Lecture 1 - Matter & Its States

ACKNOWLEDGEMENT:

Figure	Source of Figure
Figure 1	chemstuff.co.uk
Figure 2	chemstuff.co.uk
Figure 3	www.mit.edu
Figure 4	sciencelanguagegallery.wikispaces.com

Matter:

Matter is anything that has mass and occupies space. Matter exists in either one of the three states: Solid, Liquid or Gas.

Matter is made up of many small particles. These particles are held together by inter-particular forces of attraction. The strength of these forces, govern the state of matter.

Solids:

Figure 1:

In solids, the particles are held together by very very strong forces of attraction. They are packed together and cannot move. The particles can only vibrate about their fixed positions. This arrangement gives the solid, its fixed shape and fixed volume.

Liquids:

Figure 2:

In liquids, the particles are clumped together in variable clumps of different sizes. These clumps of particles are free to move within the body/volume of the liquid. The forces of attraction are strong to keep the particles together but not strong enough to bind them together. Thus, liquids have a fixed volume but no fixed shape and can take the shape of the container they are poured in.

Gases:

Figure 3:

In gases, the particles are far apart. They have very weak inter-particular forces of attraction thus can freely move. Thus, gases have no fixed volume and no fixed shape.

Table 1: Properties of the different states of matter and their comparison

	Solid	Liquid	Gas
Shape	Definite shape	Take shape of the container	Diffuse and spread into all the space provided to it
Volume	Fixed volume	Fixed volume	No fixed volume
Movement of particles	Particles vibrate about their fixed positions	Particles can move freely within the volume of the liquid	Particles diffuse and move freely in all the space available to them
Arrangement of Particles	Particles are packed together	Particles are close, but not tightly held and can move	Particles further away from one another
Compressibility	Not compressible	Slightly compressible	Easily compressible
Inter-particular forces of attraction	Very strong forces of attraction between particles	Strong forces of attraction between particles	Very weak forces of attraction between particles

Lecture 2 - Isotopes & Introduction to Radioactivity

Atomic Number: Z:

The atomic number of an atom, denoted by Z, is the number of protons present inside the nucleus of an atom.

Number of Electrons:

For a neutral atom, the number of electrons always equal the number of protons (or atomic number; Z).

Mass Number: A:

The mass number of an atom, denoted by A, is the sum of the number of protons and the number of neutrons present inside the nucleus of an atom.

(Note: The mass of electrons is almost negligible as relative to proton and/or neutron.)

Number of Neutrons:

For any case, the number of neutrons in an atom can be calculated as:

Number of Neutrons = Mass Number - Atomic Number = A – Z

Isotopes:

Isotopes are atoms of the same element with same atomic numbers but different mass numbers. This is because of the presence of different number of neutrons in the nucleus.

Example: Cl - 35 and Cl - 37, are 2 isotopes of Chlorine. Both have 17 protons and 17 electrons but Cl - 37 has 20 neutrons, while Cl - 35 has 18 neutrons.

Isotopes & Radioactivity:

Some isotopes of the same element are radioactive. For example, H - 3 (Tritium) is radioactive, while H- 1  (Hydrogen) is not. The 2 neutrons in the Tritium nucleus make it unstable and radioactive in nature.

According to a thumb’s rule; an atom is unstable if the neutron-proton ratio increases 1.5:1. In Tritium, the neutron-proton ratio is 2:1, thus it is unstable and radioactive.

Examples of Radioactive Isotopes and their disintegration:

Radioactive decay of Uranium:

Uranium disintegrates to form Thorium and release alpha particles.

Helium obtained from radioactive decay, is not regular helium, rather it is a very fast moving atom and known as Alpha particle.

Radioactive decay of Thorium:

Thorium disintegrates to form Protactinium and release beta particles.

Note the atomic number of Thorium. It is 90. Number of neutrons in Thorium are:

A – Z = 234 – 90 = 144.

Note the atomic number of Protactinium. It is 91. Number of neutrons in Protactinium are:

A – Z = 234 – 91 = 143.

In the Radioactive decay of Thorium, 1 neutron decays or breaks down to form a proton and an electron. Therefore, the atomic number of the daughter element increases by 1 (from 90 to 91) while mass number remains same. The resulting electron from this decay is very energetic and is released from the nucleus as beta particle.

Radioactive decay of Protactinium:

Protactinium disintegrates to form Uranium and release beta particles and gamma radiations.

Note the atomic number of Protactinium. It is 91. Number of neutrons in Protactinium are:

A – Z = 234 – 91 = 143.

Note the atomic number of Uranium. It is 92. Number of neutrons in Uranium are:

A – Z = 234 – 92 = 142.

In the Radioactive decay of Protactinium, 1 neutron decays or is broken down to form a proton and an electron. Therefore, the atomic number of the daughter element increases by 1 (from 91 to 92) while mass number remains same. The resulting electron from this decay is very energetic and is released from the nucleus as beta particle. This decay also yields gamma rays.

Details about radioactivity will be discussed in Chapter 26.

Lecture 1 - Nucleus of atom and Geiger-Marsden experiment

ACKNOWLEDGEMENT:

Figure	Source of Figure
Figure 1	www.livescience.com
Figure 2	commons.wikimedia.org

Atomic Structure:

Atom is the smallest particle of an element. It consists of a centralized nucleus containing Proton(s) and Neutron(s), while the Electron(s) revolve around the nucleus.

Figure 1:

Nucleus:

Nucleus is the central part of the atom. It contains proton and neutrons. It is positively charged in nature because of the presence of positively charged protons, present in it. It is the most important part of an atom and gives the atom its characteristic properties.

Neutron:

Neutron is an electrically neutral particle inside the nucleus of an atom.

Proton:

Proton is a positively charged particle inside the nucleus of an atom. Proton and Neutron are relatively same in size.

Electron:

Electron is a negatively charged particle that revolves around the nucleus of an atom. It is the smallest particle with 1/1840 in size when compared to a proton or a neutron. That is 1840 electrons together have a mass of 1 proton or neutron.

Table 1 summarizes this:

Table 1:

	Proton	Neutron	Electron
Charge	Positive	Neutral	Negative
Mass	1	1	1/1840

Geiger Marsden Experiment – Proof of the atomic structure:

Geiger Marsden or Rutherford gold foil experiment conducted between 1908 to 1913, laid foundation to the structure of the atom mankind knows today.

Experimental Arrangement:

The apparatus consisted of a radioactive substance source of alpha particles arranged parallel to a gold foil. The gold foil was surrounded by a fluorescent screen.

Figure 2:

Positively charged alpha particles were bombarded perpendicularly on the gold foil and the fluorescent screen was observed.

Experimental Observation and Conclusion:

Some distinctive patterns were seen: 

Observation	Conclusion
Most of the alpha particles passed through the foil and caused fluorescence on the screen directly in front of the source.	Atom consist largely of empty space. Confirmation of the existence of electrons in large empty orbits, around the nucleus.
A small fraction of alpha particles were deflected at angles lesser than 90° and caused fluorescence on the screen at angles lesser than 90°.	Alpha particles passing near by the nucleus were deflected slightly. Alpha particles passing near by the nucleus were deflected largely. Alpha particles that collided with the nucleus itself, bounced back towards the source, causing fluorescence on the screen behind the source. Positive charge is concentrated near/in the center of the atom. Confirmation of the existence of protons together in the center of the atom (along with the neutrons that were discovered after 1932.)
A tiny fraction of alpha particles were deflected at angles greater than 90° and caused fluorescence on the screen at angles greater than 90°.
A tiny fraction of  alpha particle bounced back towards the source and caused fluorescence on the screen behind the source.