KING FAHD UNIVERSITY OF PETROLEUM AND MINERALS PYP

KING FAHD UNIVERSITY OF PETROLEUM AND MINERALS PYP 001 Fall 2012 (Term 121) Chapter 5 The Atom

5. 2: Improvements to the Atomic Model Rutherford Theory: failed in describing the position of electrons in an atom. Bohr’s Atomic Model, Ø Electrons revolve around the nucleus at orbits with fixed orbits energy level with fixed distance from the nucleolus. Ø Electrons could not exist between energy levels. Ø Electrons don’t loose energy while travelling in the same energy level. Planck’s theory: Energy exists in tiny packets. • What happen when Electron absorbs a certain amount of energy?

5. 2: Improvements to the Atomic Model Fig 5. 8

5. 2: Improvements to the Atomic Model Fig 5. 9 Emission Line Spectrum: The narrow slits of light that released when exciting Hydrogen gas by high electric voltage.

5. 2: Improvements to the Atomic Model Bohr’s Evidence • Hydrogen Spectrum was experimental evidence that supports his atomic model. • The amount of energy released from the electron while coming back to lower energy level determines the wavelength of emitted light.

5. 2: Improvements to the Atomic Model Principal Energy Levels and Sublevels Bohr suggested that : • The principal energy levels may have sublevels ( s, p, d and f ). • The number of energy sublevels depends on the principal energy level. Ø 1 st principal energy level has one sublevel , 1 s Ø 2 nd principal energy level has two sublevels , 2 s and 2 p. Ø 3 rd principal energy level has three sublevels , 3 s, 3 p and 3 d. Ø 4 th principal energy level has four sublevel , 4 s, 4 p, 4 d and 4 f

5. 2: Improvements to the Atomic Model Energy Sublevel s p Number of electrons (e) 2 6 d f 10 14

5. 2: Improvements to the Atomic Model Chadwick’s Contributions, 1932 • One final problem remained, "short of the actual mass of an atom” • Neutrons : particles inside the nucleolus with no electric charge. • Mass of Neutrons is slightly greater than the mass of protons. ( 1. 6749 x 10 -24 g)

5. 2: Improvements to the Atomic Model Modern Atomic Theory Heisenberg, 1927 • Its impossible to know both the exact position and exact velocity of an electron in the same time. • Electron Cloud: the region around the nucleus in which the electrons are likely to exist at any specific time.

5. 3: Properties of Subatomic Particles Particle Symbol Location Charge electron e- Outside nucleolus -1 proton p Inside nucleolus +1 neutron n Inside nucleolus 0

5. 3: Properties of Subatomic Particles. Atomic Size: • Described in a very small unit “nanometer” , 10 -9. • AVG Atom diameter is about 0. 2 nm. • We can get an image of an atoms through a device called : scanning tunneling microscope.

5. 3: Properties of Subatomic Particles. Atomic Number: • The number of protons in the nucleolus is known as “atomic number”. • Every element has a unique atomic number. • Example: atomic number for Au is 79, He is 2. Isotopes : • Atoms of the same element that have a different number of neutrons in their nuclei are called “isotopes”. • “H” has two stable isotopes protium ( 1 p, 0 n) and deuterium (1 p, 1 n), one unstable isotope tritium (1 p, 2 n).

5. 3: Properties of Subatomic Particles.

5. 3: Properties of Subatomic Particles. Mass Number • The total number of protons and neutrons in the nucleus of an atom is called “mass number”. • Atomic notation : Mass number Ø Fluorine Atomic number • Number of p = • Number of e = • Number of N= • Also you can write it as ( Fluorine-19).

5. 3: Properties of Subatomic Particles. Atomic Mass: • (amu) : atomic mass unit is the unit that used to describe atomic masses. • 1 amu= 1/12 of the mass of carbon-12 atom. • The atomic mass of an element is the weighted average of all naturally occurring isotopes. • Example: calculating atomic mass of Carbon: Carbon Ø C-12 : 12. 00000 amu x ( 98. 89%) = 11. 87 amu Ø C-13 : 13. 00335 amu x ( 1. 11%) = 0. 144 amu. Ø Total = 11. 87+0. 144 = 12. 01 amu

Summary: • 5. 2: Improvements to the Atomic Model • Bohr proposed a model of the atom that suggested that electrons orbit the nucleolus in discreet energy levels. • Chadwick discovered the neutron, which is a subatomic particle that is eclectically neutral. • Acceding to the modern theory of the atom the specific locations of electrons can’t determined. Instead a region in which they are likely to exist, called an electron cloud, can be described. • .

Summary: • 5. 3: Properties of Subatomic Particles. • Protons, neutrons, and electrons are described as subatomic particles. Protons and neutrons make up the nucleus of an atom. Electrons are located outside the nucleus. • The atomic number of an atom is the number of protons in the nucleus. • The sum of the numbers of protons and neutrons in an atom’s nucleus is the atom’s mass number. • Two atoms of the same element with different numbers of neutrons are known as isotopes. Each isotope exists naturally in a different abundance, so the atomic mass of an element is calculated as weighted average.