Periodic Table & Periodic Law Chapter 6

Objectives 6.1 Trace the development and identify key features of the periodic table

Development of Modern Periodic Table Section 6.1

History of the Periodic Table Some elements like Au and Ag were known since prehistoric times Wikipedia.com

Antoine Lavoisier French scientist, late 1790s Compiled list of 23 elements known at that time Tried to organize it Wikipedia.com

1800s Electricity breaks down into component elements Spectrometer identified newly isolated elements Industrial revolution (mid-1800s) led to new chemistry related industries Petrochemicals, soaps, dyes, fertilizers Created chemical pollution

More info 1860 Scientist agreed on method to determine atomic masses 1870 70 known elements

John Newlands (1837-1898) 1864 English Chemist When elements arranged by atomic mass, properties repeated every eighth element This is periodic since it repeats in pattern He called this the Law of Octaves Critics did not like music analogy, law didn’t work for all known elements Wikipedia.com

Newland’s Table http://mooni.fccj.org/~ethall/period/period.htm

Lothar Meyer (1830-1895) 1869 German Chemist Made connection between atomic mass and element properties Same time as Mendeleev Wikipedia.com

Dmitri Mendeleev (1834-1907) 1869 Russian chemist Connection of atomic mass to elemental properties Gets credit b/c published first and demonstrated its usefulness Organized first PT Arranged by atomic mass Left spaces for “unknown” elements

Problems with Mendeleev’s PT Some element properties did not match up when placed according to atomic mass Wikipedia.com

Mendeleev’s PT http://mooni.fccj.org/~ethall/period/period.htm

Henry Moseley 1913 English chemist who discovered # p+ = atomic # Arranged PT according to atomic # and “fixed” Mendeleev’s problem Periodic Law – there is a periodic repetition of chemical & physical properties of elements when arranged by increasing atomic # Wikipedia.com

Moseley’s PT http://mooni.fccj.org/~ethall/period/period.htm

Modern PT Groups – AKA families; columns Periods – rows; 7 total and growing? Representative elements – 1A through 8A Transition elements – 1B through 8B

Classifying elements Metals Include most of Group A and all Group B shiny when smooth and clean solid at room temp good conductors of electricity & heat malleable and ductile Include most of Group A and all Group B Group 1A – Alkali metals (except H) Group 2A – alkaline earth metals Both groups chemical reactive (1A > 2A)

Classifying elements (con’t) Group B Transition metals Inner transition metals Lanthanides Phosphors – emit light when struck by e- Actinides Wikipedia.com

Classifying elements (con’t) Nonmetals Located right upper side Gases or brittle, dull-looking solids Poor conductors of heat and electricity Br is only nonmetal liquid at room temp Halogens (Group 7A) Noble gases (Group 8A) Not reactive Wikipedia.com

Classifying elements (con’t) Metalloids or semi-metals Have physical and chemical prop of metals and nonmetals Examples (uses): Ge (cell phones) Si (computer chips) Wikipedia.com

Objectives 6.2 Explain why elements in the same group have similar properties Identify the four blocks of the periodic table based on electron configuration

Classification of the Elements Section 6.2

Organizing by e- configuration Period 1 H 1s1 1s1 Period 2 Li 1s22s1 [He]2s1 Period 3 Na 1s22s22p63s1 [Ne]3s1 Period 4 K 1s22s22p63s23p44s1 [Ar]4s1

Valence e- Atoms in the same group have similar chemical properties because they have the same number of valence e- Group 1A all have 1 e- in last energy level

Valence e- and periods Energy level of element’s valence e- = the period # Ex: lithium’s valence e- is in the second energy level Lithium is in the second period

Valence e- and group # The group # = the valence e- # Applies to representative elements ONLY Ex: Group 5A has 5 e-

S-block Group 1A has e- configuration of s1 S orbital is full with 2 e-

P-block Group 3A to 8A Holds max of 6 e- S- and p- blocks comprise all of the representative elements Noble gases group 8A Nearly no chemical rxn Stable!

D-block Contains transition metals Largest block Spans 10 groups S filled and partially filled d Ex: Scandium [Ar]4s23d1 Titanium [Ar]4s23d2

F-block Contains inner transition metals Filled/partially filled s, 4f and 5f Spans 14 columns

Objectives 6.3 Compare period and group trends of several properties Relate period and group trends in atomic radii to electron configuration

Periodic Trends Section 6.3

Atomic radius Atomic size Atomic radius How close an atom lies to another atom Atomic radius Half the distance between adjacent nuclei http://www.chemguide.co.uk/atoms/properties/atradius.html

Atomic Radius Trends DECREASES INCREASES http://intro.chem.okstate.edu/1314F00/Lecture/Chapter7/Lec111300.html

Why does the atomic radius decrease within a period? Increase # p+ and e- Each e- is added to the same energy level Nuclear charge becomes more + as we move from left to right Valence e- are not shielded from increased nuclear charge What happens? Outermost e- pull closer to nucleus

Why does the atomic radius increase within a group? Add energy levels or orbital Make atom larger Outer e- are farther away Valence e- shielded by added distance and not affected by nuclear charge

Which has the largest atomic radius? C, F, Be, or Li Find the location of the elements. All P2 Arrange them Li, Be, C, F Find your answer Li

Ionic radius Atoms can gain or lose e- to form ions When atoms lose e- and form + ions, they get smaller. The e- lost is a valence e- If the orbital is empty, the atom is smaller If the atom is smaller, the + of the nucleus will pull the remaining e- towards it

Ionic radius (con’t) When atoms gain e- and form (–) ions, they become larger. Adding e- to outer shell increases electrostatic repulsion between existing e- to move them farther apart.

What does the ionic radius do within a period? Decreases as you move across the period Refer to page 166 in text DECREASES

What does the ionic radius do within a group? Increases as you move down the group Refer to page 166 in text INCREASES

Ionization energy Energy required to remove an e- from a gaseous atom The energy needed to remove the first e- is called first ionization energy The amount of energy needed to remove the second e- from a 1+ ion is called the second ionization energy, etc. The more e- you try to remove, the more energy it takes, and the less likely to occur

What does the ionization energy do within a period? Increases as you move across the period Removing the last e- makes the nucleus “hold” the remaining e- tighter INCREASES

What does the ionization energy do within a group? Decreases as you move down the group Because valence e- are farther from the nucleus, the hold on it is less and takes less energy DECREASES

OCTET RULE Atoms share, gain, or lose e- to acquire a full set of 8 valence e- (except: period 1 elements) Elements on right side of table gain e-; form (--) ions Elements on left side of table lose e-; form + ions

Electronegativity The ability for an atom to attract e- to form a bond Units: Paulings (named after American scientist Linus Pauling) F is most electroneg Cs, Fr least electroneg

What does the electronegativity do within a period? Increases as you move across a period INCREASES

What does the electronegativity do within a group? Decreases as you move down a group DECREASES

Summary of Trends Atomic radius -Size of atom Decrease Left to right Increase Top to bottom Ionic radius -Size of ion Ionization energy -Energy to lose e- Electronegativity -Ability to attract e-

Credits Clip art from Microsoft Clip art and Wikipedia as well as other sources documented throughout the presentation Information obtained mainly from Glencoe Chemistry Matters textbook, Texas ed. Arranged and explained by Michelle Estrada