Periodic Table Trends

Periodic Table Trends

• Dmitri Mendeleev arranged the elements in 1870 according to atomic mass and used the arrangements to predict the properties of missing elements.

• The modern periodic table is arranged in order of increasing atomic number.

• The atomic number is the total number of protons in the nucleus.

• Groups are vertical columns on the periodic table.

• Periods are horizontal rows on the periodic table.

• Three classes of elements are metals, nonmetals, and metalloids.

Metals

• Metals are shiny, malleable (hammered into sheets), ductile (drawn into wires), solid at room temperature, and good conductors of electricity.

Nonmetals• Nonmetals are poor conductors of electricity,

often gases at room temperature, and brittle if solid.

Metalloids• Metalloids have some properties of metals

and nonmetals.• http://www.youtube.com/watch?v=CxjNGisjGi0

• Group 1A - alkali metals (ex. Lithium)• Group 2A - alkaline earth metals (ex. Calcium)

• Group 7A – halogens (ex. Bromine)• Group 8A - noble gases (ex. Radon)

• Groups 1A through 7A - representative elements• Group B - transition metals (ex. Cobalt)

Atomic Size

The atomic radius increases from top to bottom in a group in the periodic table.

As you move down a group in the periodic table, atomic size generally increases.

• WHY?• Adding more protons, neutrons and electrons

makes for larger atoms.

The atomic radius decreases from left to right across a period in the periodic table.

• WHY?• Stronger pull on electrons to nucleus.

• List the symbols for sodium, sulfur, and cesium in order of increasing atomic radii.

• Sulfur, Sodium, Cesium

Ions and Ionization

• Ions form when electrons enter or leave atoms.

• The charge of a cation is positive. Cations are smaller than the original atom.

• An anion has a negative charge. Anions are larger than the original atom.

• Removing one electron from an atom results in the formation of an ion with a 1+ charge.

• Adding one electron to an atom results in the formation of an ion with a 1- charge.

• Ionization energy - energy required to move an electron out of an atom

• Ionization energy decreases from top to bottom and increases from left to right on the periodic table.

Among Na, K, and Cs, which element has the lowest ionization energy?

• Cesium (Cs)

Which is larger, K or K+?

• K

Which is smaller, Li, Li+, F, or F- ?

• Li+

Electronegativity

• Electronegativity is the ability of an atom in a compound to attract electrons.

• Electronegativity values tend to decrease from top to bottom and increase from left to right.

• Which element in each pair has a higher electronegativity value?

• Mg or Ne • Mg

• Which element in each pair has a higher electronegativity value?

• Cl or F• F

• Which element in each pair has a higher electronegativity value?

• C or N• N

• Which element in each pair has a higher electronegativity value?

• As or Ca• Ca

• Cs has one of the lowest electronegativity values.

Valence (outer) electrons may be transferred from one atom to

another.

Group Valence elctrons Resulting charge

1A Lose 1 1+

2A Lose 2 2+

3A Lose 3 3+

5A Gain3 3-

6A Gain 2 2-

7A Gain 1 1-

• What charge would Na likely have in a compound? _______

• 1+• What charge would Mg likely have in a

compound? _______• 2+• What charge would Al likely have in a

compound? _______• 3+

• What charge would O likely have in a compound? _______

• 2-• What charge would F likely have in a

compound? _______ • 1-