Download of the atom.

INTRODUCTION TO GENERAL
CHEMISTRY
COMPOUNDS AND ELEMENTS
chlorine
nitrogen
gold
silver
mercury
helium
oxygen
hydrogen
sodium
niobium
neodymium
carbon
Elements
• The elements,
alone or in
combinations, make
up our bodies, our
world, our sun, and
in fact, the entire
universe.
Elements
• Science has come
along way since
Aristotle’s theory of
Air, Water, Fire,
and Earth.
• Scientists have
identified 94
naturally occurring
elements, and
created about 24
others.
The most abundant element in the
earth’s crust is oxygen.
Symbols
O
Ag
Oxyden
Silver
• All elements have
their own unique
symbol.
• It can consist of
a single capital
letter,
or
a
capital letter and
one or two lower
case letters.
Common Elements and Symbols
Periodic Table
• The periodic table organizes the elements in a
particular way. A great deal of information
about an element can be gathered from its
position in the period table.
• For example, you can predict with reasonably
good accuracy the physical and chemical
properties of the element. You can also
predict what other elements a particular
element will react with chemically.
• Understanding the organization and plan of
the periodic table will help you obtain basic
information about each of the 118 known
elements.
Matter
• A chemical element or element is a chemical
substance consisting of atoms
• All matter is composed of atoms and groups
of atoms bonded together, called
molecules.
– Substances that are made from one type of
atom only are called pure substances.
– Substances that are made from more than one
type of atom bonded together are called
compounds.
– Compounds that are combined physically, but not
chemically, are called mixtures.
Elements, Compounds,
Mixtures
• Sodium is an element.
• Chlorine is an element.
• When sodium and
chlorine bond they make
the compound sodium
chloride, commonly
known as table salt.
Compounds have different properties
than the elements that make them up.
Table salt has different properties
than sodium, an explosive metal, and
chlorine, a poisonous gas.
Elements, Compounds,
Mixtures
• Hydrogen is an element.
• Oxygen is an element.
• When
hydrogen
and
oxygen bond they make
the compound water.
• When salt and water are
combined, a mixture is
created. Compounds in
mixtures
retain
their
individual properties.
The ocean is a
mixture.
Elements, compounds, and
mixtures
• Mixtures can be separated by physical
means.
• Compounds can only be separated by
chemical means.
• Elements are pure substances. When the
subatomic particles of an element are
separated from its atom, it no longer
retains the properties of that element.
Properties of Metals
• Metals
are
good
conductors of heat and
electricity.
• Metals are shiny.
• Metals are ductile (can be
stretched into thin wires).
• Metals are malleable (can
be pounded into thin
sheets).
• A chemical property of
metal is its reaction with
water which results in
corrosion.
Properties of Non-Metals
Sulfur
• Non-metals are poor
conductors of heat
and electricity.
• Non-metals are not
ductile or malleable.
• Solid non-metals are
brittle
and
break
easily.
• They are dull.
• Many non-metals are
gases.
Properties of Metalloids
• Metalloids (metal-like)
have properties of both
metals and non-metals.
• They are solids that can
be shiny or dull.
• They conduct heat and
electricity better than
non-metals but not as
well as metals.
• They are ductile and
malleable.
Silicon
A chemical element or element is a chemical
substance consisting of atoms
An ATOM is the smallest constituent unit
of ordinary matter that has the properties
of a chemical element.
Atoms have three types of sub atomic
particles. They are electrons, protons and
neutrons.
Electrons are negatively charged (e-),
protons are positively charged (p+) and neutrons
have no charge (n).
Bohr’s model of an atom :
1. An atom has a positively charged nucleus at its centre and most
of the mass of the atom is in the nucleus.
2. The electrons revolve around the nucleus in special orbits called
discrete orbits.
3. These orbits are called shells or energy levels and are represented
by the letters K, L, M, N etc. or numbered as 1, 2, 3, 4, etc.
4. While revolving in the discrete orbits the electrons do not radiate
energy.
Shells or energy levels in an atom
Atomic Number
• This refers to
how many protons
an atom of that
element has.
• No two elements,
have the same
number
of
protons.
Bohr Model of Hydrogen Atom
Wave Model
Atomic Mass
• Atomic
Mass
refers
to
the
“weight” of the
atom.
• It is derived at
by
adding
the
number of protons
with the number
of neutrons.
This is a helium atom. Its atomic mass is 4
H(protons plus neutrons).
What is its atomic number?
Atomic number and Mass number
a) Atomic number (Z)
Eg.
Hydrogen – Atomic number = 1 (1 proton)
Helium
- Atomic number = 2 (2 protons)
Lithium
- Atomic number = 3 (3 protons)
b) Mass number (A = Z+n)
Eg. Carbon – Mass number = 12 (6 protons + 6 neutrons) Mass = 12u
Aluminium – Mass number = 27 (13 protons + 14 neutrons) Mass =
27u
Sulphur – Mass number = 32 (16 protons + 16 neutrons) Mass =
32u
Key to the Periodic Table
• Elements are organized on the
table according to their atomic
number, usually found near the
top of the square.
– The atomic number refers to
how many protons an atom of
that element has.
– For instance, hydrogen has 1
proton, so it’s atomic number
is 1.
– The atomic number is unique
to that element. No two
elements
have
the
same
atomic number.
What’s in a square?
• Different periodic
tables can include
various bits of
information, but
usually:
–
–
–
–
atomic number
symbol
atomic mass
number of valence
electrons
– state of matter at
room temperature.
Atomic Mass Unit (AMU)
• The
unit
of
measurement for
an atom is an
AMU. It stands
for atomic mass
unit.
• One AMU is equal
to the mass of
one proton.
Atomic Mass and Isotopes
• While most atoms have
the same number of
protons and neutrons,
some don’t.
• Some atoms have more
or less neutrons than
protons. These are
called isotopes.
• An atomic mass number
with a decimal is the
total of the number of
protons plus the average
number of neutrons.
Isotopes
Isotopes are atoms of the same element having the
same atomic numbers but different mass numbers.
Eg. Hydrogen has three isotopes. They are Protium,
Deuterium (D) and Tritium (T).
1
1
H
2
1
H
3
1
H
Protium
Deuterium
Tritium
Carbon has two isotopes. They are
C
12
14
6
6
C
Chlorine has two isotopes They are :35
17
Cl
37
17
Cl
Relative atomic mass (Ar )
• An element can have several naturally
occurring isotopes.
• These isotopes of a element behave
in the same way.
• In calculating the relative atomic
mass of an element with isotopes, the
relative mass and proportion or
percentage of each is taken into
account.
Calculating relative atomic mass
Isotope
Relative isotopic mass
Relative abundance
(%)
Cl
34.969
75.80
Cl
36.966
24.20
Ar = (relative isotopic mass X1 % abundance) + relative isotopic mass X2 % abundance)
100
Ar (Cl) = (34.969 X 75.8) + ( 36.966 X 24.2)
100
Ar (Cl) = 2650.65 + 894.58
100
Ar (Cl) = 35.45 amu (atomic mass unit)
Your turn
• Calculate the relative atomic mass of
Boron to two decimal places
Isotope
Relative
abundance (%)
Relative isotopic
mass
10B
19.91
19.91
11B
80.09
11.009
Relative molecular mass (Mr )
• The relative molecular mass of a
compound is the mass of one molecule
of that substance relative to the
12
mass of a C
• This is calculated by taking the sum
of the relative atomic masses of the
elements in the molecular formula
(i.e. covalent compounds)
• It is called relative formula mass for
ionic compounds
Calculating relative molecular
mass
Normally to find the relative atomic mass you just
look in the periodic table!!
Oxygen (O2) Mr = 2 X Ar(0)
= 2 X 16.0
= 32.0 amu
Carbon Dioxide (CO2)Mr = Ar(C) + 2 X Ar(0)
= 12.0 + (2 X 16.0)
= 44.0 amu
What is a mole?
• What is a dozen?
• 12 of something
• The mole is like a dozen, it is a fixed
number of something
• The mole is the amount of substance of
a system which contains as many
elementary entities as there are atoms
in 12 g (0.012 kilograms) of carbon 12.
• That number is 6.02 X1023 or
• 602000000000000000000000
• a mole is a fixed number of things just
like a dozen.
Why have the mole?
• It can become very dificult to deal with
such large numbers, especially during
calculations.
• To overcome this impracticality, chemists
deal with multiples of particles, instead
of individually. This is why we have a
mole!
Where did the mole come from?
• The mole is a unit of measurement
based on work done almost 200 years
ago by Amadeo Avogadro as he studied
gas behavior.
• His work led to the association of a
number, 6.02 x 1023, with the mole.
• 6.02 x 1023, is also called Avogadro’s
constant or number
• It allows particles to be "counted.“
• The word "mole" is derived
from "gram molecular weight"
How big is the mole
• The mole can be applied to anything: number
of trucks, number of balloons, etc.
• In a mole we know there are 6.02 X1023 of
stuff it can be anything trucks, balloons etc.
• To have one mole of peas, they would have to
be a metre deep around earth and you would
need 250 earths to fit them all on
How big is the mole
• The mole is HUGE!
• But you can hold a mole of NaCl in
your hand because molecules and
atoms are so small
Examples of moles
• 1 mole of iron contains the same number
of atoms as 1 mole of gold
• 1 mole of sodium chloride contains the
same number of molecules as 1 mole of
water
• the number of atoms in 1 mole of iron is
equal to the number of molecules in 1 mole
of water.
• 1 mole of water (H2O) has 1 mole of
oxygen and 2 of hydrogen.
Moles of atoms in molecules
• How many moles of oxygen atoms are in 5
mol of O2 ?
1 mol of O2 contains 2 mol of O atoms
5 mol of O2 contains 10 mol of O atoms
• How many moles of oxygen atoms are in 5
mol of H2SO4?
1 mol of H2SO4 contains 4 mol of O atoms
5 mol of H2SO4 contains 20 mol of O atoms
Atoms to Moles
• I have 4.673 x 1011 atoms of Zinc. How many
mole do I have
• Is it a mole?
• 4.673 x 1011 atoms of Zinc x 1 mol of Zinc
6.02 x 1023 atoms of Zinc
= 7.7 x10-11 mols of zinc
• Always check the units have cancelled out
• This number is less than one therefore it is
less than one mol as it should be!
Moles to atoms
• I have 3.01 x 1023 copper atoms. How many mole
of copper atoms do I have?
• 1 mol = 6.02 x 1023 atoms of copper
• Mol of copper = 3.01 x 1023copper atoms
6.02 x 1023 atoms of copper
mol
Mol of copper = 0.5 mol
Check calculation!
Molar Mass
• Molar mass (M) is the mass of one mole
of a substance (chemical element or
chemical compound).
• The unit of molar masses is:
grams per mole ( g or g/mol or g mol–1)
mol
How do you find the molar mass of
an element?
• In general the molar mass of an
element is the relative atomic mass of
the element expressed in grams.
• The molar mass of a compound is the
relative formula mass of the compound
expressed in grams.
Example
• Calculate the molar mass of table sugar,
sucrose (C12H22O11)
Ar Carbon = 12.01
Ar Hydrogen = 1.00
Ar Oxygen = 16.00
M = (12 x 12.01)+ (22 x 1.00)+ (11 x 16.00)
M = 144.12 + 22 + 176
M = 342.12 g/mol
Grams to moles
• Use the molar mass it has grams and moles
• How many moles of Zinc chloride do I have in
2.6g ZnCl2?
• Molar mass of ZnCl2 = 65.37 + (2 x 35.45)
= 136.27 g/mol
2.6 g of ZnCl2 x 1mol of ZnCl2
136.27 g ZnCl2
= 0.019 mol of ZnCl2
Grams to moles
• I have 30.0g of NH3. How many moles of
NH3 do I have?
• Ar (NH3)= 14.00 +(1.00 x 3)
= 17g/mol
= 30.0g x 1 mol
17g
= 1.76 mol of NH3
Moles to grams
• I have 1.973 mol of I2
• How many grams of Iodine do I have?
• Molar mass of I2 = 126.90 x 2
= 253.8 g/mol
1.973 mol of I2 x 253.8g
1 mol of I2
= 500.75 g
Moles to Grams
• I have 0.300 mol of water how many
grams of water do I have?
• Ar (H2O) = (1.00 x 2) + 16.00
= 2.00 + 16.00
= 18.00 g/mol
= 0.300 mol H2O x 18.00g of H2O
1 mol of H2O
= 5.4 g of H2O
Moles to Grams
1. Find how many moles are given in the
problem.
2. Calculate the molar mass of the substance
3. Multiply step one by step two.
Grams to Moles
1. Find the number of grams given in the
problem.
2. Calculate the molar mass of the substance.
3. Divide step one by step two.
How many atoms of Iron?
• I have 5.5 g of Iron. How many atoms do I have
• Ar = 55.45g/mol
= 5.5g x 1 mol
55.45g
= 0.099 mol
= 0.099 mol x 6.02 x 1023 atoms of Iron
1 mol of Iron
= 5.96 x 1022 atoms of Iron