1. Discovering Periodic Trends
ACTIVITY

2. Atomic Mass
Definition of Atomic Mass: the mass of an atom in atomic mass units; the average mass of the atoms of an element
Units of Atomic Mass: atomic mass units (amu)

3. Atomic Mass This trend INCREASES across a period from LEFT to RIGHT.
The reason for this observed trend is: INCREASE IN #p+AND #n0

4. Atomic Mass This trend INCREASES within a group from TOP to BOTTOM.
The reason for this observed trend is: INCREASE IN #p+AND #n0

5. Atomic RADIUS
Definition of Atomic Radius: distance from th center of an atom to the 90% probability surface of the electron cloud
Units of Atomic Radius: picometers (pm)

6. Atomic RADIUS This trend DECREASES across a period from LEFT to RIGHT.
The reason for this observed trend is: INCREASE IN # p+ RESULTS IN A GREATER FORCE OF ATTRACTION (FoA) AND A STRONGER PULL ON THE ELECTRON CLOUD (COULOMBIC ATTRACTION)

7. Atomic RADIUS This trend INCREASES within a group from TOP to BOTTOM.
The reason for this observed trend is: AN INCREASE IN THE # OF EL’S OCCUPIED BY e-

8. IONIZATION ENERGY
Definition of Ionization Energy: energy required to remove the most loosely held electron from an atom
Units of Ionization Energy: kilojoules/mole (kJ/mol)

9. IONIZATION ENERGY
This trend INCREASES across a period from LEFT to RIGHT.
The reason for this observed trend is: AN INCREASE IN # OF p+ CAUSES AN INCREASE IN FoA, WHICH MAKES ITS HARDER (REQUIRES MORE ENERGY) TO REMOVE AN e- (COULOMBIC ATTRACTION)

10. IONIZATION ENERGY
This trend DECREASES within a group from TOP to BOTTOM.
The reason for this observed trend is: AN INCREASE IN ATOMIC SIZE RESULTS IN A LARGER DISTANCE BETWEEN p+ AND e-, WHICH CAUSES A DECREASE IN FoA MAKING IT EASIER (REQUIRES LESS ENERGY) TO REMOVE AN e- (COULOMBIC ATTRACTION)

11. ELECTRONEGATIVITY
Definition of Electronegativity: the relative attraction of an atom for a shared pair of electrons
Units of Electronegativity: Paulings

12. ELECTRONEGATIVITY
This trend INCREASES across a period from LEFT to RIGHT.
The reason for this observed trend is: AN INCREASE IN # OF p+ CAUSES AN INCREASE IN FoA FOR SHARED PAIRS OF e-

13. ELECTRONEGATIVITY
This trend DECREASES within a group from TOP to BOTTOM.
The reason for this observed trend is: AN INCREASE IN ATOMIC SIZE RESULTS IN A LARGER DISTANCE BETWEEN p+ AND e-, WHICH CAUSES A DECREASE IN FoA FOR SHARED PAIRS OF e-

14. DENSITY Definition of Density: mass per unit volume
Units of Density: g/mL (liquids) and g/cm3 (solids or gases)

15. DENSITY
General description of density trend, if one exists. Relate this trend to your knowledge of states of matter. The highest density elements are solids (metals and metalloids), while the lowest density elements are gases (nonmetals).

16. MELTING POINT
Definition of Melting Point: the temperature at which the vapor pressures of the solid and liquid phases of a substance are equal
…(or in simpler terms-the temperature at which a solid first begins to change into a liquid)
Units of Melting Point: oC

17. MELTING POINT
General description of melting points trend, if one exists. Relate this trend to your knowledge of states of matter. The elements with the highest melting points are solids (metals and metalloids), while the elements with the lowest melting points are gases (nonmetals).