Large mass
Alpha Particle aAlpha Particle a
Range
• Very short range• 1" -2" in air
Shielding
• Paper• Outer layer of skin
Hazards
• Internal
Sources
• Plutonium• Uranium• Radium• Thorium• Americiuma a a a
a
Characteristics
• -1 charge
• Small mass
Beta Particle bBeta Particle b
Range
• Short range
• About 10' in air
Hazards
• Skin and eyes
• Can be internal
Sources
•Radioisotopes
• Activation Products • Sealed sources
Shielding
• Plastic safety glasses
• Thin metal
Characteristics
• No charge• No mass• Similar to x-rays
Gamma Ray gGamma Ray g
Range
• Long range• About 1100' in air
Hazards
• External (whole body)• Can be internal
Sources
• X-ray machines• Electron microscopes• Sealed sources• Accelerators• Nuclear reactors• Radioisotopes
Shielding
• Lead• Steel• Concrete
Paper Plastic Lead
Characteristics
• No charge• Found in nucleus
Neutron Particle hNeutron Particle h
Range
• Extended range
Shielding
• Water• Plastic
Hazards
• External (whole body)
Sources
• Fission• Reactor operation• Sealed sources• Accelerators
Paper Lead Water
Half Life Half Life = (t1/2) The amount of time
it takes for ½ of the radioactive isotope to decay (no longer there- changed into something else.
Multiply the mass by ½ for each ½ life that passes (or divide by 2)
Estimating the AGE of Materials
Radioactive carbon-14 atoms are used to estimate the age of materials that were once living. Living things all have the same ratio of radioactive
carbon to ordinary carbon. Once something dies, the amount of C-14 begins to decrease. The ratio of C-14 to C-12 can be used to determine its age.
Radioactive uranium is used to date non-organic material such as rocks.
Examples of half Life1. How much of a 10.0 g sample of I-
131 is left after 48 days? (1/2 life = 8 days)
2. After how many days will a 24 g sample decay to 3.0 g?
3. After 95 days, a 24 g sample of radioactive material decays, leaving 0.75g. What is the half-life of this material?
Periodic Law (Periodicity)
Properties repeat at regular intervals when elements are arranged according to increasing atomic number
Group/family = column; Period = row
*
Transition Metals
Alkaline Earth Metals Noble Gases
Inner Transition Metals
HalogensAlkali Metals
Metal/Metalloid/Nonmetal
MetalsMetalloids
Nonmetals
Representative Elements (1,2,13 – 18)
6A
1A
7A 5A
4A
3A 2A
8A
B’s
. Atomic Number = # of protons
Atomic Mass = # of protons & neutrons
INC
INC
Nuclear pull = electrostatic attraction of + nucleus for the negative outer e-
Shielding = e- in between nucleus & outer e- shield pull
INC
INC
Constant
Atomic RadiusAtomic Radius = the distance
between the nucleus and the outermost electrons.
e- are added to successively higher energy levels.
We remain in the same principle energy level. Each element has one p+ and one e- more than the preceding element. The nuclear pull increases pulling each new e- closer to the nucleus.
INC
H0.030
Na0.157
K0.203
In0.150
Sr0.191
Rb0.216
Sn0.140
Sb0.140
Te0.137
I0.133
Ca0.174
Ga0.125
Ge0.122
As0.121
Se0.117
Br0.114
Mg0.136
Al0.125
Si0.117
P0.110
S0.104
Cl0.099
Li0.123
Be0.089
B0.080
C0.077
N0.070
O0.066
F0.064
The atomic radii of these representative elements are given in nanometers (nm).
Increasing atomic radii
Increasing atomic radii
Ionic Radius (Size) Size or radius of an ion
INC
Cations Anions
The overall trend is the same as Atomic size – for the same reasons, however:• Cations have lost e- so they are smaller • Anions have gained e- so they are larger
O2-
0.140F-
0.136
Be2+
0.031Li+
0.060
Cs+
0.169Tl3+
0.095
K+
0.133Ca2+
0.099
Na+
0.095
N3-
0.171
Cl-
0.181S2-
0.184P3-
0.212
As3-
0.222
Ba2+
0.135
Rb+
0.148Sr2+
0.113In3+
0.081Sn4+
0.071I-
0.216Te2-
0.221Sb3-
0.245
Ga3+
0.062Ge4+
0.053 Se2-
0.198Br-
0.195
Pb4+
0.084
Al3+
0.050Mg2+
0.065Si4+
0.041
B3+
0.020C4+
0.015
The ionic radii shown here are given in nanometers.