Ch 2 Atoms Molecules and Ions 2 1 Atomic Structure Protons Electrons and Neutrons Atoms are made up of subatomic particles 1 Protons which are positively charged 2 Electrons which are negatively charged 3 Neutrons which are electrically neutral Chemical properties of elements and molecules depend largely on the electrons in atoms 1 2 Fig 2 1 p 51 2 2 Atomic Number and Atomic Mass Atomic Number All atoms of a given element have the same number of protons in the nucleus Atomic abbreviated with a Z Clicker Q What is the atomic number of C 3 Relative Atomic Mass and the Atomic Mass Unit One atomic mass unit 1 u or amu is 1 12 of the mass of an atom of carbon with 6 protons and 6 neutrons Mass number Protons and neutrons are close to 1 u electrons are 1 2000 of that so the number of protons plus neutrons give the mass of the atom Symbol for mass number is A 4 examples 5 Clicker Q How many neutrons does 3169Ga have 27 Al3 of protons of neutrons Clicker Q of e S 33 2 Clicker Q of protons of neutrons of e 6 7 Table 2 1 p 53 2 3 Isotopes Atoms with the same atomic number but different mass numbers are called isotopes So have different numbers of neutrons One example of an isotopic series is the hydrogen isotopes 1H or protium is the most common hydrogen isotope 2H or deuterium is the second most abundant 3H or tritium is a radioactive hydrogen isotope no known natural sources 8 The stable oxygen isotopes provide another example 16O is the most abundant stable O isotope 17O is the least abundant stable O isotope 18O is the second most abundant stable O isotope Clicker Q Which one is an isotope of 14N A 14C B 16O C 15N D 19F E 3H 9 Isotope Abundance Percent Abundance number of atoms of an individual isotope 100 total number of atoms of all isotopes of that element 10 Determining Atomic Mass and Isotope Abundance http www chemguide co uk analysis masspec howitworks html Mass spectrometry MS is an analytical technique which identifies compounds based on the atomic sample composition of the molecules and their charge state http www asms org about about mass spectrometry A machine used to weigh molecules A molecular scale 11 2 4 Atomic Weight 12 Table 2 2 p 56 Clicker Q Naturally occurring Cu consists of 2 isotopes It is 69 1 63Cu with a mass of 62 9 amu and 30 9 65Cu which has a mass of 64 9 amu Calculate the atomic weight of Cu to one decimal place 13 Clicker Q Naturally occurring chromium consists of four isotopes It is 4 31 2450Cr mass 49 946 amu 83 76 2452Cr mass 51 941 amu 9 55 2453Cr mass 52 941 amu and 2 38 2454Cr mass 53 939 amu Calculate the atomic weight of chromium 14 The atomic weight of boron is 10 811 amu The masses of the two naturally occurring isotopes 510B and 511B are 10 013 and 11 009 amu respectively Calculate the fraction and percentage of each isotope 15 The atomic weight of the element is always closer to the mass of the most abundant isotope or isotopes See the previous boron example Atomic weight is given in the periodic table 16 2 5 The Periodic Table Most useful tool in chemistry 1869 Mendeleev Russian Meyer German Mendeleev arranged the known elements in order of increasing atomic weight in successive sequences so that elements with similar chemical properties fell into the same column He provided for elements that were unknown at the time and predicted their properties Discovered the periodic law The properties of the elements are periodic functions of their atomic numbers 17 Features of the Periodic Table Periods Groups The law of chemical periodicity is now stated as the properties of the elements are periodic functions of atomic number 18 Regions in the Periodic Table 19 A brief overview of the periodic table and the chemical elements Group 1A is known as the alkali metals Group 2A is known as the alkaline earth metals Group 7A is known as the halogens salt formers Group 8A is known as the noble gases inert or rare gases Generally lack reactivity Need to know the names of these groups 20 Clicker Q Na is A metal B nonmetal C metalloid Clicker Q Xe is A metal B nonmetal C metalloid Clicker Q Find the element and input its symbol into clicker that is in period 3 and a halogen 21 Elements that exist as diatomic triatomic molecules Have to know these 22 Fig 2 9 p 64 Allotropes an element can often exist in several different and distinct forms each having its own properties Carbon is an example 23 2 6 Molecules Compounds and Formulas A molecule is the smallest identifiable unit into which some pure substances like sugar and water can be divided and till retain the composition and chemical properties of the substance 2H2 O2 2H2O 24 Formulas Molecular formula describes the composition of the compound Tells you how many atoms of each are present 25 Molecular Models Several different ways of representing compounds molecules 26 Gray carbon White hydrogen Red oxygen Blue nitrogen Yellow sulfur Clicker Q What is molecular formula of the above molecule Remember to put in ABC order 27 p 69 2 7 Ionic Compounds Formulas Names and Properties Molecular compounds compounds that consist of discrete molecules at the particulate level Naming done by prefix system Ionic compounds consist of ions atoms or groups of atoms that bear a positive or negative electric charge Naming metal then nonmetal 28 Ions Have an electric charge So either lost or gained electrons There is 2 kinds Cations ions and anions ions Cations Are positive ions Lost one or more electrons remember e are negative so then has more protons and is thus positive Anions Are negative ions Gained one or more electrons 29 30 Fig 2 17 p 70 Monatomic ions Single atoms that have lost or gained electrons Metals typically lose electrons and nonmetals gain electrons 31 Ion Charges and the Periodic Table Alkali metals always 1 First column Alkaline earth metals always 2 Second column Al always 3 Halogen mostly 1 Column 6A mostly 2 Polyatomic ions Containing more than one atom Know the ones in Table 2 4 on page 72 32 Know these Clicker Q charge on potassium enter and sign Clicker Q charge on oxygen enter then sign 33 Table 2 4 p 72 Formulas of Ionic Compounds Compounds are electrically neutral so no net charge Do ions etc NaCl CaCl2 NH4 2CO3 34 Names of Ions Naming positive ions cations Name of metal plus the word ion do of e p n Ag silver ion Na NH4 Fe2 35 Naming negative ions anions Monatomic anion add ide ending to stem name O2 oxide F fluoride ClBrIP 3N 3 Clicker Q name of anion 36 Polyatomic anions Memorize Table 2 4 page 72