Chapter 1modified 1st y med chem 1 2014-15.pdf
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Transcript of Chapter 1modified 1st y med chem 1 2014-15.pdf
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Atoms, Elements,
Molecules & Compounds
.
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All substances are made of atomsAll substances are made of very tiny particles called atoms.
hydrogen (H) and oxygen (O)
atoms
carbon (C) and hydrogen (H)
atoms
Carbon (C), nitrogen (N),
hydrogen (H), oxygen (O) and
sulphur (S) atoms
Iron (Fe), aluminium (Al),
silicon (Si), oxygen (O) and boron (B) atoms
Many substances are made up of different types of atoms.
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An element is a substance made up of only one type of atom.
Atoms in elements
Copper (Cu) is an element made up of copper atoms only.
Carbon (C) is an element made up ofcarbon atoms only.
Helium (He) is an element made up ofhelium atoms only.
There are about one hundred Elements that form all substances.
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How to write symbols for
elementsTwo important rules should be followed when writing the
symbols of elements so that there is no confusion.
1. The first letter of an element’s symbol is always
a capital letter.
2. If there are two letters in the element’s symbol,
the second letter is always a small letter.
e.g. N (not n) for nitrogen
e.g. Co for cobalt (not CO)
No, Watson! It was carbon monoxide
poisoning – not cobalt.
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The symbol for many of the more common elements uses
just the first letter of the name.
Symbols of elementsA standard set of symbols is used to represent elements:
hydrogenH =carbonC =fluorineF =
oxygenO =nitrogenN =
Others elements have
the first two letters.
lithiumLi =aluminiumAl =heliumHe =
Some of the symbols are not
always as you might expect.
leadPb =goldAu =silverAg =
iodineI =
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Molecules
A molecule is formed of a group of 2 atoms or more of the
same element that are joined together.
Eg. H2, O2, N2, Cl2, Br2
An element is a substance made up of only one type of atom.
Eg. H, O, N, Cl, Br
Oxygen is an
element made up of
oxygen atoms only.
Q. How many atoms
are there in an
oxygen molecule?
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Compounds
Q. How many atoms
are there in a water
molecule?
A compound is formed of a group of different elements that
are joined together.
Eg. H2O, CO2, NH3
Q. How many elements
are there in a water
molecule?
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Molecules versus Compounds
All compounds are molecules but not all
molecules are compounds.
Molecular hydrogen (H2), molecular oxygen (O2) and
molecular nitrogen (N2) are not compounds because each
is composed of a single element. Water (H2O), carbon
dioxide (CO2) and methane (CH4) are compounds because
each is made from more than one element.
Q. Which is a molecule and which is a compound?
NaCl, H2SO4, Cl2,
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Atomic Number, Mass
Number & Isotopes
.
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10
Subatomic Element
Particle Symbol Charge Relative
Mass
Electron e- 1- 0
Proton p+ + 1
Neutron n 0 1
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11
Location of Subatomic Element
Electrons
nucleusProtons
Neutrons
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Atomic number (Z) = number of protons in nucleus
Mass number (A) = number of protons + number of neutrons
= atomic number (Z) + number of neutrons
XA
Z
Mass Number
Atomic Number
Element Symbol
2.3
Atomic number & Mass number
8 15 30
O P Zn16 31 65
8 p+ 15 p+ 30 p+
8 n 16 n 35 n
8 e- 15 e- 30 e-
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Isotopes are atoms of the same element (X) with
different numbers of neutrons in the nucleus
2.3
Isotopes
Proton 1 1 1
Neutron 0 1 2
Electron 1 1 1
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How many protons, neutrons, and electrons are in C146 ?
How many protons, neutrons, and electrons are in C116
?
Do You Understand Isotopes?
2.3
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Period
Gro
up
Alk
ali M
eta
l
Noble
Gas
Halo
gen
Alk
ali E
arth
Me
tal
2.4
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2.5
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2.5
Electropositive elements
are the elements which have tendency to
lose electrons. e.g. Metals (Na, K, Al, Mg)
Electronegative elements are
those which have tendency to attract the
electrons of the bond. e.g. Non metals
(Cl, Br, I)
In the periodic table from left to right
Electropositivity decreases
Electronegativity increases upto group
7A
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2.5
There are three major states of matter: solid,
liquid, and gas.
Solid: is something that has a definite shape and
volume.
Liquid: has a definite volume but takes the
shape of its container.
Gas: takes the shape of its container and it
expands to fill the entire container.
States of matter
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A molecule is an aggregate of two or more atoms in a
definite arrangement held together by chemical bonds
H2 H2O NH3 CH4
A diatomic molecule contains only two atoms
H2, N2, O2, Br2, HCl, CO
A polyatomic molecule contains more than two atoms
O3, H2O, NH3, CH4
2.5
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An ion is an atom, or group of atoms, that has a net
positive or negative charge.
cation : is an ion with a positive charge (+ve)
If a neutral atom loses one or more electrons
it becomes a cation.
Anion: is an ion with a negative charge (-ve)
If a neutral atom gains one or more electrons
it becomes an anion.
Na11 protons
11 electrons Na+ 11 protons
10 electrons
Cl17 protons
17 electrons Cl-17 protons
18 electrons
2.5
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A monatomic ion contains only one atom
A polyatomic ion contains more than one atom
2.5
Na+, Cl-, Ca2+, O2-, Al3+, N3-
OH-, CN-, NH4+, NO3
-
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13 protons, 10 (13 – 3) electrons
34 protons, 36 (34 + 2) electrons
Do You Understand Ions?
2.5
How many protons and electrons are in Al2713 ?3+
How many protons and electrons are in Se7834
2- ?
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2.6
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Molecular formula: it shows the exact number of
atoms of each element in the smallest unit of a
substance
Empirical formula: it shows the simplest
whole-number ratio of the atoms in a substance
H2OH2O
molecular empirical
C6H12O6 CH2O
O3 O
N2H4 NH2
2.6
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Ionic compounds consist of a cation (+ve) and an
anion (-ve)
• the formula is always the same as the empirical formula
• the sum of the charges on the cations and anions in each
formula unit must be equal zero
The ionic compound NaCl
2.6
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Some Polyatomic Ions (Table 2.3)
NH4+
ammonium SO42-
sulfate
CO32-
carbonate SO32-
sulfite
HCO3- bicarbonate NO3
- nitrate
ClO3- chlorate NO2
- nitrite
Cr2O72-
dichromate SCN-
thiocyanate
CrO42-
chromate OH- hydroxide
2.7
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Chemical Nomenclature
• Ionic Compounds
– often a metal + nonmetal
– anion (nonmetal), add “ide” to element name
BaCl2 barium chloride
K2O potassium oxide
Mg(OH)2 magnesium hydroxide
KNO3 potassium nitrate
2.7
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• Transition metal ionic compounds
– indicate charge on metal with Roman numerals
FeCl2 2 Cl- -2 so Fe is +2 iron(II) chloride
FeCl3 3 Cl- -3 so Fe is +3 iron(III) chloride
Cr2S3 3 S-2 -6 so Cr is +3 chromium(III) sulfide
2.7
Anion Cation
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HI hydrogen iodide
NF3 nitrogen trifluoride
SO2 sulfur dioxide
N2Cl4 dinitrogen tetrachloride
NO2 nitrogen dioxide
N2O dinitrogen monoxide
Molecular Compounds
2.7
TOXIC!
Laughing gas
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Acid can be defined as a substance that yields
hydrogen ions (H+) when dissolved in water.
e.g. HCl (hydrogen chloride orhydrochloric acid)
It dissolves in water to (H+ Cl-)
Oxoacid is an acid that contains hydrogen, oxygen,
and another element.
HNO3 nitric acid
H2CO3 carbonic acid
H2SO4 sulfuric acid
2.7
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Base can be defined as a substance that yields
hydroxide ions (OH-) when dissolved in water.
NaOH Sodium hydroxide
KOH Potassium hydroxide
Ba(OH)2 Barium hydroxide
2.7
Na+ OH-
K+ OH-
Ba++ (OH)2-