Matter, Elements, and Atoms PDF

College of Applied Medical Sciences Radiological Sciences Department Matter, Elements, and Atoms RAD-231 (X-Ray physics) Dr. Ashwag Alarfaj Energy and matter Physics is concerned with studying two concepts, en...

College of Applied Medical Sciences Radiological Sciences Department Matter, Elements, and Atoms RAD-231 (X-Ray physics) Dr. Ashwag Alarfaj Energy and matter Physics is concerned with studying two concepts, energy and matter, and the relationships between them. Energy Is the ability to do work; without energy nothing would happen. It exists in many forms and can be converted from one form to another, e.g…… Energy conservation law In a closed system, the total amount of energy did not change. Energy can be converted from one form to another, also it can be stored, It is not possible to create or destroy energy. In the universe, energy is constant; it is not possible to create or destroy energy.  (law of conservative energy) A basic physical principle of the universe is that energy can be neither created nor destroyed. However, we can transform it from one form or type to another (the total energy in the universe is constant). some of the energy forms used in the production of an x-ray image. Various components of the imaging system convert the energy from one form to another. Energy forms Potential energy: the energy stored in a body due to its position or state, e.g. a compressed spring and a book on a shelf. potential energy possessed by a body is equal to the amount of work required to ‘raise’ the body to its particular position or state. Kinetic energy: the energy possessed by a body because of its movement. kinetic energy is the result of the conversion of the potential energy. There are many other forms like, chemical energy, electrical energy, nuclear energy, sound energy, X-ray energy, etc. Matter The matter or material is anything that occupies space and has mass. All matters are made up of one substance called elements, or more substances called compounds. Atoms, Ions, Molecules, Furniture, People, Plants, Water, and Rocks are all examples of matter. The smallest unit of Matter is atom, and anything made up of atoms.  States of matter Solids: These are the substances, which have definite volume and definite shape. The molecules are held together by strong forces. Liquids: These are the substances, which do not have definite shape. The molecules are held by relatively weak forces. Gases: These are the substances where the molecules move randomly and there is space between them. Also liquid crystal and plasma are matter states. Changes of Matter Physical Changes: Changes in matter that do not change the composition of a substance such as: changes of state, temperature, volume, etc. Chemical Changes: Changes that result in new substances.  Is matter conserved? In everyday situations, the total amount of matter involved remain constant. For many years, the conservation of matter was believed to be as fundamental concept as the conservation of the energy. Since the beginning of 20th century, the concept has been changed, when the nuclear fusion process is created, which generates the energy from losing of matter. The relationship between the energy and matter Albert Einstein showed that it possible to convert matter to energy and vise versus. It seems that matter is a special type of stored energy, and in certain circumstances, its energy can be released and used. Albert Einstein's famous formula: E = m c2 E= ENERGY 8 m=mas , c= speed of (c = about 3×10 m/s)  Elements and Molecules Elements: which have specific chemical and physical properties and cannot be broken down into other substances, e.g.; O,C, H. Molecules: the smallest part of a compound which retains the chemical properties of the compound. Oxygen, and Hydrogen for example, are two different elements, and together form water molecule. Elements There are about 118 elements, but only 94 occur naturally. The remaining elements have only been made in laboratories and are unstable. elements with proton numbers above 92 do not occur naturally but have to be manufactured artificially; e.g. plutonium (Z = 94) is produced in a nuclear reactor. Elements Each element is specified by its chemical symbol, which is a single capital letter or, when the first letter is already “taken” by another element, a combination of two letters.  Matter and elements Some elements follow the English term for the element, such as C for carbon and Ca for calcium. Other elements’ chemical symbols come from their Latin names; for example, the symbol for sodium is Na, which is a short form of Natrium, the Latin word for sodium. Matter and elements The four elements common to all living beings are oxygen (O), carbon (C), hydrogen (H), and nitrogen (N), which together make up about 96% of the human body. Questions about Smallest unit of the matter What atom made of? Electrons, protons neutrons. Are they matters? Yes, why? Is there any thing in the universe is not matter? Yes, any massless particle such as photons, or other energy phenomena or waves such as light or heat. Atom structure An atom is the smallest unit of matter that retains all of the chemical properties of an element. For example, a gold coin is simply a very large number of gold atoms(Au) molded into the shape of a coin. Gold atoms cannot be broken down into anything smaller while still retaining the properties of gold. Atom structure An atom consists of two regions. The first is the atomic nucleus, which is in the center of the atom and contains positively charged particles called protons and neutral, uncharged, particles called neutrons. Atom structure The second, much larger, region of the atom is a “cloud” of electrons, negatively charged particles that orbit around the nucleus. The attraction between the positively charged protons and negatively charged electrons holds the atom together. Atom structure The nucleus contains 2 of the 3 subatomic particles: Protons: positively charged subatomic particles Neutrons: neutrally charged subatomic particles The 3rd subatomic particles, negatively charged Electrons, located outside of the nucleus in the electron cloud. Atom structure How do these particles interact? Protons and neutrons live compacted in the tiny positively charged nucleus accounting for most of the mass of the atom. The negatively charged electrons have a relatively small mass but occupy a large volume of space outside the nucleus. How do the subatomic particles balance each other? In an atom: The number of protons(+) = the number of electrons(-) If 20 protons are present in an atom then 20 electrons are there to balance the overall charge of the atom—atoms are neutral. The neutrons have no charge; therefore, they do not have to equal the number of protons or electrons. Atom structure Most atoms contain all three of these types of subatomic particles—protons, electrons, and neutrons. Hydrogen (H) is an exception because it typically has one proton and one electron, but no neutrons. Atom structure The number of protons in the nucleus determines which element an atom is, while the number of electrons surrounding the nucleus determines which kind of reactions the atom will undergo. Protons and neutrons do not have the same charge, but they do have approximately the same mass, about: 1.67× 10−24 grams = 1 amu amu: atomic mass unit Atom structure Electrons are much smaller in mass than protons and neutrons. Protons, neutrons, and electrons are very small, and most of the volume of an atom—greater than 99 percent—is actually empty space. Atomic number Atoms of each element contain a characteristic number of protons. In fact, the number of protons determines what atom we are looking at. The number of protons in an atom is called the atomic number. In contrast, the number of neutrons for a given element can vary.  Together, the number of protons and the number of neutrons determine an element’s mass number: Mass number(nucleon number )= protons (atomic number) + neutrons If you want to calculate how many neutrons an atom has, you can simply subtract the number of protons, or atomic number, from the mass number: Neutrons = Mass number - protons (atomic number) What about the electrons? The electrons are equal to the number of protons, so: e- = p = Z atomic # Atomic number= 8 Atomic mass= 15.999 Mass number = 16 p+ = 8 no = 8 e- = 8 Atom Nucleus: containing neutrons( ) and protons(+ ). Is quite small in comparison to total atom dimensions. most of the mass of the atom is contained within the nucleus. Electrons: Are much smaller and lighter than nucleus particles. The electrons located at different distances from the nucleus. Each proton has a positive charge equal in strength to the negative charge carried by an electron, in this situation (atoms are stable) Atomic mass A= Z+N A (atomic mass) Z (atomic number=proton number) N ( neutron number) Nuclides=Isotopes Isotopes are different forms of an element that have the same number of protons but different numbers of neutrons. Many elements—such as carbon, potassium, and uranium— have multiple naturally occurring isotopes. Some of the carbon isotopes are: Nuclides=Isotopes Protons carry similar charges, and electric forces are set up between them, which cause them to repel each other. If unrestrained, the protons would separate, causing the nucleus to break up. However, the presence of neutrons in the nucleus is associated with strong nuclear forces of attraction, which counteract the repelling. In order for the repulsion forces to be overcome, The ‘neutron:proton ratio’ must be correct. Nuclides=Isotopes Radioactivity is a nuclear process; i.e. it involves the nuclei of atoms rather than the electrons in orbit around the nuclei. If too many or too few neutrons are present, sooner or later, nuclear disintegration will take place. Why? Nuclides=Isotopes Nuclides break up, ejecting particles and/or radiation energy. We call this process of nuclear disintegration(decay); radioactivity, and the unstable nuclides are known as radionuclides. Radioactivity, or radioactive decay, is defined as a process whereby some nuclides undergo spontaneous changes in the structure of their nuclei, accompanied by the emission of particles and radiation. Nuclides=Isotopes After the disintegration of a radionuclide, a new nuclide is formed, which may or may not be stable. The nuclides which result from radioactive transformations are known as daughter products. Natural and artificial radioisotopes Many unstable isotopes occur naturally in the earth, Other radioisotopes have been produced by man in nuclear reactors, nuclear bombs and high-energy machines called particle accelerators e.g. (Iodine) Transformation processes When radionuclides break down, several different types of emissions may be produced, depending on which particular decay process has occurred. Alpha-particle (α) emission: (2 protons+ 2neutrons) Negative beta-particle (β−) emission. :A nucleus has too many neutrons. Positive beta-particle (β+) emission: A nucleus has too many protons. Gamma-ray (γ) emission: changing the status of nuclide from excited to stable state. mainly combined beta decay process.  Nuclides=Isotopes Some isotopes are stable, but others can emit, or kick out, subatomic particles to be more stable. Such isotopes are called radioisotopes or radioactive atom, and the process in which they release particles and energy is known as decay. Activity of Radionuclides The strength (energy emision) of a radioactive source is called its activity, which is defined as the rate at which the isotope decays. Specifically, it is the number of atoms that decay and emit radiation in one second. (disintegrations or decays per second). Radioactivity may be thought of as the volume of radiation produced in a given amount of time. It is similar to the current control on X-ray generator. Activity Formula The SI unit for activity is one decay per second and is given the name becquerel (Bq), so: 1 Bq = 1 decay/s Activity is often expressed in other units, such as decays per minute or decays per year. One of the most common units for activity is the curie (Ci). 1 Ci = 3.70× 1010 Bq Activity Over Time  Nuclides=Isotopes Although there are 118 different elements, each element can have different forms (neutron numbers). Actually, at least 1,300 different neutron-proton combinations are now known. Element Nuclide refers to the classification of a refers to its classification by both substance according to its atomic atomic number and number of number. neutrons. About 118 types About 1,300 types