Aristotle 400 B.C. - Democritus thought matter could not be
divided indefinitely. 350 B.C - Aristotle modified an earlier
theory that matter was made of four elements: earth, fire, water,
air. Democritus Aristotle was wrong. However, his theory persisted
for 2000 years. fire air water earth This led to the idea of atoms
in a void.
Slide 5
Relied on experimentation not the development of scientific
theories. Developed some useful techniques in distillation,
evaporation, crystallisation and filtration Aristotle rejected the
idea of atoms, but accepted and refined the notion of four elements
water, air, fire and earth One of the major goals of an alchemist
was to discover a substance that would turn base metals such as
iron, copper, and lead into gold.
Slide 6
Robert Boyle Attempted to isolate Aristotles four elements
Defined an element as being a substance that could not be broken
down into simpler substances Was able to distinguish clearly
between elements, compounds and mixtures
Slide 7
Antoine Lavoisier Changed chemistry from a qualitative to a
quantitative science through his tin experiment Showed that the
mass of the products in a reaction is equal to the mass of the
reactants proving the law of conservation of mass
Slide 8
1800 -Dalton proposed a modern atomic model based on
experimentation not on pure reason. All matter is made of atoms.
Atoms of an element are identical. Each element has different
atoms. Atoms of different elements combine in constant ratios to
form compounds. Atoms are rearranged in reactions. His ideas
account for the law of conservation of mass (atoms are neither
created nor destroyed) and the law of constant composition
(elements combine in fixed ratios).
Slide 9
Discovery of subatomic particle i) The Discovery of Electrons
*1897 J.J. Thomson- cathode ray experiment Thomsons experiment
involved the use of cathode-ray tube. When a sufficiently high
voltage is applied across the electrode, an electric current flows
through the tube from negatively charged electrode ( the cathode)
to the positively charged electrode (the anode).
Slide 10
Slide 11
Later experiments had shown that cathode-ray can be deflected
by electric or magnetic field. Because the beam is produced at a
negative electrode and is deflected toward a positive plate,
Thomson proposed that cathode rays are negatively charged
fundamental particles found in all atoms which, we now called
electrons. Furthermore, because electrons are emitted from
electrodes made of many different metals, all these substances must
contain electrons. By careful measuring the amount of deflection
caused by electric and magnetic fields of known strength, He
established the ratio of mass to electric charge for cathode ray
that is, m/e = -5.6857x10 -9 g/coulomb.
Slide 12
Complete revision questions page 32 (1 2) Summarise how
subatomic particles were originally discovered through
investigations on electricity What is a cathode ray?
Slide 13
1) Daltons Billiard ball model (1800-1900) Atoms are solid and
indivisible. 2)Thompson Plum pudding model (1900) Negative
electrons in a positive framework. 3)The Rutherford model (around
1910) Atoms are mostly empty space. Negative electrons orbit a
positive nucleus. Materials, when rubbed, can develop a charge
difference. This electricity is called cathode rays when passed
through an evacuated tube (demos). These rays have a small mass and
are negative. Thompson noted that these negative subatomic
particles were a fundamental part of all atoms.
Slide 14
1896 Antoine Becquerel discovered uranium ores emit invisible
rays through working with some photographic plates Marie and Pierre
Curie experimented with radioactivity discovering that uranium,
radium and polonium were disintegrating over time and emitting
radiation
Slide 15
Rutherford shot alpha ( ) particles at gold foil. Most
particles passed through. So, atoms are mostly empty. Some positive
-particles deflected or bounced back! Thus, a nucleus is positive
& holds most of an atoms mass. Radioactiv e substance path of
invisible -particles Lead block Zinc sulfide screen Thin gold
foil
Slide 16
1909 Ernest Rutherford ~ use particle to study the inner
structure of atoms. When he directed a beam of -particles at a thin
gold foil, he found that The majority of -particles penetrated the
foil undeflected. Some particles experienced slightly deflections.
A few (about one in every 20,000) suffered rather serious
deflections as they penetrated the foil. A similar number did not
pass through the foil at all, but bounced back in the direction
from which they had come.
Slide 17
James Chadwick Proposed the existence of uncharged particles
through his experiments with Beryllium foil Showed that neutrons
had almost the same mass as protons
Slide 18
Therefore Modern picture of an atom, then, consist of three
types of particles- electrons, protons and neutron. Electric Charge
Mass ParticleSI (C ) Atomic SI (g)amu Located Electron -1.602x10
-19 -1 9.109x10 -28 5.49x10 -4 outside nucleus Proton+1.602x10 -19
+1 1.673x10 -24 1.0073 in nucleus Neutron 0 0 1.675x10 -24 1.0087
in nucleus
Slide 19
Modern physics has revealed successively deeper layers of
structure in ordinary matter. Matter is composed, on a tiny scale,
of particles called atoms. Atoms are in turn made up of minuscule
nuclei surrounded by a cloud of particles called electrons. Nuclei
are composed of particles called protons and neutrons, which are
themselves made up of even smaller particles called quarks. Quarks
are believed to be fundamental, meaning that they cannot be broken
up into smaller particles.
Slide 20
Complete the revision questions page 36 (3 9). Check and review
your answers.
Slide 21
Frederick Soddy Found two kinds of thorium and isolated the
difference in the number of neutrons. The Mass Spectrometer
(provides information about;) The number of isotopes in a given
sample of element The relative isotopic mass of each isotope The
percentage abundance of the isotopes
Slide 22
Most elements consist of a mixture of isotopes The relative
atomic mass (A r )of an element represents the average mass of one
atom, taking into consideration the number of isotopes of the
element, their relative isotopic mass (RIM) and their relative
abundance.
Slide 23
(RIM first isotope x abundance)+(RIM second isotope x
abundance) A r =
______________________________________________________ 100
Slide 24
Using the data in the table calculate the RIM of Cl 37
IsotopeRIM% Abundance Cl 35 (Z = 17)34.9775.80 Cl 37 (Z =
17)unknown24.20 (RIM first isotope x abundance)+(RIM second isotope
x abundance) A r (Cl) =
______________________________________________________ 100 Check
your answer and workings on page 38
Slide 25
Complete the revision questions page 39 (10 18). Check and
review your answers.
Slide 26
Modern atomic theory is concerned primarily with electron
arrangement around the nucleus and has helped the understanding of
the chemical properties and behaviour of atoms. In chemical
reactions, when atoms react bonds are broken and atoms rearrange
themselves to form new bonds. The formation of new bonds involves
the redistribution of electrons.
Slide 27
There are 2 types of spectra: continuous spectra & line
spectra. Its when electrons fall back down that they release a
photon. These jumps down from shell to shell account for the line
spectra seen in gas discharge tubes (through spectroscopes).
Electrons orbit the nucleus in shells Electrons can be bumped up to
a higher shell if hit by an electron or a photon of light.
Slide 28
If atoms emit only discrete wavelengths, they must have
discrete energies. Each orbit corresponds to a different energy
level An electron can move between energy levels but cannot remain
between levels Quantum jump moving from one energy level to another
A specific quantity of energy (a photon) is associated with each
quantum jump made by an electron
Slide 29
An electron can move from a lower energy level to a higher
level by absorbing energy (eg flame) When the electron falls back
to a lower level, energy is released as a consequence of the
quantum jump. The energy given out is the difference in energy
between the two energy levels and will be associated with a
specific wavelength. Each wavelength corresponds to a coloured line
in the emission spectrum.
Slide 30
Slide 31
In the Quantum Mechanical Model an electron around a nucleus
may be visualised as a cloud of negative charge.
Slide 32
1. The energy levels of electrons are designated by principal
quantum numbers, n, and are assigned specific values : n = 1, 2, 3,
4, 5 etc. These principal quantum numbers may be referred to as
shells and are also called the K, L, M, and N shells. 2. Within
each shell, several different subshells exist. The number of
subshells equals the shell number Eg Shell number 2, has 2
subshells Each subshell corresponds to a different electron cloud
shape Subshells are represented by the letters: s, p, d, f
Slide 33
The way in which electrons are arranged around the nucleus
generally lowest energy first Note that the 4s subshell is filled
before the 3d subshell (3d is of a higher energy)
Slide 34
Electron Configuration Exited States When an atom moves to a
higher energy level than the ground state by absorbing energy, its
electron configuration changes The outermost electron moves to a
higher energy level subshell Eg Ne (ground state) 1s 2 2s 2 2p 6 Eg
Ne (exited state) 1s 2 2s 2 2p 5 3s 1
Slide 35
Electron Configuration The group and period in which an element
is found is easily read from the electron configuration (is the
number of valence electrons in the last shell being filled) Eg Be
(Z = 4) 1s 2 2s 2 (the highest shell number being filled) Group ?
_______ Ar (Z = 18) 1s 2 2s 2 2p 6 3s 2 3p 6 Period ? _______
Slide 36
Electron Configuration Group number is found by using the total
number of electrons in the last shell to count across the periodic
table The period is the number of the last shell occupied by
electrons Work through Sample Problems 2.2 and 2.3
Slide 37
Consider an atom of Potassium: Potassium has 19 electrons.
These are arranged in shells Nucleus The inner shell has __
electrons The next shell has __ electrons The next shell has the
remaining __ electron Electron structure = 2,8,8,1
Slide 38
ElementShell 1Shell 2Shell 3Shell 4 Hydrogen H 1 electron0
electron Helium He 2 electron0 electron
Slide 39
ElementShell 1Shell 2Shell 3Shell 4 Lithium Li 2 electron1
electron0 electron Beryllium Be 2 electron 0 electron
Slide 40
ElementShell 1Shell 2Shell 3Shell 4 Boron B 2 electron3
electron0 electron Carbon C 2 electron4 electron0 electron
Slide 41
ElementShell 1Shell 2Shell 3Shell 4 Nitrogen N 2 electron5
electron0 electron Oxygen O 2 electron6 electron0 electron
Slide 42
ElementShell 1Shell 2Shell 3Shell 4 Fluorine F 2 electron7
electron0 electron Neon Ne 2 electron8 electron0 electron
Slide 43
ElementShell 1Shell 2Shell 3Shell 4 Sodium Na 2 electron8
electron1 electron0 electron Magnesium Mg 2 electron8 electron2
electron0 electron
Slide 44
ElementShell 1Shell 2Shell 3Shell 4 Aluminium Al 2 electron8
electron3 electron0 electron Silicon Si 2 electron8 electron4
electron0 electron
Slide 45
ElementShell 1Shell 2Shell 3Shell 4 Phosphorus P 2 electron8
electron5 electron0 electron Sulphur S 2 electron8 electron6
electron0 electron
Slide 46
ElementShell 1Shell 2Shell 3Shell 4 Chlorine Cl 2 electron8
electron7 electron0 electron Argon Ar 2 electron8 electron 0
electron
Slide 47
ElementShell 1Shell 2Shell 3Shell 4 Potassium2 electron8
electron 1 electron Calcium Ca 2 electron8 electron 2 electron
Complete the revision questions pages 44, 45 (21 26) Work
through the Sample Problems 2.4, 2.5 Complete the revision
questions page 45 (27 31)
Slide 52
Atomic numbers, Mass numbers There are 3 types of subatomic
particles. We already know about electrons (e ) & protons (p +
). Neutrons (n 0 ) were also shown to exist (1930s). They have: no
charge, a mass similar to protons Elements are often symbolized
with their mass number and atomic number E.g. Oxygen: O 16 8 These
values are given on the periodic table. For now, round the mass #
to a whole number. These numbers tell you a lot about atoms. # of
protons = # of electrons = atomic number # of neutrons = mass
number atomic number Calculate # of e , n 0, p + for Ca, Ar, and
Br.
Slide 53
3545358035Br 1822184018Ar 20 4020Ca ee n0n0 p+p+
MassAtomic
Slide 54
3 p + 4 n 0 2e 1e Li shorthand Bohr - Rutherford diagrams
Putting all this together, we get B-R diagrams To draw them you
must know the # of protons, neutrons, and electrons (2,8,8,2
filling order) Draw protons (p + ), (n 0 ) in circle (i.e. nucleus)
Draw electrons around in shells 2 p + 2 n 0 He 3 p + 4 n 0 Li Draw
Be, B, Al and shorthand diagrams for O, Na
Slide 55
11 p+ 12 n 2e 8e 1e Na 8 p+ 8 n 2e 6e O 4 p+ 5 n Be 5 p+ 6 n B
13 p+ 14 n Al
Slide 56
Isotopes and Radioisotopes Atoms of the same element that have
different numbers of neutrons are called isotopes. Due to isotopes,
mass #s are not round #s. Li (6.9) is made up of both 6 Li and 7
Li. Often, at least one isotope is unstable. It breaks down,
releasing radioactivity. These types of isotopes are called
radioisotopes Q- Sometimes an isotope is written without its atomic
number - e.g. 35 S (or S-35). Why? Q- Draw B-R diagrams for the two
Li isotopes. A- The atomic # of an element doesnt change Although
the number of neutrons can vary, atoms have definite numbers of
protons.
Slide 57
3 p + 3 n 0 2e 1e 6 Li 7 Li 3 p + 4 n 0 2e 1e For more lessons,
visit www.chalkbored.com www.chalkbored.com
Slide 58
Chapter 2 Review Practice your electron dot diagrams here
Complete the multiple choice questions pages 48, 49 Consider each
of the review questions 1 - 11