Post on 18-Dec-2015
Law of Conservation of Matter
By 1800, chemists had noted that the mass of reactants equals the mass of products - provided you capture any escaping gas
Matter is not created or destroyed in a chemical reaction
Law of Constant Composition
Chemists (notably Proust) The relative amount (percentage) of each
element in a compound was the same no matter how the compound was made
These two laws lead Dalton to revive the Atomic Theory Matter is made up of small, indivisible
particles
Dalton’s Atomic Theory
An element is composed of atoms. All atoms of a given element are the
same. Atoms of different elements are different
and have different properties.
Dalton’s Theory-II
Atoms are not changed, created or destroyed in a chemical reaction.
Compounds are the combination of more than one element. A given compound has the same relative
number and kind of atoms.
Law of Multiple Proportions
Accorrding to Dalton’s Theory Two elements (A and B) form two distinct
compounds The amounts of B combining with a fixed amount
of A would be a small whole number ratio. Water: 1 g hydrogen + 8 g oxygen Hydrogen peroxide: 1 g hydrogen +16 g
oxygen
Atomic Structure
Roentgen discovered X-rays (1895) Becquerel discovered radioactivity
(1896) J. J. Thompson discovered the
electron (1897) Rutherford classified radioactivity
emissions: alpha (), beta () and gamma ()
Alpha, beta, gamma
Rutherford’s findings: Alpha are positive particles (+2) ;
heavier than electrons Beta are high speed electrons;
negatively charged particles (-1) Gamma are neutral rays Alpha particles are nucleus of He atom
Thompson’s Model
“Plum pudding” model
A cloud of positive charge holding the negatively charge electrons in place
Rutherford’s alpha experiment
Scattering of alpha particles by gold foil Most particles were undeflected Some were deflected by large angles
Rutherford’s Model
Centre - the nucleus - is small but positively charged
Most of the atom is empty spaces Electrons rotate about the nucleus -
like the solar system
Modern Model
Additional experiments showed Nucleus consists of protons (positive) and
neutrons (neutral) Electrons (negative) exist around the
nucleus Number of protons = number of electrons
Mass of Elementary Particles
Protons and neutrons have a mass of about 1 amu
Electrons have very small mass Most of the mass of an atoms comes from
nucleus (1 amu is 1.66054 10-24 grams)
Atomic Mass & Atomic Number
A
SyZ
A is Mass Number,protons + neutrons
Z is Atomic Number,number of protons
Isotopes
All atoms of a given element have the same number of protons. All Carbon atoms have 6 protons (and 6 electrons).
The number of protons is different for each element.
Atoms of a given element that differ in the number of neutrons are called isotopes.
Examples : carbon-12 and carbon-14C126 C146
Atomic Masses
By international agreement, the carbon-12 atom is defined as having a mass of exactly 12 atomic mass units (amu’s).
All atomic masses are referenced to this standard.
Periodic Table (II)
Elements in the periodic table are arranged in Groups or families – they have similar
chemical and physical properties Metals – towards the left Nonmetals – towards the right Metalloids – in the middle region
Atomic Masses in the Periodic Table
Question: why is the mass of C in the periodic table reported as 12.01 amu and not as 12.000 … amu, exactly?
Another example: the atomic mass of Cl is = 35.453 amu’s. We would expect Cl to be 35 amu?
Ionic Compounds
Tables of common ions in textbook (pages 62 and 64).
Ionic compounds Cation name followed by anion name, e.g.,
sodium bromide (NaBr) Multiple ion types
FeCl2 – iron (II) chloride
FeCl3 – iron (III) chloride
Binary Molecular Compounds
Binary compounds containing two nonmetals name of the first element in the formula
followed by the stem of the name of the second element with the suffix -ide.
The number of atoms of each element in the compound is indicated by a prefix.
mono di tri tetra
1 2 3 4
Some common names must be committed to memory.
Examples – nitrous oxide, N2O, and nitric oxide, NO.
Formulas and Names of Acids
An acid usually is a compound of hydrogen and a nonmetal or a polyatomic anion.
Treat the hydrogen atoms of the acid as H+ ions.
For acids containing monatomic anions, When these acids are found in water solution, add
the prefix hydro- and the suffix -ic to the stem of the name of the anion
Hydrofluoric acid (HF), hydrochloric acid (HCl)
Acids From Polyatomic Anions
If the anion name ends in ‘ate’, the ‘ate’ in the name of the anion is replaced by ‘ic acid ’ The acid of the sulfate ion is sulfuric acid (H2SO4)
The acid of the nitrate ion is nitric acid (HNO3)
If the anion names end in ‘ite’, we change the suffix to –ous and add the word acid. The acid of the nitrite is called nitrous acid, HNO2
The acid of the hypochlorite ion is called hypochlorous acid, HClO
Average Atomic Masses
Most elements in nature exist as mixtures of isotopes.
Atomic masses reported in the periodic table - weighted averages of the different isotopes.
The amount of each isotope in a sample of as an element may vary considerably with the source of the sample. This is the reason why some elements in the
periodic table have few significant figures for their mass.
Organic Compounds
Many organic compounds have complex three dimensional structures chains, and/or rings branches.
The highlighted groups are called functional groups. They are primarily responsible for the
chemical and some physical properties of the molecules.
Methane (CH4)
Ethane (C2H6)
Propane (C3H8)
Butane (C4H10)
Alkanes
C
H
HH
H
C
H
HH
C
H
HH
CH
HH
C
H
H
C
H
HH
CC
CH
C
H
HH
H
HH
H
HH
Methanol (CH3OH)
Ethanol (CH3CH2OH)
1-Propanol (CH3CH2CH2OH)2-propanol (CH3CH(OH)CH
3)
Alcohols
C
H
OHH
H
C
H
HH
C
H
HOH
CH
HH
C
H
H
C
H
OHH
CC
CH
H
HH
HOH
H
H
Methyl Amine (CH3NH2)
Dimethyl amine ((CH3)2NH)
Ethyl Amine (CH3CH2NH2)
Organic Amines
C
HNH2
HH
NH
CH3
CH3
C
H
HC
H
NH2H
H