CHEM 1305: Introductory Chemistry The Periodic Table From Chapter 5 Textbook Introductory Chemistry: Concepts and Critical Thinking Seventh Edition by Charles H. Corwin
Classification of Elements By 1870, more than 60 elements had been discovered Dmitri Mendeleev proposed that properties of different elements (such as formula of oxide) repeat at regular intervals when they are arranged in order of increasing mass 2
The Periodic Law Concept In 1913, H. G. J. Moseley discovered that nuclear charge (number of protons) increased by 1 for each element in the periodic table This led to the periodic law which states that properties of elements recur in a repeating pattern when arranged in order of increasing atomic number and not increasing atomic mass Element pairs circled in red are in order of increasing atomic number, but have a decrease in atomic mass 3
Groups and Periods of Elements A vertical column in the periodic table is called a group (18 groups) A horizontal row in the periodic table is called a period (7 periods) alkali metals halogens alkaline earth metals noble gases 4
Representative Elements and Transition Elements Groups of elements are also classified as either representative elements, transition elements, or inner transition elements hydrogen s properties are unlike any one group IUPAC (1-18) American (IA-VIIIA) lanthanide series (rare earth elements are Ce-U) actinide series (transuranium elements) 5
Periodic Trends Visualize atoms as spheres, where the atomic radius is the distance from the nucleus to the outermost electrons, atomic radius is expressed in nanometers (nm) Two trends atomic radius decreases up a group (number of energy levels decreases) atomic radius decreases across a period, left to right (nuclear charge pulls electrons closer to the nucleus) 6
Periodic Trends Metallic character changes in a similar way Which has smaller radius? Na or K P or N Ca or Ni Si or S Which is most metallic? Sn or Pb Ag or Sr Al or B Br or As 7
Periodic Trends Metallic character changes in a similar way Which has smaller radius? Na or K P or N Ca or Ni Si or S Which is most metallic? Sn or Pb Ag or Sr Al or B Br or As 8
Properties of Elements It is possible to predict physical properties of elements based on trends shown by other elements in the same group Properties of Francium (Fr) can be predicted: atomic radius >0.266 nm, density >1.87 g/ml, melting point >28.4 C, atomic mass >132.91 amu Fr is just below Cs on the periodic table 9
Predicting Physical Properties Predict the missing value for each physical property listed below Ca 0.197 1.54 (?) Sr 0.215 (?) 769 Ba (?) 3.65 725 Ni 0.125 8.91 (?) Pd 0.138 (?) 1554 Pt (?) 21.5 1772 10
Predicting Physical Properties Predict the missing value for each physical property listed below Ca 0.197 1.54 813 (?) (839) Sr 0.215 2.60 (?) (2.63) 769 Ba 0.233 (?) (0.217) 3.65 725 Ni 0.125 8.91 1336 (?) (1455) Pd 0.138 15.2 (?) (12.0) 1554 Pt 0.151 (?) (0.139) 21.5 1772 11
Exceptions The Melting Spoon Al: melting point is 660 C, In: melting point is 157 C, what about Ga? See video at this link: http://www.youtube.com/watch?v=cvrcuewjbu0 The melting point of Ga is very low: 30 C 12
Predicting Chemical Properties Elements in the same group have similar chemical properties For example, Mg and O react to give MgO Ca, Sr, and Ba should react similarly and they do, to give CaO, SrO, BaO, respectively Sodium + Chlorine NaCl, predict the following: Lithium + Chlorine?? Potassium + Chlorine?? Given formulas for oxides CaO, Ga 2 O 3, K 2 O, GeO 2, predict the formula: rubidium oxide,?? strontium oxide,?? indium oxide,?? lead oxide,?? 13
Predicting Chemical Properties Elements in the same group have similar chemical properties For example, Mg and O react to give MgO Ca, Sr, and Ba should react similarly and they do, to give CaO, SrO, BaO, respectively Sodium + Chlorine NaCl, predict the following: Lithium + Chlorine LiCl Potassium + Chlorine KCl Given formulas for oxides CaO, Ga 2 O 3, K 2 O, GeO 2, predict the formula: rubidium oxide, Rb 2 O strontium oxide, SrO indium oxide, In 2 O 3 lead oxide, PbO 2 14
Blocks of Elements Energy sublevels: 1s < 2s < 2p < 3s < 3p < 4s < 3d < 4p < 5s < 4d < 5p Periodic table is arranged by which sublevel is filled 15
Electron Configuration of Elements Electron configurations of elements can be abbreviated by indicating the innermost electrons with the symbol of the preceding noble gas, and the outermost electrons with knowledge of blocks of elements For example, electron configuration for Na is 1s 2 2s 2 2p 6 3s 1 and for Ne is 1s 2 2s 2 2p 6 The abbreviation is written as: [Ne] 3s 1 Write the full and abbreviated electron configurations for each: P Co Zn Se 16
Electron Configuration of Elements Electron configurations of elements can be abbreviated by indicating the innermost electrons with the symbol of the preceding noble gas, and the outermost electrons with knowledge of blocks of elements For example, electron configuration for Na is 1s 2 2s 2 2p 6 3s 1 and for Ne is 1s 2 2s 2 2p 6 The abbreviation is written as: [Ne] 3s 1 Write the full and abbreviated electron configurations for each: P 1s 2 2s 2 2p 6 3s 2 3p 3, or [Ne] 3s 2 3p 3 Co 1s 2 2s 2 2p 6 3s 2 3p 6 4s 2 3d 7, or [Ar] 4s 2 3d 7 Zn 1s 2 2s 2 2p 6 3s 2 3p 6 4s 2 3d 10, or [Ar] 4s 2 3d 10 Se 1s 2 2s 2 2p 6 3s 2 3p 6 4s 2 3d 10 4p 4, or [Ar] 4s 2 3d 10 4p 4 17
Valence Electrons When an atom undergoes a chemical change (reaction), only the outermost electrons are involved, known as valence electrons Ignoring transition elements, valence electrons are what occupy the outermost s and p orbitals Number of valence electrons is predicted using the group number Predict the number of valence electrons for: Na Al S Xe C 18
Valence Electrons When an atom undergoes a chemical change (reaction), only the outermost electrons are involved, known as valence electrons Ignoring transition elements, valence electrons are what occupy the outermost s and p orbitals Number of valence electrons is predicted using the group number Predict the number of valence electrons for: Na 1 Al 3 S 6 Xe 8 C 4 19
Electron Dot Formulas An electron dot formula (also referred to as a Lewis structure) shows the symbol of an element surrounded by its valence electrons The symbol of the element represents the core electrons in an atom Dots are placed around the symbol to represent the valence electrons To draw an electron dot formula: Write the symbol of the element Draw a maximum of two dots on each side of symbol, (total maximum 8 e - : s + p = 2 e - + 6 e - = 8 e - ) Determine number of valence e - from periodic group, draw one dot per e - 20
Electron Dot Formulas Draw the electron dot formulas for each of the following elements Si N Xe Mg K Al Br S 21
Electron Dot Formulas Draw the electron dot formulas for each of the following elements Si Si N N Xe Xe Mg Mg K K Al Al Br Br S S 22
Ionization Energy It is possible to for all elements to lose electrons, but metals lose electrons more easily than nonmetals Electrons are negatively charged, so metals become positively charged after losing an electron any atom bearing a charge is called an ion The amount of energy required to remove an electron from a neutral atom (in the gaseous state) is called the ionization energy Na Na + + e - There are general trends in the periodic table regarding ionization energy it increases up a group of elements and increases from left to right across a period of elements ionization energy 23
Ionization energy Which has the higher ionization energy? Li or Na O or F Na or Mg O or S 24
Ionization energy Which has the higher ionization energy? Li or Na O or F Na or Mg O or S 25
Reactions of Alkali Metals with Water Alkali metals react vigorously with water The order of their reactivity is related to each element s ionization energy See video at this link: http://www.youtube.com/watch?v=eachisv5ur0 26
Ionic Charges Generally, metals tend to lose electrons from their valence shell and nonmetals tend to add electrons to their valence shell metals become positive and nonmetals become negative, they acquire an ionic charge The typical ionic charge of an element is related to its number of valence electrons Predict ionic charge: Al S Mg Br P 27
Ionic Charges Generally, metals tend to lose electrons from their valence shell and nonmetals tend to add electrons to their valence shell metals become positive and nonmetals become negative, they acquire an ionic charge The typical ionic charge of an element is related to its number of valence electrons Predict ionic charge: Al 3+ S 2- Mg 2+ Br - P 3-28
Isoelectronic Ions A sodium ion (Na + ) and a fluoride ion (F - ) and neutral neon (Ne) each have 10 electrons but their properties are very different Two or more ions having the same number of electrons are said to be isoelectronic For example, which of the following are isoelectronic with Ar? K +, Br -, Ca 2+, or O 2- Both K + and Ca 2+ have 18 electrons, the same as Ar Find the noble gas which is isoelectronic with the following: Cs + Cl - La 3+ Se 2- Xe Ar Xe Kr 29
Isoelectronic Ions A sodium ion (Na + ) and a fluoride ion (F - ) and neutral neon (Ne) each have 10 electrons but their properties are very different Two or more ions having the same number of electrons are said to be isoelectronic For example, which of the following are isoelectronic with Ar? K +, Br -, Ca 2+, or O 2- Both K + and Ca 2+ have 18 electrons, the same as Ar Find the noble gas which is isoelectronic with the following: Cs + Cl - La 3+ Se 2- Xe Ar Xe Kr 30
Electron Configuration of Ions To write the electron configuration for a positive ion, remove the number of electrons that corresponds to the positive charge For example Note transition metals lose two electrons from the highest s sublevel first before losing electrons from their outer d subevel For example Electron configurations can be simplified using a noble gas symbol to represent core electrons this method is called core notation Na atom loses 1 e - Na + ion 1s 2 2s 2 2p 6 3s 1 1s 2 2s 2 2p 6 Mn atom loses 2 e - Mn 2+ ion 1s 2 2s 2 2p 6 3s 2 3p 6 4s 2 3d 5 1s 2 2s 2 2p 6 3s 2 3p 6 3d 5 31
Electron Configuration of Ions To write the electron configuration for a negative ion, add the number of electrons that corresponds to the negative charge For example (using core notation) Write the electron configuration for each of the following ions: Fe 3+ Se 2- Cd 2+ P 3- Mg 2+ F - Cl atom gains 1 e - Cl - ion [Ne] 3s 2 3p 5 [Ne] 3s 2 3p 6 32
Electron Configuration of Ions To write the electron configuration for a negative ion, add the number of electrons that corresponds to the negative charge For example (using core notation) Write the electron configuration for each of the following ions: Fe 3+ [Ar] 3d 5 Se 2- [Kr] Cd 2+ [Kr] 4d 10 P 3- [Ar] Mg 2+ [Ne] F - [Ne] Cl atom gains 1 e - Cl - ion [Ne] 3s 2 3p 5 [Ne] 3s 2 3p 6 33
Where Did the Elements Come From? It is estimated that the universe is 14 billion years old and began with an event known as the Big Bang During this time, there is evidence for both hydrogen and helium atoms being formed what about heavier elements? Two hydrogen atoms combine to form a helium atom a process known as nuclear fusion It is speculated that heavier nuclei formed similarly Through a process called nucleosynthesis, it may be possible that H and He can form Li, which in turn forms Be and eventually C, and so on... 34