Presentation on theme: "The structure of the atom"— Presentation transcript:
1 The structure of the atom Chapter 4.3How Atoms Differ
2 Atomic numberThe number of protons in an atom that identifies it as an atom of a particular element (also equals the number of electrons)Every element has a unique atomic number (unique number of protons that cannot be changed without change the identity of the element)Atomic number = number of protons = number of electronsIn a neutral (no charge) atom, the number of electrons (- charge) always equals the number of protons (+ charge)The periodic table is organized left to right and top to bottom by increasing atomic number.
3 Atomic Number Problem Complete the following table: ElementAtomic NumberProtonsElectrons1935Ne10K1919Br35351010
4 Mass of atoms Measured in atomic mass units (amu) Based on carbon-12 as a standard1 amu = 1/12 the mass of the carbon-12 atomMasses of subatomic particles:Electron = amuProton = amuNeutron = amu
5 Mass number Mass number = number of protons + number of neutrons How heavy the atom isNucleus is heaviest - Contains protons and neutronsMass number = number of protons + number of neutronsA single element can have different mass numbers if there is more than one “version” of the element – called an isotope
6 IsotopesAtoms of the same element with the same number of protons but different numbers of neutrons.The mass of isotopes increases with increasing neutrons but chemical behavior stays the sameChemical behavior is determined only by the the number of electrons that an atom has.
7 Isotope identification Each isotope of an element is identified with the mass numberCopper-63 (Cu-63): mass number = 63 (29 protons + 34 neutrons)Copper-65 (Cu-65): mass number = 65 (29 protons + 36 neutrons)Atomic Mass: the weighted average mass of all of the isotopes of a particular elementThis is the mass number listed on the periodic table with decimal places!!!
8 (Protons or electrons) Isotope notation***Isotopes are often written using a notation involving the chemical symbol, atomic number, and mass numberMass Number(Protons + Neutrons)Copper-6563Cu65Cu2929Copper-63Atomic Number(Protons or electrons)
9 Isotope problem: Determine the number of protons, electrons and neutrons for the isotopes in the table below; name each isotope and write its symbolElementAtomic NumberMass Numbera.Neon1022b.Calcium2046c.Oxygen817d.Iron2657e.Zinc3064f.Mercury80204
10 Calculating Atomic Mass Atomic mass: the weighted average mass of all of the isotopes of that elementMass of each isotope and isotope abundances are required to calculate thisIsotope abundancesAmount of element isotopes that readily exist (presented as percentages)
11 CALCULATING Atomic Mass An element has 3 isotopes with the following mass numbers and abundances:23A: mass 23 amu; abundance 7%25A: mass 25 amu; abundance 76%26A: mass 26 amu; abundance 17%(23 x 0.07)+(25 x 0.76)+(26 x 0.17) = 25.03
12 Isotope Mass (amu) Percent Abundance Atomic Mass Problem: Calculate the atomic mass of the element X and identify the element from the periodic table knowing that it has the isotopes listed in the table belowIsotopeMass (amu)Percent Abundance54X53.9405.9%56X55.93591.72%57X56.9352.1%58X57.9330.28%
13 Ion formation Ions are formed when atoms gain or lose electrons. Positive Ion formationWhen an atom LOSES one or more electronsWhen an electron (negative charge) is lost, the ion ends up with a net positive charge (Ca – 2 e- = Ca2+)Negative Ion FormationWhen an atom GAINS one or more electronsWhen an electron (negative charge) is gained, the ion ends up with a net negative charge (O + 2 e- = O2-)