WELCOME
TO AP CHEMISTRY
MAHUA CHAKRABORTY
What is Matter
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Matter is anything that has mass and
takes up space.
Examples are rockets, paper,
notebook, a car.
Atoms and Elements
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Smallest particle of any element is called
an atom.
An element is a substance composed of
only one kind of atom. Each element is
represented by a chemical symbol made
up of one or two letters.
Example for one letter elements are
Hydrogen H, Nitrogen N ..
Example for two letter elements are
Magnesium Mg, Calcium Ca, Silicon Si.
The Nuclear Atom
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Atoms are made up of subatomic particles
called electrons, protons, and neutrons.
Protons and Neutrons form a compact,
central body which is the nucleus of the
atom.
Electrons are like a cloud around the
nucleus.
Protons are positively charged and
electrons are negatively charged.
Neutrons however don’t have any charge.
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Nuclear atom
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The number of protons in an atomic
nucleus is called the atomic number.
It is denoted by Z.
There is an equal number of electrons
surrounding the nucleus.
The atom has no charge.
The total number of protons and neutrons
is called the mass number .
This is denoted by A.
Neutrons and protons jointly are called
nucleons.
Isotopes
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Atoms with same atomic number but with
different mass numbers are called
isotopes.
An isotope is named by writing its mass
number after the name of the element, as
in neon-20,neon-21,and neon 22.
Symbol is written by adding the mass
number as a superscript to the left of the
chemical symbol of the element
e.g.20Ne,21Ne,and 22Ne.
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Carbon isotopes
Properties Of Isotopes
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Isotopes of the same element have the
same number of protons and the same
number of electrons they have essentially
the same properties.
An exception of this is hydrogen. The
mass differences between isotopes are
relatively large. As a result hydrogen
isotopes have differences in the
properties.
Examples of isotopes of hydrogen are
Deuterium(2H) and Tritium(3H).
Class Practice
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How many protons, neutrons and
electrons are present in a) an atom
of nitrogen-15 b) an atom of iron-56.
Write the symbols of the isotopes of
a) argon b) calcium that have the
same number of neutrons as 40K.
The Periodic table
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The periodic table is made up of vertical columns
called groups and horizontal rows called periods.
The members of each group show similarity with
one another.
The 1st group is the alkali metals.
The 2nd group is the alkaline earth metals.
Groups 3-11 contain the transition metals.
Groups 12,13 and 14 are the having less active
metals. E.g. Pb and In.
Group 17 constitutes the halogen group.
Group 18 constitutes the noble gas.
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The long block shown below the main
table is the inner transition metals.
Elements in the upper row begins
with lanthanum so it is called the
lanthanides.
Elements in the lower row begins
with actinium hence it is called as
actinides.
Metals, Nonmetals and Metalloids
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Metals conduct electricity, has a metallic
luster and is malleable and ductile e.g. Na,
Cu, and Au.
Nonmetals do not conduct electricity and
is neither malleable nor ductile e.g. S, C,
and P..
Metalloids has the appearance and some
physical properties of a metal but behaves
chemically like a nonmetal e.g. Ge, Si..
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Part of the periodic table.
What are Compounds
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Compound is a substance that consists of
two or more different elements with their
atoms in a definite, characteristic ratio.
Two types of compounds Organic and
inorganic compounds.
Organic compounds are compounds
containing Carbon and Hydrogen.
Inorganic compounds include water,
ammonia, hydrochloric acid etc.
Molecules
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Molecule is a definite electrically
neutral group of atoms bonded
together e.g. H2O.
All gaseous elements are found as
diatomic molecules. e.g. O2 , Cl2.
Formulas
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Chemical Formula tells us which element is
present and the subscript tells us how
many atoms of that element is present.
e.g. O2 ,S8 and P4.
Structural Formula represents the atoms
by their elemental symbols and use lines
to show which atoms are joined together.
E.g.
Models
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Ball and Stick Model
The colored balls depict the atoms and
the sticks indicate the links between
them.
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Tube Structure
This structure omits the balls and
represents the atoms and the links
between them by colored lengths of
tube.
Ions and Ionic Compounds
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Ionic compounds consists of positive and
negative ions held together by the attraction
between their opposite charges. E.g. Sodium
chloride consists of alternate Na+ and Cl – ions.
Positively charged ions are called cations and
negatively charged ions are anions.
Na+ means sodium atom that has lost one
electron and hence has a single positive charge.
Cl- means chlorine has gained an electron that
increases the negative charge by one atom.
Chemical Formulas Of Ionic
Compounds
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Ionic compounds does not consist of
individual molecules.
Ratio of the number of cations to the
number of anions is the same for any
sample of a given compound we can
use that ratio to write its formula.
In sodium chloride there is one Na+
cations for each Cl- ion, so its
formula is NaCl.
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Examples of poly atomic cations
ammonium ion NH4+.
Polyatomic anions are called oxo anions
e.g. CO32Formula unit is a group of ions with a
composition given by the formula of an
ionic compound.
Formula unit for NaCl consists of one Na+
and one Cl- ion. For ammonium sulfate
consists of two NH4+ ions and one SO42ion.
Class Practice
Identify the type of each substance
and give the number of atoms of
each element in the formula units or
molecules of the compounds a)N2O4
b)(NH4)3PO4 c)P4
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Mixtures
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Elements and Compounds are pure
substance.
Mixtures are simple substance which are
neither element nor compounds.
Gasoline is a mixture of hydrocarbons and
additives blended together to achieve
efficient combustion.
Alloys are mixtures of metals formulated
for maximum strength and resistance to
corrosion.
Mixture And Compounds
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Mixtures
Compounds can be
separated by using
physical techniques.
Composition is
variable.
Properties are related
to those of its
components
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Compounds
Components cannot
be separated by using
physical techniques.
Composition is fixed.
Properties are unlike
those of its
components
Types Of Mixtures
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Heterogeneous
In this type we can
identify the different
components of the
mixture.
Examples are sand
and sugar
Milk if seen through
microscope you can
see individual globules
of butterfat.
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Homogenous
In this type the
individual components
cannot be separated
Example syrup of
sugar and water.
White vinegar.
Separation techniques
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To analyze the composition of a sample
that we suspect is a mixture we need to
separate its components.
Filtration: Makes use of differences in
solubility. The sample is shaken with a
liquid and then poured through a mesh,
the filter. You can separate the soluble
material that passes through the filter and
the insoluble is captured by the filter.
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Distillation: This technique makes
use of the difference in the boiling
points. Can be used to separate two
liquids having different boiling point
or a mixture of a salt and water
where the boiling point of the salt is
much higher than the boiling point of
water.
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Distillation
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Chromatography: This technique
depends on the different abilities of
substances to adsorb or stick to
surfaces. The mixture is washed
across a strip of filter paper.
Substances that adsorb weakly move
far apart than others. Colored
components give rise to separate
patches of color on the paper.
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Paper chromatography
Molecular Compounds
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Binary molecular compounds are built
from 2 elements.
Example Phosphorus trichloride PCl3 and
carbon monoxide CO.
The oxo acids are molecular compounds
that are the parents of oxo anions e.g.
sulfuric acid is the molecular
compound.SO42- has 2 negative charges.
To balance this two H+ ions are needed.
Class Practice
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Give the systematic names of the
compounds a) N2O4 b)ClO4