Topic 2: Structure of matter

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)


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


• 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.


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.


• 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”


• 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%


1.11%


<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


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. 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


Draw the Dot & Cross diagrams for the following elements;

O Cl8 17

16 35a) b)


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

Science

Topic 2: Structure of matter