Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Download Chapter 3 Atomic Structure
Document related concepts
Transcript
CHAPTER 3 ATOMIC STRUCTURE All matter is made of atoms – a tiny particle that makes up all elements. Democritus – a Greek philosopher – was the first to suggest the existence of atoms and thought they were indivisible and indestructible. The modern process of discovery regarding atoms began with John Dalton All atoms are composed of tiny indivisible particles. Atoms of one element are identical and are different from atoms of a different element. Atoms of different elements can mix together or chemically combine in simple whole number ratios to form compounds. In chemical reactions atoms are separated, joined or are rearranged, but never change into atoms of another element. Atoms are very small. A penny contains about 2.4 x 1022 atoms. There are only 6 x 109 people on earth. The radii of most atoms falls between 5 x 10-11 m and 2 x 10-10 m. Despite their small size, atoms can now be seen with scanning tunneling microscopes. Subatomic particles Electron – discovered by J.J. Thomson in 1897 He performed experiments passing electric current through a gas at low pressure. Because the beam was attracted to the positive plate, Thomson concluded the electrons were negative in charge. Further experiments by Robert A Millikan determined the mass of an electron: 1/1840 the mass of a hydrogen atom. The Plum Pudding model of the atom electron Positively charged mass Protons further studies with cathode ray tubes lead to the discovery of the proton by Eugene Goldstein in 1886. They have a positive charge and a relative mass of 1 Neutrons James Chadwick discovered the neutron in 1932. They have no charge and a mass equal to a proton. The gold foil experiment In 1911, Ernest Rutherford performed an experiment where he bombarded a piece of gold foil with positively charged helium nuclei known as alpha particles. He predicted that all the alpha particles would pass through the gold foil while some would be deflected if they passed close to an electron. Something very unexpected happened. http://micro.magnet.fsu.edu/electromag/java /rutherford/ Atomic Number – the number of protons in an atom. This determines the identity of the atom. It also tells us the number of electrons because atoms are electrically neutral. P+ N N hydrogen (tritium) P+ N P+ N helium P+ N P+ N lithium P+ Mass Number – this is the number of protons and neutrons added together in the nucleus of the atom. If you know the atomic number and the mass number you can determine the number of all the particles in an atom. Manganese has an atomic number of 25 and a mass number of 55. How many protons, electrons and neutrons does manganese have? This is called a nuclear symbol and shows the mass number on top and the atomic number on the bottom. # of protons and neutrons A X Z # of protons Represents element 60 27 Isotopes – atoms of the same kind with a different number of neutrons and a different mass. P+ hydrogen P+ N deuterium P+ N N tritium Hyphen notation is another way to express isotopes of an element. Co - 60 Measured in atomic mass units The mass of an atom is a relative mass. The masses of all atoms are determined by their relative mass to one atom of Carbon-12. A hydrogen atom has a mass of 1/12 the mass of a carbon atom so its mass is 1.0 amu A magnesium atom is twice as heavy as a carbon atom so its mass is 24 amu Most atoms have at least one isotope – an atom of the same kind having a different number of neutrons. The mass of an atom is an average of the masses of all the isotopes of that atom. Mass of each isotope x % of their occurrence added together. ex. Cu-63 (69.17%) and Cu-65 (30.83%) Average atomic mass = ? (63 x .6917) + (65 x .3083) = 43.5771 + 20.0395 = 63.6166 Round the number to the 0.01 place The average atomic mass of copper is 63.62 amu
