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AN ATOM
Atom - smallest unit of all matter, that is composed of 3 sub-atomic particles called protons, electrons and Atom neutrons Proton Proton - the 'heavy' positively-charged particle in the nucleus of an atom Electron Electron - the very 'light' negatively-charged particle that orbits the nucleus of an atom Neutron Neutron - the 'heavy' uncharged particle in the nucleus of an atom Uncharged or unreacted atoms have atoms have the same number of positive protons and negative electrons. Approximate size of atoms atoms - Millions of atoms could fit on the sharp point of a needle. Also, if you imagine that an atom is the size of an oval, a proton and a neutron would be the size of footballs in the middle of the oval, and the electron would be the size of a rice grain racing around the running lane.
ATOMIC NUMBER AND ATOMIC MASS
An Example from the Periodic Table
Atomic Number - the number of protons in an unreacted atom Mass Number - the number of protons and neutrons together ATOMIC DIAGRAMS
Protons and neutrons are in the nucleus. Protons are p+ Neutrons are n Electrons orbit the nucleus in electron levels or 'rings'. Electrons are eA limited number of electrons are situated in each electron 'ring'. First ring - maximum of 2 electrons Second ring - maximum of 8 electrons Third ring - maximum of 8 electrons Fourth ring - maximum of 18 electrons
Electron rings close to the nucleus are filled first. ELEMENTS AND COMPOUNDS
Element - An element is a substance composed of the same type of atoms (e.g. gold Au, oxygen O 2). Compound - A compound is a substance made of more than one type of atom (e.g. water H2O, carbon dioxide CO2). Molecule - A molecule is the smallest particle of either an element or a compound. INERT OR NOBLE GASES
Inert or Noble Gases are unreactive gases. They do not corrode nor react. Examples of Noble Gases are: He - Helium Ne - Neon Ar - Argon Kr - Krypton Xe - Xenon Rn - Radon
The electron rings of these unreactive gases are full, therefore they become stable. IONS (CHARGED ATOMS)
When atoms react, they may either gain or lose electrons. Electrons have a negative charge. An atom gaining or losing electrons will get an overall charge. 1+ Positive Ions are atoms that have lost electrons (e.g. sodium Na ) 1Negative Ions are atoms that have gained electrons (e.g. chlorine Cl ) In chemical reactions, atoms tend to gain or lose electrons to resemble the electron numbers of the stable Noble Gases. COVALENT AND IONIC COMPOUNDS
Covalent Compound - a compound where electrons are shared between the atoms (e.g. carbon dioxide CO2) Ionic Compound - a compound formed from the attraction between positive and negative ions. For example 1in the ionic compound sodium chloride NaCl, the chlorine ion (Cl ) gains one electron that was given by the 1+ sodium ion (Na ). COMMON ELEMENTS AND SYMBOLS TO LEARN Element Symbol
Element Name
Element Symbol
Element Name
H
Hydrogen
Mn
Manganese
He
Helium
Fe
Iron
Li
Lithium
Co
Cobalt
C
Carbon
Ni
Nickel
N
Nitrogen
Cu
Copper
O
Oxygen
Zn
Zinc
F
Fluorine
Br
Bromine
Ne
Neon
Ag
Silver
Na
Sodium
Sn
Tin
Mg
Magnesium
I
Iodine
Al
Aluminium
Ba
Barium
Si
Silicon
W
Tungsten
P
Phosphorus
Pt
Platinum
S
Sulphur / Sulfur
Au
Gold
Cl
Chlorine
Hg
Mercury
Ar
Argon
Pb
Lead
K
Potassium
Cr
Chromium
Ca
Calcium
Ti
Titanium
Pu
Plutonium
U
Uranium
NAMING COMPOUNDS PREFIX OR SUFFIX
MEANING
EXAMPLE
Mono-
There is 1 atom of that type in that molecule
Carbon monoxide (CO)
Di-
There are 2 atoms of that type in the molecule
Carbon dioxide (CO2)
Bi-
Hydrogen is present in the molecule
Sodium bicarbonate (NaHCO3)
-ide
There are only 2 types of atoms present in the molecule
Lead oxide (PbO)
-ate
There are 3 or more types of atoms in the molecule, and 1 type is oxygen
Calcium carbonate (CaCO3)
VALENCY TABLE Valency - the charge of an ion or radical which has either lost or gained electrons Note that metals lose electrons easily to become positive ions. This is why most metals are good conductors of electricity.
1+ H
+
2+ Mg
+
3+ Al
+
1F
-
2O
-
PO4
oxide +
Na
Ca
+
Fe
+
Cl
-
S
ferric Li
+
Cu
+
-
-
CO3
-
carbonate K
+
Zn
+
OH
-
SO4
hydroxide Ag
+
Pb
+
NO3
-
nitrate NH4
+
ammonium
Fe
+
ferrous
HCO3
-
bicarbonate
-
phosphate
sulphide Br
3-
-
sulphate
WORKING OUT FORMULAE OF IONIC COMPOUNDS (THE CROSS-OVER METHOD)
Step 1 - In the ionic compounds to be learnt in junior science, there are two parts to the ionic compound - the 1+ 1first is a positive ion (usually a metal e.g. Na ) and the second is a negative ion (e.g. Cl ). Step 2 - Using the valency table, write the two ions and their valencies. Step 3 - Now ignore the positive and negative signs. Cross-over the top valency number to the bottom of the other ion symbol. Do this for both. Step 4 - Write the completed formulae with those same numbers at the bottom. Step 5 - If the numbers on each part are the same (e.g. Na 1 Cl1 or Mg2 O2), ignore them and rewrite the formulae without them (e.g. Na Cl or Mg O). Step 6 - Brackets may be used around radicals (groups of atoms that are charged e.g CO 3).
EXAMPLES OF CHEMICAL NAMES OF COMPOUNDS CHEMICAL FORMULA
CHEMICAL NAME
CO2
carbon dioxide
CO
carbon monoxide
Na Cl
sodium chloride
Cu O
copper oxide
Ag Br
silver bromide
KI
potassium iodide
H Cl
hydrogen chloride (hydrochloric acid)
NH4 Cl
ammonium chloride
K OH
potassium hydroxide
Na OH
sodium hydroxide
Ca (OH)2
calcium hydroxide
Ca S
calcium sulphide
Na NO3
sodium nitrate
H NO3
hydrogen nitrate (nitric acid)
Na HCO3
sodium bicarbonate
Zn SO4
zinc sulphate
Mg CO3
magnesium carbonate
Ca SO4
calcium sulphate
Cu CO3
copper carbonate
Al PO4
aluminium phosphate
Fe SO4
iron sulphate
Fe CO3
iron carbonate
NH4 NO3
ammonium nitrate
NH4 HCO3
ammonium bicarbonate
H2 SO4
hydrogen sulphate (sulphuric acid)
Na2 SO4
sodium sulphate
(NH4)2 CO3
ammonium carbonate
EXAMPLES OF NUMBERS AND TYPES OF ATOMS IN VARIOUS ELEMENTS AND COMPOUNDS NAME OF SUBSTANCE
