Download Classification of Matter

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What is chemistry?
Chemistry
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Chemistry is the study of the composition of matter and the changes in the composition of matter. There
is a vocabulary that you must know and understand in order to communicate successfully as a chemist,
the following are some the words and concepts necessary.
Chemistry, as in any science, gains knowledge through making careful observations.
Observations are facts gained through the senses.
Qualitative observations are descriptive facts gained with unaided senses.
Quantitative observations are precise facts gained through aided senses.
Matter is anything that has mass and occupies space.
Mass is the amount of matter which remains constant.
Weight is the force of gravity acting on an object and can vary depending on location.
Pure substance is matter that has a uniform and definite composition one kind of matter present.
Solid is matter that has definite shape and volume
Liquid is matter that flows, has definite volume and takes the shape of the container.
Gas is matter that takes both the shape and volume of its container.
Vapour describes a substance in the gaseous state that at room temperature and pressure is normally
either a solid or a liquid.
Mixture a physical blend of two or more substances.
Heterogeneous is not uniform in composition.
Homogeneous is completely uniform composition.
A solution is a homogeneous mixture
A phase has uniform composition and properties. There are 4 phases solid, liquid, gas and aquous
(dissolved in water).
Element contains one kind of atom and is the simplest form of matter.
Compound contains two or more different kinds of atoms bonded together and can be separated into
simpler substances (elements)
Classification of Matter
Matter
Pure substance
Definite composition
Homogeneous
Element
One kind of atom
Mixture
variable composition
Physically separated
Compound
Homogeneous
Heterogeneous
Two or more kinds
of atoms chemically
combined
uniform composition
solution
no uniform
composition
distinct phases
Solution contains a solvent that is the dispersing medium and a solute that is the substance that is
dissolving.
Saturated solution – the solvent cannot dissolve any more solute.
Heterogeneous mixtures – emulsion liquid mixed with a liquid ex salad dressing separates
Suspension – solid and liquid ex Maalox separates.
Colloid – 2 phases don’t separate ex – milk particles are too small for gravity
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Chemistry
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A physical property is a quality or condition of a substance that can be observed or measured without
changing the substance’s composition.
Physical change will alter a substance without changing its composition.
A chemical property is the ability of a substance to under chemical reactions to form new substances.
A chemical change is one or more substances that change into new substances.
Solid
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6
2
1
1.solidification (freezing)
3. condensation
5. sublimation
2.melting
4. vaporization
6. sublimation
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Gas
Liquid
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The chemical symbol is used to represent an element.
The Periodic Table is used to organize the elements according to similarities in chemical properties.
Periodic Table
The Periodic Table is more than a list of elements. The Periodic Law states that Chemical and Physical
properties repeat in a regular pattern when the elements are arranged according to increasing atomic
number, the Periodic Table results. Elements end up in columns because of similar properties. Each
column is called a group or Family. A period occurs between members of the Family.
The table is set up according to the number of protons in the nucleus; called the atomic number (Z).
When arranged this way the chemist found that the properties of the elements started to repeat on a
regular bases. The chemist then started to list the elements with similar properties under each other,
Groups or Families. Grouping the elements creates rows, which we call Periods.
Some common Family or groups:
Group 1 (1A) - Alkali Metals
Group 17 (7A) – Halogens
Other classifications shown below are:
Group 2 (2A) - Alkaline earth metals
Group 18 (8a or 0) - Noble Gases
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Representative elements
Lanthanide series
Metals, Nonmetals and Metalloids
Chemistry
Transition metals
Actinide series
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Each block in the table contains important information:
Atomic number – Z – the number of protons, which never changes.
Atomic mass – the weighted average of the atomic masses of the isotopes (by relative abundance).
Mass number – A the number of protons + neutrons – changes because the number of neutrons can
vary within the element. The mass number is the average atomic mass rounded.
Representative elements show all the possible variation in chemical and physical properties.
Metals exhibit the following properties:Luster – shiny.
heat and electricity
Malleable – hammered into sheets.
Ductile – drawn into wires
Conductors of
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Chemistry
Non-metals are Dull, Brittle and Nonconductors- insulators
Metalloids or Semimetals have Properties of both metals and non metals are Semiconductors
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Atomic Theory
Democritus, an ancient Greek, believed that all matter is composed of atoms, which are bits of matter
too small to be seen. These atoms CANNOT be further split into smaller portions. The atomists hold that
splitting stops when it reaches indivisible particles.
In other words, there is a lower limit to the division of matter beyond which we cannot go. Atoms were
impenetrably hard, meaning they could not be divided. In Greek, the prefix "a" means "not" and the
word "tomos" means cut. Our word atom therefore comes from atomos, a Greek word meaning
uncuttable.
Aristotle believed that all matter was made up of 4 elements:
Fire
Earth
Water
Air
Aristotle was more popular and a better debater so his ideas won out and were around for thousands of
years.
In 1803, John Dalton of England re- introduced the atomic idea to chemistry (and is called the Father of
Modern Atomic Theory for his efforts).
The four basic ideas in Dalton's chemical atomic theory are:
1) chemical elements are made of atoms, small indivisible particles
2) the atoms of an element are identical, in their masses and shapes
3) atoms of different elements have different masses and shapes
4) atoms only combine in small, whole number ratios such as 1:1, 1:2, 2:3 and so on.
Dalton's idea of an element is what we believe today - an element is a chemical substance that cannot be
broken down by chemical means.
Atoms of the same element have the same properties, such as weight. Atoms of different elements have
different properties, including a different weight.
In other words, while it was claimed atoms of different elements had different weights, no one could
figure out what the different weight values were. Dalton was the first to do so.
A fifth idea implicit In Dalton's theory, but usually not discussed is this: atoms can be neither created
nor destroyed. An element's atoms do not change into other element's atoms by chemical reactions. For
example, nitrogen and oxygen atoms stay as themselves even when combined. They can be recovered by
decomposing the substance.
J.J. Thomson was the first to say that the electrons were building blocks of the atom. It was a risky thing,
but he was proved right and for his courage he is remembered as the discoverer of the electron.
In 1897, J.J. Thomson discovered the electron, the first subatomic particle. He also was the first to
attempt to incorporate the electron into a structure for the atom.
Thomson’s model is often referred to as Thomson's "plum pudding model," where the pudding
represents the sphere of positive electricity and the bits of plum scattered in the pudding are the
electrons. Today we may wish to call it the "blueberry muffin" model. All those round little blueberries
surrounded by the bread of the muffin.
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Chemistry
The nuclear model of the atom Ernest Rutherford has discovered the nucleus
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Rutherford never used the word "nucleus" in his paper. His phrase was "charge concentration." In 1912,
in a book he published, he devotes a few pages to the nuclear model and uses the word nucleus once.
1) The nucleus is so small that the odds are overwhelmingly in favour of a given alpha
particle motoring right on through the gold foil as if nothing were there. It turns out that
the atom is a very empty place, indeed!
2) Some alphas, by pure random chance, will pass near some gold atom nuclei during
their passage through the foil and will be slightly deflected. By pure chance, some or all
of the small deflections will add up and shove the alpha particle off a straight-line path.
Those alphas will emerge slightly deviated (say one or two degrees) from a straight-line
path. (It might be helpful to remember that the gold nucleus and the alpha particle are
both positively charged, so they will repel each other as they come close together.)
3) A very, very few alphas, by pure, random chance, will hit a nucleus almost head-on.
The alpha, traveling at 10% the speed of light, penetrates the atom and gets very close to
the nucleus. However, the repulsion between the alpha and the atom nucleus is so great
that the atom flings the alpha back out, and it does so in a hyperbolic path. Depending on
various factors, this occasionally results in the alpha being turned around 90° or more.
The very heavy nucleus recoils a bit from the impact, but essentially goes nowhere.
Rutherford is not prepared to take the next step, which is to determine how the electrons are arranged in
the atom.
BOHR MODEL
The Bohr model shows electrons circling the nucleus, which contains protons and neutrons. The
electrons are in different energy levels or shells much like planets circle the sun. Electrons move from
one energy state to another but can only exist at definite energy levels. The energy absorbed or released
when electrons change states is in the form of electromagnetic radiation (light).
The first shell or energy level can only hold a maximum of 2 electrons. (0, 1 or 2)
Every level afterward can hold a maximum of eight electrons as the outside level (the level with the
highest number).
8e
8e
8e
2e
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The Nuclear Symbol
A is mass number (number of p+ + no) and Z is atomic number (number of p+)
The nuclear symbol consists of three parts: the symbol of the element, the atomic number of the element
and the mass number of the specific isotope.
Here is an example of a nuclear symbol:
A
ZE
The element symbol, Li, is that for lithium.
The three, subscripted left, is the atomic number and the seven, superscripted left, is the mass number.
Here's another:
The atomic number is:
The number of protons in the nucleus of the atom.
The mass number is:
The number of protons and neutrons in the nucleus of the atom.
Here is one last example:
The 22 is the atomic number for titanium and 48 is its mass number. The number of neutrons is 48
minus 22 = 26.
Now, write the nuclear symbol for the chlorine isotope with 18 neutrons.
Here is the answer:
There is a slight twist to the way the question was phrased. It DID NOT give the mass number, but
forced you to add the atomic number and number of neutrons (17+18) to get the mass number of 35.
What is the nuclear symbol for the krypton isotope with 48 neutrons?
Here are two tips:
1) The element name (or symbol) uniquely determines the atomic number. In the example
just above Ti is the only element with an atomic number of 22. So, if you need the atomic
number, and all you know is the specific element, go to a periodic table and find its
atomic number.
2) Suppose you are asked to write a nuclear symbol from scratch and the teacher requires
it be a realistic one. Do this:
a) Select an element, making sure it is a naturally occurring one. This will
determine its atomic number.
b) Take the element's atomic weight and round it off to the nearest whole
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Chemistry
number. More often than not, this will be the mass number of the most
abundant stable isotope
Let's try an example. Write the nuclear symbol for silver
Here is the answer:
8
Notice the mass number is rounded off from the atomic weight on the periodic table (107.868)
Periodic Table
Back to Bohr. The atom is now seen as a nucleus surrounded by electrons distributed around the nucleus
in different energy levels. Like Bohr’s orbits, electrons close to the nucleus have lower energy content
than electrons that are further away. Electrons are distributed with the atom go to the lowest energy level
available. If the first energy level is full then additional electrons are added to the second energy level
until it is full and then to the third energy level and s on.
The outermost energy level is called the valence shell; the diagram above shows the maximum number
of electrons that each shell can hold. The electrons in this outermost (valence) shell are called valence
electrons. When atoms react it is these valence electrons from both atoms that control how the atoms
react.
The periodic table is set up according to chemical properties, so groups (families) have the same number
of valence electrons, which explains why the members of the group have the same chemical properties.
The group number can be used to help determine the number of valance electrons.
Group
# of valence electrons
1
1
2
2
13
3
14
4
15
5
16
6
17
7
18
8
Most stable Group 18 the noble gases complete octet and other elements try to have same stable
configuration.
The chemist displays the number of valence electrons by using an electron dot diagram or Lewis
diagram (keeping track of and presenting the valence electron structure).
∙
∙
∙
∙
∙∙
∙∙
∙∙
∙∙
Li
Be∙
B∙
∙C∙
∙N∙
∙O:
∙F:
:Ne:
∙
∙
∙
∙
∙∙
∙∙
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The Octet rule is an atom having a complete (full) valance shell. All atoms want to end up with a full
valance shell because the atom becomes stable (low in energy). Group 18, the noble gases are the most
stable of elements because their valence shell is full with eight electrons (lower energy content).
During chemical changes atoms will change in electron configuration (the arrangement of valence
electrons) to try to get a full valence shell.
Metal atoms have few valence electrons and will lose valence electrons leaving a full inner shell (metals
are born losers)
Non-metal atoms have larger number of valence electrons (close to full) and tend to gain electrons.
(Non-metals are winners)
Metals, during chemical reactions will undergo a loss of electrons to form cations – particles with a
greater number of protons than electrons. The metals will lose their valence electrons so the particle
becomes positively charged (more p+ than e-). Metals lose electrons to get to the previous noble gas. Na
atom will look like Ne if it loses 1 electron. Electrons in the Na atom is 2, 8, 1 but the sodium cation
(lose of one electron) is 2, 8 (Ne is 2, 8) Na+ and Ne look the same on the outside (10 electrons in each)
but Ne has 10 protons and Na+ has 11 protons).
Non-metals, during chemical reactions will undergo a gain of electrons to form anions – particles with a
smaller number of protons than electrons. The no-metals will gain valence electrons so the particle
becomes negatively charged (less p+ than e-). Non-metals gain electrons to get to look like the
succeeding noble gas. F atom will look like Ne if it gains 1 electron. Electrons in the F atom is 2, 7 but
the fluorine anion (gains of one electron) is 2, 8 (Ne is 2, 8) F- and Ne look the same on the outside (10
electrons in each) but Ne has 10 protons and F- has 9 protons).
One of the main theories used in Chemistry is the Kinetic Molecular Theory. Matter is made up of
particles. All particles are in constant motion. This constant motion results in collisions. When atoms
collide their electron clouds overlap. The nuclear charges repel each other because they are like charges.
As the atoms move away from each other one the following could occur
One atom may lose (an) electron(s) – form cation
One atom may gain electron(s) – form anion
Because the ions have opposite charges there is a strong attraction between the ions – we call this
attraction an ionic bond. This ionic bond occurs between metal and non-metal atoms. The metal forms
the cation and non-metal the anion. Oppositely charged ions attract each other (this force of attraction is
called a chemical bond (ionic bond).
Another possibility is that the colliding atoms may share electron – the electrons become attracted to
both nuclei and become trapped between them. The mutual attraction to the valance electrons by the
nuclei hold the atoms together and we now call the electrons bonding electrons. These bonds are called
covalent bonds. The atoms can share one, two or three pairs of electrons. One pair shared – single
covalent bond, two shared pairs – double covalent bond and three shared pairs of electrons – a triple
covalent bond. Atoms that share valence electrons are usually both nonmetals. The bonded atoms are
called molecules. These substances composed of molecules are molecular compounds. Some of the
elements are molecular that is exist as two atoms joined together – diatomic molecules. HON Halogens
– hydrogen, oxygen, nitrogen, fluorine, chlorine, bromine and iodine.
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+1 +2
10
+3
+4 -3
-2
-1
0
Using the Periodic Table to predict reactions
In ionic bonds the total number of electrons lost has to equal the total number of electrons gained. Each
ion will have a full shell. Metals lose electrons (cation +) and non-metals gain electrons (anion -). The
oppositely charged ions have a strong attraction (ionic bond).
Li with Cl
Li group 1 loses 1
Cl group 17 gains 1
Li+ Cl- = LiCl
Mg with F
Mg group 2 loses 2
F gains 1 so we need 2
Mg2+ 2F- = MgF2
Al with Br
Al group13 loses 3
Br gains 1 so we need 3
Al3+ 3Br- = AlBr3
Na with O
Na group 1 loses 1
O group 16 gains 2
2 x Na+ O-2 = Na2O
Ca with S
Ca group 2 loses 2
S group 16 gains 2
Ca2+ S2- = CaS
Ga with O
Ga group 13 loses 3
O group 16 gains 2
2xGa3+ = 6 lost 3x O2- = 6 gained = Ga2O3
K with N
K group 1 loses 1
N group 15 gains 3
K+ N3- = K3N
Mg with N
Mg group 2 loses 2
N group 15 gains 3
Mg2+ N3- = Mg3N2
Al with N
Al group 13 loses 3
N group 15 gains 3
Al3+ N3- = AlN
Nonmetal with a nonmetal
In covalent bonding, atoms sharing a number of electrons so that each atom in the molecule has an octet
(complete shell).
H with Cl
Both need to gain one
Each offers 1 to share
Single covalent bond
H:Cl
F with F
Both need to gain one
Each offers 1 to share
Single covalent bond
F:F
O with O
Both need to gain two
Each offers 2 to share
double covalent bond
O::O
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H with O
H needs 1 O needs 2
Must have 2 H
H2O H:O:H
N with H
N needs 3 H needs 1
Must have 3xH
NH..3
H:N:H
..
H
Chemistry
F with O
F needs 1 O needs 2
Must have 2 F
F2O F:O:F
N with I
N needs 3 I needs 1
Must have 3xI
NI3
I:N:I
..
I
11
C with H
Carbon needs four H needs 1
must have 4 H for each C
CH4
H..
H:C:H
..
H
C with S
C needs 4 S needs 2
must have 2xS
CS2
S::C::S