Download Chapter 4 Notes

PreAP Chemistry Chapter 4 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.
Most of the atom is ______________________________.
3.
__________________________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. Two isotopes of Pepsium exist. If Pepsium-327 is 30.5% abundant, then what is the second
isotope?
Mass Spectrometry
If a sample of a pure element
A mass spectrometer has three
is placed in the spectrometer,
parts:
then all the ions formed will
1. ionizer
have the same charge. For
2. magnetic field
example Cl → Cl-
3. detector
And might look like this →
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) 35Cl is about 75% abundant and 37Cl is
about 25% abundant.
Unstable Nuclei and Radioactive Decay
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
?
→ 𝟐𝟐𝟐
𝟖𝟔𝐑𝐧 + ??
i)
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
𝟒
𝟐𝐇𝐞 or 𝟐𝛂
B)
The second type of radiation to be discovered was called ____________________ radiation and came from beta particles.
𝟏𝟒
𝟔𝐂
→ 𝟏𝟒𝟕𝐍+ ???
i)
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
𝟒
?
→ 𝟐𝟑𝟒
𝟗𝟎𝐓𝐡 + 𝟐𝐇𝐞 + ??
i)
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 ____________________;
𝟎
𝟎𝛄