topic 2: structure of matter
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TOPIC 2: Structure of Matter
OUTLINE
2.0 STRUCTURE OF MATTER
2.1 Early models of atom 2.2 Modern models of atom
2.3 Structure of atom
OUTLINE
2.1 Early models of atom2.1.1 Democritus2.1.2 John Dalton
2.1.3 J.J.Thompson 2.1.4 Ernest Rutherford
2.1.1 Democritus (460 B.C. – 370 B.C.)
Greek philosopher (“atomos”) IDEAS
1.All matter composed of atoms in void
2.Atoms were indivisible & indestructible
3.Properties of atom differ in shape, arrangement and sizes
IDEAS
4.Shape of atom determined
the substance properties
*Eg: -Fire atoms had sharp points-Wine atoms were spheres-Clay atoms were jagged
2.1.2 John Dalton (1766 – 1844)
2.1.3 J.J Thomson – (1856 -1940)
2.1.3 J.J Thomson – (1856 -1940)
Sir William Crookes - 1875
From experiments he
was able to prove the ray was
matter
When he connected the plates to the + and
-terminals of a high voltage battery he
observed amysterious glowing
blue ray
He removed almost all
the air from the tube and sealed
it
Constructed a glass tube
with two metal plates inside it
Extra Note
2.1.3 J.J Thomson – (1856 -1940)
2.1.3 J.J Thomson – (1856 -1940)
2.1.3 J.J Thomson – (1856 -1940)
Result’s Experiment
The ray composed of negatively charged matter
The ray attracted to + plate and repelled by - plate
100 years earlier, Dalton proposed atoms were neutral, solid spheres
Thomson’s experiment disproved Dalton’s theory
IDEAS
Proposed that matter was made of atoms with negatively charged particles embedded in a positive
cloud
He called these negative particles “electrons”.
The negative particles and positive cloud neutralized each other so the
atom had an overall neutral charge.
2.1.3 J.J Thomson – (1856 -1940)
Plum Pudding Model
2.1.4 ERNEST RUTHERFORD (1871-1937)
Rutherford used this alpha particleto investigate the
structureRutherford and Geiger in the
Cavendish Lab of the atom.
This particle was called an
alpha particle (α).
One type of radioactivity is
whenan atom throws out
a positivelycharged particle from the nucleus
4. A screen around the gold
to detectwhere the alpha particles were
traveling.
2. He fired these positive particles at athin piece of gold (dense metal).
3. This produced a beam of alpha particlestraveling in a straight line
1. He encased uranium in lead(which absorbs alpha particles)
2.1.4 ERNEST RUTHERFORD (1871-1937)
Gold Foil Experiment
Uranium is a radioactive element that gives off
positive particles (alpha particles).
Rutherford used these positive particles to
investigate the makeup of the atom.
URANIUM
2.1.4 ERNEST RUTHERFORD (1871-1937)
• Rutherford shot alpha particles at a thin sheet of gold to observe what happened when the positive α particles
passes through the gold atoms.
• If Thompson’s model was correct, the alpha particles should pass through the diffused positive cloud with ease.
2.1.4 ERNEST RUTHERFORD (1871-1937)
Gold Foil experiment
He concluded that the atom had a dense,
positive central nucleuscomposed of + charged
protons
He proposed hisPlanetary Model of the Atom.His model created positively
charged protons located in the nucleus and placed
electrons in orbit around the nucleus - like
planets around the sun.
2.1.4 ERNEST RUTHERFORD (1871-1937)
• Based on his experimental evidence:– The atom is mostly empty space– All the positive charge, and almost all the
mass is concentrated in a small area in the center. He called this a “nucleus”
– The electrons distributed around the nucleus, and occupy most of the volume
– His model was called a “nuclear model”
2.1.4 ERNEST RUTHERFORD (1871-1937)
• VIDEO 1• VIDEO 2
SUMMARY
· Dalton's model of the atom - solid, tiny, indivisible particles.· Thomson's model - often describe as the "plum pudding" model - electrons are scattered throughout the atom.· Rutherford's model - includes the solid nucleus in the center of the atom.
OUTLINE
2.2 Modern models of atom2.2.1 Niels Bohr2.2.2 James Chadwid
2.2.1 NIELS BOHR
Modification of Rutherford Model
The Bohr model of the atom is based on the quantum mechanics.
2.2.1 NIELS BOHR
1 •Electrons orbit the nucleus (in orbits) that have a set size and energy (7 Energy level)
2 •The energy of the orbit is related to its size. The height energy is found in the largest orbit
3 •The arrangement of these electrons in certain energy levels determines the chemical and physical properties of the elements
4 •Radiation is absorbed or emitted when an electron moves from one orbit to another. And the energy change E = E2 – E1
IDEAS
VIDEO 3
2.2.2 JAMES CHADWICK
1 •In 1932 James Chadwick discovered a 3rd subatomic particle in the atom
2 •He called this particle a neutron because it was neutral
3 •He proposed that neutrons resided in the nucleus of the atom along with protons
VIDEO 4
2.1 Early models of atom2.1.1 Democritus2.1.2 John dalton 2.1.3 J.J.Thompson 2.1.4 Ernest Rutherford
OUTLINE
2.3 Structure of atom2.3.1 Defining the atom2.3.2 Distinguishing among atoms
OUTLINE
2.3.1 Defining the atom2.3.1.1 Electron2.3.1.2 Nucleus2.3.1.3 Structure nucleus
2.3.1 Defining the atom
Neutrons have no lectrical charge
1 •Atomic radius: 40 -270 picometer
2 •Smallest part of an element
3 •3 subatomic particles: protons, neutrons, electrons
4•Protons = Positive (+) charge•Neutrons = Neutral•Electron = Negative (-) charge
2.3.1.1 Electron
ELECTRONDiscovery
J J Thomson-Cathode ray tube- Cathode rays composed of negatively charged particles (electrons)
Mass(0.005 amu)
Determine the atomic
number (Z) (the atom’s
identity)
LocationOutside nucleus
(Orbital)
ChargeNegative charge
2.3.1.2 Nucleus
NUCLEUS
DiscoveryErnest
Rutherford
Determine the Atom's
mass
Location Central part of an atom
Made upProton and
neuton
2.3.1.2 Nucleus2.3.1.3 Structure of Nucleus
NEUTRONSMass = 1 amu, charge
= 0
Neutrons act as a type of “insulation”
between the protons, preventing them
from repelling each other
PROTONSMass = 1 amu,
charge = +1
Determines the atom's identity
(atomic number)
OUTLINE
2.3.2 Distinguishing among atoms 2.3.2.1 Atomic Number2.3.2.2 Mass Number2.3.2.3 Atomic Mass2.3.2.4 Isotopes2.3.2.5 Electronic Configuration
2.3.2.1 Atomic Number (Z)
5. Atoms are neutral, # proton = # electron
1. Atoms are identified by their atomic number
4. The atomic number of an element never changes
6. Eg: Hydrogen atoms, contain one proton and
have an atomic number 1
2. Number of protonsdetermine an element's
atomic number
3. Periodic Table is in order of increasing
atomic number
Element # of protons Atomic # (Z)
Carbon 6 6
Phosphorus 15 15
Gold 79 79
2.3.2.1 Atomic Number
Example…….
Mass number is the number of protons and neutrons in the nucleus
p+ + n0 = Mass #
2.3.2.2 Mass number
Nuclide p+ n0 e- Mass #
Oxygen 8 10 8 18
Arsenic 33 42 33 75
Phosphorus 15 16 15 31
2.3.2.2 Mass number
Example…..
1. An element's or isotope's atomic number tells how many protons are in its atoms.
2. An element's or isotope's mass number tells how many protons and neutrons in its atoms.
SUMMARY
1. An element's or isotope's atomic number tells how many protons are in its atoms.
2. An element's or isotope's mass number tells how many protons and neutrons in its atoms.
SUMMARY
X Massnumber
AtomicnumberSubscript →
Superscript →
SUMMARY
Br80
35
Find each of these: a) number of protonsb) number of neutronsc) number of electronsd) Atomic numbere) Mass Number
Lv298
116
QUIZ……
QUIZ….. If an element has an atomic number
of 34 and a mass number of 78, what is the: a) number of protonsb) number of neutronsc) number of electronsd) complete symbol
QUIZ……
Measuring Atomic Mass• Instead of grams (because the numbers would
be too small), the unit we use is the Atomic Mass Unit (amu)
• It is defined as one-twelfth the mass of a Carbon-12 atom.– Carbon-12 chosen because of its isotope purity.
• Each isotope has its own atomic mass, thus we determine the average from percent bundance.
2.3.2.3 Atomic mass
Eg: How heavy is an atom of oxygen? It depends, because there are different kinds
of oxygen atoms.
We are more concerned with the average atomic mass.
2.3.2.3 Atomic mass
To calculate the average:• Multiply the atomic mass of each isotope
by it’s abundance (expressed as a decimal), then add the results.
A = [(mass of isotope) (%abundance) ] + [(mass of isotope) %abundance)] + 100
2.3.2.3 Atomic mass
Atomic Masses
Isotope Symbol Composition of the nucleus
% in nature
Carbon-12 12C 6 protons6 neutrons
98.89%
Carbon-13 13C 6 protons7 neutrons
1.11%
Carbon-14 14C 6 protons8 neutrons
<0.01%
Atomic mass is the average of all the naturally occurring isotopes of that element.
Carbon = 12.011
2.3.2.3 Atomic mass
The natural abundance for boron isotopes is: 19.9% 10B (10.013 amu) and 80.1% 11B (11.009amu). Calculate the atomic weight of boron.
Atomic Mass = [19.9)(10.013)] + [(80.1)(11.009)] 100%
= [199] + [882] 100% = 10.81 amu
so, the atomic weight of B = 10.81 amu
PROBLEM 1
Verify that the atomic mass of magnesium of 24.31 amu, given the following: 24Mg= 23.985042 amu, 78.99%
25Mg= 24.985837 amu, 10.00%26Mg= 25.982593 amu, 11.01%
Atomic mass = [(0.7899)(23.985042)] + [(0.1)(24.985837)] + [(0.1101)(25.982593)]
= 18.946 + 2.499 + 2.861
= 24.306 amu
PROBLEM 2
Solution:
PROBLEM 3The atomic mass of lithium is 6.94 amu, the naturally occurring isotopes are 6Li = 6.015121 amu, and 7Li = 7.016003 amu. Determine the percent abundance of each isotope.
6.94 = [(% 6Li)(6.015121)] + [(%7Li)(7.016003)]
Since I don’t know what the percentage are, I will have to use variables.100% of Lithium is determined by these two naturally occurring isotopes.
We will let 6Li = x and 7 Li = 1-x; we use 1 – x instead of 100 – x because the small number is easier to work with.(in other words we reduced 100% to decimal form 1.00)
Solution:
PROBLEM 4PROBLEM 3
6.94 = [(% 6Li)(6.015121)] + [(%7Li)(7.016003)]
6.94 = [(x)(6.015121)] +[(1-x)(7.016003)]
6.94 = 6.015121x + 7.016003 – 7.016003x
6.94 -7.016003 = (6.015121x - 7.016003x)
-0.076003 = -1.000882 x
Solve for x:
x = 0.075936
6Li = x and 7 Li = 1-xTherefore, 6Li = 0.075936 x 100% = 7.59% 7Li = (1- 0.075936 ) x 100% =
Copper exists as two isotopes: 63Cu (62.9298 amu) and 65Cu (64.9278 amu). What are the percent abundances of the isotopes?
Atomic mass for Cu = 63.546 amu 63Cu % = 1-x 65Cu % = x
63.546 = [(1-x)(62.9298)] + [(x)(64.9278)]63.546 = 62.9298 - 62.9298x + 64.9278x
1.3818 = 1.998x x = 1.3818 / 1.998 x = 0.6916
65Cu = 0.6916 x 100% =69.16% 63Cu = 1 – x = 1 – 0.6916 = 0.3084 x 100% =30.84%
PROBLEM 4
Solution:
PROBLEM 5
Lithium has an elemental atomic mass of 6.941 and has two naturally occurring isotopes, 6Li and 7Li. Their masses are 6.0151 and 7.0160 respectively. What are the natural abundances (to 2 decimal places in percentage) of the isotopes of Lithium?
Answer:6Li: 7.49%, 7Li: 92.51%
• Frederick Soddy (1877-1956)• Proposed the idea of isotopes in 1912• Elements with the same number of
protons and a different number of neutrons (thus have different masses)
• different masses
2.3.2.4 Isotopes
2.3.2.4 IsotopesEXAMPLES:
ATOMIC STRUCTURE
Electrons are arranged in Energy Levels or Shells
around the nucleus of an atom.
• first shell = a maximum of 2 electrons
• second shell = a maximum of 8 electrons
• third shell = a maximum of 8 electrons
2.3.2.5 Electronic Configuration
ATOMIC STRUCTURE
There are two ways to represent the atomic structure of an
element or compound;
1. Electronic Configuration
2. Dot & Cross Diagrams
2.3.2.5 Electronic Configuration2.3.2.5 Electronic Configuration
ELECTRONIC CONFIGURATION
With electronic configuration, elements are represented numerically by the
number of electrons in their shells and number of shells. For example;
NNitrogen
7
14
2 in 1st shell
5 in 2nd shell
Configuration = 2 , 5
2 + 5 = 7
2.3.2.5 Electronic Configuration
1. Electronic Configuration
ELECTRONIC CONFIGURATION
Write the electronic configuration for the following elements;
Ca O
Cl Si
Na20
40
11
23
8
17
16
35
14
28B
11
5
a) b) c)
d) e) f)
2.3.2.5 Electronic Configuration
2. DOT & CROSS DIAGRAMSWith Dot & Cross diagrams elements and compounds are represented
by Dots or Crosses to show electrons, and circles to show the shells.
For example;
NitrogenN XX X
X
XX
X N7
14
2.3.2.5 Electronic Configuration
Draw the Dot & Cross diagrams for the following elements;
O Cl8 17
16 35a) b)
2.3.2.5 Electronic Configuration
SUMMARY
1. The Atomic Number of an atom = number of protons in the nucleus.
2. The Atomic Mass of an atom = number of Protons + Neutrons in the nucleus.
3. The number of Protons = Number of Electrons.
4. Electrons orbit the nucleus in shells.
5. Each shell can only carry a set number of electrons.
VIDEO 5
LINK….
https://www.nde-ed.org/EducationResources/HighSchool/Radiography/hs_rad_index.htm
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