Chemistry 101 Exam #3 - Ch. 7.9 - 7.12

19th Century Scientists

Grouped elements by atomic mass

1864 - John Newlands

Every 8th element had similar properties: “Law of Octaves”

1869 - Dimitri Mendeleev

Grouped elements by property (66 elements)

-left space for future elements

-predicted properties of undiscovered elements

Atomic Mass

Eka-aluminum (Ea)

• 69.9 amu

Gallium (4 yrs later) (Ga)

• 69.7 amu

Density

Eka-aluminum (Ea)

• 5.94 g/cm³

Gallium (4 yrs later) (Ga)

• 5.94 g/cm³

Oxide Formula

Eka-aluminum (Ea)

• Ea2O3

Gallium (4 yrs later) (Ga)

• Ga2O3

1870 - Lothar Meyer

Similar table

1913 - Henry Moseley

X-ray like pattern when each element was struck with electrons

-atomic number

Periodic Classification of Elements - 1A - 7A

Representative elements (main groups) are groups

• Have incomplete s or p outermost shells

• Noble gases (except He) have completely filled p shells

Electron Configuration of Ions

-If you form a cation, there is one less electron

-If you form an anion, there is one more electron

*For cations of transition metals, electrons removed first from the s orbital and then d orbitals

Periodic Properties

1. Atomic Radius - ½ the distance between 2 nuclei in 2 adjacent atoms

2. Ionic Radius - affects physical and chemical properties of ionic compounds

3. Ionization energy - minimum amount of energy needed to remove an electron from gas atom in its ground state

4. Electron Affinity - energy change associated by acceptance of an electron in its gas state

Atomic Radius

Determined by strength of attraction between protons and electrons

• Fr is stronger than H because it has more valence electron shells

• The more left and down you go on the periodic table, the higher the strength of attraction

Ionic Radius

-forms anion: radius increases (more electron/electron repulsion (repel each other))

-forms cation: radius decreases (less electron/electron repulsion (repel each other))

Arranges in order of increasing radius

1. O

2. P

3. Al

4. Ca

5. Rb

Ionization Energy

-X(g) → x^1+(g) + electron 1st I.E.

X^1+(g) → x^2+(g) + electron 2nd I.E.

X^99+(g) → X^100+(g) + electron 100th I.E.

• The righter and up you go on the periodic ,