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Symbol : A short form of an element. John Dalton -1807
1814 – Berzelius: Representation of the elements by the l etters of their names. ( either English or Latin or Latin))
First letter is always capital and second is small.
NO
1 2 3 4
NAME
Hydrogen Mercury Fluorine Sodium
5 Phosphorus 6 Copper 7 Zinc
Berzelius
SYMBOL
NO
H Hg F Na
8 9 10 11
P Cu Zn
12 Mercury 13 Lead 14 Gold
NAME
Silver Potassium Iron(Ferrum) Tin
SYMBOL
Ag K Fe Sn Hg Pb Au
Valency : It is the number of electrons gained, lost or shared by an atom during the formation of a chemical compound. OR
Na = +1
Cl = -1
The number of hydrogen atoms which can combine with or displace one atom of element or radical so as to form a compound. O = 2
Cl = 1
FORMATION OF IONS
Sodium has 1 electron in its outer shell. It will lose its outer electron to complete its octet and acquire stable electronic configuration.
Chlorine has 1 electron in its outer shell. It will gain 1 electron to complete its octet and acquire stable electronic configuration.
FORMATION OF IONS
Magnesium has 2 electrons in its outer shell. It will lose its 2 outer electrons to complete its octet and acquire stable electronic configuration.
Oxygen has 6 electrons in its outer shell. It will gain 2 electrons to complete its octet and acquire stable electronic configuration.
METALS
Na
-1e
VALENCY
Na +
+1
Mg
-2e
Mg ++
+2
Al
-3e
Al+++
+3
NON METALS
Cl S N
+1e
+2e +3e
VALENCY
Cl -
-1
S --
-2
N ---
-3
Atoms of elements like iron, copper sometimes lose more electrons than are present in its outermost shell ( valence shell) i.e loss from penultimate shell and exhibit more than one valency called variable valency. Eg. Fe 2+ and Fe 3+ ; Cu 1+ and Cu 2+.
RADICALS: A radical is an atom or group of atoms with valency and charge.
RADICALS POSITIVE
NEGATIVE
UNIVALENT
UNIVALENT
BIVALENT TRIVALENT
BIVALENT TRIVALENT
Nitride
N 3-
Representation of a molecule of an element or a compound by symbols is known as chemical formula. Eg. The chemical formula for: 1] Oxygen is O2 2] copper sulphate is CuSO 4 3] potassium permanganate is KMnO 4
WRITING FORMULA OF A COMPOUND Step 1 - Write the positive ion on the left side and the negative ion on the right side. Step 2 - Write their valencies. Step 3 – Interchange the valency and shift to lower right sides. Step 4 - Write the completed formulae with those same numbers at the bottom. Step 5 – Reduce to the simplest ratio if possible.
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CHEMICAL EQUATIONS
CHEMICAL EQUATIONS : Chemical equation is a shorthand for a chemical reaction. Eg.
NH4OH +
HCl
NH4Cl
+ H2O
Reactants
Products
[left side]
[right side]
INFORMATION PROVIDED BY EQn.
LIMITATIONS OF EQUATION
• Reactants
• The concentration
• Products
• The speed of reaction
• Direction [rev or irrev]
• Change in colour
• States of matter
• Completion of reaction • Evolution of sound or light
EXAMPLES OF CHEMICAL EQUATIONS:
One reactant and two or three products. 2Pb(NO3)2
Two reactants and one product. NH3 + H2O
NH4OH
Two reactants and two products. Mg + 2HCl
2PbO + O2 + 4NO2
MgCl2 + H2
Two reactants and three or four products. K2Cr2O7 + 14HCl
2KCl + 2CrCl3 + 7 H2O + 3Cl2
BALANCED CHEMICAL EQUATIONS: A equation is balanced if… No of atoms of each element [ L.H.S.]
=
No of atoms of
each element [ R.H.S.]
Rules for Balancing Equations
1. Write the correct formulas for all the reactants and products in the reaction. 2. Count the number of atoms of each element in the reactants and products. 3. Balance the elements one at a time by using coefficients. 4. It is best to begin with an element other than hydrogen or oxygen. 5. Check each atom to be sure that the equation is balanced. 6. Finally, make sure that all the coefficients are in the lowest possible ratio.
Note! Subscripts should never be changed when trying to balance a chemical equation.
Balancing of a chemical equations-An e quations-An example K2Cr2O7 + HCl
KCl + CrCl3 + H2O + Cl2
Balance the potassium and Chromium atoms. ( generally generall y metals first)
