Periodic Trends

Periodic Patterns

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::: :Ne

: :. .X

H.

X. Be:X:

X: .Al.

: C:. .

. .X:

:. ..N

. . .

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: :.F:

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:He:

[:x:]::[:x:]::[x] [x]+4-4

+1 +2 +3 -3 -2 -1

s1

s2 s2p1 s2p2 s2p3 s2p4 s2p5

s2p6

Ion formation: Loss (oxidation) or gain (reduction) of electrons

Periodic Trends• Trends in atomic radius, ionization energy, &

electronegativity are determined by:• The number of energy levels present.• The attraction between the positive nucleus and the

outer shell electrons.• Interfering “shielding” by electrons on inner shells.• How close an atom is to completing the stable octet

of outer “valence” electrons.

Atomic Radius (1 of 3)

• Alkali metals are the largest atoms. • Noble gases are the smallest atoms.

Atomic Radius (2 of 3)

Atomic radius trends:

1) Atomic radius increases down a group or column.

2) Atomic radius decreases across a period or row.

Atomic Radius (3 of 3)How do we explain the trends?1. Atomic radius increases down a group:

• Each row adds an energy level.• Interior electrons interfere with attraction of

valence electrons toward the nucleus “shielding effect”

2. Atomic radius decreases across a row even while the atomic number increases:

• While in the same energy level, the nucleus becomes more positive & attractive.

Ionization Energy (1 of 4)• Ionization energy is

the energy required to remove a negative electron and leave an atom with a positive charge – as an ion.

• Occurs in solar cells, geiger counters & smoke detectors with Amerecium 241

Ionization Energy (2 of 4)

• Alkali metals lose their electrons most easily.• Noble gases hold their electrons most tightly.

Ionization Energy (3 of 4)

• Removing an electron becomes more difficult across a row.

• Removing electrons becomes easier down a column.

Ionization Energy (4 of 4)

• Removing electrons is more difficult across a row as the nuclear attractions become stronger.

• Removing electrons is easier down a column as each additional energy level increases the distance from the nucleus and weakens the nuclear attraction.

• Repulsive shielding by interior electrons also decreases the attraction for each added level.

Electronegativity (1 of 3)

• Electro-negativity is the ability of an atom to attract electrons that are shared in a covalent bond.

Electronegativity (2 of 3)• What are the trends in electronegativity?

Electronegativity (3 of 3)

• Electronegativity increases up & to the right.

• This trend corresponds to stronger attractions to the nucleus.

• Less shielding effect strengthens attractions to the nucleus in upper rows.

Periodic Patterns Quiz

Atomic Radius Question – What is the size surprise? Why does it occur?

Ionization Energy – Why are the lowest ionization energies in the bottom left?

Electronegativity – Arrange each set of atoms in order from least to greatest electronegativity: Mg, Ba, Sr; Cl, F, I; Fe, K, Br

Periodic Patterns of Reactivity

• Choose an element from the periodic table.• Predict how you think it will react with air,

water, acids or bases.• Observe the laserdisc video.• Record the reactivity on a 1R-10R scale.• Examine no more than 3 per group.• Identify patterns of reactivity.