Unit 2 Atomic Number, Mass Number and Isotopes

Homework  Complete worksheet 4A  Read Pages  Chapter 2 problems: 8, 10, 14,16  Test scheduled for Nov. 17, 18 and 19 (Wed., Thursday or Friday)

Distinguishing Between Atoms  Atomic Number –Unique for each element. –Equal to the number of protons in the nucleus of an atom of that element. –The number of protons must equal the number of electrons.

Distinguishing Between Atoms  Mass Number –Mass is concentrated in the nucleus –Depends on the number of protons and neutrons.

Distinguishing Between Atoms  Determining atomic composition from mass number and atomic number –Number of protons = number of electrons = Atomic number –Number of neutrons = mass number – number of protons.

Distinguishing Between Atoms  Representing atomic composition using atomic number and mass number

Distinguishing Between Atoms  Elements can also be represented using name and mass number –Carbon - 12

Distinguishing Between Atoms ElementSymbolAtomic #Mass ## of Neutrons Nitrogen-15 Neon-22 Beryllium-9

Distinguishing Between Atoms ElementSymbolAtomic # Mass ## of Protons # of Electrons # of Neutrons Carbon126 K Helium Mercury80120

Distinguishing Between Atoms  Isotopes –Equal number of protons and electrons. –Different number of neutrons –Different mass number  Chemically alike

Distinguishing Between Atoms  Atomic Mass –Mass of proton or neutron is small (1.67 x g) –Mass of electron is negligible in comparison (9.11 x g)  The mass of even the largest atom is incredibly small

Distinguishing Between Atoms  Compare relative mass using a reference isotope as a standard  Isotope C-12 assigned a mass of 12 amu  Atomic mass unit (amu) defined as one-twelfth the mass of carbon-12

Distinguishing Between Atoms  If atomic mass is determined by the number of protons and neutrons, why isn’t the mass of an element a whole number?  Most elements occur as a mixture of two or more isotopes.

Isotopes of hydrogen  Hydrogen – 1 (protium 99.98%)  Hydrogen – 2 (deuterium %)  Hydrogen – 3 (tritium trace quantities)

Protium  1 proton  1 electron  0 neutrons

Deuterium  1 proton, 1electron, 1neutron  D 2 O = heavy water  Concentrated with neutrons during slow electrolysis of water  Greater density and higher boiling point then H 2 O  Not radioactive

Tritium  1 proton, 1 electron, 2 neutrons  Formed continuously in upper atmosphere in nuclear reactions by cosmic rays  Compounds can be labeled with D or T by comparing the location of the heavy Hydrogen

Distinguishing Between Atoms  The atomic mass of an element is a weighted average mass of the atoms in a naturally occurring sample of the element.

Distinguishing Between Atoms  You can calculate the atomic mass if you know three values: –The number of stable isotopes of the element. –The mass of each isotope. –The natural percent abundance of each isotope.

Distinguishing Between Atoms  Chlorine, symbol Cl, has two isotopes –Cl-35 (34.97) abundance 75.77% –Cl-37 (36.97) abundance 24.23% Calculate the atomic mass of chlorine

4A Atomic Structure amu 4a. 5b. 16c. 38d. 79 5a. hydrogenc. lithium b. irond. argon amu

4A Atomic Structure element# of p + # of e - # of n 0 atomic # mass # manganeseMn sodiumNa bromineBr yttriumY arsenicAs actiniumAc

Chapter protons, 134 neutrons 10. Fe Fe 14. a. 34b. 41c. 34 d. 41 n 0, 34p +, 36e

Chapter 2 #16 symbolchargeprotonsneutronselectrons Br N As Zr

Homework  Read Chapter 2 pages  WS: 5.4 The Periodic Table  Chapter 2: problems 20, 22, 24 and 26  Webassign Due Nov. 19  Test: Nov. 17, (Wed. Thurs. Fri)

The Periodic Table  Dmitri Mendeleev ( ) –Russian chemist –Listed elements in columns in order of increasing atomic mass. –Arranged columns so that elements with similar properties were side by side.

The Periodic Table  Mendeleev left blank spaces where there were no known elements with the appropriate properties or mass.  Predicted the properties of the missing elements.

THE PERIODIC TABLE Dmitri Mendeleev ( )

Henry Mosely ( )  Determined atomic numbers of the elements.  Arranged elements in table by atomic number instead of mass. THE PERIODIC TABLE

Henry Mosely ( ) THE PERIODIC TABLE

HORIZONTAL ROWS: PERIODS  seven periods  2 to 32 elements in a period  properties of the elements change as you move across a period  this pattern repeats from period to period: The Periodic Law

 Elements in a group have similar physical and chemical properties.  Groups identified by A or B and a #  Group A are the representative elements  Group A can be divided into three broad classes VERTICAL COLUMNS: GROUPS/FAMILIES

 high electrical conductivity  high luster when clean  ductile  malleable 1. METALS

divided into:  alkali metals – group 1A  alkaline earth metals – group 2A  transition metals – group B  inner transition metals 1. METALS

 poor electrical conductivity  non-lustrous  group 7A – halogens  group 8A – noble gases 2. NONMETALS

properties are intermediate between metals and nonmetals 3. METALLOIDS

5.4 The Periodic Table… 1. groups10. alkaline earth 2. periodsmetals 3. atomic #11. group 7A 4. group12. metalloids 5. rep. elements13. ST 6. noble gases14. AT 7. transition metals15. AT 8. inner tr. metals16. NT 9. alkali metals

5.4 The Periodic Table… 17. E25. nonmetals: N, P 18. G metalloids: As, Sb 19. A metal: Bi 20. F26. malleable, ductile, 21. C conduct electricity, etc. 22. D 23. H 24. B

Mass Defect – missing mass? Masses of particles that make up an atom are added, the sum is always larger than the actual mass of the atom. The missing mass is the matter converted into energy when the nucleus was formed from its component protons and neutrons.

Mass Defect Calculate the mass defect of a chlorine-35 atom. The actual mass of chlorine-35 is 5.81 x grams e = 9.11 x g p = 1.67 x g n = 1.67 x g