Periodic Trends: Electronegativity, Metallic Character

Electronegativity An atom’s ability to pull electrons to itself in a chemical bond Cannot be directly measured Trend: increases decreases

How does this affect atoms? Chemical bonding Ionic Bonds Formed between 2 atoms with a HUGE difference in electronegativity---electron cloud is pulled closer to the more electronegative atom. Covalent Bonds Atoms equally sharing electrons (nonpolar covalent) Atoms with a difference in electronegativity will exhibit unequal sharing with the more electronegative atom pulling electrons toward it (polar covalent)

Example 1: Which of the following atoms is the most electronegative? S As P Se Cl Br

Example 2: Which of these atoms are arranged based on DECREASING electronegativity? C > Si > P >As > Se O > P > Al > Mg > K Na > Li > B > N > F K > Mg > Be > O > N Li > Be > B > C > N

Metals, Nonmetals, Metalloids How can you identify a metal? What are its properties? What about the less common nonmetals? What are their properties? And what the heck is a metalloid?

A Different Type of Grouping Besides the 4 blocks of the table, there is another way of classifying element: Metals Nonmetals Metalloids or Semi-metals. The following slide shows where each group is found.

Metals Metals are shiny, malleable, ductile, and are good conductors of heat and electricity. They are mostly solids at room temp. Want to LOSE valence electrons Form positive ions s block (not H and He), d/f blocks, some p block elements

Nonmetals Nonmetals are the opposite. No color, no shine They are dull, brittle, nonconductors (insulators). Gases at room temperature Want to GAIN electrons Form negative ions p block elements, H and He

Transition Metals Middle of the periodic table Forms positive ions, multiple types Shine, malleable, ductile, good conductors s/d orbitals—electrons lost from these subshells.

Metalloids/Semi-Metals Metalloids, aka semi-metals are just that. They have characteristics of both metals and nonmetals. They are shiny (like metals) but brittle. And they are semiconductors. “on the fence, middle of the road” B, Si, As, Te, At, Ge, Sb, Po

Noble Gases Group 18 (He, Ne, Ar, Kr, Xe, Rn) Do NOT react with other elements Atmospheric gases Naturally in elemental form , single atoms Not completely unreactive

Metallic Character This is simply a relative measure of how easily atoms lose or give up electrons. Tendency to LOSE electrons Related to atomic radius/ionization energy, how easy to remove electrons

Metallic Character Decreases Increases

Nonmetallic Character Atoms with a tendency to GAIN electrons Increases Decreases

Homework Beer’s Law Lab Report Read over your lab procedure