CHEM1010/HZ
Chapter Summary/Chapter 2
Review and Summary for Chapter 2
Lavoisier: The law
of mass conservation
Chemistry as a quantitative science
The law of mass conservation
Proust: The law of
definite proportions
The law of definite proportions
Significance of the law of definite proportions
Dalton: The law of multiple proportions
Dalton’s atomic theory of matter and its changes
How Dalton’s atomic theory explains the three fundamental laws about matter and its changes
How to explain the law of
conservation of mass
How to explain the law of definite proportions in mass
How to explain the law of multiple proportions in mass
Various types of relative atomic mass
Introduction to Mendeleev’s Periodic Table
Atomic mass data accumulating for various elements
Accumulation of data of physical and chemical properties of various elements
Attempts to set order for various elements
Mendeleev’s Periodic Table
How Mendeleev set up his Periodic Table
What does Mendeleev’s Periodic Table look like?
Gap in the table or Map for chemistry?
Revisit to matter classification
Operational classification vs. theoretical classification
Modern Periodical Table
Group A and Group B
Metals, non-metals, and in between (metalloids), noble gases
Basic language of today’s modern chemistry
Chemical letters: 114 atoms discovered so far
Chemical molecules: Chemical words
Chemical reactions: Chemical sentences
Questions about atoms: Their components and structure?
In science and
chemistry, we are working on two ends, one is the scientific observations, and
the other is the scientific theory. And then, the next is to connect the two,
i.e., we need to create theories and hypotheses to explain the observations and
predict new chemical changes.
In science and
chemistry, both facts and theories need to be quantitative, meaning we need
numbers for observations, and the theory and hypotheses need to be able to
explain the observations quantitatively. Being qualitative is fine, which is
often the first step (very important), but it’s not enough.
A. Matter is non-continuous, separable
B. Matter is continuous, inseparable
The thinking of the Greek
Democritus: Matter is composed of inseparable particles called atoms.
Aristotle (ca. 384-ca. 322 b.c.): Matter is continuous, not atomistic.
The
Aristotle’s idea dominated for about 2000 years until the emergence of modern
chemistry.
Modern chemistry
started with Antoine Lavoisier (1743-1794, a French scientist/chemist)
He did many quantitative chemical experiments and measurements.
An important step was he weighed the total mass of the substances involved in a reaction before and after the reaction took place (doing chemistry quantitatively).
Example: 2HgO (red) = 2Hg (liquid metal) + O2
100.00g 93.57g 6.43g
This is the most important reaction he performed. He named the gas
oxygen.
It is a
generalization of certain natural phenomenon based on many observations of
similar individual cases. The approach of induction: From many individual cases
to come up with the generalization.
Example: All horses have four legs.
The law of mass
conservation formulized by Lavoisier
Matter is neither
created nor destroyed during a chemical reaction; in other words, the total mass
of the reaction products (ending substances) is always equal to the total mass
of the reactants (starting substances)
This is the scientific basis for chemical reaction equations.
We cannot create things out of
nothing.
We need resources.
We cannot destroy things we don’t want completely.
We have to deal with wastes.
Things are limited in our Earth, at least.
If we create some things, then we cannot avoid loosing something else.
The law of definite proportions formulized by Joseph
Louis Proust (1754-1826, born in France, living in Spain)
In a certain chemical composed of two or more components, the components are always present in a definite proportion by mass.
Suppose a chemical has two components of A and B, then the mass ratio is fixed, so for example the ratio may be
Mass of A : Mass of B = 1:2
A case study:
10.00 g lead + 1.55 g sulfur = 11.55 g lead sulfide
10.00 g lead + 3.00 g sulfur = 11.55 g lead sulfide + 1.45 g sulfur
(leftover)
18.00 g lead + 1.55 g sulfur = 11.55 g lead sulfide + 8.00 g lead
(leftover)
Clearly, the mass ratio is fixed:
10.00 : 1.55 for lead : sulfur
Another case study:
32.00 g oxygen gas + 4.00 g hydrogen gas = 36.00 g water
32.00 g oxygen gas + 8.00 g hydrogen gas = 36.00 g water + 4.00 g
hydrogen gas
36.00 g oxygen gas + 4.00 g hydrogen gas = 36.00 g water + 4.00 g oxygen
gas
Clearly, the mass ratio is fixed: 8 : 1 for oxygen gas : hydrogen gas
Significance of
the law of definite proportions
Many chemicals are composed of one or more different components.
The components are in proportion to each other at a fixed ratio in mass,
in other words, not random ratio.
The proportion is universal, no matter where and when a chemical is
found or produced or in which way it is made, naturally or artificially, by this
method or another.
The law of
multiple proportions formulized by John
Dalton (1766-1848, an
English schoolteacher)
More than one ratio
or proportion can exist for combination of the same set of two or more
components.
A case study
1.00 g carbon + 1.332 g oxygen = 2.332 g carbon monooxide
1.00 g carbon + 2.664 g oxygen = 3.664 g carbon dioxide
Clearly, here we see two mass ratios of carbon over oxygen:
1st ratio Carbon : oxygen = 1 : 1.332 = 3 : 4
2nd ratio
Carbon : oxygen = 1 : 2.664 = 3 : 8
Dalton’s law of multiple proportions is actually an extension of
Proust’s law of definite proportions. In other words, Proust’s law of
definite proportions is only a special case of Dalton’s multiple proportions.
Dalton’s
atomic theory
1. All matter is composed of extremely small particles called atoms.
2. There are different kinds of atoms.
3. Each kind of atoms has many many identical individual atoms. Since
they are all the same kind, they represent one particular chemical element. This
element has a symbol to represent all the same atoms and each of them.
4. Compounds are formed when atoms of different elements (different kinds of atoms) combine in fixed or definite proportions or ratios.
5. A chemical reaction is simply a rearrangement of atoms, changing the combination of the different kinds of atoms.
The mass values of
atoms are extremely small, for example:
electron mass = 9.11×10-31
kg
proton mass = 1.67×10-27
kg
It is very difficult to work with these small numbers.
Relative mass of
atoms
Dalton assembled relative masses for a number of atoms based on hydrogen:
Relative mass = Mass of an atom/Mass of hydrogen
This way, the small values are canceled and you get a ratio of the
masses, which give you a number that is much easier to work with.
Example: relative mass of fluorine is 19
This means: Mass of F/Mass
of H = 19
Relative mass of carbon is 12
This means: Mass of C/Mass of H = 12
How to explain
the law of conservation of mass
Following the fifth point: “A chemical reaction is simply a
rearrangement of atoms, changing the combination of the different kinds of
atoms,” then, since any rearrangement of the combination of the atoms neither
increases nor decreases the amount of atoms, the total mass of all the atoms
remains the same before and after the reaction. As a matter of fact, the total
number of the atoms involved remains unchanged in the reaction.
How to explain
the law of definite proportions:
Fact: 1 g hydrogen + 19 g
fluorine = 20 hydrogen fluoride
the mass ratio
of Hydrogen:Fluorine = 1:19
Known: Mass of Fluorine is 19 times the mass of hydrogen
Theory:
1 atom of hydrogen combines with 1 atom of fluorine to form 1 compound of
hydrogen fluoride (HF)
Reasoning:
Suppose mass of 1 hydrogen atom is 0.1 g, to form 1 HF, you need 1 atom of
fluorine, and its mass should be 0.1×19 = 1.9 g.
If you have 10 atoms of hydrogen, then you need 10 atoms of fluorine to
form 10 HF, then the total mass of 10 H is 0.1 × 10 = 1 g, and the total mass
of 10 F is 1.9 × 10 = 19 g.
Since we have understood that we just need to adjust the ratio of the component atoms for a particular compound, then we can predict different mass ratios for different compounds having the same component atoms. Example: CO and CO2,
The approach here is the ratio of component atoms, then from this ratio,
we can find out the mass ratio.
This theory still cannot
explain a bunch of other observations and facts and chemical reactions.
Example:
It
cannot explain how a battery works.
It
cannot tell the structure of compounds.
It
does not tell how atoms get together to form the compounds or elemental
substances.
It
does not tell why some reactions are easy to happen but some are not.
It
does not tell under what conditions a reaction can happen, and if it needs
energy or releases energy?
And
more…
Efforts to search a logic or systematical way to organize the chemical elements
Precursors of the
Periodic Table
Dalton, attempt to arrange the elements according to relative atomic
mass.
Dobereiner(German chemist), “Triads”: three similar elements (Li,
Na, K; Ca, Sr, Ba)
De Chancourtois (French geologist), Telluric Helix
Newland (English chemist), every eighth element had similar properties
Meyer (German chemist), a much similar periodic table (1870) to
Mendeleev’s (1869)
The most successful
attempt was made by Dmitri Mendeleev, a Russian chemist.
Mendeleev arranged the elements following atomic
mass in an increasing order. By this arrangement, a number of properties of the
elements exhibit periodic regularity, in other words, they change with atomic
mass periodically (with peaks and valleys).
The periodic
regularity is called the periodic law: If the elements are listed in order of
increasing atomic mass, certain sets of properties recur periodically in this
listing.
Some properties showing
periodicity
-atomic volume = atomic mass/density
-electrical conductivity
-thermal conductivity
-hardness
In Mendeleev’s
Periodic Table, he left some blank spaces or gaps.
The most amazing thing was he did not think this was a defect of the
table, but instead, he predicted existence of some unknown elements to be
discovered.
..As an example, Germanium was later discovered:
Properties of Germanium: Predicted and Observed
Property
Predicted (1871)
Observed (1886)
Atomic mass 72 72.6
Density (g/cm3) 5.5 5.47
Color Dirty gray Grayish white
Density of Oxide EsO2: 4.7 GeO2: 4.703
Boiling point of
chloride EsCl4: < 100 °C GeCl4: 86 °C
Density of chloride
EsCl4:
1.9
GeCl4:
1.887
The powerful
predictability of Mendeleev’s Periodic Table makes it become a map for
elements. This is an excellent example of the power of induction in science.
Induction: from particular cases a generalization is formulized and it can
predict new particular cases that are unknown.
Operational
definitions: Those in which a definition is given by a certain practical
operation without referring to its meaning in a relevant context
Theoretical
definitions: Those in which a definition is formulized based on theoretical
ideas or models and thus each definition has theoretical meaning in a relevant
context
Example: Define qualified apples
of a certain kind for Standard A apples
Operational definition: Any apples that can pass a net with holes of the
size of 3.5 inch×3.5 inch and also remain in a net with holes of the size of 3
inch×3 inch
This means the Standard A apples have a size in between 3 inch and 3.5
inch and any apple with this size will be classified as a Standard A apple.
This definition calls for an operation which can be performed in
practice.
Theoretical definition: Any apple of species B with T type of cells
containing F type of genes.
This definition involves certain theoretical concepts and models and has
clear theoretical meanings to those who know species of plants, the meaning of T
type cells and F type genes.
Operational
definition: Matter is
classified as compounds and elements as pure substances and mixtures of
different pure substances put together physically
Compounds: Those that can be further decomposed or separated by chemical
changes into simpler substances with a fixed ratio in mass
Elements: Those that cannot be further decomposed or separated into
simpler substances by chemical changes
So,
you can distinguish between compounds and elements by conducting some chemical
operations, examples:
water (H2O) = hydrogen gas (H2) + oxygen gas (O2)
mercury oxide (HgO) = mercury (Hg) + oxygen gas (O2)
Operational definitions for matter classification were historically created and used by experimental chemists and may encounter confusion because the definitions depends on how you conduct the chemical operations.
If you conduct the chemical operations in different ways under different conditions, you may end up with different results, that is, your simpler substances depend on the chemical operations. Example:
H2O = H2 + O2;
O2 + sunlight = O + O
Theoretical
definition: Matter is
composed of atoms and molecules
Molecules are composed of either the same kind of or different kinds of
atoms combined together in a certain ratio (example: H2O,
O2)
So, these definitions are based on the theory of atoms as formulized by
Dalton.
The
theoretical definitions have much more clarity and consistency. Now, any kind of
matter can fall into the theoretical definitions.
No operational variations and differences are involved to cause
confusion.
In
a sense, atoms are special cases of molecules. We can say an atom is a molecule
composed of only one atom. In this sense, chemistry is about molecules
(different molecules, small or large) or chemistry is the science of molecules.
Match between operational definitions and theoretical
definitions in chemistry for matter: Hybrid definitions
Here, the
terminologies from both historical operational definitions and modern
theoretical definitions are hybridized together:
An element is a pure substance composed of only one kind of atom
A compound is a pure substance composed of atoms of different elements
combined in definite ways.
To a chemist, a substance always is a pure substance, either an element
or a compound.
You need to
realize that the traditional, historical operational definitions and the hybrid
definitions may not always converge or be consistent with each other.
Example: Ozone (O3),
2O3
= 3O2;
So, according to the operational definitions, then it’s a compound;
but, according to the hybrid definitions, it is then an element.
The elements as listed in the table actually refer to atoms of each of
the elements
Most of the properties listed in the table for each element or atom are
the properties or characteristics of each of the atoms.
In some Periodic Tables, some physical properties listed (such as
boiling point, melting point, density, etc.) are those of the elements in their
simplest forms that can exist normally under the conditions near ground at the
Earth surface (e.g, for oxygen, it is O2
not O3).
New
elements are still being discovered from time to time. Currently, 114 elements
with 109 elements officially named.
The
modern Periodic Table is arranged by atomic number (its meaning will be
discussed in next chapter), rather than atomic mass as in the history.
The
modern Periodic Table is called a long version table. It has more than 114 atoms
or elements, each in a box basically with atomic number, chemical symbol, and
atomic mass in amu (relative atomic mass based on carbon at 12), and many
tables with a host of characteristics and properties of atoms and some
properties of the elements.
The
vertical columns that list elements with similar chemical and chemical
properties are called groups numbered from I to VIII and divided
into A groups and B groups (example, IA, IIIB).
A groups are for the representative or main-group elements
B groups are for the transition elements in between the two areas of main-groups.
Inner transition elements are the Lanthanide series and the actinide series that appear at the bottom of the table.
The horizontal rows are called
periods. These periods are related to the energy levels for electrons in atoms
(discussed in next chapter).
87 elements
are metals (special physical properties and appearance) in Groups IA, IIA, parts
of Groups IIA to VIIA, and the B groups
Characteristic physical properties of metals:
-malleability (beaten into thin sheets, Al foil)
-ductility (stretched into wires, copper wire)
-thermal and electrical conductivity
7
elements are non-metals appeared in the upper right corner of the table.
Physical and chemical properties of non-metals:
generally just opposite to those of metals
example: bad thermal and electrical conductivity (insulator)
Metalloids:
Part of the non-metal elements boarding the metals and non-metals in the right,
like Si, Ge, As, which are semiconductors (excellent for computer chips).
Noble
gases: Group VIIIA, very inert chemically
The Periodic Table
of Elements is an excellent summary, compilation, and generalization of the
observations and facts in chemistry.
The Periodic Table of Elements provide the basic letters for chemistry:
114 letters representing 114 different kinds of atoms.
Each molecule composed of either the same or different atoms combined in
a certain ratio would be regarded as one chemical word. Thus, each particular
substance is one chemical word.
A chemical reaction between different chemical molecules to form new
molecules may be regarded as a chemical sentence.
From now on, all discussion on chemistry will be based on the basic chemical language, that is, we are now seeing the material world or the things or matter as molecules; Now, we only see molecules and changes of molecules from one kind to another. This is our modern chemical view on matter. We need to know what things or substances are what molecules. We need to study various molecules, their physical and chemical properties, their structures, and their interactions with each other. These are what we will discuss on chemistry from now on, and these are what chemistry about.
A scientific law is based on
(a) a few times of similar observations;
(b) many repeatable similar observations;
(c) theory;
(d) guess.
A scientific law is correct
(a) for ever;
(b) a few years;
(c) until a majority of people are against it;
(d)
before new observations contradicting to it occur.
The scientific basis of chemical reaction equations is:
(a) a vote by scientists;
(b) an
agreement between scientists and people;
(c)
mass conservation law;
(d) mysterious
inspiration.
Given 10.00
g lead + 1.55 g sulfur = 11.55 g lead sulfide, 20.00 g lead + 3.10 g sulfur
would result:
(a)
11.55 g lead sulfide;
(b) 11.55
g lead sulfide + 10.00 g lead;
(c)
11.55 g lead sulfide +
1.55 g sulfur;
(d) 23.10
g lead sulfide + 0.00 g lead + 0.00 g sulfur
Given 32.00 g
oxygen gas + 4.00 g hydrogen gas = 36.00 g water, how much of hydrogen gas would
be needed to produce 0.18 g water using 0.16 g oxygen gas:
(a)
0.2 g; (b) 0.02 g; (c) 0.4
g; (d) 0.1 g.
We know: oxygen : hydrogen = 8:1,
or oxygen =
32 g
hydrogen
4 g
32 =
0.16 ; => 8 = 0.16 =>
8*X = 0.16* X =>
8*X = 0.16 =>
X = 0.16/8 = 0.02
4
X
X
X
So, the hydrogen gas needed is
0.02 g. Also, the approach of
cutting by ½, then 1/100.
The observation
that 10.00 g lead + 1.55 g sulfur = 11.55 lead sulfide is not only an example of
the law of definite proportions, but also a good example of
(a)
the law about emotion;
(b) the
law about motion;
(c)
promotion of chemicals;
(d) the
law of conservation of mass
The various mass
ratios for reacting components in a reaction to form a new chemical, or in other
words, the law of definite proportions, is explained in Dalton’s theory by
(a)
the number of hydrogen
required;
(b) mass
of hydrogen;
(c)
size of hydrogen atom;
(d) various
ratios of the numbers of different kinds of atoms forming a compound
Dalton’s atomic theory about matter is a reflection of
which philosophical approach profoundly adopted in science, is that
(a) the holistic approach, meaning things are connected all together as a whole, and cannot be reduced to sub-level components;
(b) the romantic approach;
(c) the reductionism, meaning reduction of different things at a higher level to certain components at a lower level, and by studying the components separately, these components can be used to explain the various things at the higher level;
(d)
the fuzzy approach.
Dalton’s atomic
theory in chemistry may be considered to be analogous to
(a)
car racing;
(b) poll;
(c)
statistics;
(d) the
cell theory in biology.
A chemical element
represents
(a)
many different kinds of
atoms;
(b) one
single atom of a certain kind;
(c)
numerous identical atoms
of a specific kind with certain physical and chemical properties;
(d) (d)
an elemental substance containing identical atoms combined together in a certain
ratio.
The existence of
unknown elements was predicted by
(a) the gravitation theory;
(b) the periodic appearance of the Sun;
(c) Mendeleev’s Periodic Law;
(d) circulation of the Earth around the Sun.
The discovery of
new elements predicted by Mendeleev is
(a) a rejection of Mendeleev’s Periodic Law;
(b) a failure of Mendeleev’s Periodic Law;
(c) a tragedy of Mendeleev’s Periodic Law;
(d) a validation of Mendeleev’s Periodic Law.
The Periodic Table
was created as a result of
(a) Dalton’s personal effort only;
(b) Mendeleev’s personal work only;
(c) the Russian chemists’ efforts only;
(d) many many repeatable observations in chemistry made by many chemists
and their continuous efforts to make an order for the various chemical facts.
The basic chemical
language in modern chemistry is based on
(a) the stars in the night sky;
(b) the basic letters of a specific human language;
(c) the basic music notes;
(d) the 114 atoms each denoted by a symbol.
The number of the
kinds of atoms in chemistry is
(a) fixed for ever;
(b) variable all the time;
(c) is determined by textbooks;
(d) fixed for a certain time until a new atom or element is discovered.
The periodicity of
chemical and physical properties of elements appears in the Periodic Table in
(a) horizontal periods;
(b) the lanthanide series;
(c) the actinide series;
(d) vertical columns (groups) in which the elements share similar
properties.
In the Periodic
Table, non-metals appear mainly in
(a) left side B groups;
(b) left side A groups;
(c) middle B groups;
(d) right side A groups.