Chemistry Chapter 2 2 1 Atoms First atoms are the small building blocks of matter atom is the smallest quantity of matter that still retains the properties of matter element is a substance that cannot be broken down into two or more simpler substances Ex gold oxygen and helium Dalton Said that atoms are tiny indivisible particles NOT TRUE ARE NOT INDIVISIBLE 2 2 Subatomic Particles And Atomic Structure radiation the emission and transmission of energy in the form of waves cathode ray tube consists of two metal plates sealed inside a glass tube from which most of the air has been evacuated negatively charged plate is called the cathode emits radiation called cathode rays anode positively charged plate A cathode ray moves toward the positively charged plate Coulomb s Law opposite charges attract one another to propose that the rays are actually a stream of negatively charged particles Thomson performed experiments in which he applied a variable electric field and mea sured the degree of deflection of cathode rays This enabled him to determine the charge to mass ratio of the tiny negatively charged particles electrons J J Thomson R A Millikan Determined the charge on an electron by examining the motion of tiny oil drops Calculated the actual mass of an electron x rays energetic rays to penetrate matter and causes materials to fluoresce give off light radioactivity the spontaneous emission of radiation radioactive substances can produce three types of radiation alpha rays beta rays and gamma rays alpha rays consists of positively charged particles called particles beta rays are electrons so they are deflected away from a negatively charged plate gamma rays gamma rays have no charge and are unaffected by external electric or magnetic fields Thomson proposed that an atom could be thought of as a sphere of positively charged matter in which negatively charged electrons were embedded uniformly Plum Pudding Model According to the Rutherford experiment the scattering of a particles meant that most of the Rutherford proposed that the atoms positive charges were concentrated in the central core space in the atom had to be empty within the atom the nucleus James Chadwick bombarded a thin sheet of beryllium with a particles later experiments showed that the rays consisted of a third subatomic particle the neutron neutrons have a mass slightly greater than that of a proton 2 3 Atomic Number Mass Number and Isotopes atomic number Z the number of protons in the nucleus of each atom of an element also indicates the number of electrons the elemental identity of an atom can be solely determined from its atomic number mass number A is the total number of neutrons and protons present in the nucleus of an atom mass number A atomic number Z number of neutrons Number of neutrons Mass number A Atomic Number Z mass number A X element Z atomic Number Contrary to DALTON S ATOMIC THEORY atoms of a given element ARE NOT all identi cal MOST elements have two or more isotopes isotopes atoms that have the same atomic number Z but different mass numbers EX three isotopes of hydrogen protium deuterium and tritium 2 4 Average Atomic Mass atomic mass is the mass number of an atom in atomic mass units when determining the atomic mass of a number you measuring its average atomic mass of the occurring mixture of isotopes 2 5 The Periodic Table the periodic table consists of 118 elements vertical columns are called groups or families Horizontal rows are called periods in order of increasing atomic number elements can be categorized into metals and nonmetals property used to distinguish between the two would be the ability to conduct heat and or electricity metal is a good conductor of heat and electricity nonmetal poor conductor of heat and electricity metalloid is an element with properties that are intermediate between those of metals and nonmetals GROUP 1A Alkali metals GROUP 2A alkaline earth metals GROUP 6A Chalcogens GROUP 7A Halogens GROUP 8A noble gases GROUP 1B GROUP 3B 8B transition metals 2 6 The Mole and Molar Mass mole the amount of a substance Avogadro s number 6 022 x 10 23 molar mass of a substance is the mass in grams of one mole of the substance mass to moles to atoms grams moles atoms 1 divide by molar mass then multiply by Avogadro s number atoms moles grams 1 divide by Avogadro s number then multiply by molar mass