Atom Table of Contents 1. Atom and History of Atom 2. Subatomic Particles 3. Isotopes 4. Ions 5. Atomic Terminology
The History of The Atom Warm up Make a list of inferences about any properties of objects in the box. How could you learn more about the objects in the box without opening the box? Scientist face these same questions as they try to learn more about atoms.
The History of The Atom Table of Contents 1. Atomic Models 2. Modern Atomic Model 3. Quantum Numbers 4. Electron Configuration
The History of The Atom Warm up Make a list of inferences about any properties of objects in the box. How could you learn more about the objects in the box without opening the box? Scientist face these same questions as they try to learn more about atoms.
The History of The Atom The idea of an atomic theory is more than 2000 years old. Until recently, scientists had never seen evidence of atoms. Democritus (460-400BC), a Greek philosopher, first thought that the universe was made up of very small particle and named them atomos, meaning indivisible. Aristotle, however, thought that matter was continuous, that there was no limit on how finely you could cut it up. In the twentieth century, the scientists studied about atom are Dalton, Rutherford, Planck, Einstein, Bohr and Schrödinger.
1. Atomic Models 1. Dalton s Atomic Model In 1803 John Dalton proposed some ideas about atom; 1. Atom or atom groups have all the characteristic properties of substances. 2. Atoms of an element are completely identical. 3. An atom is a filled sphere like a billiard ball. 4. Different types of atoms have different masses. 5. Atoms are the smallest unit of substances and cannot be further divided. 6. Atoms form molecules in a definite numerical ratio.
1. Atomic Models 2. Thomson s Atomic Model In 1897 J. J Thomson discovered the electron. 1. Protons and electrons are charged particles. 2. In neutral atoms since the number of electron and number of protons are equal, net charge is zero. 3. An atom has a shape of sphere with 10-8 cm radius. Protons and electron are distributed in arbitrary positions. 4. The mass of an electron is so small that it can be neglected.
1. Atomic Models 2. Thomson s Atomic Model
1. Atomic Models 2. Thomson s Atomic Model
1. Atomic Models 3. Rutherford s Atomic Model In 1911 Ernest Rutherford discovered the nucleus and in 1919 proton. He proposed α-particle experiment. His ideas; 1. There is a small positively charged, dense region called nucleus in an atom. 2. The mass of the atom approximately equal to the mass of the protons and electrons. 3. Protons are in the nucleus and electrons are distributed around nucleus.
1. Atomic Models 3. Rutherford s Atomic Model
1. Atomic Models 3. Rutherford s Atomic Model
1. Atomic Models 3. Rutherford s Atomic Model
1. Atomic Models 4. Bohr s Atomic Model In 1913 Niels Bohr proposed places of electrons around the nucleus of atoms. He concluded his ideas as follows; 1. Electrons are found in certain places so called energy levels or shell around nucleus with certain energies. 2. Electrons move in each stationary state in circular paths. 3. When an electron falls back to a lower energy level from a higher one, it emits a quantum of light that is equal to the energy difference between these two energy levels.
1. Atomic Models 4. Bohr s Atomic Model 4. The possible stationary energy levels of electrons are named either by letters, K, L, M, N, O... or by positive integer numbers starting from the lowest energy level. These numbers are generally denoted by n where n = 1, 2, 3,... Discovery of Neutron In 1930s James Chadwick thought that since protons have same charges in the nucleus and they found together, there must have been some neutral particles which hold protons together, then he called them neutron.
2. Modern Atomic Model Although Bohr s model was valid for atoms of H or He +1 or Li +2, it did not work for atoms having more than one electron. But his ideas lead to a step forward in the development of modern atomic theory. The pioneers to modern atomic theory are Lois de Broglie, Heisenberg and Schrödinger. In 1924 Lois de Broglie proposed that small particles sometimes show wave-like properties. In 1920 Werner Heisenberg stated his uncertainty principle which explains position of electrons.
2. Modern Atomic Model
2. Modern Atomic Model
2. Modern Atomic Model
2. Modern Atomic Model Comparison of Bohr s Atomic Model and Modern Atomic Model
1. Atom Warm up What is all matter made up? And to what do they look like? Make a list of inferences about any properties of objects in the box. How could you learn more about the objects in the box without opening the box? Scientist face these same questions as they try to learn more about atoms.
1. Atom Scientist have accepted that the smallest parts of substances are called atoms. Atom means indivisible derived from atomos in Greek language because of its very small size. Atom has basically two parts, nucleus and electrons. Nucleus is located in the center of atom and electrons are rotating around nucleus with high speed.
2. Subatomic Particles Scientist believed that atoms were indivisible up to 20 th century. Today it is well known that atoms have subatomic particles, called protons, neutrons and electrons. Protons are positively charged particles found in the nucleus of an atom, and denoted by p. Each element has certain number of protons which differ the element from others.
2. Subatomic Particles Neutrons are neutral particles found in the nucleus of an atom, and denoted by n. Electrons are negatively charged particles placed around the nucleus of an atom, and shown by e -. Protons and neutrons almost have the same masses, but electrons have negligible mass with respect to protons and neutrons.
2. Subatomic Particles
2. Subatomic Particles
2. Subatomic Particles
2. Subatomic Particles Neutral atoms have the equal number of protons and electrons. Electrons are rotating in certain places called orbit, energy level or shell. Energy levels are represented by letters, K, L, M, N, O etc, or numbers, 1, 2, 3, 4, etc. Each shell can hold a certain number of electrons calculated by the equation of 2n 2 where n refers to number of shell. The electrons located in the outermost shell of atoms are called valance electrons.
2. Subatomic Particles
2. Subatomic Particles In the 1 st shell, No. of e - = 2x1 2 = 2e - In the 2 nd shell, No. of e - = 2x2 2 = 8e - In the 3 rd shell, No. of e - = 2x3 2 = 18e - In the 4 th shell, No. of e - = 2x4 2 = 32e - Example 1 Show the electron configuration of 6 C and 13 Al atoms. Solution 6C: 2) 4) 13Al: 2) 8) 3)
2. Subatomic Particles
3. Isotopes Isotope atoms have the same number of protons but different number of neutrons. Example 2 12 6 C 13 6 C 14 6 C atoms are isotopes. All they have 6 protons but 6, 7 and 8 neutrons respectively. They have similar chemical properties but different physical properties.
3. Isotopes
3. Isotopes
3. Isotopes Isotones, atoms with the same number of neutrons, but different numbers of protons. Example 3 31 32 P S 15 16 atoms are isotones. Each have 16 neutrons but 15 and 16 protons respectively. Isotone atoms are completely different atoms, they have different chemical and physical characteristics.
4. Ions Electrically charged atoms are called ions. When an atom loses electrons it becomes positively charged ion, called cation. When an atom gains electrons it becomes negatively charged ion, called anion. Charge of an atom, q, can be found with q = p - e.
4. Ions
4. Ions
4. Ions Atom Neurtal Atom Ion p=e (Charged Atom) Cation (+) Anion (-) (p>e) (p<e)
4. Ions
4. Ions Example 4 Find the charge and ion type of atom. Atom Proton Electron Charge Ion Fe 26 24 Al 13 10 O 8 10 P 15 15 Cl 17 18
4. Ions Solution Atom Proton Electron Charge Ion Fe 26 24 +2 Cation Al 13 10 +3 Cation O 8 10-2 Anion P 15 15 0 Neutral Cl 17 18-1 Anion
4. Ions Example 5 Li +1, Ca +2, Al +3, Pb +4 are cations. F -1, O -2, P -3 are anions. NH 4 +1 OH - - -2-3 NO 3 CO3 PO4 are polyatomic ions
5. The Atomic Terminology 1. Atomic Number, Z Atomic number = Number of Protons Each type of atom has different number of protons. For a neutral atom, Atomic number = Number of protons = Number of electrons Z = p = e
5. The Atomic Terminology 2. Atomic Mass Number, A Atomic mass number = Number of Protons + Number of Neutrons A = p + n Example 6 Fill in the blanks in the table below. Atom p n Z A Ti 22 48 Al 14 27 S 16 16 Br 45 35
5. The Atomic Terminology Solution Atom p n Z A Ti 22 26 22 48 Al 13 14 13 27 S 16 16 16 31 Br 35 45 35 80
5. The Atomic Terminology Atomic Mass Number, XA Neutrons, n Protons, p Atomic Number, Z Charge, q Electron, e A = p + n q = p - e
5. The Atomic Terminology Example 7 What is the number of protons and atomic mass number of Zn.? Zn +2 35 28?
5. The Atomic Terminology Solution q = p - e A = p + n +2 = p 28 p = 30 A = 30 + 35 A = 65 65 35 30 Zn +2 28
5. The Atomic Terminology Example 8 Cr +3 ion has 21 electrons and its atomic mass number is 52. What is the number of neutrons for Cr? Solution q = p - e A = p + n 3 = p 21 p = 24 52 = 24 + n n = 28
End of the chapter 3