Download Chapter 4 Cornell Notes

PreAP Chemistry Chapter 4 Cornell Notes
____________________ was the early (around 400BC) Greek philosopher who is credited with the concept
of the atom (atomos) – which means ____________________
____________________ (around 1800AD) is an English school teacher who proposed the law of
conservation of mass, the law of definite proportions, and the law of multiple proportions. His many
experiments with gases proved these law are true, if atoms exist. He is also known as the
____________________________________________________________
Dalton’s atomic theory
1.
All matter is composed of very small particles called ____________________
2.
Atoms of a given element are identical in ____________________, ____________________, and
other properties; atoms of different elements differ in these properties.
3.
Atoms cannot be ____________________, ____________________, or ____________________
4.
Atoms of ____________________ elements combine in simple ____________________ ratios to
form chemical compounds.
5.
In chemical reactions, atoms are ____________________, ____________________, or
____________________
Two aspects of Dalton’s atomic theory proven to be incorrect:
a.
We now know atoms are ____________________
b.
Atoms of the same element can have different ____________________
____________________ - smallest particle of an element that retains the ____________________ of that
element.
____________________ is the man credited with the discovery of the electrons in the late _____, using
cathode ray tubes.
____________________ discovered the mass of the electron.
Knowledge of electrons led to two inferences about atomic structure:
1.
Because atoms are electrically ____________________, they must contain
____________________ charge to balance the negative electrons.
2.
Because electrons have so little mass, atoms must contain other particles to account for most of
their ____________________
Nucleus of the atom—discovered by ________________________________________
Gold foil experiment—actually done by ____________________ and ____________________
Observations:
a.
Majority of the ____________________ particles penetrated foil ____________________
b.
About ____________________ in ____________________ were ____________________
deflected
c.
About ____________________ in ____________________ were deflected
____________________
Conclusions:
1.
___________________ of the atom and the ____________________ charge are concentrated in
small regions called ____________________
2.
3.
Most of the atom is ______________________________.
__________________________of charge on the nucleus is__________________ for different
atoms.
4.
Number of ____________________ outside the nucleus = number of units of
____________________ (to account for the fact that the atom is electrically
____________________
Atoms are electrically neutral because they contain equal numbers of ____________________ and
____________________
A couple years later Rutherford presented evidence for a neutral particle which was also in the nucleus and
contained a similar mass to that of a proton – called a ____________________________________
Mass of one____________________= mass of one ____________________= mass of 1837
____________________
Thus the total mass of an atom is basically the sum of the protons and neutrons, called the
___________________ ___________________ or ____________________ ____________________,
abbreviated A.
Atomic number

number of ____________________in the ____________________of the atom.

number of ____________________ ____________________ the element and is equal to the
number of ____________________

symbol is Z.
____________________are atoms of the same element that have different masses because they have
different numbers of ____________________, but they still have similar chemical
____________________
____________________is the general term for any isotope of any element
______________ _____________
___________ (1 _______) is exactly 1/12 the mass of a carbon-12
atom.
______________ _____________ _____________ is the weight average of the atomic masses of the
naturally occurring isotopes of an element.
Ave. Atomic mass = (%abundance × mass of isotope 1) + (%abundance × mass of isotope 2) +…..
Example 1:
Element Sciencium has two isotopes. Sciencium-301 has an abundance of 59.5%, and Sciencium-304 is
the other. What is the average atomic mass?
Example 2:
Element Pepsium has an average atomic mass of 335. If only two isotopes of Pepsium exist, Pepsium-327
and Pepsium-338, then what is the abundance of Pepsium-327?
Mass Spectrometry
If a sample of a
A mass
pure element is
spectrometer has
placed in the
three parts:
spectrometer,
1. ionizer
then all the ions
2. magnetic field
formed will have
3. detector
the same charge.
And might look
For example Cl
like this →
→ Cl-
The ions then pass
through a magnetic
field that will
change their paths.
Which will change
direction more,
something heavy
or something light?
The computer attached to the detector gives a readout like this →
The locations tell the masses – one group of Cl had a mass of 35 amu’s
and the other had a mass of 37 amu’s.
The sizes of the bars indicate the relative amounts of each isotope.
As the bar for 35Cl is 3 times bigger than 37Cl (measuring with a ruler)
35
Cl is about 75% abundant and 37Cl is about 25% abundant.
Unstable Nuclei and Radioactive Decay (Chapter 24)
1) When referring to nuclear reactions people commonly think of nuclear ____________________ (the
____________________ of large atoms into smaller pieces) and nuclear ____________________ (the
____________________ of small atoms into one large one), but on earth these reactions do not occur
naturally.
2) Naturally occurring nuclear reactions result from the unusual number of neutrons of an isotope which
makes it ____________________ (unusually high in energy). This often results in the isotope
____________________ from one element into another element in an attempt to become more stable
(lower in energy).
A) These reactions are called ____________________ reactions, as they involve changes in the
nucleus.
B) During these nuclear reactions, rays and particles are given off, which is called
____________________.
C) Sometimes an unstable nucleus will change into many different elements as it tries to become
more stable. This is called ____________________ decay.
3) When radioactive decay occurs, there are three different types of radiation that can be given off. Each
type has a different ____________________, and sometimes a ____________________.
A) The first type of radiation to be discovered was called ____________________ radiation and
came from alpha particles.
𝟐𝟐𝟔
𝟖𝟖𝐑𝐚
i)
?
→ 𝟐𝟐𝟐
𝟖𝟔𝐑𝐧 + ??
Because the mass numbers must be equal, 226 = 222 + x. So the mass of the alpha particle
must be ____________________.
ii) Because the atomic numbers must be equal, 88 = 86 + x. So the atomic number of the alpha
particle must be ____________________.
iii) The element ____________________ has a mass of 4 and an atomic number of 2, so the
alpha particle is just like a helium atom without any electrons;
𝟒
𝟐𝐇𝐞
or 𝟒𝟐𝛂
B) The second type of radiation to be discovered was called ____________________ radiation and
came from beta particles.
𝟏𝟒
𝟔𝐂
i)
→ 𝟏𝟒𝟕𝐍+ ???
Because the mass numbers must be equal, 14 = 14 + x. So the mass of the beta is
____________________.
ii) Because the atomic numbers must be equal, 6 = 7 + x. So the atomic number must be
____________________.
iii) The ____________________ has a mass of zero and a charge of -1, so the beta particle is just
like an electron;
𝟎
−𝟏𝛃
C) The last type of radiation to be discovered was called ____________________ radiation and came
from gamma particles.
𝟐𝟑𝟖
𝟗𝟐𝐔
i)
𝟒
?
→ 𝟐𝟑𝟒
𝟗𝟎𝐓𝐡 + 𝟐𝐇𝐞 + ??
Because the mass numbers must be equal, 238 = 234 + 4 + x. So the mass of the gamma
particle must be ____________________.
ii) Because the atomic numbers must be equal, 92 = 90 + 2 + x. So the atomic number must also
be ____________________.
iii) The gamma particle was the last to be found because it has no ____________________ and
no ____________________; it is just high energy waves of radiation
𝟎
𝟎𝛄