The Chemical Elements (Section
1.10; page 23)
An element is a fundamental, irreducible constituent.
Element: (Ebbing; 5th ed.)
(a) a substance that cannot be decomposed by any chemical reaction into simpler substances.
(b) a type of matter composed of only one kind of atom, each atom of a given kind having the same properties.
(c) a substance whose atoms all have the same atomic number.
Each chemical element has a unique name and is represented in the periodic table by a symbol, which most often is based on the English or Latin names of the elements.
Presently, there are more than 110 known elements but only 90 are found in nature.
The vast majority of elements are metals.
Of the remainder, 18 are nonmetals and 6 are metalloids (semimetals).
Metals have characteristic properties.
With the exception of mercury, all metals are solid at room temperature.
Metals conduct heat and electricity.
They are ductile, that is to say they can be drawn into wire.
They are malleable, which means they can be hammered or rolled into sheets.
They can be polished so as to have a luster.
The densities of most metals are fairly high.
The properties of the nonmetals contrast with those of the metals.
The physical state (solid, liquid, or gas) of the nonmetals vary.
For instance, the vast majority do not conduct electricity.
Metalloids (semimetals) are elements which possess both metallic and nonmetallic properties.
The metalloids are B, Si, Ge, As, Sb, & Te.
Some elements exist as molecules. In other words, some elements exist in chemically bonded units of identical atoms. There are seven elements that exist as diatomic molecules Br2, I2, N2, Cl2, H2, O2, F2.
[A mnemonic device for these seven elements is Brinclhof.]
Allotropes are different forms of the same element
that
exist in the same physical state at the same temperature
and pressure. The allotropes of oxygen are O2 (dioxygen) and O3
(ozone). Allotropes of carbon are diamond, graphite, and a relatively
recently discovered form of caged carbon atoms known as fullerenes. One
type of fullerene has the formula C60 and is called
buckminsterfullerene.
Factoids:
Br and Hg are the two elements that are liquids at room temperature.
Eleven elements are gases at room temperature. H2, He, N2, O2, F2, Ne, Cl2, Ar, Kr, Xe, Rn
The Periodic Table (Section 2.9; page 62)
Law of Chemical Periodicity
Properties of the elements are periodic functions of atomic number. That is, when the elements are arranged by order of atomic number, within a group their properties are similar to one another.
The atomic number (Z) is the number of protons in the nucleus of the atom.
The periodic table is a tabular arrangement (chart) of all the known elements, that provides information on the properties of the elements.
Each element has a unique name and is represented in the periodic table by a symbol, which most often is based on the English or Latin names of the elements.
The periodic table is a chart which organizes the elements into groups which have roughly similar properties.
The periodic table is a chart of the elements arranged by increasing atomic number so that elements in a given group have similar chemical properties.
The periodic table is composed of vertical columns called groups and horizontal rows called periods.
Groups are numbered 1 through 8 and each number is followed by either an A or a B.
The A group elements are known as main group elements.
The B group elements are known as transition elements.
Periods are the horizontal rows
in the periodic table.
There are seven periods in the periodic table.
From left to right across a period, elements become less metallic in nature and more nonmetallic.
Group 1A Alkali metals
Group 2A Alkaline Earth Metals
The transition metals occupy the
middle of the periodic table in periods 4 through 7. They take their
collective name from their role as a bridge between the chemically active metals
of Groups 1A and 2A and the much less active metals of groups 3A.
The two rows listed separately at the
bottom of the periodic table are the inner transition metals. The
elements from Ce to Lu are referred to as the Lanthanides. The
elements from Th to Lr are referred to as the Actinides.
Group 7A Halogens
Group 8A Noble Gases
Groups 1A, 2A, 3A - 8A are referred to as main group elements.
|
3. Nomenclature
(systematic name)
a-D-Fructofuranosyl-b-D-glucopyranoside
4. Common Names
Saccharose
Sucrose
Table sugar
SCIENTIFIC
METHOD
Hypothesis is a tentative explanation for an
observed
natural phenomenon.
Experiment an observation of a natural
phenomenon,
carried out in a controlled manner so that the results can be
duplicated
and rational conclusions obtained.
Data or Facts obtained from observation and
measurements
during an experiment. Data should be reproducible.
Scientific Law a concise statement or
mathematical
equation about a fundamental relationship or regularity of nature.
Theory a tested explanation of basic natural
phenomena.
Model makes a theory more concrete; can be
physical
or mathematical
Physical Properties of Matter
Matter is the building block material of the
universe.
It is anything that takes up space and has mass.
A substance is a type or form of matter, which
has a definite (constant) composition and distinct properties. A
substance
is a single, pure form of matter, even on the microscopic level.
A physical property is a characteristic of a
substance,
which can be observed or measured without changing the composition or
identity
of that substance. A substance can be identified by its physical
properties. Physical properties include: temperature, pressure, mass,
volume,
state (solid, liquid, gas), melting point, boiling point, density,
color,
crystal shape, hardness or brittleness, heat capacity, thermal
conductivity,
electrical conductivity.
A physical change is a process that occurs
without
a change in chemical composition or identity of a substance. A physical
process does not change a substance into another substance.
Melting wax is an example of a physical change.
It can by represented as: C50H102(s)
---> C50H102(l)
Temperature is a measure of how hot or cold an
object is relative to another object. It is the property of an object
that
measures the amount of random energy of motion of its molecules and
determines
the direction of spontaneous heat flow.
Three Scales for Measuring Temperature
Reference |
Fahrenheit |
Celsius |
Kelvin |
Water MP |
32 oF |
0 oC |
273.15 K |
Water BP |
212 oF |
100 oC |
373.15 K |
Interconversions Between Temperature Scales
K = 273.15 + oC (The temperature
interval
of oC and K are equal.)
TF = (1.8 x oC) +
32 or [9/5 TC]
+ 32
TC = (Fo -
32)/1.8
or [TF
- 32](5/9)
Example Temperature Conversion
98.6 oF = ? K
TC = [TF - 32 oF](5/9)
TC = [98.6 oF - 32oF](5/9)
= 37.0 oC
K = 273.15 + oC = 273.15 + 37.0 oC
= 310.2 K
Density
Density (d) is the ratio of mass to volume. d = mass /
volume
Sample Density Questions
1. What is the density of a sample of
metal that
has a mass of 118.26 g and a volume of 43.8 mL?
[
2.70 mL
]
2. What is the mass in grams of a 9.00 cm3
piece of lead? The density of lead is 11.3 g/cm3.
[102. g]
3. What is the volume of a sample of mercury
that
has a mass of 938.22 g and a density of 13.5 g/mL?
[ 69.5 mL]
4. When a 26.048 g sample of metal was
placed
in a graduated cylinder containing water, the water
level rose
from
25.00 mL to 28.31 mL. What is the density of the
metal?
[7.86 g/mL]
5. What volume of ethanol
will have the same mass
as a 50.00
mL volume of mercury?
(dmercury = 13.5 g/mL; dethanol = 0.798 g/
mL]
[846. mL]
Dimensional
Analysis and Problem Solving
A proportionality factor is a ratio (fraction)
derived
from an equality statement and whose numerator and
denominator have differing
units but refer to the same thing. It is also referred to as a
conversion
factor.
Because 1 kg = 1 x 103
g, the ratio of 1 kg/1 x
103 g
or 1 x 103 g / 1 kg could be used as a
conversion factor.
Because 1 in = 2.54 cm, the ratio of 1 in./ 2.54 cm
or
2.54 cm / 1 in. could be used as a conversion factor.
Sample Dimensional Analysis Problems
1. How many kg are in 1.24 x 105
g? [124. kg]
2. How many cm are in 3.45 x 104
in? [8.76 x 104 cm]
Chemical Changes and Chemical
Properties
A chemical change (chemical reaction) is a
process that results in
a change in the chemical composition or
identity of a substance. A chemical
change transforms a substance (reactant) into another substance
(product).
In a chemical reaction the reactants are transformed
into the products. This process is indicated by writing
the reactants,
an arrow, and the products.
Reactants ----> Products
A chemical property describes a substance's
composition
and its reactivity. It describes how the substance
reacts, or changes into
other substances (e.g., iron rusts and a candle burns). A
substance
can be identified
by its chemical properties.
Candle wax (C50H102) burning is an example of a chemical change and
can be represented by:
2 C50H102(s) + 151 O2(g)
---> 100 CO2(g) + 102 H2O(g)
The universe is composed of matter and energy. Matter
includes all tangible things, and has mass and volume that can be
measured.
The concept of energy is more difficult to grasp because energy is
intangible.
Energy, unlike matter, cannot be held in your hand.
Energy can be defined as the
capacity to do work (move matter) or produce
heat. A wound clock acquires "something" with which it can do work.
This
"something" that enables the clock to do work is energy. Energy comes from compression of atoms in a material,
separation of attracting bodies, rearrangement of electric charges in
the
molecules of a substance.
Both chemical and physical changes are accompanied by the transfer of
energy
Substances, Mixtures, and Separations
A mixture is matter, which can
be separated into two or more substances by a physical process.
A heterogeneous mixture has physically distinct parts, each with different properties. Often, the non-uniformity of the composition of a heterogeneous mixture can be observed without magnification or a microscope (e.g., oil & water; concrete). Sometimes magnification is necessary to observe that a mixture is heterogeneous (e.g., blood). Properties in one region of a heterogeneous mixture will be different from the properties in another region.
A homogeneous mixture (solution) is a
mixture uniform
in its properties throughout
(e.g., gaseous: air; liquid: Coca Cola; solid:
brass).
Only on the atomic level can differences be seen
in a
homogeneous mixture.
Separation processes could include filtering, magnetic separation, or boiling.
Elements and Compounds
A substance is
matter that has a fixed composition and that cannot be further purified by a physical process.
In other words, it is matter which cannot be separated
into other kinds of matter by a physical process. Substances
can be classed as either elements or compounds.
Elements are
substance composed of only one kind of atoms (e.g., carbon,
sodium, or helium).
Compounds are
substances composed of two or more different kinds of atoms (e.g.,
water, carbon dioxide, sodium chloride).
Matter comes in the three forms (physical states) of
solids, liquids, or gases.
STATE |
VOLUME |
SHAPE |
COMPRESSIBLE |
Solid |
Fixed |
Fixed |
NO |
Liquid |
Fixed |
No fixed shape (assumes shape of the space of the container is occupies) |
Relatively incompressible |
Gas |
No fixed shape |
No fixed volume
(fills the container it occupies) |
YES |
Matter can be placed in the following outline form.
Matter (solid, liquid, or gas) comes in two basic
forms.
1. Heterogeneous (non-uniform composition)
2. Homogeneous (uniform composition)
a. Solutions (homogeneous mixtures)
b. Substances
i.
Elements (cannot be subdivided by physical or chemical process)
ii. Compounds (elements bonded in fixed ratios)
Macroworld is a term used to
describe natural phenomenon
when large objects and large amounts of
energy are involved.
Macroscale denotes quantities and characteristics that can be observed with the unaided eye.
Microworld is a term used to describe natural
phenomenon
when small objects and small amounts of
energy are involved, as in the
case of atoms and molecules.
Microscale quantities are observed only with
the
aid of special instruments. The microscopic world is
largely hidden from our senses and our common sense.
Nanoscale is on the level of size where matter is in the nanometer range.
An atom is the smallest distinctive unit in a sample of matter that can be chemically altered. Atoms are electrically neutral.
A molecule can be defined as a definite group of chemically bonded atoms that are
chemically bonded
together--that is, tightly connected by attractive
forces.
Molecules are neutral particles composed of two
or more atoms combined
in a definite ratio of whole numbers.
A molecule is the smallest particle of an
element or compound that
has the chemical properties of the element or compound.
The Kinetic-Molecular Theory states that
matter
is constantly moving on the molecular level.
The amount of movement is dependent upon state
and temperature.
Particles in the solid state are packed
closely
together and are restricted in movement.
Their movement is restricted to vibrational
types of
movement.
Particles in the liquid state are relatively
close
to one another but are not as restricted in space
as the particles
in a solid and therefore can move from place to
place
in the liquid.
This movement is referred to as translational.
Particles in the gaseous stateare the least
restricted
and move chaotically within the vessel that confines
them.
The distance between two gas particles is much,
much
larger than the actual size of the gas particle
itself.
The speed at which the gas particle moves can be
well
over 1000 mph.
Movement is directly proportional to temperature. The higher the temperature, the greater and faster the movement.
Atomic Theory
An atom is the smallest distinctive
unit comprising an element. Atoms of a given element will have
identical chemical
and physical properties.
Atoms are electrically neutral.
An element is a substance that cannot be decomposed into a simpler substance by a chemical process.
In 1803 John Dalton introduced his atomic
theory. The modern atomic theory has four basic tenets
The Atomic Theory
1. All matter is composed of indivisible atoms,
which
are extremely small.
2. An element is a type of matter composed of
only one
kind of atom, and the chemical properties of each of
the atoms of a given element are identical.
3. A compound is composed of atoms of two or
more elements
that have been chemically combined.
4. A chemical reaction consists of rearrangement
of the
atoms present in the reacting substances to give
a new substance. The atoms cannot be destroyed
or created
in this process.
Antoine Lavoisier (1743-1794) found that the total
mass
of a chemical reaction remains constant.
He formulated the law of Conservation of Mass
which states that the total mass remains constant
during a chemical reaction.
EXAMPLE:
When 2.53 g of mercury was heated in the
presence of
oxygen, 2.73 g of a red-orange solid were produced.
What mass of oxygen was reacted?
Mercury + oxygen -----> red-orange solid
2.53
g
?
g
2.73 g
2.73 - 2.53 = 0.20 g oxygen
Joseph Proust (1754-1826) formulated the law of constant composition (law of
Definite
Proportions)
which states that a pure compound, whatever its source,
always contains definite or constant proportions
of the
elements by mass.
In a given chemical compound, the elements are
always
combined in the same proportions by mass.
For example when 1.0000 g of NaCl is broken down into
the elements sodium and chlorine, there are 0.3934 g Na and
0.6066 g of
chlorine. This gives a ratio of 0.3934 g Na/0.6066 g Cl or 0.6485 g Na/g Cl. This means that for
any size
sample of NaCl that is decomposed, there will be 0.6485 g of Na for
every 1.000 g of Cl or 1.542 g of Cl for every
1.000 g of Na.
Chemical Symbolism
Chemical symbols are shorthand notations used to
represent
the elements.
Chemical formulas numerically describe composition.
Chemical symbols and chemical formulas are related to
the macro and micro scale properties of the substances.