2The Modern Model The modern atom is composed of two regions: 1. Electron cloud- Most of the volume of an atom and is the region where the electron can be found (extranuclear)2. The nucleus – with protons and neutrons so that it has a Positive charge and almost all the mass
3Major Subatomic Particles NameSymbolChargeRelative Mass (amu)Actual Mass (g)Electrone--11/18409.11x10-28Protonp++111.67x10-24NeutronnoAtoms are measured in picometers, metersHydrogen atom, 32 pm radiusNucleus is tiny compared to atomIf the atom were a stadium, the nucleus would be a marbleRadius of the nucleus is on the order of mDensity within the atom is near 1014 g/cm3
4Nuclear SymbolsEvery element is given a corresponding symbol which is composed of 1 or 2 letters (first letter upper case, second lower), as well as the mass number and atomic numberEAZelemental symbolmass numberatomic number
5Elemental Classification Atomic Number (Z) = number of protons (p+) in the nucleusDetermines the type of atomLi atoms always have 3 protons in the nucleus, Hg always 80Mass Number (A) = number of protons + neutrons [Sum of p+ and nº]Electrons have a negligible contribution to overall massIn a neutral atom there is the same number of electrons (e-) and protons (atomic number)
6W F Br 184 74 19 9 80 35 Find the number of protons number of neutrons number of electronsatomic numbermass numberW18474F199Br8035
7If an element has 91 protons and 140 neutrons what is the: If an element has an atomic number of 34 and a mass number of 78 what is the:number of protons in the atom?number of neutrons in the atom?number of electrons in the atom?complete symbol of the atom?If an element has 91 protons and 140 neutrons what is the:atomic number?mass number?number of electrons?complete symbol?
8IsotopesAtoms of the same element can have different numbers of neutrons and therefore have different mass numbersThe atoms of the same element that differ in the number of neutrons are called isotopes of that elementH1Protium2Deuterium3Tritium
9Naming IsotopesWhen naming, write the mass number after the name of the elementExamples:carbon- 12carbon -14uranium-235
10Review:Write the nuclear symbols ( ) and name including mass for three isotopes of oxygen in which there are 8, 9, and 10 neutrons respectively.
11IonsWhen atoms gain or lose electrons they form something called IONS. Energy is released when this happens.Ions are electrically charged atoms. (positive or negative)
12Cations (+)CATIONS: are positively charged ions. Cations are formed when an atom loses electrons.Metals and Hydrogen form cationsEx: Na lose 1 electron Na1+
13Anions (-)ANIONS: are negatively charged ions. Anions are formed when atoms gain electrons.Most non-metals form anions.Ex: Cl gains one electron Cl1-
14Charges of Ions Group 1 loses 1 electron = +1 Group 2 loses 2 electrons = +2Group 13 loses 3 electrons = +3Group 15 gains 3 electrons = -3Group 16 gains 2 electrons = -2Group 17 gains 1 electron = -1Group18 has a full outer shell= very stable
15Noble Gases Group 8A (He, Ne, Ar, etc.) Have a full valence shell (complete octet)They neither want to gain or lose electronsTherefore, DO NOT form IONS********Handout chemical familes discuss
16(+) charge = subtract electrons from # protons Only the number of electrons can change:(+) charge = subtract electrons from# protons(-) charge = add electrons from
17How many protons and electrons do each of the following have? Br-1Ca+2Se-2e) Mg+2f) Au3+g) P-3h) Mn+4
18Average Atomic MassDid you ever notice that the mass number on the periodic table is not a whole number?There are the decimal numbers on the periodic table.**This is because it is an average mass for all the isotopes of each atom
19How heavy is an atom of oxygen? There are different kinds of oxygen atoms (different isotopes)16O, 17O, 18OWe are more concerned with average atomic masses, rather than exact onesBased on abundance of each isotope found in natureWe can’t use grams as the unit of measure because the numbers would be too smallInstead we use Atomic Mass Units (amu)Standard amu is 1/12 the mass of a carbon-12 atomEach isotope has its own atomic mass
20Calculating AveragesYou have five rocks, four with a mass of 50 g, and one with a mass of 60 g. What is the average mass of the rocks?Total mass = x 50 g + 1 x 60 g = 260 gAverage mass = (4 x 50 g + 1 x 60 g)/5 = (260 g)/5= (4 x 50 g)/5 + (1 x 60 g)/5 = 260 g/5
21Calculating Averages Average mass = 0.8 x 50 + 0.2 x 60 80% of the rocks were 50 grams20% of the rocks were 60 gramsAverage = (% as decimal) x (mass1) (% as decimal) x (mass2) (% as decimal) x (mass3) + …
22Calculating AveragesCalculate the av atomic mass of copper if copper has two isotopes69.1% has a mass of amuThe rest (30.9%) has a mass of amuMagnesium has three isotopes78.99% magnesium 24 with a mass of amu10.00% magnesium 25 with a mass of amuThe rest magnesium 26 with a mass of amuWhat is the atomic mass of magnesium?
23Average Atomic MassesIf not told otherwise, the mass of the isotope is the mass number in amuThe average atomic masses are not whole numbers because they are an average mass valueRemember, the atomic masses the decimal numbers on the periodic table