Chapter 11 Introduction to Atoms

1. Chapter 11Introduction to Atoms

2. An atomis the smallest particle into which an element can be divided and still be the same substance. • See timelinehandout for the development of the model of the atom. • Identify atom models of Thomson, Rutherford, Bohr, and the Modern Model.

3. What do I need to know? • Know the scientist • their contribution to the developing model of an atom (their experiment) • their atom model!

4. Structure of the atom • The atom contains a nucleus surrounded by one or more electrons • The nucleus contains protons and neutrons. Draw an atom here (Page 320)

5. Structure of the atom nucleus energy level

16. Terms to copy in notes: atomic number – the number of protons in the nucleus of an atom. (*The number of protons identifies an element!) atomic mass – the average mass of oneatom of an element. atomic mass unit (amu) – a measurement of the mass of one proton or oneneutron.

17. Chemical Symbols • A chemical symbol is one or two letter(s) representing an element. • If the symbol is one letter, it is a printed capital. Hydrogen symbol is H • If two letters, the first is a printed capital and second is lower case. Cobalt symbol is Co

18. Know the Following Elements! The first 20 elements and symbols, plus 7 others, must be properly identified together. iron copper silver gold mercury tin lead • The symbols must be written in correct form. • Spelling counts!

19. Electrons • Electrons are located in an electron cloud around the nucleus. • There are different energy levels (“orbits” in the Bohr model) that electrons fill. 1st energy level can hold 2 electrons 2nd can hold 8 electrons 3rd can hold 18 electrons 4th can hold 32 electrons

20. Energy Levels of carbon atom

21. Today’s periodic table is based on atomic number. Each element’s square contains: atomic number (protons) chemical symbol element name atomic mass (protons & neutrons) This is an average 26 Fe Iron 55.847

22. How to find the number of neutrons in an atom • Round the atomicmass to the nearest whole number. • Subtract the number of protons(atomicnumber). • The difference is the number of neutrons. boron 10.81 atomic mass (protons + neutrons) 11 rounded - 5 atomic number(protons) 6 neutrons

23. Aluminum atomic mass rounded - atomic number neutrons

24. Practice calculating the number of neutrons in an atom • Number a blank sheet of paper 1 to 10. • Write the name for each element from the periodic table for elements 1-10. • Use the right side of your paper to calculate the number of neutrons for elements 1-10. • Write your answer next to the elements name.

25. Gaining or losing a neutron makes an atom an isotope. Isotopes are still the same element, just more or less neutrons. carbon 12 has 6 neutrons (always 6 protons) carbon 14 has 8 neutrons (always 6 protons) The 12 refers to the mass number (protons + neutrons)

26. Valence electronsare electrons farthest away from the nucleus (outer energy level). - involved with chemical reactions. - gives an atom its chemicalcharacteristics. - can be shared, or transferred. - Atoms with a full valence energy level are most stable (less reactive).

27. electron dot diagram – represents the valence electrons of an element. - uses an element symbol surrounded by dots representing valence electrons. H O C Ne hydrogen oxygen carbon neon

28. The Periodic Table of Elements Chapter 12 Notes • In 1869 a Russian scientist Dmitri Mendeleev arranged elements in order of increasing atomic mass, and chemical properties. • He used his table to predict properties of elements not yet discovered!

29. Today’s periodic table is based on atomic number! Each element’s square contains: atomic number (protons) chemical symbol element name atomic mass (protons & neutrons) This is an average 26 Fe Iron 55.847

30. An element’s properties can be predicted by its location on the periodic table. Groups or families: vertical columns numbered 1-18. elements have similar properties Periods: across rows numbered 1-7 elements have predictablydifferent patterns.

31. Metals • Metals are found to the left of the stair step. • Physical properties: • Hardness • Shininess (luster) • Malleability (pound into shapes) • Ductility (drawn out into a wire) • Good conductors • Magnetic (Co, Ni, Fe) • Mostly solids at room temp.

32. Metals • Chemical properties: • wide range • Some violently react with water (Na, K) • Some unreactive (Au, Cr) • Some corrode (react slowly with O2 and flake off) • Alloys (mixture of metals) • bronze (Cu + Sn) • stainless steel

33. Metals • Elements are increasingly nonmetallic reading left to right. • Tend to lose electrons forming positive ions (1+, 2+) • Alkali Metals • Group 1 (1 valence electron) • Most reactive metals! • Very soft & shiny

34. Metals • Alkaline Earth Metals • Group 2 (2 valence electrons) • Not as reactive as Group 1 but more reactive than most metals. • Fairly hard, grey-white color • Good conductors of electricity

35. Metals • Transition Metals • Groups 3-12 • Fairly stable, react slowly with H2O • Similar reactivity between columns • Hard and shiny • Good conductors of electricity

36. Metals • Lanthanides and Actinides • Called rare earth metals • Fit in Periods 6 and 7 between alkaline earth metals and the transition metals. • Placed below periodic table for convenience. • Soft, malleable, shiny, very conductive

37. Nonmetals • Located right of the stair step • Physical properties: • Most are gases at room temp. (low boiling point). • dull • brittle • lower densities • poor conductors of heat & electricity

38. Nonmetals • Chemical properties: • Most readily form compounds • Will take electrons from metals forming negative ions (1-, 2-) • Will also share electrons • Many form diatomic molecules (O2, N2, H2) • Halogen Family • Group 17 (7 valence electrons) • Very reactive! • Dangerous to humans

39. Nonmetals • Noble Gases • Group 18 • Chemically stable (unreactive) • Do not gain, lose, or share valence electrons • Hydrogen • Alone in upper left corner • Simplest element • Not grouped in a family

40. Metalloids • Along the stair step (7 elements) • Have some properties of metals & nonmetals • Used to make semiconductors